The morphology and anatomy of thebarley (Hordeum vulgare L.) awn

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Authors Paluska, Michele Marie, 1946-

Publisher The University of Arizona.

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THE MORPHOLOGY AND ANATOMY OF THE BARLEY (HORDEUM VULGARE L,) AWN

by .Michele Marie Paluska

A Thesis Submitted to the Faculty of theDEPARTMENT OF■PLANT SCIENCES

In Partial Fulfillment of the Requirements For the Degree ofMASTER OF SCIENCE

WITH A MAJOR IN AGRONOMY AND PLANT GENETICSIn the Graduate College

THE UNIVERSITY OF ARIZONA

1 9 7 6

STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfill­ment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowl­edgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the inter­ests of scholarship. In all other instances, however, permission must be obtained from the author.

SIGNED: //V-_ _ _ _ _ _ 6 _ _ _ _ _

APPROVAL BY THESIS DIRECTORThis thesis has been approved on the date shown below:

R. T/ RAM AGE, Professor of Agronomy and Plant Genetics

acknowledgments

Thfe authoi: wishes to expzress her appreciation to Dr R. T. Ramage for his advice in the planning, execution/ and writing of this thesis. Thanks are due to Dr, D. D. Rubis for his constructive advice on the written thesis. And a special riiention of appreciation is due to Dr. A. K. Dobrenz for his Unselfish giving of time/ advice, and moral support

TABLE OF CONTENTS

PageLIST OF ILLUSTRATIONS I . * ,! ... . ViABSTRACT i « • . « » « e » i i i e • • • e . « • • » • VI1

INTRODUCTION 4 1LITERATURE REVIEW . 4 * 4 . * & 4 * * 3

Awn Structure .*'■•* **».*•'«.» 4 4 35̂ ]_ Z ̂5 « e • e • e * *4 44 4 4 * 4 4 4 * 4 * 4 * 3Anatomy * 4 4 * * * * *.* 4 4 * * » * * * 4 * 5

Awn Function * * , 4 a 4 * s * * * * * , * . 4 * . 7Laboratory Measurements * * , . 4 . * . 4 * 4 7Field Trials • * 4 . * * • s . * * 4 . a 4 4 4 4 9

Genetic Studies * .• * * , » » ■ * . 4 . . . * 4 4 * 10MATERIALS AND METHODS * . * » * ........ .. » . * * 15

Seed Source * 4 4 4 * 0 4 4 * * 4 * * 4 4 4 * 4 * 15Experimental Procedure . * * . , * . i * . * . . * 15

Morphological Observations 4 * . . * . . . * . 15Anatomical Observations 4 * * * 4 . * * . . . 16

RESULTS AND DISCUSSION .* . 4 .., * * , . . * * . . * , * 18Morphological Characteristics * * , . * * ̂ . * . 18

Spike Length * * * * * » « * * * . * , . . . . 18Number of Florets * * . * . . . . 4 4 . . , * 20Awn Length * . . * « * * * * . * » . . . * 4 * 22AWn Width * * * * * , . . * . . . . . * * * . 22Awn Thickness * , * * . 24Dry Weight of Awns . * * 4 . . * . . * . . . . 24Per Cent Awn * . , 4 * 4 * * * * . 24

Anatomical Observations * . . * * * , . . * * , * 29Shape * * * * * 4 * * * * * 4 * * * - * * * * * 29.Epidermal Tissue , . * * * . , * . * .. . * . . . 2 9Conductive Tissue * . * „«•/•.»' . * , * * . * . . 33Parenchyma * * * * * * * * * * * • * * * *. * * 33

iv

TABLE! OF CONTENTS— ContinuedV

Pageappendix a> TABLE of barley spike and awn

MORPHOLOGICAL MEASUREMENTS 39LITERATURE CITED » • , i •* , . . ,'' i . * * V * ........ 42

list of illustrations

Figure / Page.1* Range in spike length of six-row* six-row,

tri-awn and two-row genotypes *. •* . « * . 192. Number, of florets per Spike on six-row,

six-row, tri-awn and two-row gepotypes . \ , 213*. Range in awn length of six-row, six-roW,

tri-awn and two-row genotypes * . ; .. » « , • 23• 4. . Range in awn thickhesS of six-row, six-

row, tri-awn and two-row genotypes . . . . . . 255. Range in total dry weight of awns from

six-row, six-row, tri-awn and two-row. g e ho type S . , . . . « . . # . . . * . . * . . . * 2 6

6. Range in percentage of dry weight of awnsper spike for six-row, six-row, tri-awnand two-row genotypes 28

7. Triangular shaped barley awn cross-sections (100X) t .. . 30

8. six-row, tri-awn ctross-sections . . . . . . . . .319. Barley, awn cfoss-SectiOns (400X) , , . . . , . . 32

vi

Abstract

. _ 'iA survey of morphological and anatomical character­istics of the barley (HOrdeum vulgare L.) awn was conducted on a group of genotypes produced with the male sterile facilitated recurrent selection breeding technique* The population was established from Composite Cross XXX popula­tions. A wide range in variation in most characters was observed. Spike length varied from 3.7 to 13.6 cm. Number of florets per spike ranged from 26 to 94. Awn length varied from 3.8 to 18.4 cm. Awn width ranged from less than1.0 to greater thah 1.5 mm. Awn thickness varied from .30 to .52 mm. Awn dry weight ranged from .059 to .593 g. Thepercentage of awn per head varied from 25.5 to 58.7.

