Hordeum chilense resistance to powdery mildew and its potential use in cereal breeding

~taphvttca 67:215 -220.1993. © 1993 Kluwer Academic Publishers. Printed in the Netherlands.

Hordeum chilense resistance to powdery mildew and its potential use in cereal breeding

D. Rubiales 1, J.K.M. Brown 2 & A. Martfn 1 J lnstituto de Agricultura Sostenible, C.S.L C., Apdo 3048, 14080 C6rdoba, Spain; 2 Cambridge Laboratory, LPS.R., Colney Lane, Norwich NR4 7UJ, UK

Received 6 January 1993. accepted 9 April 1993

Key words: disease resistance, Erysiphe graminis f. sp. triticL Erysiphe graminis f. sp. hordei, Hordeum chilense, intergeneric hybridization, powdery mildew, tritordeum

Summary

Hordeum chilense is a wild barley with high crossability with Triticum, Hordeum and Secale. Its amphiploid with wheat, tritordeum, has potential as a new crop. H. chilense is highly resistant to the powdery mildew diseases of both wheat and barley. Whereas tritordeum is resistant to barley powdery mildew, its reaction to wheat powdery mildew is similar to that of its wheat parent. However H. chilense contributes to a reduced density of mildew colonies. This quantitative resistance of tritordeum is diluted at higher ploidy levels.

Introduction

Powdery mildew diseases of wheat and barley, caused by Erysiphe graminis f. sp. tritici and E. graminis f. sp. hordei, respectively, are widely distrib- uted in the world and are of great economic importance. Breeding for resistance is considered to be the most effective and economically feasible mean of powdery mildew control in cereals. Because mildew has the ability to overcome new resistance genes rapidly there is a need to extend the range of resistance to mildew (Bennett, 1984). There is considerable variation for resistance available in related species and genera. Resistance to E.g. tritici has been reported in species of Triticum, Aegilops, Agropyron, Secale, Haynaldia, and Eremopyron (Wahl et al., 1978; Bennett, 1984). Resistance to E.g. hordei has been found in cultivated barley (Mose- man, et al., 1965; Jorgensen, 1992) and in wild Hor- deum species (Wahl et al., 1978; Gustafsson & Claesson, 1988).

Hordeum chilense is interesting in cereal breeding due to its high crossability with Triticum, Hor- deum, and Secale (Finch & Bennet, 1980; Martfn & Cubero, 1981). H. chilense x Triticum spp. amphiploids (tritordeum) have a potential as a new crop (Cubero et al., 1986; Martfn, 1988; Alvarez et al., 1992). Moreover, these amphiploids could be used as bridging parents to transfer desirable traits to cultivated cereals. H. chilense itself has potential as a fodder crop.

The objective of the present study was to deter- mine the level of resistance of H. chilense and tritordeum to mildew diseases of cereals.

Material and methods

Seedling test

A set of tritordeum lines and their H. chilense and wheat parents was studied for seedling reaction to

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E. graminis f. sp. tritici and E. graminis f. sp. hordei. The origin of the materials was described in Ru- biales et al. (1991, 1992a, 1992b, 1993).

Two experimental runs were performed. Each run consisted of six plants per line, grown individu- ally in jiffy pots. When the second leaf was fully ex- panded the middle 30-mm segment of the first formed leaf of each plant was excised. The segments were placed, adaxial surface up, on 0.4% agar containing 125 ppm benzimidazole in transparent boxes, following a randomized design.

The following isolates of the powdery mildew fungus were used in the study: E. graminis f. sp. tritici, (Egt): - WC7 (virulent for Pm4a, Pm4b). - WCl l (Pm3a, Pm3c, Pm4a, Pm5, Pm8). - WC21 (Pml, Pm2, Pm3a, Pm3c, Pm4a, Pm4b,

Pm5, Pm6, Pm8, Mid, cv. Wembley). - WC28 (Pml, Pm2, Pm3a, Pm3b, Pm3c, Pm4a,

Pm4b, Pm5, Pm8, Mid, cvs. Broom, Tonic, Wem- bley).

