NICE AND - Plant Physiology · PLANT PHYSIOLOGY greenhouse. Teni suecessful grafts of hair sprout scions onl normiial stocks were obtained. Two of these are pictured in plate II,

HAIR SPROUT OF POTATOES1

R. B. HARVEY, A. REICHENBERG, BER NICE LEHNER,AND P. C. HAIMI

(WITH FOUR PLATES)

Introduction

Hair sprout of potato tubers is only sporadic in its oceurrence in Minne-sota potatoes. In miost years it is not promllinenit but in the crop of 1938 thefrequenicy was sufficiently imiiportant to decrease the value of potatoes forseed purposes. The hair sprout conditioni does lnot decrease the value oftable stock, in fact from coiimmon experien-ce hair sprout tubers keep betterin storage than normiial tubers, and there is nio discolorationi detectable. Theopinion of growers is that it appears especially duringc a-ears in whiich theyield is very high. It is most prominent in Bliss Triuimph, being greater inlate than in early strains, and White Rose, with less oecurrenlee in Cliippewa,Warba, Green Mountain, and Burbank Russet. Accurate data oni occur-renee and varietal susceptibility are not available, because it is sporadic,unpredictable from field conditions or plant appearaniee, anid has niot beenpossible of artificial production.

Anatomical distribution of hair sprouts on tubers

Hair sprout is characterized by the early sproutinig of affected tuibers,that seem to have only a short or no rest period. The tubers ulnder the usualconditions of storage at about 65° F. for cuiring after digging, sprout atonce. The hair sprouts are generally less thani 2 mmiiii., friequently 1 mmll., indiameter. They grow rapidly anid frequently producee small tubers 1 to 2cm. in diamiieter, inimediately appressed to the miiother tuiber, or on a shortstoloin one to several cenitimiieters in length, or on side bralnehes several inlcheslong (plate I, fig. 1; plate III, fig. 1; plate IV, fig. 2). The comparativegrowtth un-der the same conditions in darkness is shlowni in plate I, figure 1.The hair sprouts show abnormal responise to the stimulus of gravity, grow-imug in all directions from first growth wheni stem weakniess is not the causeof orienitation. The sprouts continue to grow under favorable conditions,in darkness to 6 to 8 ft. long with branichinig and rudimentary leaves, butmaintaining a diameter essentially the same as at first sprouting. Theyseem unable to grow radially, and mainitaini a uiiiformui diaiimeter, like lnor-mal stolons underground, but of smaller diamiieter than stolons. In theirdiaimieter, gravitationial response, and tuber formiiation, tlhey resemble stolonsmore tlhan stems. Somiie of the early sproutinig buds produce rapidly glrow-ing shoots of a diameter intermediate between normiial and extreme hairsprouts (plate III, fig. 3; plate IV, figs. 1 alnd 3). The early sprouting

1 Published by permiission of the director of the Minniesota Agricultural ExperillmentStation as Journal Series Paper no. 2112.

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HARVEY, REICHENBERG, LEHNER AND HAMM: HAIR SPROUT

serves to differentiate these from nlormal sprouts. These intermediates haveless tendenicyv to tuber formation than the extreme hair sprouts. It is acommlloni opiulioui among potato growers that the tip eyes produce hair sproutmore frequiently than side eyes, but this may be due to the observation beingdepenidenit uiponi the earlier sprouting of the most dominant eye at the apexof the tuber. In plate IV, figure 2, a normal sprout is showln emerging froma bud of the apical eye, with hair sprout tubers anid sprouts from lateral eyes.

On the same tuber normal, intermediate, anid extreme hair sprouts mayappear, or any combination of these (plates III anid IV) or all of the eyesmay produce intermediate or extreme hair sprout (plate III, fig. 1). A lineof demiiareation between hair sprout and normal eyes may be indicated insome tubers; it may be spiral lengthwise of the tuber; or only one end, tipor basal, or onily one side, may show hair sprouts.