The anatomy of the barley genotypes displayed wideVariation in shape, number, and location of stornates, andextent Of triesophy 11. This Study indicates that a tremendous variability exists in the morphology and anatomy of the barley awn;

vii

introduction

The number tif tillers>. the number of seed per spike, and the Seed dry weight are the parameters on which yields in small grains are based. Each of these parameters is in turn affected by its anatomy# morphology, and physiological processes. The complex of interactions of yield parameters, their structures, and functions can either enhance or in­hibit the productivity Of a plant, in this case# grain yield.

One variable component of yield is seed weight* one approach to increasing yield is to develop a breeding pro­gram involving increasing kernel Weighti It is known that barley seed size is under the influence of awns. Barley awns are also known to be photosynthetic structures* A breeding program to increase seed Weight needs to include attempts to maximize the potential of the barley awn as a photosynthesizing structure.

Before a desirable characteristic can be bred into an agronomic crop, the function Of this Characteristic heeds to be understood. And in order to understand function# the structure first needs to be described* The purpose of this study is to describe the range of variation in the morphology and anatomy of the barley ;awh of randomly

selected genotypes from a population having a diverse genetic background.

LITERATURE REVIEW

Awn Stirtictufe

SizeThe importance of the awn as a photosynthetic organ

in barley (Hordeum vulgare L«) and wheat (Triticnm aestivum L. cm* Thell.) has been accepted because of evidence from a number of varied studies which have shown that awn length is

* positively related to seed size and yield* There have been many investigations comparing the performance of isogenic lines of barley and Wheat differing only in awn length (Suneson, tiayies, and Fifieid, 1948; Evans et al.> 1972; Atkins and Norbis, 1955; McDonough and Gauch, 1959; Grundbacher* 1963)*

It has been reported that the importance of the awn is directly related to its length (Gauch, 1937; Vervelde, 1953). Schaller, Qualset, and Rutger (1972) designated values of 10.01, 4.51, 0.28, and 0.04 cm for the mean awn lengths of full-, half-, and quarter-awned and awnless iso­genic lines of 'Atlas' barley* McDonough and Gauch (1959) reported that awn length of wheat ranged from 100 to 140

"-mm* Teare and Peterson (1971) classified 30 wheat cultivars according to awn length. They reported a range in mean

3

length from 5,71 cm (long-awned), to 3.75 cm (medium-awned), to 0-20 cm (short-awned)-

Variation in seed size is one component of yield that has been associated with awn length. Schaller et al. (19 72) reported a linear increase it kernel weight with increasing awn length, and that grain yield was not directly related to awn length. in addition to their observation that the longer awned plants had larger seed, they stated that the awrts provided protection to developing seed from infection by foliar pathogens -

Paris (1974) investigated yield- components of iso­genic lines of bailey« His data agreed with previous reports of the relationship between seed size and awn length. He considered the larger seed to be due mainly to increased photosynthetic Surface in proximity to the growing kernel. The larger awn pfovides a source of photosynthate potential- There is ah advantage in having efficient assimilate translocation from the awn to the seed.

Variation in awn thickness has also been reported. Using radioactive carbon dioxide, Derera and Stoy (1973) found a negative relationship between the weight per unit length Of awn and residual c recovered at harvest. They reported a strong positive correlation between the total awn weight and the per cent Of "^C uptake. They suggested thicker awns to be more efficient organs of assimilation, and translocation. Johnson, Willmer, and MoSs (1975) measured

seven genotypes of bafley. They found that awn length remained constant during Seed development, but that awn dry weight increased during this time i. They concluded that awn dry weight Was an important criterion in describing the amount of photosynthetic surface area available to the plant.

AnatomyThe anatomy of the barley awn gives an indication of

its photosynthetic capability. Biscoe, Littleton, and Scott (1973) studied gaseous Exchange in barley awns as influenced by stomatal changes. They reported that the awn's photo­synthetic processes and transpiration depend on the ability of stomata to open in response to light, and close in response to water stress. These researchers reported to longitudinal rows of Stomata on each of the abaxial awn surfaces and none oh the adaxial surface of 'Proctor' and 1 Impala' barley cultivars. These rows of stomata stopped at the awn-lemma junction. In a study of frequency and distribution of stomata in barley, Miskin and Rasmusson (1970) measured 649 cultivars from the U.S. Department of Agriculture's World Collection. They reported two rows of stomata on the outer awn surface and a mean frequency of 30 per mm in each row. They also found no stomata on the adaxial aWn surface. Kj ack and Witters (1974) found sig­nificant differences in stomata number among awn lengths of

isogenic lines of Atlas barley* These differences were reported to be equivalent to 99, 97, and 65 per cent of the total number of stomata per spike for full-, half-, and quarter-awned isolineS, respectively. Tears, Law, and Simmons (19 72) measured stomatal frequency and distribution on the glume, lemma, palea, and awn in nineteen cultivars of wheat * They reported a range of from 6 to 3 8.0 stomata per awn. These differences Were reported to be a function of awn length* They suggested that there Was a relation­ship between the photosynthetic efficiency of awned culti­vars and the increased photosynthesizing area of the awh. They also suggested that this efficiency may be associated with stomatal number and its closely linked gaseous ex­change capacity.

