Variation of resistance to Pseudocercosporella herpotrichoides (Fron) Deighton in wheat genotypes carrying the gene Pch-1

The effect of the gene Pch-1 on the resistance of wheat to Pseudocercosporella herpotrichoides was studied at four growth stages. The germplasm used consisted of adapted cultivars, genotypes provided by European plant breeders, near-homozygous lines and double haploid lines developed from our own breeding projects. The resistance was measured by ELISA. At all growth stages, genotypes carrying Pch-1 differed significantly in resistance. At early growth stages, there was a strong effect of the gene in most genotypes, but later the effect decreased and significant genotypes-environment interactions appeared. In addition, minor genes became more important and determined the level of adult plant resistance that proved to be inherited quantitatively. Pch-1 was of minor importance for this type of resistance. It is concluded that a high and long-lasting resistance level could be attained if the two genetically different sources of resistance were combined (resistance at juvenile stages, induced by Pch-1, and quantitative resistance at adult stages).     

Analyses of Interactions of Wheat Cultivars in Tests for Resistance to Pseudocercosporella herpotrichoides

A total of 20 cultivars of winter wheat were tested by ELISA for resistance to Pseudocercosporella herpotrichoides in six environments and three growth stages. In a three-factor statistical analysis, the contribution of the different factors to their respective interactions was studied. The genotype × environment interactions exerted a considerable influence which could be reduced by increasing the number of test locations. Environments with a high disease level were less suited to measuring resistance than those environments with a medium level. Estimates of heritability from 0.54 to 0.78 show that successful selection may be possible using ELISA. Significant correlations of quantitative resistance at different environments were only obtained under similar environmental conditions (the same location, the same year) and with P. herpotrichoides populations of similar composition (the same inoculum). The contributions of the individual cultivars to the genotype/ environment interactions were not significantly different, except for ‘Roazon’ and ‘Rendezvous’. Due to high environmental effects in growth stage H5, the determination of quantitative resistance was more reliable in younger stages (65, 75). Nevertheless, the use of the values from that late stage did not reduce the genetic parameters (σ², h₂) if they were combined with the earlier measurements.     

A New Source of Resistance to Pseudocercosporella herpotrichoides, Cause of Eyespot Disease of Wheat, Located on Chromosome 4V of Dasypyrum villosum

Resistance to Pseudocercosporella herpotrichoides in five wheat cultivars, accession W6 7283 of Dasypyrum villosum, and ‘Chinese Spring’ disomic addition lines of the D. villosum chromosomes IV, 2V, 4V, 5V, 6V and 7V, was evaluated in seedlings by measuring disease progress 6 weeks after inoculation with a β—glucuronidase—transformed strain of the pathogen and by visual estimates of disease severity. D. villosum and the disomic addition line of chromosome 4V were as resistant as wheat cultivars ‘VPM—1’ and ‘Cappelle Desprez’, but less resistant than ‘Rendezvous’. Resistance of the chromosome 4V disomic addition line was equivalent to that of D. villosum.‘Chinese Spring’ and disomic addition lines of IV, 2V, 5V, 6V and 7V were all susceptible. These results confirm Sparaguee's (1936) report of resistance in D. villosum to P. herpotrichoides and establish the chromosomal location for the genes controlling resistance. The presence of chromosome 4V in the addition line and its homocology to chromosome 4 in wheat were confirmed by Southern analysis of genomic DNA using chromosome group 4-specific clones. This genetic locus is not homoeologous with other known genes for resistance to P. herpotrichoides located on chromosome group 7, and thus represents a new source of resistance to this pathogen.     