Wlheni tubers are desprouted, the new sprouts are always hair sproutfromii the abnlormal e\es, and norIal from normal eyes, the seconidary budsalways produciing the same type of sprout, as long as there are buds to pro-duce sprouts. Hence the condition seems to be common to all buds in oneeye. No exceptions to this have been seen. Tubers were kept in storage forover a year without variation from this behavior, although they were de-sprouted many times.

If healthy (plate I, fig. 2, 2), and hair sprouts (plate I, fig. 2. 1) aregrown in eontinuous artificial light of intensity sufficient to cause the pro-ductioni of ehlorophyll, but insufficien-t to prevenit root formationl, the hairsprouts streteh up more rapidly than normal sprouts. They respond to thedirection of ineidence of light but the stems are weak. More roots areformed oni normal than oni hair sprouts. Wheni planited in soil in pots in thegreenhouse hair sprouts (plate I, fig. 3, 1) grow spindling with leaves resem-bling those produced from potato seeds. They are positively pliototropicbut fall over from stem weakness after a few inehes of growth, whereasnormal shoots of the same age and unider the same conditions are erect(plate I, figr. 2, 2). Hair sprout plants were growni in the greenihouse andproduced small tubers that on replantinig produeed normal planits. Hairsprouts were grown in light anid rooted and then the mother tubers wereremoved. The shoots retained the small diameter of hair sprout plants butproduced tuibers from which normal plants were grown. This indicates thatthe condition is niot due to physiological correlatioil induced by the mothertuber, but is inherent in the shoot, but disappears after tuber formation.In plate III, figure 1, however, a small tuber appressed to the mother tuberis showni still producing numerous hair sprouts from the buds of the smalltuber. This mav be an indication of §hort distance hormone or virus trans-mission of the hair sprout, that does not affect tubers gyrowln at greaterxdistanees.

Grafting experimentsTo test the possible hormonal or virus nature of the hair sprout condition,

Bliss Triuimph hair sprouts (plate IIT fia. 1, 4) were grown in pots in the

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PLANT PHYSIOLOGY

greenhouse. Teni suecessful grafts of hair sprout scions onl normiial stockswere obtained. Two of these are pictured in plate II, figure 1 (2 and 3).Although the hair sprout seiolns on normal stock grewm-iore than hair sproutson their owvn roots, the spinidlingr stemis are still noticeable, and of smallerdiameter than normal (plate II, fig. 1, 1) Bliss Triumliph on its own roots.

By imarching a hair sprout planit (plate II, fig. 2, 1) on a normal BlissTriumph (plate II, fig. 2, 2) each part of the graft retainied its originalcharacteristics, although the imiarchiing aided the growvth of the hair sprouttop above the union, but did not change the diameter or leaf form below theunion.

Eight successful grafts of niormal Bliss Triumplh on hair sprout wereobtained, one of which is shown in plate II, figure 2, 3. The two sections ofthis graft maintained their original characteristies of diameter and leafform, the heavy norimal top requiring, support, but obtaining its water anldsoil nutrienits through the hair sprout section. This differenee in stemdiamiieter was maintaiiied for three months after grafting.

A graft of hair sprout Bliss Triunmph scion on normal stock is slhown inplate II, figure 2, 4, made at the saim-e time as the previous reciprocal graft,with a seconid normal shoot (plate II, fig. 2, 5) growing from the miiotlhertuber. Each maintained its individual characteristies.

From these data it is inldicated that the hair sprout conldition is niotcapable of transmission through grafting, as one might expect it to be, ifthe conidition is hormonal in niature. If the condition is virus-like in niature,such virus must be not easily transmiiitted through grafting or imarchingof the plant tops. The normal, or the hair sprout conidition is not affectedeither by normal scion receiving its water ancd soil nutrients throulgh a hairsprout stock, or the reciprocal of this. Likewise the passage of photo-svnthate from the sciomi to the stock does not change the condition.