In addition to the aforementioned relationships between aWn length and total number of stomata, there is, an increase in the total area of chlorophyll-containing tissue on barley spikes With longer aWnS (Kj ack and Witters, 1974) « They found no significant differences ini;chlorophyll con­centrations among isogenic lines of varying awn length, but the full-aWned line had a greater Surface area of chlorophyll-containing tissues * Teare and Peterson (1971) investigated the surface area of chlorophyll-containing tissue on the inflorescence of 30 cultivars of wheat. They reported a variation in the ratio of awn area to total spike

area of 5 per cent for fehort-awn types to 46 per cent for long-awn types.

Awn Function

Laboratory MeasurementsIt has been nearly eighty.years since the first

experiments measured the amount of carbon dioxide assimi­lated by barley spikes in a closed system, demonstrating that awns carry on photosynthesis,(Schmid, 1898). Porter> Pal, and Martin (1950) reported a mean rate of assimilation of 1.29 mg CO^ per Spike per hour for 'Spratt Archer' barley. The authors stated that the contribution of photo­synthesis in the inflorescence to the final dry weight of the grain was 70 per Cent. Thorne (1965) measured gas ex­change in ears and flag leaves, and reported that 50 per cent of the carbohydrates in the grain was supplied by the inflorescence of Proctor and 'Plumage Archer' barley. In a study of the photosynthetic activity of the ear during grain filling in wheat, PuttioSe (1962) reported a slower growth of the grain in the first three weeks after anthesis. The florets Contributed approximately 0.2 mg per day per grain. This was equivalent to 50 per cent of the grain dry weight increment. During the latter half of the grain growth, florets contributed more than 0.6 mg per day per grain, which was equivalent to 60 per cent of the weight increment. Using infrared gas analysis, Evans and Rawson (1970)

reported an estimated 32,8 per dent contribution from ear photosynthesis for an awned cultivar and 20.4 per cent for a short-awned cultivar of wheat.

Teare, Sij et al. (1972) estimated the photo­synthetic activity of awned and awnless isogenic lines of wheat during the soft dough stage of development* They reported a CO^ assimilation ratb of 4.68 mg per hour (1.93 head + 1.18 awns + 1.57 flag leaf) for an awned selection.An awnless selection Wad reported to have a,rate of 2.94 mg COg per hour (1.93 head + 1.01 flag leaf), The authots calculated that 34 per cent of the photosynthate was supplied by the flag leaf and 66 per cent by the inflores­cence .

14Labeled carbon ( C) has been used to examine thecarbon uptake and assimilate distribution by exposing plant

* i 14parts to radioactive carbon dioxide ( CO2 )* McDonough and' 1 AGauch (1959) expoSed awns of 1 Durum' wheat to CO2 and

reported that 41 per cent of the kernel dry weight could be attributed to photosynthesis in the awns, Derera and Stoy (1973) studied five wheat cultivars of Swedish, Australian, and Mexican origin by comparihg the amount of labeled carbon taken up in the spike and the distribution within the spike. They reported differences among cultivars in the amount.of "^C assimilated. These differences were correlated with the total awn length and total awn thickness. Buttrose and May (1959) studied three six-row varieties of barley of

differing awn development, 'Arlington' (awnless), 'Mars'(one awn per floret) , and 'Long-Awned Outer Glume' (three awns per floret)» The authors used an ear shading technique and labeled carbon as a tracer, They reported significant reduction in yield of 9> 23, and 18 per cent in awnless, single-̂ -awried, and triple^awned varieties, respectively.

Field TrialsIn addition to the previously reported ear shading

technique of Buttrose and May (1959), Frey-Wyssling and Butttose (1959) applied a spike Shading technique to 'Prior' barley, TheSe same researchers estimated that a maximum of 76 per cent of the carbohydrates in the barley kernel originated from photosynthesis in the spike, Thorne (1963), using both spike shading and CO^ measurements, estimated the spike contribution to grain weight for Plumage Archer and PrOctor barley. She reported that 68 per cent of the net assimilation was accounted for by spike photosynthesis at rates of 1,0 mg CQ^ per Spike per hour. Shading reduced dry weight accumulation of grain dry weight Of both varieties by 26 per cent.

Awn removal has been used by a number of investi­gators to determine awn contribution to yield. Harlan and Anthony (1920) studied 'Manchuria' and 'Hanchen' barley and reported a smaller volume and lower dry weight of kernels from clipped Spikes, This difference was not considered due

10to plant injury or shock* They found awnless and hooded varieties to have yields comparable to awn-clipped plants. Millet, Gauchf and Gries (1944) reported decreases of 50 to 80 per cent in grain weight When awns were clipped in wheat. Vervelde (1953) reported a 10.8 per cent reduction in weight per 1000 grains in de^awned spring barley. Paluska and Ramage (19̂ 2). clipped awns of Arivat barley using three treatmentsi awns clipped, flag leaves clipped, and awns plus flag leaves clipped. They reported average reductions in seed weight of 19.4, 3.3, and 23.3 per cent, respectively, for the three treatments. The authors also reported an increase in shattering of awn-clipped spikes, which is in agreement with observations reported by Harlan and Anthony (1920) .