Linkage relations among eyespot resistance gene Pch2, endopeptidase Ep-A1b, and RFLP marker Xpsr121 on chromosome 7A of wheat

Marker-based selection of Ep-D1b has been used successfully to incorporate Pch1, the gene for eyespot resistance on chromosome 7D, into commercial wheat. However, attempts to transfer resistance conferred by Pch1 (on chromosome 7A) through selection for Ep-A1b have not always been successful. Linkage relations among eyespot resistance gene Pch2, a gene encoding for an isozyme of endopeptidase, Ep-A1b, and RFLP marker Xpsr121 on chromosome 7A were determined using 80 homozygous recombinant substitution lines. The recombinant lines were derived from eyespot susceptible ‘Chinese Spring’ hybridized with a resistant disomic substitution line of ‘Cappelle Desprez’ that has chromosome 7A substituted into ‘Chinese Spring’. Segregations of Pch2, Ep-A1b and Xpsr121 fit an expected 1:1 single-locus ratios based on χ² tests. Linkage analysis revealed that Pch2 was not tightly linked to Ep-Alb (15% recombination). However, close linkage (3.8% recombination) existed between Ep-A1b and Xpsr121. The order of these loci is Pch2-Xpsr121-Ep-A1b. Unlike Pch1 and Ep-D1b, where little or no recombination is found, Pch1 and Ep-A1b showed considerable recombination and therefore linkage cannot be utilized efficiently in marker-based selection.     

Measuring the Severity of Eyespot Disease Induced by Pseudocercosporella herpotrichoides (Fron) Deighton in Wheat Cultivars at Different Growth Stages

From the total soluble protein of Pseudocercosporella herpotrichoides (Fron) Deighton, specific proteins were isolated and used as antigens. One antiserum proved to be highly sensitive and was used for quantitative determination of eyespot severity in 16 wheat cultivars. The detection limit in ELISA was calculated as 2.2 μg total fungus protein per ml plant sap. From anthesis, genotypes showed the most characteristic and reliable differentiation for a longer period of time, viz. at growth stages 60 and 75. These quantitative differences could be more successfully demonstrated with ELISA than with eye-spot scoring. There was, however, a close correlation between both traits. The most resistant genotypes carried the gene Pch-1 with the resistance originating from ‘Capelle Desprez’. Some genotypes originating from this cultivar showed rather low levels of susceptibility, which might be explained by additional effects of the genotypic background.     

The Influence of Plant Developmental Stage on Expression of Resistance to leaf Rust (Puccinia recondita) in Two Near Isogenic Lines of Wheat

Cultivar ‘Thatcher’, and ‘Thatcher’ lines with Lr 21 and Lr 22 were studied against a number of races of Puccinia recondita for seedling and adult plant reaction. The study has established that Lr 21 and Lr 22 are genes effective against P. recondita at adult plant stage. It has also shown that these genes confer resistance against all races when plants are inoculated at boot leaf stage.     

Novel gene for adult plant resistance to Puccinia recondita in the wheat cultivar'Arjun'

Inheritance of resistance in the wheat cultivar‘Arjun’(HD 2009) against leaf rust pathotype 77–1 revealed that its durable resistance is attributable to a novel dominant adult plant resistance (APR) gene. Lr13, another gene reported in the cultivar played no role. This new gene is established as different from Lr34, the only effective APR gene from Triticum aestivum known for durability.     

Location of a Gene for Resistance to Eyespot (Pseudocercosparella herpotrichoides) on Chromosome 7D of Bread Wheat

Chromosome 7D of the wheat line VPM1 derived from a cross of Aegilops ventricosa with wheat confers resistance to the facultative fungal parasite Pseudocercosporella herpotrichoides. To determine the number of genes responsible fur this resistance, homozygous recombinant lines were developed from an F₁ between the wheat variety ‘Hobbit sib’ and a substitution line carrying chromosome 7D of VPM1 in a ‘Hobbit sib’ background. Resistance to Pseudocercosporella herpotrichoides is shown to be determined by a single gene located distally on the long arm of chromosome 7D. EpD1b, a unique allele of a gene encoding the readily detectable isoenzyme — endopeptidase, maps without recombination to Pch1 suggesting for two separate genes a maximum recombination value of 0.03 (P 0.05). Resistance to Pherpotrichoides could alter-natively be a product of Ep-D1b. Pch1 is also mapped against a gene for adult plant resistance to brown rust (Puccinia recondita), to Rc3 which confers coleoptile colour, and to α-Amy-D2, an isozyme that encodes α-amylase production.     

