Genetics of Powdery Mildew Resistance in  Barley Cultivars

M. R. Naghavi, B. Yazdi-Samadi and M. R. Ghannadha

 

Plant Breeding Dept., Faculty of Agriculture, University of Tehran, Karaj, Iran

Soroush3000@yahoo.com

 

Abstract

Eleven winter barley cultivars screened for resistance to powdery mildew in glasshouse and were also evaluated in the field to determine disease progress. ‘Afzal’ was the most susceptible cultivar in seedling (IT 9) and adult plant stages (relative AUDPC 100%). Cultivars with adult plant resistance, ‘Cwb’, ‘Reyhan’ and ‘Cyna’ showed susceptibility to moderate susceptibility response in seedling stage. In the field study, ‘Radical’ and ‘Cwb’ were highly resistant (relative AUDPC 5% of Afzal). These two resistant cultivars were crossed with highly susceptible cultivar, ‘Afzal’, to study the genetics of resistance. The parents, F1, F2 and F3 generations of the two crosses were evaluated for powdery mildew resistance in glasshouse and field. The χ2 analysis of the segregating ratios in the F3 generations indicated that the resistance was controlled by one gene at seedling stage, and by two or three genes in ‘Cwb’ and ‘Radical’, respectively at adult plant stage.

Keywords: Barley-Powdery mildew-Resistance gene-Inheritance.

 

Introduction

Powdery mildew of barley caused by Erysiphe graminis f. sp. hordei is one of the most important disease of barley particularly widespread in north parts of Iran. Based on the gene-for-gene hypothesis of Flor (1955), which was confirmed for powdery mildew of barley by Moseman (1959), many race-specific powdery mildew resistance genes from different origions have been recognized in barley (Moseman 1959, Wiberg 1974, Gorge et al. 1993, Giese at al. 1993, Jorgensen 1994, Schonfeld et al. 1996), but most of them have already been overcome by new virulent strains (Jahoor and Fischbeck 1993). It seems, therefore, necessary to look for  new resources of resistance. Many sources of resistance to powdery mildew in cultivated varieties and in their wild relatives have been reported in the past (Moseman et al. 1980, Xu and Kasha 1992, Jahoor and Fischbeck 1993, Jorgensen 1994, Mastebroek et al. 1995, Schonfeld et al. 1996, Czembor and Johnson 1999). Most studies suggested that resistance controlled by single or two genes with dominant inheritance, depending on mildew culture ( Jensen et al. 1982, Jahoor and Fischbeck 1993, Pickering et al. 1998).

 

Powdery mildew has been present in barley field in Iran for many years and has caused serious damage in some years when the climatic conditions were favorable. There is limited information on the genetics of powdery mildew in Iranian lines and cultivars. The objectives of the present study were (i) to evaluate the resistance of some Iranian cultivars of barley in greenhouse and field, and (ii) to determine the mode of inheritance of resistance in two cultivars.

 

Materials and Methods

Erysiphe graminis f. sp hordei isolate Gorgan  provided by Dr Torabi (Plant and seed improvement institute, Karaj, Iran) used for all experiments in glasshouse and field. This isolate was purified by single  pustule isolation and multiplied on young seedling of ‘Afzal’, a susceptible cultivar. Virulence spectrum of isolate was determined using Pallas isolines differential set of powdery mildew (Kolster et al. 1986).

 

Experiment I: The reaction of 11 Iranian winter cultivars of barley  to powdery    mildew assessed in seedling  and adult plant stages. The design was a randomized complete block with three replicates.

 

In greenhouse ten seeds per cultivar were sown in 15-cm-diameter pots. Seven days after planting, seedlings were inoculated with conidiospores of the mildew culture by shaking sporulating plants above them. During the period of inoculation a temperature of 18-20ºc was maintained. Ten days after inoculation, each primary leaf was evaluated for its mildew reaction using the 0-9 scale of Masterbroek and et al.(1995),where 0 and 9 were completely resistant and fully susceptible respectively. Plant with infection type 0-7 are classified as resistant and with infection type 8-9 as susceptible.