Genetic Studies Comparing isogenic lines differing in awn length is

one of the most direct methods of demonstrating the impor­tance of the awn as a photosynthetic structure* It is a method in which the response of awned and awnless genotypes of essentially uniform genetic backgrounds are compared over a range of environmental conditions. Qualset, Schaller, and Williams (1965) investigated the relationship between yield, components of yield, and awns in four backcrossed derived lines of.Atlas barley* They reported increased kernel weight over awnless of 22.4 per cent for full-awned,

' ' . 1 1

11.6 per cent for half-awned, and 3,4 per cent for quarter- awned lines. Yield increases of 16.3,23.0, and 8.4 per cent greater than awnless were Obtained.. They also reported that grain weight ihcreased linearly with increasing awn length. Schaller et al. (1972) studied the response ofawned and awnlesS genotypes of Atlas barley over a range of environmental conditions at 18 locations in the western United States and Canada. They reported a linear relation­ship between awn length and seed size. They also observed that the full-awned isoline had Superior yield in good environments, but under stress conditions this same isoline yielded lower than haIf-awned and was comparable with quarter-awned. The authors suggested that lower yields of full-awned types under stress conditions were due to competition for substrate during awn development. They

_ . Istated that this competition dttring the early phases of , plant development resulted in a depressing effect on initia­tion and development of additional florets and tillers. The full-awned genotype was affected more than the half-awned type because the total awn length of the half-awned was only about 50 per cent of full-awned types. Paris (1974) grew isogenic lines of Atlas barley in northern Alberta and confirmed the observation of Qualset et al. (1965) andSchallef et al. (19 72) that seed weight is linearly related to awn length.

12Shannon and Raid Cl976) studied four pairs of awned

and awnless isogenic winter barley lines grown under both humid (Maryland) and irrigated (Arizona) environmental conditiohs* They reported k more consistent yield advantage for the awned isogenic line ever the aWnless isogenic line under irrigated than under humid Conditions# in locations where severe lodging or leaf Scald occurred, the authors suggested that awns' may have had an effect in preventing serious yield reductiohS# Their data indicate that awns may offset yield reductions in Situations where leaves are less effective in photosynthesis<

Atkins and Norris (1955) investigated ten pairs of isogenic awned and awnless lines of Wheat grown under different environmental conditions over several years, They reported that awned lines produced significantly higher yieldsf heavier kernels> and higher test weight than awnless lines« Also, during years of water stress, the differences in yields and kernel weight Were greater in favor of awned Wheat. On the other hand, PattersOn et al* (1962), usinghear isogenic awned and awnletted lines of eastern soft wheat, found that awned wheat performed best under high moisture conditions. EVans et al, (1972) reported that drought increased the proportion of assimilates ‘contributed by photosynthesis in the ears from 13 to 24 per cent for awnless and 3 4 to 43 per cent for awned isogenic lines of

13wheat. Awns increased grain weight in the dry > But not in the irrigated, treatment,

Backcrossed derived lines of differing awned con­ditions have been used to investigate the influence of awns on yield. Clark and Quisenberry (1929) investigated lines derived from the cross of 1 Marquis' (awnletted) x 1 Kotaf (awned) spring.wheats in Montana, They reported that the awnletted and Segregates Outyielded the awned segre­gates , The authors suggested that the degree of difference in yields between awned and awnletted types was a result of greater shattering in awned types * Shattering estimates accounted for a yield reduction Of 8.25 per cent for awnletted types ahd 14.38 per cent for awned types. The Kota parent, however, outyielded the Marquis parent. Aamodt and Torrie (1934) reported that the awned 1 Caesium* cultivar had significantly higher yields than the awnletted 1 Reward1 cultivar in spring wheat, They Observed no significant relationships between awns and yield in awned and awnletted strains of F^ hybrids from the cross of Caesium and Reward. They concluded that the relation between awns and grain yield differs depending on varieties crossed and environ­mental conditions under which the plants are grown. Suneson . et al. (1948) studied awnleSs 'Baart1 and awned ’onas,1 derived by reciprocal backcrosses of 1Baart1 x 1Onas.1 The authors conducted field trials at 16 locations in the United States and Canada. They observed that the awned

14forms generally had higher kernel weight and test Weight under both irrigated and semi~arid conditions. They authors concluded that effects of awns were independent of soil moisture supply* McKehSie (.1972) investigated awn- letted 'Lee* and awned 'Thatcher,' derived by reciprocal backcrosses of Lee (awned) x fhatdher (awnletted)„ The author reported that awnletted wheat butyielded awned ones. He reported that the kernel weights of the awned and awn­letted isolihes were the Same*

He reported more spikes per unit area for awnletted Lee lines than their awned counterparts, but no difference between awnletted and awned Thhtcher pairs.

MATERIALS AMD METHODS

Seed SourceA male sterile facilitated recurrent selection

population for awn ‘variation was grown on The University of Arizona Campbell Avenue farm in the winter of 1974-75, The population was established from barley Composite Cross XXX populations (Ramage et # 1976)»

This population was chosen for study because it originated from an extremely diverse genetic background and would segregate for a wide range of characteristics.

Experimental Procedure

Morphological ObservationsThree spikes Were collected from each selected

plant. All spikes were collected at the time of first pollen shed (antheSis) to insure similarity in inflorescence development. Peduncles were cut at the collar, the spikes were wrapped in moist paper toWels, and taken to the laboratory for measurements, The numerical values for each morphological characteristic observed on each of the three spikes Were used to Obtain an average for each genotype.

Spike Length. Each spike was measured from the collar to the lemma-awri junction of the Upper most fertile floret,

15

16Number of Florets, Florets were counted on one side

of each spike and the number multiplied by either six or two depending on whether it was a six-row or two-row Spike,

Awn Length. TO be consistent, all awn measurements Were taken from the third floret from the basal node on each

■ ' : i '

spike. Awn length was measured from the lemma-awn junction to the awn tip»

Awn Width. Awn Width Was measured two mm tip from the lemma"awn jtincticn.