Novel complementary genes for adult plant leaf rust resistance in a wheat stock carrying the 1BL-1RS translocation

The wheat-rye translocation (IBL-IRS) that carries the tightly linked genes Lr26/Sr31/Yr9, has been widely exploited in the development of wheat cultivars worldwide. This resistance, however, has become ineffective owing to the evolution of new pathotypes of Puccinia recondita that neutralize the resistance of Lr26. Inheritance studies on ‘Federation4′/‘Kavkaz’ revealed complementary genes derived separately from ‘Federation’ and ‘Kavkaz’ for adult plant resistance. This previously undescribed source of resistance appears to be widely effective and could therefore be used to broaden the genetic base for resistance in India. Its effectiveness in other geographical areas is unknown.     

Endopeptidase EP-1 as a Marker for the Eyespot Resistance Gene Pch-1 from Aegilops ventricosa in Wheat Line 'H-93-70'

Biochemical marker endopeptidase EP-1 was used to determine that an eyespot resistance gene, transferred from Aegilops ventricosa to the hexaploid wheat line ‘H-93-70’ is located on the long arm of the chromosome 7D.     

Detection of Resistance to the Russian Wheat Aphid in Hexaploid Wheat

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), poses a serious threat to wheat (Triticum aestivum L.) production in many parts of the world. This research was initiated to evaluate wheat accessions for detection of resistance to the RWA. Over 12,000 wheat cultivars and plant introductions (PIs) from the USDA-ARS National Small Grains Collection were evaluated for reaction to RWA feeding damage. Twenty-nine PIs from Iran, Afghanistan, and the former Soviet Union, of various agronomic backgrounds were identified as having moderate to high levels of RWA resistance. This information is useful to wheat breeders searching for sources of resistance to the RWA to incorporate into their breeding programmes.     

Association of Eyespot Resistance in Wheat cv. 'Cappelle-Desprez' with Endopeptidase Profile

To test for the association of the eyespot of wheat cv. ‘Cappelle-Desprez’ with the structural gene encoding the isozyme Ep-A1, F₃, families from the cross ‘Cappelle-Desprez’ (resistant) X ‘Chinese Spring’ (susceptible) were selected on the basis of endopeptidase phenotype. Analysis of eyespot reaction showed that Ep-Alb homozygotes were associated with a higher level of resistance than Ep-Al a homozygotes. Thus selection of the Ep-Alb allelc should assure concurrent selection of at least a part of the eyespot resistance of ‘Cappelle-Desprez’.     

Effectiveness and environmental stability of quantitative powdery mildew (Blumeria graminis) resistance among winter wheat cultivars

Powdery mildew in wheat (Blumeria graminis f. sp. tritici) is a major disease in Northern and Central Europe. The aim of the study was to analyse the effectiveness and environmental stability of quantitative powdery mildew resistance under high epidemic pressure in the field across years in the absence/presence of ineffective race‐specific resistances. Cultivars with and without Pm (major) genes were inoculated in three experiments with a genetically broad mildew population with all matching virulences. Resistance was measured three times by assessing the percentage of leaf area covered by powdery mildew on a plot basis (0–100%). Mean powdery mildew severity of the highly susceptible cv. ‘Kanzler’ varied across 10 years from 24% to 66% (Exp. 1). Means of three cultivars without Pm genes, ‘Ramiro’, ‘Miras’ and ‘Zentos’, and several cultivars with ineffective Pm genes varied quantitatively from 4% to 13%. Environmental stability of the quantitative resistances was on average higher than that of susceptible genotypes, as revealed by a regression approach. In the second experiment, all groups of cultivars with ineffective Pm gene(s) contained a large proportion of entries with a similar low mildew rating as the quantitatively resistant standard ‘Miras’. Mildew severity of pairs of cultivars with the same Pm gene(s) was significantly different across 6 years (Exp. 3) indicating the presence of additional quantitative resistances in some of these cultivars. In the analysis of variance, genotypic variance had a high impact (P < 0.01) with low importance of genotype × environment interaction. Consequently, heritabilites were high (0.95–0.97). In conclusion, breeders have already accumulated effective minor genes for powdery mildew resistance in many of the released German winter wheat cultivars. These quantitative resistances are long lasting, environmentally stable and provide a high level of protection to powdery mildew.