 

In field the powdery mildew epidemic was initiated by inoculating of ‘Afzal’, that planted among each 10 rows, at tillering stage. The sufficient moisture was maintained throughout the experiment to achieve an optimum disease development on susceptible cultivar. Average disease severity on upper three leaves was first recorded  according modified Cobb scale (Peterson et al. 1948), when the susceptible cultivar had reached 90 to 100 % disease severity. Two additional reading were taken at weekly intervals. The three disease ratings were used to calculate the area under the disease progress curve (AUDPC) via shaner and finney (1977) formula. The relative AUDPC(%) of each cultivars was calculated  using the actual AUDPC of any cultivar divided by the AUDPC of ‘Afzal’. 

 

Experiment II: In order to study the genetic basis of resistance in ‘Radical’ and ‘Cwb’ , the crosses were made between ‘Afzal’ and them. The F1 were harvested in bulk and the seed was space planted as F2 in college agricultural experiment station, karaj, during 1999 growing season. F3 lines were obtained by harvesting approximately 90 single plants from each F2 population.P1, P2, F1, F2and F3 of each crosses  were evaluated for their reaction to powdery mildew in both glasshouse and field. The  five generations were planted in a randomized block design with three replications.

 

In the glasshouse, 20 seeds of parents, 350 of F2 and 90 families of F3 for each cross were  sown and infection type was recorded as done for ExpI.  In the field each replication consisted of  one row of P1, P2 and F1, 10 rows of F2  and 30 rows of F3 generations. Field rows contained  two 1 m rows seeded 15 cm apart with 50cm between rows. Infection type recorded  similar to Exp I but on flag leaf.

 

Chi-square employed to test the goodness of fit between observed data and the theoretically expected ratios.

 

Results

The IT of 11 Iranian cultivars (Table 1) showed  reactions ranging from completely resistance to completely susceptible (IT 0 to 9), Which frequently differed between the cultivars. ‘Cwb’, ‘Reyhan’, ‘Cyna’, ‘Kavir’, ‘Korgan’, ‘Walfajr’ and ‘Zarghan’ were susceptible in seedling stage but their ITs were less than the IT of ‘Afzal’ ( IT 8 to 9). among the 3 remaining resistant cultivars, ‘Radical’ was the most resistance (IT 0 to 1).

 

Table 1: Barley cultivars, seedling infection type, final severity response and relative AUDPC in the field

Cultivar

IT1

Final severity response2

Relative AUDPC3

Radical

0 to 1

3.3

1.8

Cwb

8

3.3

1.8

Productive

4 to 5

6.0

4.0

Reyhan

7 to 8

10

8.8

Jonoob

5 to 6

25

19.1

Cyna

8

36

33.2

Kavir

7 to 8

51

37.2

Korgan

7 to 8

75

48.4

Walfajr

7 to 8

70

69.0

Zarghan

7 to 8

78

79.8

Afzal

9

100

100

1ITs are based on a 0 to 9 Mastebroek (1995); where 0= no symptoms visible; 1= distinct necrosis without visible mycelium; 4= distinct necrosis with moderate sprolation;5= moderate necrosis with moderate sporulation;7=weak necrosis and/or moderate chlorosis with heavy sporulation; 8=weak chlorosis with heavy sporulation and 9=n0 resistance reactions, abundant sporulation.

2Final disease severities are based on the modified Cobb Scale(Peterson et al. 1948).

3Relative AUDPC is the actual AUDPC of each cultivar divided by the AUDPC of ‘Afzal’ and multiplied by 100.

 

 According to Table 1 differences in relative AUDPC and final disease severity (FDS) among cultivars were highly significant in field. ‘Afzal’ was the most susceptible cultivar with AUDPC and also FDS of 100%. Both ‘Radical’ and ‘Cwb’ had the lowest relative AUDPC(3.3%) and FDS(1.8%) . It was followed by  ‘Productive’ and ‘Reyhan’ with relative AUDPC of 4 and 8.8 respectively.

 

The F1 plants from the cross of ‘Radical× Afzal’, displayed complete dominance resistance at seedling and adult plant stages because the infection type of the F1 reaction was the same as resistance parent. While  the reaction of F1 plants of ‘Cwb×Afzal’ indicated moderate susceptibility at seedling stage as the infection type was closer to the susceptible parent than to resistant one, but it was moderately resistant at adult plant stage (data not shown).