GRAFTING OF POTATO EYES INTO TUBERS

Since it was indicated by experiment and observ-ationi, that the hairsprout condition occurs in all of the buds of a potato eye, if it has beendemiolnstrated by onie bud, and since it was indicated that the hair sproutcondition could be prodclued on small tubers growing directly out of themother tuber, reciprocal eyle grafting was undertaken. The surface oftubers of Bliss Triumph known to be normal or hair sprout in particulareyes bv the growth of shoots from them, was sterilized. The "saturated"chlorinated lime solution made according to directions on the containier wasdiluted to 0.5 per cent. anid the tubers immersed in this for 14 hours. A tan-gential slice was taken from the side of the bud with a safety razor, and thecut and razor sterilized in the sterilizant. A second tangential incision wasmade by the razor 1 ineh below the bud. Then with a sterilized sharp corkborer the bud was cut ouit from the tuber, dipped into the sterilizant, andinserted into the hole from which a similar bud had been removed for thereciprocal transfer. The tubers were then set to sprout in covered, steril-

188




ized cry-stallizingy dishes on moist filter paper. Sufflcieiit successful steriletransfers. were obtained to give good growth of the buds thereafter, thetransferred bud formiiing firmn union with the mother tuber. Infected tranis-fers were discarded. The sprouts that grew from these eye grafts main-tained their characteristies after the reciprocal grafts, hair sprouts remainedof small diameter, and normal shoots of niormal diameter. This indicatesthat the hair sprout condition is characteristic of the bud and that it cannotbe tranismiiitted from the tuber to niormal buds or corrected in hair sproutbuids by reciprocal bud grafting in wbhieh all the shoot growth occurs in thepresenice of the niormal mother tuber with which it has made a growth union.

Growth stimulation experimentsEtlhylene is a comiimon plant emanation and affects the sprouting of

potatoes'alud the geotropic responises of stems, both of which seem, in hairsprouit tubers, to be abnormal. The early sprouting, and lateral geotropicgrowtlh response of shoots of hair sprout tubers has beeni mentioned previ-ously. Tuibers of the White Rose variet,v bothnormal andhair sprout, weretreated in a sealedlnloist chamber of 8.2 eu. ft. capacity with ethylene 1 partper 1000 parts of air at 65° F., renewi-ingc the concenitration each day byaeration and reestablishment to 1: 1000 until sprouting occurred. Althoughthe rest period of hair sprout tubers is short, it was found that sproutingwashastenied by this ethylene treatment. Thereafter, on removing from theethylenechlamlber, hair sprout eves prodcieed hair sprouts, and normal evesproduiced normiial sprouts. Such ethylene treatment neither produces thecondition, nor corrects it. The treatment, however, may be of slight advan-tagein obtaininig early information oni the incidence ofhair sprout in tubersimmediately after digging. In similar treatments at proper concentrationsof etvyleene chlorhydrini and tetrachlorethylene, no change in the hair sproutconiditioni was fouind. A proper count of hair sprout eyes oni tubers can bemade after any of these stimulating treatments.

Ithas already been noted that hair sprouts produce poor rooting, bothinnumiiber of roots and the rate of root extension (plate I, fig. 1, 1 and 2).Soakinig sterilized eyes in 1-ounce pieces of cut tubers before sprouting inwater solutions of KI1nO4, varying from 1 per cent. down to 0.015 per cent.,gave somewhat thieker stems and increased considerablv the number andlength of roots formiied, with the optimum at 0.25 per cent. Thiamine hydro-ehloride 0.001 and 0.0001 per cent. did not increase the number or length ofroots or the thiekness of shoots formed from the hair sprout tubers. Thesewere grown in darkness at 24° C. Subsequent growth in soil in the green-

houise didcnot correct the tendency to produce spindling stems.Seed pieces of Bliss Triumph both withnormal and with hair sprout eyes

were sterilized as above and placed with the cut surface down in sterile Petridishes lined with filter paper, wvhich was moistenied with 10 ml. of indole-3-propionic acid 6.45mg. per liter. No roots were formed after 14 days, andsteins were-less than 2 mum. in diameter, althoughhavingf small tubers and

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PLANT PHYSIOLOGY

stems 3 to 5 inches long. Normal pieces gave numerous long roots anid2-in. x 3-in. stems. with no tubers.