Awn Thickness t Awn thickness was measured two mm up from the lemma-awh junction with a caliper which was accurate to .01 mm.

Awn Weight> Awhs were Cut from each inflorescence, oven dried at 80dC for 24 hour’s, and weighed on a Mettler balance«

Per Cent Awn, The percentage of awn dry Weight per spike was calculated by dividing aWn weight by the total dry Weight of the spike.

Anatomical ObservationsMaterial for histological study was collected from

individual plants, selected at random. Collections were made from the Central florets when the aWn tips had first emerged from the flag leaf sheath. Tissue was collected

17from the basal portion of the awn in sections ohe to 1.5 cm up from the lemma-awn junction* Awn sections were killed and fixed in a modified FAA solution of 5 per cent formalin, 20 per cent acetic acid, and 75 per cent ethanol (.70%). Samples were aspirated for five minutes to remove air bubbles and stored in modified FAA. Plant tissue was de­hydrated in a teitiafy-‘•butanol (TEA) series and embedded with paraffin according to techniques described by Johansen (1940).

Prior to sectioning, the embedded plant material and microtome blade were placed in a freezer at 10°C for one hour. This cooling proved helpful in sectioning tissue as a means to avoid the pulling effect of cells during sectioning. •

Serial sections were made fof each of the awn samples, at 12 y thick. Sections were stained in Safranin O and Fast Green and mounted in Permount.

Microphotographs, at 100X, 250X, and 400X were made of the awn cross section from selected plants. Each sample was evaluated for awn shape, tissue types present, and location of stomates,

RESULTS AND DISCUSSION

Morphological Characteristics

Spike LengthSpike length varied from 3*7 to 13,6 cm in the six-

tow genotypes (Fig * 1), Thirty-two per cent of the six-row genotypes had spikes which ranged from 8.0 to 8.7 cm in length. There were maikedly fewer six-row plants with a spike length greater than 8,7 cm. Only 14 per cent of the plants had spikes that ranged from 9#2 cm to 13,6 cm in length.

The six-row genotypes which displayed spikes segre­gating for wide, split awns are discussed as a Separate spike type, They are hereafter referred to as six-rowy tri-awn. - • . 1

The six-row> tri-awn and the two-row genotypes hada narrower range in Spike length, This Was# possibly due to the lower number of genotypes which Was evaluated within each of these barley types. The six-row, tri-awn genotypeshad a range in spike length from 7.2 cm to 10,5 cm. Thetwo-row genotypes had a range in spike length from 7,3 cm to 10.0 cm.

18

NO.

OF

GE

NO

TY

PE

S

14

12

10

864

2AY

□ 6 ROW

6 ROW, TRI-AWN

2 ROW

n0 6 7 8 9 10

SPIKE LENGTH (cm)

II 12 13

Fig. 1. Range in spike length of six-row, six-row, tri-awn and two-row genotypes.

Number of FloretsThe average number of florets per Spike ranged from

48 to 9 4 for the six-row types (Fig« 2)< Sixteen per cent of the genotypes had a range from 48 to 6 0 florets per spike, 57 per cent had a range from 66 to 78 florets per spike, and 27 per cent from 80 to 94 florets per spike»

The six-row, tri-awn types had a range in average number of florets per spike from 68 to 84, with much less variation than the sik-row genotypes *

in the two-row genotypes the average number of florets per spike ranged from 26 to 36* The smaller sample sizes within the tri-awn and two-row spike types may have limited the range for this morphological characteristic.

Qua!set et a!* (1965) reported that half- andquarter-awned Atlas isogenic lines produced more kernels (fertile florets) than full-awned and awnless. Data for awn length and number of florets per spike from the population under study were arranged in a 3 x 2 chi square contingency table. A chi square value for independence of ,853 (P —.975 to .950) was obtained, According to the chi square value, no association between awn length and number of florets per spike was indicated.

Also, data from spike length and number of florets per spike were arranged in a 2 x 2 chi square contingency table. A chi Square Value of 9*91 (P - .625 to .010) was obtained. According to the value obtained, a definite

NO.

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GE

NO

TY

PE

S

Fig. 2

14

12

10 h-

8 6 4

21

| | 6 ROW

P I 6 ROW, TRI-AWN

0 2 ROW

25- 31- 36- 41- 46- 51- 56- 61-30 35 40 45 50 55 60 65

66- 71- 76- 70 75 80

81- 86- 91- 85 90 95

NUMBER OF FLORETS / SPIKE

Number of florets per spike on six-row, six-row, tri-awn and two-row genotypes.

22association exists between spike length and number of florets per spike, although spikes which had the highest number of florets Were not always the longest. Rachis internode length could prove ah important selection cri-* terion in a barley breeding program.

Awn LengthAwn length varied from 3.8 to 18.4 cm in the six-

row selections (Fig, 3). Except for one genotype which hadan awn length of 3.8 cm; all othei plants measured over10.0 cm. Thirty-four pdr cent of the Six-row genotype had an awn measurement from 13.0 to 13,9 cm.

All of the tri-awn genotypes had awns that were over15.0 cm in length With a range of 15.1 to 18,0 cm. The two- row genotypes had an awn length,measurement from 12.0 cm to 18.5 cm.