 

The F3 data from ‘Radical× Afzal’ and ‘Cwb×Afzal’ were applied to study the inheritance of resistance in Radical and Cwb and to estimate the number of genes, since F3 gives more authenticity than the F2 populations. Seedling stage of two crosses showed a good fit of ratio 1 resistance: 2 segregating: 1 susceptible, indicating that resistance in both crosses is monogenetically controlled. But at adult stage, with considering either homozygous or segregating individuals as resistant (Singh et al. 1995, Chen and Line 1995), the ‘Radical×Afzal’ and the ‘Cwb×Afzal’  gave 63:1 and 15:1 ratios, indicating that resistance being controlled by 3 and 2 dominant  genes respectively(Table 2).

 

 

Table 2: Distribution and χ2 tests for F3 from crosses between the susceptible, ‘Afzal’, and two resistant cultivars, ‘Radical’ and ‘Cwb’, in glasshouse and field.

 

Cross

Number of F3 lines

Expected ratio

 

χ2 value

HR1

Seg2

HS3

Glasshouse:

 

 

 

 

 

Radical×Afzal

22

44

24

1:2:1

0.13

Cwb×Afzal

19

48

23

1:2:1

0.48

 

 

 

 

 

 

Field:

 

 

 

 

 

Radical×Afzal

83

5

2

59:4:1

0.081

Cwb×Afzal

56

28

6

10:5:1

0.026

1 Homozygous resistant

2 Segregation for resistance

3 Homozygous susceptible

 

Discussion

Among 11 cultivars tested, 3 were resistant (IT 0 to 6) to powdery mildew in glasshouse (Table 1). The different resistant ITs of the cultivars may be explained by the presence of different resistance genes. In the field study ‘Radical’ and ‘Cwb’ were highly resistant (relative AUDPC<5% of ‘Afzal’). ‘Productive’, ‘Reyhan’ and ‘Jonoob’ had acceptable resistance levels (relative AUDPC<20%). ‘Cyna’ and ‘Kavir’ displayed moderate resistance levels (relative AUDPC<51%). The results of IT at seedling stage in glasshouse and also the relative AUDPC in field varied from almost completely resistance to completely susceptible. This may be due to different virulence spectrum of the mildew in glasshouse and in field  or to differences in growth stage(Masterbroek et al. 1995).’Cwb’, ‘Reyhan’ and ‘Cyna’, were susceptible in seedling but resistant in adult plant stage. Hence they showed slow rusting response (relative AUDPC 8.8%, 33.28%, and 1.8% respectively). But the development of powdery mildew was much faster on ‘Cyna’ than ‘Cwb’ and ‘Reyhan’. It is likely that different resistance genes affect powdery mildew development and they are difficult to be distinguished by measuring IT under greenhouse conditions in cultivars carring moderate resistance. If these resistance are controlled by different additive genes ,combinations of these effective resistance genes may afford better genetic control (Singh and Rajaram 1994, Ma and Singh 1996).

 

The expression of  resistance genes in F3 generations of glasshouse and that of field were quite different (Table 2). Based on segregation ratios, resistance sound to be controlled by only one gene in seedling stage in both ‘Radical’ and ‘Cwb’. This is in agreement with the findings of Jensen et al. (1982), Jahoor and Fischbeck (1993), Mastebroek et al. (1995), Schonfeld et al. (1996) and Czembor and Johnson (1999). The results suggested that the number and most probability the kind of genes affecting resistance in adult plant stage were different in ‘Radical’ (Two genes) and ‘Cwb’ (Three genes). Consequently, the accumulation of all resistance genes in one cultivar is expected to show even less disease infection. Thus ‘Radical’ and  ‘Cwb’ cultivars should have a greater potential in further powdery mildew resistance breeding work and may serve as a suitable genetic material.

The information obtained in this study might provide a better understanding of the genetic resistance to powdery mildew and it is a prerequisite to apply pyramiding of several resistance genes. The development of appropriate markers linked to resistance genes would greatly enhance the feasibility of such a strategy.

 

Acknowledgements

The authors thank Yosefi, Ghazvini and Patpour for providing powdery mildew isolate and for seed of cultivars.