After treatmiient of cut seed pieces with Auxilin the shoots from hairsprout Bliss Triumph tubers growni in peat still tended to be mllore spindlilngthan normal untreated tubers.

Application of borax (10-5/M solutioll) to peat in which hair sproutBliss Triumph tubers were grown, did not correct the hair sprout condition.

Chemical composition of potato tubers in relation to hair sprout2

Bliss TriuLmph and White Rose varieties of potato tubers havinog lhairsprouts were used, with checks from the same field. Those that producedhair sprout, and normal tubers, were selected by allowing the sprouts toappear, then paired tubers were selected of the same size from these lots.In some instanees, tubers were used which showed various degrees of thick-ness of the sprouts, and three classes were established: extreme hair sprout;intermediate hair sprout; and normal. The tubers from the field were keptunder the same storage conditions of teimiperature and time, first at 20° C.(68° F.) to allow sprouts to appear and make the classification, tlhen partwere put at low, and at intermediate storage temperature to nlote the effectof the storage temperature on the composition of the tubers. A lot of WhiteRose divided int.o lots of equal pairs of both normal, and hair sprolit tulbers,were placed in storage, one at + 2° C. (35.6° F.) and the other at 8° C.(46.4° F.). The tubers were stored for 4 days to allow the carbolhl-dratesto come to equilibriumi, because it is known that the temperature of storageaffects the sugar conten-t. Pentosans, total nitrogen, and pentoses, on adry weight basis, were determined oni paired Bliss Triumph tubers after 200C. (68° F.) storage (table I). Dry weight, reducing and total sugar, andstarch, were determined on WVhite Rose tubers both after storaoe at 20° C.(68° F.) (table II), alnd after storage at lowver temperature (table III).

For analysis the potato samples were washed and scrubbed clealn. Theywere then sliced thin, directly into 80 per cent. alcohol containing sufficientCaCO3 to neutralize acids. An aliquot of each sample was takeni for dryweight and total nitrogen determinationis. Dry weight wvas determinedby heating in a vacuum oven at 60° C. to con-stant weight. Sugars weredetermined by the Munson-Walker gravimetric procedure, starch by theacid hydrolysis method, using HCl (sp. gr. 1.125), and nitrogen by theusual Kjeldahl method, using 30 ml. of H1204 anid 5 gmn. K2S04.

Analyses reported in table I inidicate that there is no considerable differ-ence betweeln hair sprout and normal Bliss Triumph tubers in total niitroaen,pentosans, or pentoses, onl the dry weight basis. Further uniform miiaterialoni this variety was not available for further determinations.

White Rose tubers (table II), in which selection of the tubers wasdivided into normal, intermediate, ancd extreme hair sprout tubers, slhowed

2 Assistance in the preparation of these materials was furnished by the personnel ofthe Work Projects Administration, Official Project no. 65-1-71-140. Sponsored by theUniversity of Minnesota, 1940.