E. graminis f. sp. hordei, ( Egh ): - CC21 (Mla3, Mla6, Mlg, Mlh, Mira, Mlc). - CC52 (Mla7, Mla9, Mlal2, Mla13, Mlg, Mlh,

Mlk, Mira, MI(CP), MlalO). - CC91 (Mlal, Mla6, Mlal2, Mlg, Mlh, Mira, Ml

(Ab), MI(CP), MI(La), Mlc). - CC134 (Mla6, Mla7, Mla13, Mlg, Mlh, Mlk, Mira,

MI(Ab), Ml(CP)). The mildew spores were multiplied on the susceptible wheat cv. Cerco, and barley cv. Golden Prom-

ise, respectively. Heavily infected leaf segments from detached leaf culture were used to provide a high inoculum load. Inoculations were performed by blowing young conidia into a spore settling tower containing the boxes in a completely randomized design. The boxes were then incubated in a growth cabinet held at 15 ° C, with 16 hours photoperiod.

The Infection Type (IT) produced on each line was determined seven days after inoculation ac- cording to a 0--4 scale (Moseman et al., 1965). The Infection Frequency (IF) was recorded as the number of colonies per cm 2, by counting the number of mildew colonies that developed on each segment and measuring the leaf width. IF was determined in the two runs for Egt isolate WC28, but only in the second run for the other three Egt isolates. Statisti- cal analyses were based on a randomized complete blocks design. An analysis of variance was run, and the means were separated by the LSD test.

Field experiments

The accessions were grown as rows in nurseries at C6rdoba during 1988-89, 1989-90 and 1990-91. En- tries included varied between trials depending on seed availability. Mildew infection occurred natu- rally. Disease scores were based on the percentage leaf area covered by mildew.

Table 1. Infection type (T) with Erysiphe graminis ft. spp. tritici (Egt) and hordei (Egh) in seedlings of H. chilense, wheat and t r i tordeum

Egt Egh

WC7 W C l l WC21 WC28 CC21 CC52 CC91 CC134

H. chilense I 0 0 0 0 0 0 0 0 Whea t 2 0/44 0/4 0/4 0/4 0 0 0 0 Tri tordeum 3 0/4,1, s 0/4,1, 0/4,l, 0/4,1, 0 0 0 0

Checks:

W. 'Cerco' 4 4 4 4 0 0 0 0 B. 'Golden Promise ' 0 0 0 0 4 4 4 4

Based on observations of 20 H. chilense lines. 2 Based on observations of 17 wheat lines, parents of the t r i tordeum studied. 3 Based on observations of 23 tr i tordeum lines. 4 The lines studied showed either IT 0 or IT 4.

s 4,1, = fully susceptible IT, but with a reduced IF (see Fig. 1, Table 2).

217

120 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

= 100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . " . . . . . . . . . . . . . a . . . . a . . . . . . . . . 80 b . . . . . . . .

,o . . . . . . . . . . . . . . . . . . . . . . - ' a . . . . . . . . . . . . . . . . . .

'S :: ',',', b c

40 . . . . . . . . . . . . . . . . . . . . . . . - . . . . . . . . . .

ab ~i~ :: ~:~: ::~ ::~i:. :~:~ ~ e

b a i i i i , i i i i i : e d

o 2: WC7 WC 11 WC21 WC28

2 2

~]DDDO F~HHDD ~AABB ~HHAABB ~AABBDD V~HHAABBDD Fig. 1. Infection Frequency 1 (IF) of isolates of E. graminis f. sp. tritici on a set of wheat and tritordeum lines grouped by ploidy levels. 1 Based only on observations of the material with a susceptible IT. 2 T. tauschii and its tritordeum (4 x) offspring were resistant (IT 0) to isolates WC7 and WCll. 3 Letters in common over columns per isolate indicate that differences are not statistically significant (P < 0.05, LSD).

Resul t s

Seedling tests

Response to Egt. All H. chilense lines (Table 1) and

the barley check were inmmune (IT 0) to the four Egt isolates. The ITs of the tr i tordeums were 0 or 4, and were very similar to those of the respective wheat parental lines. The average IF (Fig. 1) of the susceptible wheat lines to the four isolates (15, 44, 50 and 50 colonies/cm 2, respectively) was significantly higher than the average of their t r i tordeum offspring (3, 15, 11 and 14 colonies/cm2). This state- ment was also true for each wheat and its tritordeum offspring (Table 2). The IF tended to be high-

er in the durum wheats than in the bread wheats used in this experiment. The reduction in the IF in the tr i tordeums with respect to their parental wheats was higher at the lower ploidy levels. The tetraploid t r i tordeum (HchHchDD) had more than 20,1, × reduction of IF in comparison to its wheat parent; hexaploids tr i tordeums ( H c h H c h A A B B ) had a 7-14,[, × reduction; and octoploid tri tordeums ( H c h H c h A A B B D D ) a 1.5-2.55 × reduction (Fig. 1).

