ITEMS FROM ESTONIA

 

INSTITUTE OF EXPERIMENTAL BIOLOGY AT THE ESTONIAN AGRICULTURAL UNIVERSITY

76902, Harku, Estonia.

 

Monosomic analysis of disease resistance in common wheat cultivars and introgressed lines. [p. 41-44]

T. Enno, H. Peusha, and O. Priilinn.

During the last several years, we made a series of aneuploid monosomic analyses in order to locate genes controlling resistance to powder mildew in common wheat cultivars and also in a hybrid line derived from T. timopheevii. In Europe, most of the genes for powdery mildew resistance in commercial wheat cultivars have been overcome by new virulent strains of pathogen. Therefore, the need exists for effective novel sources of genetic resistance to this disease.

A new, common wheat cultivar Meri was bred using Finnish varieties. The pedigree of Meri is 'Kärn/Tammi//Veka/Kolibri//R125/4x Hjan Ulla//Hja 22058/WW21220//Bor/Hja 24471' (T. Juuti, Boreal Plant Breeding, Jokioinen, Finland; personal communication).

A monosomic analysis of Meri revealed that one, major dominant gene conferring resistance is located on chromosome 1B (Table 1). The new gene was designated Pm28 (Peusha et al. 2000a) and can be found in the Catalogue of Gene Symbols for Wheat.

Table 1. Segregation for resistance to powdery mildew in F2 monosomic families derived from crosses between the Chinese Spring monosomics lines with the cultivar Meri.
   Monosomic line  Powdery mildew isolate N2  Powdery mildew isolate N9
 Resistant  Susceptible  X2 (3:1)  Resistant  Susceptible  X2 (3:1)
 1A  114  32  0.738 110 36 0.008
 2A  57  17  0.161 111 41 0.314
 3A  102  37 0.193 106 33 0.117
 4A  113  39 0.034 116 36 0.140
 5A  90  33 0.218 88 35 0.782
 6A  90  33 0.218 93 30 0.024
 7A  92  27 0.338 87 32 0.226
1B  127  10 22.89* 121 16 12.96*
2B   71  25 0.054 70 26 0.221
 3B  112  40 0.140 117 35 0.314
 4B  113  35 0.144 112 36 0.036
 5B  109  33  0.234 103 39 0.460
 6B  111  36  0.020 104 43 1.416
 7B  106  43  1.182 117 32 0.985
 1D  117  33  0.720 113 37 0.008 
 2D  101  43  1.814 108 36 0.000
 3D  117  37  0.077  112 42 0.424
 4D  85  27  0.047  78 34 1.713 
 5D  110  39  0.109  110 39 0.109
 6D  54  17  0.041  50 21 0.792
 7D  81  24  0.256  78 27 0.028
 CS/Meri  110  38  0.036  114 34 0.324 
 *P < 0.05

 

The Swedish cultivar Tjalve has the pedigree 'Reno / WW16679 // WW15432'. WW16679 is a backcross line with the cultivar Kolibri as the recurrent parent and WW15433 is a backcross line where the cultivar Drabant as recurrent parent (JÖ Jösson, Cereal Breeding Department, Svalöf Weibull AB, Sweden; pers comm). Results of the monosomic analysis indicated that the powdery mildew-resistance gene in Tjalve was controlled by one dominant gene and one recessive gene, which are located on the chromosomes 1A and 3B, respectively (Table 2) (Peusha et al., 2000b).

 

Table 2. Segregation of F2 for seedling reaction to powdery mildew isolates 9 and 10 in progenies of monosomic F1 plants from crosses of monosomic and euploid Chinese Spring with the cultivar Tjalve.
   Monosomic line    Powdery mildew isolate N9  Powdery mildew isolate N10
 Number of plants  Resistant  Susceptible  X2 (13:1)  Resistant  Susceptible  X2 (13:1)
 1A  300 294 6 55.24* 276 24 45.45*
 2A  --- --- --- --- --- --- ---
 3A  140 118 22 0.846 115 25 0.072
 4A  82 70 12 0.909 69 13 0.440
 5A  143 120 23 0.663 121 22 1.061
 6A  109 90 19 0.132 91 18 0.345
 7A  130 107 23 0.095 109 21 0.574
1B  93 79 14 0.830 77 16 0.144
2B   111 93 18 0.467 94 17 0.856
 3B  189 177 12 19.07* 175 14 16.01*
 4B  33 28 5 0.820 29 4 0.945
 5B  112 95 17 0.935 96 16 1.464
 6B  147 123 24 0.565 125 22 1.380
 7B  87 74 13 0.826 75 12 1.412
 1D  149 118 31 0.414 120 29 0.049
 2D  142 118 24 0.316 120 22 0.987
 3D  130 108 22 0.284 105 25 0.019
 4D  138 114 24 0.167 116 22 0.714
 5D  79 65 14 0.054 67 12 0.656
 6D  138 116 22 0.712 113 25 0.035
 7D  141 114 27 0.014 113 28 0.114
 CS/Tjalve  301 245 56 0.003 247 54 0.128
 *P < 0.01

The gene Pm3, known to confer resistance to powdery mildew, is located on chromosome 1A and consists of at least seven different alleles or very closely linked loci (Briggle and Sears 1966, McIntosh and Baker 1969, Sourdille et al. 1999). The cultivar Kolibri and line WW 16679 also possess allele Pm3d. We assume that the resistance in Tjalve is from one of Pm3 alleles, but this assumption only can be verified by an allelism test of the F2 and F3 populations. So far, only one recessive, powdery mildew gene with allelic series is known - pm5. This gene, derived from T. dicoccum and located on chromosome 7B, was initially introgressed into the common wheat Hope (McIntosh et al. 1998, Zeller et al. 1998, Hsam et al. 2001). Thus, in Tjalve, the 3B chromosome carries a new recessive gene.

The significant decrease in the genetic variability in the gene pool of common wheat was caused by improvements in productivity and adaptability of wheat cultivars resulting in genetic uniformity. The result is vulnerability in the wheat plant to disease. We made interspecific hybridizations with the aim of transferring disease-resistance genes from tetraploid wheat (Peusha and Enno 1992).

In some of the introgressed lines selected from the progeny of these wide crosses that were derivatives of T. timopheevii, resistance genes Pm2 and Pm6 were identified using powdery mildew tester isolates (Peusha et al. 1995).

Using cytogenetic analysis at meiosis in monosomic F1 hybrids, C-banding, and SDS-PAGE of gliadin fractions, we showed that the line 146-155-T has a reciprocal translocation that involved chromosome 6B (Badaeva et al. 1995, Enno et al. 1998a, b). Monosomic analysis revealed that 146-155-T has a single, dominant gene conferring powdery mildew resistance located on chromosome 6B (Järve et al. 2000).

RFLP and microsatellite analyses detected the presence of a T. timopheevii segment translocated to chromosome 6BS with the breakpoints between the loci Xprs8/Xpsr964 and Xpsr154/Xpsr546. A microsatellite locus Xpsp3131 is located on the T. timopheevii segment transferred to the 6BS of T. aestivum. This novel powdery mildew resistance gene has been designated by symbol Pm27 (Järve et al. 2000).

This work was supported by Estonian Science Foundation (Grant N 3162).

References.