Awn WidthThere was not a wide range in awn width. Nearly 80

per cent of all six-row genotypes had awns that averaged1.0 mm wide. Approximately 16 per cent measured greater than 1,6 mm but less than 1.5 mm.

The six-row, tri-awn types were generally Wider than the six-row types. Most selections were greater than 1.5 mm wide. '

The two-row genotypes Were generally narrower than the six-row types, with an awn width of 1,0 mm, ot less.

NO.

OF

GE

NO

TY

PE

S

16

14

12

108 6

—\Yoo AV 10 II

a

| | 6 ROW

E$T| 6 ROW, TRI-AWN

2 ROW

n_.rm12 13 14AWN LENGTH (cm)

15 16 17 18

Fig. 3. Range in awn length of six-row, six-row, tri-awn and two-row genotypes

MU>

Awn ThicknessMost (89 per cent) of the six-row genotypes had an

average awn thickness within a range, from *34 to ,45 mm (Fig. 4)* Five of the six-row types had an awn thickness greater than .46 mm* The thickest genotype Was .52 mm. The two-row types were usually thinner than the six-row and six- row > tri-awn types. tfhe thickest awn measurement was ,41 mm and the thinnest was .30 mm for the two-row type.

Dry Weight of AwnsThere was a wide range of dry weight of awns for the

Six-row genotypes (Fig* 5), AWn dry weight varied from ,098 to , 488 g in the six-row genotypest

The six-row, tri-awn types had a range in dwn dry weight from .336 to .593 g. The two-row genotypes had a range in awn dry weight from ,059 to .223 g.

Awn dry weight has been reported to best describe the amount of photosyhthetic tissue present in the spike (Johnson et al., 1975) and to provide a measure of photo­synthetic activity (Derera and Sttiyr 1973). There is a remarkable range in awn dry Weight in the population under study. This emphasizes the importance of awn dry Weight as a valuable selection criterion for improved barley yield.

Per Cent AwnThe range in percentage of the total dry weight of

the inflorescence that is awn tissue Was from 25,5 to 50.9

14 —

12COLU -CL 10 —>h- -o 8zLU -O 6 —u_o 4 —

dz 2 —

0 AY ■ ■

n 6 ROW

[ig l 6 ROW, TRI-AWN

2 ROW

.30-33 ,34-.37 .38- 41 .42-.4S .46-.49

AWN THICKNESS (mm)

.50-53

Fig. 4. Range in awn thickness of six-row, six-row, tri-awn and two-row genotypes.

MLH

NO.

OF

GE

NO

TYP

ES

I 2 r -

10 -

8 -

6 —

4 -

2 —

0 .05

□ 6 ROW

6 ROW TRI

g 2 ROW

.10 .15 .20 .25 .30 .35 .40 .45

AWN DRY WEIGHT (g)

-AWN

.50

Fig. 5. Range in total dry weight of awns from six-row, six-row, tri-awn and two-row genotypes.

per cent for the six*-row genotypes (Pig, 6)? 40,9 per cent of the spikes had awns that comprise from 40,3 to 44,4 per cent of the total inflorescence^ Another large portion of. the population/ 36.4 per cent, had 45.3 to 49.8 per cent awn per spike; and 15.9 per cent of the genotypes had from 36,4 to 39.7 per cent awn tissue per.Spike.

All but one of the slx^row, tri-awn genotypes had50,0 per cent or more awn tissue per spike. The highest percentage Of awn per Spike in tri^awn genotypes was 56.7, The two-row genotypes, because Of the lower number of florets pet spike, had. considerably less percentage of awn per spike. The percehtcige of awn per spike ranged from 28 to 35 per cent in the two-row plants.

The light Six-roW spikes (dry weight less than ,20 g) had 43 per cent or less awn tissue per spike, The heavy six-row spikes (dry weight greater than ,41 g) all had greater than 43 per cent awn tissue per spike.

The tri-awn Spikes had awn dry weights comparable to the heavy six-row spikes. But the percentage of awn tissue per.'spike was greater than the six-row genotypes .

This demonstrates that in the population under study the greater aWn dry Weight the higher the percentage- of the entire spike is awn tissue.

NO.

OF

GE

NO

TY

PE

S

Fig.

20

18

16

14

12

10

864

2

0 AV

3 6 ROW

[% j 6 ROW, TRI-AWN

§ § 2 ROW

25

1

30I

35 40

AWN %

45 50 55

6. Range in percentage of dry weight of awns per spike for six-row, six-row, tri-awn and two-row genotypes.

txj00

: • i 29Anatotnical Observations

The anatomy of the six-row; six-row, tri-awn; and two-row genotypes is described collectively6 Any deviation from this will be noted.

ShapeThe barley awn was triangular in cross-section. (Fig,

7a), howeverj variation in this triangular shape was Observed (Fig. 7b.) » An exception to the triangular shape was noted iti the six-row, tri-awh genotypes 6 These geno­types had rectangular aWn cross-section that was tapered at both ends (Fig. 8a) .

Epidermal TissueA single layered epidermis was present» Outer and

tangential walls were thick and highly cutinized. Epidermal hairs (barbs) were noted in the tough awned selections.