The analysis of variance indicated a significant race effect for the density of colonies. The genotype-race interaction was significant for the species. The correlation coefficients between wheat parents and their t r i tordeum offspring for colonies density

218

Table 2. Infection Frequency (IF) of wheat (T-number) and tritordeum (HT-number) lines to isolates of E. graminis f. sp. tritici

Wheat Ploidy Isolate tritordeum level

WC7 W C f l WC21 WC281

T6 4 x 0 0 79 109

HT1052 4 × 0 0 1 4

T22 4 × 45 83 84 98

HT22 6 x 9 9 6 9

T29 4 × 13 20 74 81

HT19 6 × 1 4 6 21

T30 4 × 3 16 8 8

HT16 6 × 0 1 0 0.5

T34 4 x 50 98 97 106

HT23 6 x 1 11 6 13

T35 4 × 0 4 0 20

HTI7 6 × 0 0.4 0 0.4

T39 4 x 5 42 86 90

HT84 6 × 0 0 2 0

T49 4 × 26 43 83 79

HT49 6 × 0 3 0.2 8

HT59 6 x 0.4 5 16 17

T102 4 x 10 49 54 55

HT79 6 x 1 7 3 7

T103 4 × 6 16 16 45

HT85 6 x 0 4 1 8

T173 4 x 17 38 75 70

HT78 6 x 0 2 1 12

T20 6 × 15 20 53 52

HT20 8 x 2 15 6 12

T26 6 x 1 85 2 3

HT26 8 x l 43 3 3

T59 6 x 5 33 26 41

HT18 8 x 0.7 15 10 24

T87 6 x 33 63 73 78

HT92 8 x 10 22 19 35

T90 6 x l0 - 63 46

HT81 8 x 3 - 37 18

T98 6 x 0 35 26 37

HT103 8 x 0 0.7 0 0.1

W. Cerco 47 100 126 116

B. Golden Promise 0 0 0 0

Average of two series. Data on IF of the remaining isolates available on only one series. 2 HTI05 is a tetraploid tritordeum (HHDD) from the cross between tetraploid H. chilense (HHHH) and tetraploid T.

tauschii (DDDD).

were sigmficant (P< (I.05)only lor isolates WC7 and WCll.

Response to Egh. The barley check was very susceptible (IT 4) to the four isolates (Table 1). All H. chi lense, wheat and tritordeum lines showed IT 0.

Field response. The mildew incidence varied between years, being erratic in the 1989-90 trial (Table 3). No mildew was observed on any of the 14. chilense lines. Disease severity was significantly lower in tritordeum than in wheat. The reduction in disease severity was lower at the octoploid level. Field observations not presented from other locations and years support these results.

Discussion

H. chilense could be a valuable source of resistance to E. graminis f. sp. triticL and E. graminis f. sp. hordei that might be incorporated in cultivated cereals. H. chilense resistance was found to be suppressed by the wheat genomes in the case of rust fungi (Ru- biales et al., 1991, 1992b, 1993). However, tritordeum is more resistance than wheat to Septoria tritici (Rubiales et al., 1992a), to S. nodorum, and to Fusarium culmorum (Rubiales, unpublished data). The present study indicates that H. chilense resist ance to powdery mildew causes a reduced density ol mildew colonies in its amphiploids with wheat. This quantitative contribution of the H. chilense genome is diluted at higher ploidy levels. A quantitative contribution has also been reported for Aegilops longissima mildew resistance in 'Chinese Spring'-A. longissima addition and substitution lines (Zeller & Heun, 1985). Amphiploids involving A. caudata, A. ovata or Agropyron intermedium and Triticum parents were resistant to powdery mildew (Sinigovets & Lapchenko, 1975). The resistance of H. bulbosum to E. graminis f. sp. hordei was ex- pressed in hybrids with H. vulgare (Xu & Snape. 1989) and a major gene has been transferred to barley (Xu & Kasha, 1992).