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TABLE IANALYSES OF NORMAL AND HAIR SPROUT BLISS TRIUMIPH TUBERS (DRY WT. BASIS)

NUMBER PERCENTOAGE PERCENTAGE PERCENTAGE

TUI-BERS TUERTYE N., (+ NTO,) PENTTOSANS PENTOSES

TUBERS~ N%(NOo10 Hair sprout

Aver . 1.99 3.81 4.41Sx. .. 0.26 0.62 0.75P.E . ... 0.18 0.42 0.51

10 NormalAver. 2.09 3.31 3.84Sx. ........... 0.38 0.73 0.83P.E. 0.26 0.49 0.56

a conisiderable illerease in the content of both reducing and total sugars, asthe hair sprout condition increased in severity. The tubers selected asnormal, showed no hair sprouts from any eyes, those called intermediateshowed sprouts with diameters intermediate between normal and extremehair sprout, and may have been nearly normal for some sprouts. For theextreme hair sprout sample, only tubers with all extremely thin sproutsfromii all eyes were taken. The ilntermediate group may be between thenoriimal anid the extreme group because the whole tuber was intermediatein its reactions, or because individual portions of the tubers varied in theirsugar conitent according to the influence of each eye on the composition ofthe portion of the tuber surroundinog it. In the discussion of the morphologyof the distribution of hair sprout over the tuber it is shown that each eyeoni a tuber may be different from its fellows, and shows either all normal

TABLE IIANALYSES OF NORMAL AND HAIR SPROUT WHITE ROSE TUBERS

NUM BER PERCENTAGE PERCENTAGE PERCENTAGE PERCENTAGEOF TUBER TYPE DRY REDUCING TOTAL STARCH

TUBERS WEIGHT SUGAR SUGAR

7 NormalAver. .... 22.73 2.82 4.11 58.97Sx . 2.85 0.61 0.64 6.12P.E. 1.92 0.41 0.43 4.13

7 Intermediatehair sprout

Aver. 20.55 5.44 7.14 58.17Sx .2.81 1.39 1.75 4.94P.E. 1.90 0.93 1.18 3.33

7 Ecxtremehair sprout

Aver. ..... 17.19 8.65 10.60 60.12Sx .. 2.65 2.61 2.86 6.00P.E. 1.79 I 1.76 1.93 4.04

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PLANT PHYSIOLOGY

or all hair sprouts from the primary and secondary buds in the eye. It maybe postulated, since the growth processes of each eye are individual, that themetabolic processes there are individual. The separation between normalsprouts and intermediate sprouts is miore difficult than bet-ween normal andlhair sprout eyes. The basis of selection into the intermediate group was theprecociously early sprouting of the eyes and the rapid growth of the shootstherefrom, a growth indicating that the tendency to early sprouting waspresent in the eyes of this group, but that the growth produced was thickerthan in extreme hair sprout, thinner than in normal tubers.

The average range for dry weight from 22.73 per cent. for normal,20.55 per cent. for intermediate, to 17.19 per cent. for extreme hair sprout

TABLE IIIANALYSES OF NORMAL AND HAIR SPROUT WVHITE ROSE TUBERS (DRY WT. BASIS)

NUAIBER PERCENTAGE PERCENTAGE PERCENTAGEOF TUBER TYPE REDUCING TOTAL TA

TUBERS SUGAR SUGAR STRCH

5 Normal + 20 C.Aver. ........ 1.35 2.85 66.26S. 0.41 0.36 3.45P.E. 0.27 0.24 2.33

5 Hair sprout + 20 C.Aver. 2.38 7.4 60.83Sx 0.85 3.9 5.02P.E. .... 0.57 2.63 3.39

5 Normal + 8° C.Aver. 0.49 1.09 64.3Si ........ 0.29 0.32 4.85P.E. 0.20 0.22 3.27

5 Hair sprout + 80 C.Aver. 2.8 6.14 65.03Sx 1.61 1.92 7.31P.E . .. 1.09 1.29 4.93

indicates that the hair sprout conditioni is associated with a tendency tohold more water in the tuber. The range of total sugars from 4.1 per cent.for normal, to 7.14 per cent. for intermediate, to 10.6 per cent. for extremehair sprout suggests that the greater water content is associated with greateramnounts of osmotically active substanees. The experience expressed bygrowers who have extensively observed the behavior of healthy and hairsprout tubers in lon-g time storage is that those that show extreme hair sproutdo not shrink as rapidly as normal tubers. It is claimed that selection ofturgid hair sprout tubers can be made in the spring. The tendency of hairsprout tubers to sprout early should lead to earlier loss of water unless thestorage temperature is kept low enough to prevent sprouting.

