Detached Leaf Assay Coupled with Microscopic Conidial Quantification: An Efficient Screening Method for Powdery Mildew Resistance in Pea.

The genetic resistance in high yielding pea cultivars against powdery mildew provides a cost effective and reliable strategy to reduce the yield losses and save quality of the harvest. The dependable selection of powdery mildew resistant source(s) is the most crucial step in breeding for disease resistance. The efficiency of a simple, reliable and reproducible screening method on detached leaves of pea under controlled environmental condition was evaluated in comparison with field screening under natural conditions. The detached leaf assay coupled with microscopic quantification of susceptibility percentage (%S) appeared ten times more precise and reproducible than field screening based on visual observation of percentage of leaf area affected with disease. A new 0-5 microscopic disease scale proposed here is more robust and stringent for making selections for powdery mildew resistant parents and effectively challenging the segregating populations against different isolates of Erysiphe pisi simultaneously. The disease scale is based on susceptibility percentage (%S) as a function of percentage of germinated conidia with mycelial growth. For making more precise calculations non germinated conidia without germ tube were not taken in to account. The use of detached leaf assay and microscopic quantification of conidia has provided a simple and reliable screening method to clearly distinguish between escape and resistance mechanisms and the results are not prone to fluctuations in environmental conditions. The assay results were highly correlated (0.993) with the disease severity of whole plants under field conditions; moreover, dCAPS markers have also validated the assay results. Two pea genotypes (It-96 and No. 267) have been selected as highly resistant to powdery mildew, which could be used as a source for breeding disease resistant pea cultivars. [ABSTRACT FROM AUTHOR]