The high IT of tritordeum to Egt contrast with the resistance of triticale. The H. chilense resistance to Egt results in a reduced infection frequency in tri-

tordeum although the IT of tritordeum is that of the wheat parent. On the other hand rye resistance to Egt confers a lower IT in triticale (Linde-Laursen, 1977; Heun & Friebe, 1990). There seems to be a dilution of the resistance at higher ploidy levels in both tritordeum and triticale. Linde-Laursen (1977) found low IT to Egt in all hexaploid triticales but only in 90% of the octoploid triticales studied. Ri- gin & Lebedeva (1990) also reported a degree of at- tack by Egt in some octoploid triticales. A dose effect towards powdery mildew has also been found in A. ventricosa addition lines in wheat (Dosba et al., 1980). Triticales and rye addition lines on wheat are resistant to E. graminis f. sp. secalis (Linde- Laursen, 1977). Both tritordeum and H. chilense

were resistant to the isolates of Egh used in this experiment. The behaviour of tritordeum to a powdery mildew isolate or forma specialis virulent on H. chilense should be determined. That virulence has not been found.

There is a considerable variation in disease response in wild species and related genera. Resist- ance has been transferred to wheat from Triticum and from the genera Aegilops, Secale and Agropy- ron. Wild Hordeum species are less accessible as gene donors to cultivated barley. They are more dis-

Table 3. Field response of wheat, tritordeum and H. chilense to

powdery mildew. Disease severity (% of leaf area covered by

mildew).

Field trial

88-89 j 89-902 90-913

W h e a t - 4 x 4 32 "5 2.2 b 35 ~

Tritordeum-6 x 4 b 0.04 c 8 c

Wheat-6 x 11 b 5.2" 30 b

Tritordeum-8x 8 b 0.15 ~ 10 ~

H. chilense 0 ~ 0 ~ 0 J

1 Based on observations of 13 wheats-4 x, 3 wheats-6 x, 11 tritor-

deums-6 x, 5 tritordeums-8 x, and 35 H. chilense lines. z Based on observations of 17 wheats-4 ×, 9 wheats-6 x, 20 tritor-

deums-6 x, 9 tritordeums-8 x, and 35 H. chilense lines. 3 Based on observations of 12 wheats-4 x, 11 wheats-6 x, 12 tritor-

deums-6 ×, 11 tritordeums-8 ×, and 35 H. chilense lines.

4 Ploidy level.

5 Letters in common within a column indicate that differences

are not statistically significant (P _< 0.05, LSD).

219

tantly related to cultivated barley than are Aegilops

and Triticum species to bread wheat. Furthermore the diploid nature of barley makes it more sensitive to minor genetic imbalances (Bothmer et al., 1991). Resistances to E. graminis f. sp. hordei were intro- duced from H. vulgare ssp. spontaneum and H. bulbosum to H. vulgare (Moseman, et al., 1965; Jahoor & Fischbeck, 1987; Xu & Kasha, 1992). The resistance of H. chilense to E. graminis f. sp. hordei might be used in barley breeding as H. chilense - H. vulgare homoeologous chromosome pairing has been observed (Martin, 1991; unpublished). Quantitative resistance has been identified in many plant-pathogen systems, including barley - E. graminis f.sp. hordei (Asher & Thomas, 1983), wheat - E. graminis f.sp. tritici (Royer et al., 1984) and barley - P. hordei (Parlevliet, 1978). The resistance to E. graminis f.sp. tritici conferred by H. chilense to tritordeum is also quantitative. The genetic basis of the resistance contributed by H. chilense should be determined and its durability followed after wide- spread use in agricultural conditions (Johnson, 1984). The genotype -race interaction also requires investigation since this has implications for the durability of the resistance.

Acknowledgements

We are greatly indebted to Mrs. J. Ballesteros. C. Martinez, P. Smith and G. Mukherjee for their technical assistance; to Dr. R.E. Niks for the critical reading of the manuscript; the C.I.D.A., and E.T.S.I.A.M., C6rdoba, Sp., for allowing the use of their facilities. We acknowledge the EEl. program of the Spanish M.E.C. and Project AGR92-0184 of the C.I.C.Y.T. for the financial support to the senior author.

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Hordeum chilense resistance to powdery mildew and its potential use in cereal breeding