Abstract in English and Russian.

Peer-review: No - Open Access: No

Peer review

During Helminthosporium leaf blight surveys performed in 2003, 2004 and 2005 between May and August on winter and spring wheat in various regions of Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan and in Western Siberia (Russia), samples of wheat leaves showing leaf spot and leaf blight symptoms were collected at 113 locations or plots and analysed at the Université catholique de Louvain, Belgium. The analysis under a microscope and/or isolation revealed the presence of Pyrenophora tritici-repentis on 77% of the samples. Its prevalence fell to 31% on the samples from the Omsk region in Western Siberia where Phaeosphaeria nodorum was detected on all analysed samples. Overall, P. nodorum was associated with lesions on 50% of the samples, with a strong decline in prevalence in South Kazakhstan, Kyrgyzstan and Uzbekistan. Mycosphaerella graminicola was detected on 23% of the samples and appeared more frequent than P. nodorum in the latter regions. Mixed infections of two or even three of these pathogens were observed on 43% of the samples. Cochliobolus sativus was detected on only 10% of the samples. Some 101 single conidia strains of P. tritici-repentis were inoculated for race characterization on a set of differential wheat genotypes. Of these, 87% belonged to race 1, while only 7%, 5% and 1% were identified as race 2, race 3 and race 4, respectively. Evolution in race prevalence in Central Asia might affect the stability of tan spot resistance. The distribution of the mating type ideomorphs was determined for 49 P. nodorum isolates. The proportion of MAT-1 and MAT-2 isolates appeared balanced (23:19) among the Kazakh and Russian origins, but no MAT-2 isolate has yet been found in
Tajikistan. The role of ascospores in glume blotch epidemiology might be reduced for a population with a skewed proportion of the mating types. MAT-1 and MAT-2 ideomorphs of M. graminicola were present in a rather balanced proportion (24:17) throughout the surveyed area. Sensitivity in vitro of the P. nodorum and M. graminicola isolates to propiconazole (Tilt) and azoxystrobin (Amistar) was assessed in PDB. No resistant isolate was detected. The EC50 values of propiconazole and azoxystrobin ranged for M. graminicola from <0.003 to 0.013mg/L and 0.01 to 0.078mg/L, respectively; and for P. nodorum from 0.013 to 0.085mg/L and 0.016 to 0.267mg/L, respectively. The abundance of crop residues associated with conservation tillage practices, together with the frequent observation of Pyrenophora tritici-repentis pseudothecia on the stubbles as well as the regular isolation of both mating types of Phaeosphaeria nodorum and M. graminicola from the leaves, highlight the risk of a rapid evolution in the population structure of these pathogens with regard to the dispersion of virulence or fungicide resistance genes.

Research and Partnership Program

Text in Russian

INT1237