Typicallyt two rows of stomata Were located on each outer (abaXial) surface of the awn. In some genotypes two to three rows of stomata were observed (Fig. 9a), It was common to find Stomata located on the flat inner (adaxial) awn surface (Fig, 9b)» The occurrence of stomata on the adaxial awn surface has been reported previously (Paluska, Ramage, and Dobrenz, 1973). No other reference could be found by the author in which the Occurrence of stomata on the adaxial surface was reported. This was undoubtedly due to the narrow germ plasm base of barleys previously

30

Em

Fig. 7. Triangular shaped barley avm cross-sections (10OX).

31

Fig. 8. Six-row, tri-awn cross-sections *— A: Six-row, tri-awn cross section (100X). B: Six-row, tri­awn cross-section (250X); co— collenchyma tissue, vb'— vascular bundle, st--stoma, ch--chloroenchyma tissue.

Fig. 9i Barley awn dross-sections (400X) •— A: Showingthree rows of stomata (st) on abaxial surface.B: Showing stomata (st) on abaxial andadaxial surfaces.

•V< V

\ .

t -> V -\S t B

Fig. 9. Barley awn cross-sections (400X).

33investigated. In the Six-row, tri-awn types up to twelve rows of stomata were observed. They were located on all epidermal surfaces.

Conductive Tissue ,A large typically monocot vascular bundle was

located in the middle of the awm Two smaller vascular bundles Were located in the coiners formed by the flattened surface. Vascular areas, comprised of one or more xylem vessels were occasionally found directly within the meso- phyll, in the large Six-roW, tri-awn selection six to eight VasCular bundles were present.

ParenchymaMost of the awn Was comprised of large, thin-walled

parenchyma cellsi These cells were largest surrounding the central vascular bundle and decreased in size toward the epidermal layers. Directly inside the epidermis was one or two layers of thick-walled collenchyma (Fig. 8b). This supportive tissue was most commonly observed in the corners of the awn',

Typically, there were two large zones of chloren- chyma. This chlorophyll-containing meSophy11 Comprised up to one-third of the total volume of the awn in cross- Section. The chlorenchyma extended to the epidermis where the photosynthetic cells were associated with the rows of

34.stomata. In the large Six-row, tri-awn genotype four major zones of chlorenchymaWhre noted»

There Was variation in the extent of mesophyll among genotypes. However, the larger awns did not necessarily have a greater volume of chlorenchyma in cross-section.This variation indicates the possibility of using the . extent of mesophyll tissue per awn as a Selection criterion for increased photosyuthetic potential Of the awn.

The anatomy of the barley awn was similar in structure and cellular organisation to the Durum wheat awn described by McDonough and Gauch (1959). Both the barley and wheat awns had meSophyll Strands overlain by rows of stomata and a closely associated Vascular system. This appeared to be an ideal cellular System for gaseous ex­change, photosynthate production, and translocation of photosynthate to the developing Seed.

in contrast, the Durum wheat awn in cross-section had fewer number of cells, smaller and more densely Com­pacted Cells than the typical barley aWn cross-section.Also, the barley awn appeared more flattened which may allow for more total Surface area of chlorophyll-containing tissue to be exposed for light interception.

SUMMARY

A jpUYvey of ItioYphblogicAl and anatomical character­istics was conducted on barley awns from various composite cross populations. Three separate Spike types were sur­veyed « They were six-tow? six-row, tri-awn; and two-row genotypes# Results indicate a wide range in variation of most characters. . .

In the six-fOw genotypes Spike length Varied from3.7 to 13.6 cm# The six-row, tri-awn and two-row types had a much narrower range in Spike length# The six-row# tri-awn spike length ranged from 7.2 to 10«5 cm. The two-row geno­types ranged from 7.3 to 10.0 cm#

The number of florets per Spike ranged from 48 to 9 4 for the Six-row spikes? from 68 to 84 for the six-row, tri-awn spikes; and 26 to 36 for the two-row spikes#

A tremendous variation was observed in awn length# The six-row genotypes had a range of 3.8 to 18.4 cm# Except for one plaht that had an awn measurement of 3,8 cm, all other measurements Were over 10.0 cm. The six-row, tri-awn measurements ranged from 15*1 cm to 18.0 cm. The two-row types had a range from 12*0 to 18.5 cm in awn length.

There was not a wide range in awn Width, Most six- ' row genotypes had an awn Width of 10.0 mm. In general, the six-row, tri-awn types had wider awns than other genotypes.

35

36Most awns were 1,5 mm Wide, Most two-row types had awns of1.0 mm width/ of leSs.

Collectively> awn thickness varied from .30 to 52 mm for all head types. The six^fOW/ tri-aWn types were typically thicker than other hhad types. The two-row types generally were thinner than both Six-row.and six-row, tri­awn types.

There Was a Wide fancje in the dry Weight of awnd for the six-row genotypes. Awn diy weight Varied from > 098 to .488 g. The Six-rOW/ tri-awn types generally had a heavier total awn weight. The Weights Varied from ,336 to .593 g6 As expected, the two-row types had less total dry Weightf with a range of .059 to .223 g*

A remarkably wide range ih the per cent awn of total spike weight was observed, in the six-row genotypes a range of 25,5 td 50.9 per cent Of the Spike weight was awn tissue. In the six, row, tri-awn, all but one had 50,0 per cent or more of the spike as awn tissue. As expected, the two-row types had considerably less per cent awn tissue pet spike.The two-row types ranged from 27.8 to 35,4 per cent awn,

The anatomy of the barley awn for the six-row; siX- row, tri-awn; and tWO-row types has been described col- < lectively, The barley awn Was typically triangular in shape, although much variation in this triangular shape was ob­served. All awns contained conductive tissue, supportive

37tissue (coilenchyma), chlorophyll-containing mesophyll, and epidermal tissue»

There was a variation ih the numbers of stomatal rows. Also, many genotypes had stornates located on both abaxial and adaxial Surfaces. Iri the large six-row geno­types, up to twelve rows of stomata were located on all epidermal surfaces.

