Marie Eve Renard

Genetic Diversity of the Mating Type and Toxin Production Genes in Pyrenophora tritici-repentis

Pyrenophora tritici-repentis, the causal agent of tan spot on wheat, is a homothallic loculoascomycete with a complex race structure. The objectives of this study were to confirm the homothallic nature of the pathogen, characterize mating type diversity and toxin production genes in a global collection of strains, and analyze how these traits are associated between each other and with existing races. The pseudothecia production capacity, race identification, mating type locus (MAT), internal transcribed spacer, and glyceraldehyde-3-phosphate dehydrogenase regions were analyzed in a selection of 88 strains originating from Europe, North and South America, North Africa, and Central and South Asia. Some (60%) strains produced pseudothecia containing ascospores, independent of their origin. Race identification obtained using the multiplex polymerase chain reaction targeting host-selective toxin (HST) genes was consistent, overall, with the results based on the inoculation of a set of differential wheat cultivars and confirmed the predominance of race 1/2 strains ( approximately 83%). However, discrepancies in race identification, differences from the reference tester strains, and atypical ToxA profiles suggest the presence of new races and HSTs. The MAT1-1 and MAT1-2 coding regions are consecutively arranged in a single individual, suggesting putative heterothallic origin of P. tritici-repentis. Upstream from the MAT is an open reading frame of unknown function (ORF1) containing a MAT-specific degenerate carboxy-terminus. The phylogenetic analysis of the MAT locus reveals two distinct groups, unlinked to geographical origin or ToxA profile. Group I, the best-represented group, is associated with typical tan spot lesions caused by races 1, 2, 3, and 5 on wheat. It is more homogenous than group II encompassing race 4 strains, as well as isolates associated primarily with small spot lesions on wheat leaves or other hosts. Group II could contain several distinct taxa.

A convergent asymmetric synthesis of γ-butenolides

Addition of aldehydes to the new enantiomerically pure lithiated sulfoxide 4 yielded gamma-butenolides of high enantiomeric purities after elimination of phenylsulfinic acid. The reaction with ketones was less stereoselective

EFFECT OF POTASH DEFICIENCY ON HOST SUSCEPTIBILITY TO COCHLIOBOLUS SATIVUS CAUSING SPOT BLOTCH ON WHEAT

Helminthosporium leaf blight is the most important disease of bread wheat in the Indo-Gangetic plains and is caused by Cochliobolus sativus and Pyrenophora tricirepentis. Late planting and unbalanced fertility increase disease severity. A study on two genotypes BL2217(moderately resistant) and Ciano 79 (susceptible) was conducted in a greenhouse under controlled-environment with 3 levels of potassium fertilisation. Treatments consisted of half-strength standard Hoagland solution pH7.0 as control , and two levels of potassium deficient solutions containing only 36.8% and 13.5% potassium of the standard half-strength solution. Plants were inoculated with a C. sativus virulent isolate from Nepal. Disease severity (% DLA) and chlorophyll content measured as SPAD value (SPAD-502, Minolta Co. Ltd., Japan) at 3,7,10,14,17 and 21 days after inoculation were evaluated in inoculated and control plants, respectively. To assess the interaction of the pathogen with host cells, microscopic analysis and histochemical assays for H2O2 detection were performed 24-h and 48-h after inoculation. Potassium deficiency significantly increased disease severity in both genotypes. A significant(P<0.01) negative linear correlation between AUDPC and chlorophyll content was observed for both genotypes. Microscopic analysis and histochemical assay for H2O2 detection showed that cell wall apposition formation and hypersensitive reaction were significantly reduced in BL 2217 under potassium deficiency , stressing the importance of the soil fertility as part of an integrated crop management of HLB.