Estimation of phenotypic divergence and powdery mildew resistance in a collection of Cucumis sativus L.

Genetic diversity in thirty cucumber (Cucumis sativus L. var. sativus) collections from Karnataka, Southern India, was assessed by examining variation among thirty phenotypic characters and powdery mildew resistance. The collection showed appreciable phenotypic diversity in vein length, leaf length, tendril length, fruit length, fruit breadth, fruit weight, seed index and seed weight. Principal component analysis (PCA) was performed on 19 quantitative and 11 qualitative characters to determine relationships among populations and to obtain information on the usefulness of those characters for the definition of groups. When the 30 populations were plotted on the first two principal components, accounting for 46% of the total variation, five clusters were identified, accounting for 28 morphological attributes used in the study. The greater part of diversity was accounted for leaf length, fruit length, cavity length, node number, flesh colour, fruit weight, colour of stripes, pericarp thickness, fruit shape, seed length and seed index. CSC-71 (yellow skin and 678 g/fruit) and CSC-83 (774 g/fruit) are considered to be the most important collections to be stressed for further breeding purpose. CSC- 04, CSC-76 and CSC-77 showed gene specific banding for both the sequence tagged site, specific to powdery mildew resistance (EAACMCAC391-395STS and EAAGMCAT280-282STS). Collection CSC-71 (yellow skin and 678 g/fruit) showed gene specific amplification in primer EAACMCAC391-395STS. This evaluation of fruit trait variability combined with powdery mildew resistance can assist geneticists and breeders to identify populations with desirable characteristics for inclusion in variety breeding programs.Key words: Cucumis sativus, genetic diversity, phenotypic traits, principle component analysis