 

References

Chen, X., and R. F. Line, 1995: Gene number and heritability of wheat cultivars with durable, high-temperature, adult-plant (HTAP) resistance and interaction of HTAP and race-specific seedling resistance to puccinia striiformis. Phytopathology 85,573-578.

Czembor, J. H. and M. R. Johnston, 1999: Resistance to powdery mildew in selections from Tunisian landraces of barley. Plant Breeding 118, 503-509.

Flohr, H. H., 1955: Host-parasite interaction in flax rust-It genetics and other implications. Phytopathology 45, 680-685.

Giese, H., A. G., H. P. Jensen,  and J. Jensen,  1993: Localization of the Laevigatum powdery mildew resistance gene to barley chromosome 2 by the use of RFLP markers. Theor. Appl. Genet. 85, 897-900. 

Gorge, R., K. Hollricher, , and P. Schulze-Lefert, 1993: Functional analysis and RFLP-mediated mapping of the Mlg resistance locus in barley. Plant J. 3, 857-866.

Jahoor, A. and G. Fischbeck, 1993: Identification of new genes for mildew resistance of barley at the Mla locus in lines derived from Hordeum spontaneum. Plant Breeding 110, 116-122.

Jensen, H. P., J.H. Jrgensen, and J. Jensen, 1982: Attempts of locate powdery mildew resistance gene MI(La) to a barley chromosome. BGN. 12, 65-68.

Jorgensen, J. H., 1994: Genetics of powdery mildew resistance in barley. CRC Critical Reviews in Plant Sciences 13, 97-119.

Kolster, P., L. Munk, O. Stolen and J. lohde, 1986: Near-Isogenic barley lines with genes for resistance to powdery mildew. Crop Sci 26, 903-907.

Ma. H., R. P. Singh, 1996: Expression of adult resistance to stripe rust at different growth stages of wheat. Plant Disease 80, 375-379.

Mastebroek, H. D., and A. G. Balkema-boomstra, 1995: Genetic analysis of powdery mildew resistance derived from wild barley. Plant Breeding 114, 121-125.

Moseman, J. G., 1959: Host-pathogen interaction of the genes for resistance in Hordeum vulgare and for pathogenicity in Erysiphe graminis f. ssp. hordei. Phytopathology 49, 469-472.

Moseman, J. G., P. S. Baenziger, and R. A. Kilpatrick, 1980: Hordeum spontaneum-an overlooked source of disease resistance. In: Europe and Mediterranean Cereal Rust Foundation, 91-93.

Peterson, R. F., A. B. Campbell, and A. E. Hannah, 1948: A diagrammatic scale for estimating rust intensity on leaves and stems of cereal. Can. J. Res. 26, 496-500.

Pickering, R. A., B. J. Steffenson, A. M. Hill and I. Borovkova , 1998: Association of leaf rust and powdery mildew resistance in a recombinant derived from Hordeum vulgare×Hordeum bulbosum hybrid. Plant Breeding 117, 83-84.

Schonfeld, M., A. Ragni, G. Fischbeck,  and A. Jahoor,  1996: RFLP mapping of three new loci for resistance genes to powdery mildew (Erysiphe graminis f. sp. hordei) in barley. Theor. Appl. genet. 93, 48-56.

Shaner, G. and R. E. Finney, 1977: The effect of nitrogen fertilization on the expression of slow-mildewing resistance in knox wheat. Phytopathology 67, 1051-1056.

Singh, G., S. Rajaram, J. Montoya and G. Fuentes-Davila, 1995: Genetic analysis of resistance to karnal bunt (Tilletia indica, Mitra) in bread wheat.Euphytica 81, 117-120.

Singh, R. P., and S. Rajaram, 1994: Genetics of adult-plant resistance to stripe rust in ten spring bread wheats. Euphytica 72, 1-7.

Wiberg, A., 1974: Sources of resistance to powdery mildew in barley. Hereditas 78, 1-40.

Xu, J., and K. J. Kasha, 1992: Transfer of a dominant gene for powdery mildew from Hordeum bulbosum into cultivated barley (H. vulgar). Theor. Appl. Genet. 84, 771-777.