There was also a variation in the extent of chlor- enchyma tissue. in the Six**row> tri-awn genotype four major zones of chlorenchyma Were noted*

The importance Of the barley awn as a photosynthetic organ has been established by numerous researchers investi­gating the effects of mechanical awn removal/ in field trials comparing isogenic lines of barley differing in awn length, and by observing differences in the amount of COg assimilated by barley spikes varying in aWn length.

This study demonstrates that there is a tremendous variation in the morphology and anatomy of barley awns selected from the male sterile facilitated recurrent Selection population established for awn variation. Photo- synthetic efficiency and associated increased grain yield may be increased by incorporating favorable awn character­istics into a barley breeding program. The range in variation in such characters as Spike length, awn length, aWn dry weight, stomatal number and location, and extent of

38meSophy11 indicates the importance of these characteristics as valuable selection criteria for improved barley yield.

APPENDIX A

TABLE OF BARLEY SPIKE AND AWN MORPHOLOGICAL MEASUREMENTS

39

Spike Number1 of Awn length florets/ length

Plant number , (cm) . spike- (cm)Six-row

421-7 8.1 75 13.9-10 7..5 . 72 16. 6-12 10. 2 68 16. 8-13 8. 0 80 ' 18,4-14 8.7 78 13.5—18 7,1 68 . 14,3-21 6.5 72 . 13,1-27 8,6 76 16.4-28 10.5 94 5 12,8-29 8,2 74 ' 14.3-3 0 7. 2 72 ■ 14.0—31 5,2 48 . 12,4-32 6.9 68 13. 4-33 8.0 84 14.0—34 7.4 84 13,4-35 7,8 66 13.0-36 8.7 73 12.4-37 5.4 54 11.2-3 9 3,8 72 10,3-42 8. 5 7 0 13.3-43 5.6 48 13 . 4—44 8,1: 76 13,4

. -45 6.6 74 10. 9-46 8.1 8 6 10.3-47 9. 7 72 15.5-4 9 7.8 66 13.3-52 3-7 56 11.5-55 8,7 82 13,4-62 1 4. 3 60 10.8— 6 3 6.8 66 11. 8—66 5,9 66 13,2

' Awn Awn Awnwidth thickness dry weight Per cent (mm) (mm) (g) . awn

>1,0 .46 .416 43.1>1.0 .41 .395 49. 81.0 • .44 . 415 49.41.0 .43 . 488 46.11. 0 ,42 .311 ■ 40. 71.0 .43 .334 46.51.0 .42 .314 46.7>1.0 .46 .475 50.9>1.0 ,48 .482 45.9>1.5 .47 - .451 48.6>1.0 .48 .385 4 9.41.0 ,40 .237 49.61,0 .40 .320 44.8:>1.0 .42 .40 9 45.31.0 .37 ,417 42.51,0 .34 .226 37.71.0 .41 .278 42.51. 0 .35 .198 42.91,0 ,43 .256 48.61.0 .38 .319 45.41.0 . .36 .170 41,81.0 .40 .389 48.41.0 .43 .309 • 43.51.0 ,37 .277 40.51,0 .45 . .353 46.21.0 ,38 .296 44.41.0 ,38 .190 41.91.0 .36 .256 39.71.0 .36 .189 40.31.0 .35 .158 37.51,0 .41 .19 9 42.7

Plant numberSpike Number of Awn length florets/ length '(.cm) spike ̂(cm)

-68 7.1 68 13.8— 69 4,6 58 11,3'-73 5,8 80 11.7-74 9,7 92 17.3-79 5.5 60 12.7-83 8,2 78 13.1-85 8,3 84 15. 4—86 13,6 72 11. 5-90 8.4 92 12. 6-91 9,2 80 - 13.9-92 4.2 72 ' 3. 8-93 6,9 86 14.1

Six-row, tri-awn-9 9, 2 • 84 18.0-16 8.2 74 15,4-19 7. 2 68 16.9-20 7.8 72 15,1-41 7.9 68 16.6-58 8,3 6 8 15,8

Two-row75-T-421-22 9.1 26 15.1

-23 10.5 36 18.5-54 8,2 30 12,0-56 10,0 36 13. 6-81 7.3 31 13.1

Awn Awn Awnwidth thickness dry weight Per cent (mm) (mm) (g) awn1.0 .391.0 . 421.0 .381.0 .351,0 ,361. 0 .351.0 .411.0 .341.0 .41

>1.0 . 44>1.0 ,361,0 ,40

>1,5 .48>1,5 ,46>1,0 .48>1, 0 .52>1.5 . 4.8>1.5 .50

1.0 .301.0 ,41

<1,0 ,321.0 .391.0 .41

,2 03 47.4.187 43.1.265 36.4.331 43.0.239 42.1. 203 38.7.330 45.8.183 . 33.3.2 83 39,6. 330 42,2.0 98 25.5.320 42.5

.593 50,3

.475 52.6

.458 44.5

.461 51.0

.559 58.7

.336 50.0

.143 35.4

.223 35.1

. 059 27.8

.176 33.8

.123 30,4

H

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