A novel way to identify specific powdery mildew resistance genes in hybrid barley cultivars

Powdery mildew, a common cereal disease caused by the fungus Blumeria graminis, is a major limiting factor of barley production and genetic resistance is the most appropriate protection against it. To aid the breeding of new cultivars and their marketing, resistance genes can be postulated in homogeneous accessions. Although hybrid cultivars (F1) should be homogeneous, they are often not genetically uniform, especially if more than two genotypes are involved in their seed production or due to undesirable self-pollination, out-crossing and mechanical admixtures. To overcome these problems the accepted method of postulating specific resistance genes based on comparing response type arrays (RTAs) of genetically homogeneous cultivars with RTAs of standard genotypes was substituted by analysing the frequency of response types to clusters of pathogen isolates in segregating F2 generations. This method combines a genetic and phytopathological approach for identifying resistance genes. To assess its applicability six hybrid cultivars were screened and from three to seven with a total of 14 resistance genes were found. Two genes were newly located at the Mla locus and their heritability determined. In addition, three unknown dominant genes were detected. This novel, comprehensive and efficient method to identifying resistance genes in hybrid cultivars can also be applied in other cereals and crops.

Mycotoxin production, chemotypes and diversity of Czech Fusarium graminearum isolates on wheat

Fusarium head blight (FHB) is a serious cereal disease in the CzechRepublic. The most important pathogen associated with FBH is Fusarium graminearum, which can produce trichothecenes, mainly deoxynivalenol (DON) and its derivates. A set of 103 F. graminearum isolates were isolated from naturally infected wheat ears collected from 20 localities (25 ears from one locality) within the Czech Republic, in the year 2004. The ears were evaluated for DON content by ELISA. Maximum detected value was 30.7 mg/kg. A group of PCR assays targeting the segments of the Tri7, Tri13 and Tri3 genes were used to determine the chemotypes of F. graminearum isolates. All the isolates belonged to DON producing chemotype. Further discrimination revealed that almost all (99.03%) isolates belonged to 15-ADON chemotype, and only one (0.97%) isolate belonged to 3-ADON chemotype. The genetic variability of the isolates was assessed from their AFLP fingerprints. The populations were highly heterogeneous both within and between locations, and no clear evidence for the association between AFLP profile and geographic origin was found out.