The tendency to produee hair sprouts is maintained throughout thelife of the tuber, and is as marked in June after winter storage as in Septem-

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HARVEY, REICHENBERG, LEHNER AND IIA'MMi: HAIR SPROUT 1

ber immiiiiediately after digging, if the tubers are placed at growing tein-peratures.

Beeause it is clearly proveen by the work of several investigators that thesuoar conteint of potato tubers is depenidenit upon the storage temperature,ancd sugars greatly increase at temperatures just above (± 2° C.) the freezingpoint, but not at + 8° C., the effect of the storage temperature on both normiialand( extreme hair sprout tubers was studied. Table III shows the analysisof tubers that were paired for size, andl separated into normal and extremehair sprout after storage at 20° C. They were then placed at 20 C. andat 8° C. for four days, a timiie deemed sufficiently long to allow the conversioniof starch to sugar at 2° C. but not long enough to allow the differences inrate of respiration to overbalance the conv-ersion effect of the temperature.At 2° C. the reducing ancd total sugars on a dryweight basis in extreme hairsprout tubers, are approximately double the pereentage in normal tubers.At 8° C. storage, the reducing and total suoars in hair sprout, are approxi-mately 6 tiniies as great as in normal tubers. The higher sugar contenlt ofthe hair sprout tubers is not due to the differential effect of storage temiipera-ture oni the two types of tubers, but to inherent differenees in behavior.

SummaryThere was no large differenee between normiial and hair sprout tubers

in the total nitrogen, pentoses, or pentosans oni a dry weight basis of BlissTriumnph potatoes.

There was a consistently greater percentage of reduc-eing and total sugars,ancd a decrease of percentage dry weight in hair sprout tubers, over normaltubers of AAhite Rose potatoes. The differenices in sugar content are main-taineed at high, and at low storage teiimperatures. There was no consistenttren-cd in the percentages of stareh.

THE MI-N-NESOTA AGRICULTURAL EXPERIMIESNT STATIONST. PAUL, -MINNESOTA

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PLANT PHYSIOLOGY

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PLATE I

FIG. 1. Upper, 1, 2, 3, hair sprout; 4, normal tuber; sprouted in darkness.FIG. 2. Middle, 1, hair sprout; 2, normal tuber; sprouted in light.FIG. 3. Lower, 1, hair sprout; 2, normal plant.

PLATE I

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PLATE IIPLANT PHYSIOLOGY

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PLATE II

FIG. 1. Upper, 1, normal; 2 and 3, hair sprout scion on normal stock; 4, hair sprout.FIG. 2. Lower, 1, lhair sprout imarchled on 2; normal; 3, normiial scion on hair sprout

stock; 4, hair sprout scion on normal stock; with 5, normal shoot.

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PLANT PHYSIOLOGY

PLATE III

FIG. 1. Extreme hair sprout with small tubers on sprouts, and one tuber attached to

mother tuber, producing hair sprouts.FIG. 2. Intermediate hair sprouts in center portion of tuber normal at tip and base.FIG. 3. Extreme hair sprout at tip enid, intermediate hair sprout at basal end.

PLATE III



PLANT PHYSIOLOGY

PLATE IV

Intermediate hair sprouts at tip, normal at base.Normal sprout from tip, hair sprout tubers from three eyes.Extreme hair sprout from two eyes, others normal.

FIG. 1.FIG. 2.FIG. 3.

PLATE IV



Documents

NICE AND - Plant Physiology · PLANT PHYSIOLOGY greenhouse. Teni suecessful grafts of hair sprout scions onl normiial stocks were obtained. Two of these are pictured in plate II,