Genetic analysis and historical perspective of cashew (Anacardium occidentale L.) introduction into India.

Cashew (Anacardium occidentale L.), introduced into India about 400 years ago, is distributed widely in the coastal regions as spontaneous populations as well as in cultivation. Despite the plant's commercial exploitation, little is known about its actual introduction and diversification. We attempted to construct these events by investigating the level of genetic variation and genetic structure of cashew populations collected from different geographical regions of India. A total of 91 individuals from four populations were analysed using AFLP markers and morphometric data. AFLP analysis based on 354 polymorphic loci revealed Indian cashew to have low but relatively substantial genetic diversity for an introduced species (H(E) = 0.262 and I(S) = 0.404). Twenty-seven qualitative and quantitative traits also revealed the existence of considerable morphometric variation (24% around the mean values). Bayesian cluster analysis based on AFLP data did not indicate the existence of definite population differentiation. Morphometric analysis allocated 12% variation among all four populations, whereas AFLP variation observed in cashew individuals was entirely within populations. The results, supporting the possibility of cashew having been introduced into India repeatedly over a period of time but at a single location (west coast), are discussed and their implications for germplasm management are described.

Comparative assessment of DNA fingerprinting techniques (RAPD, ISSR and AFLP) for genetic analysis of cashew (Anacardium occidentale L.) accessions of India.

Nineteen cashew accessions were analysed with 50 random primers, 12 ISSR primers and 6 AFLP primer pairs to compare the efficiency and utility of these techniques for detecting variation in cashew germplasm. Each marker system could discriminate between all of the accessions, albeit with varied efficiency of polymorphism detection. AFLP exhibited maximum discrimination efficiency with a genotype index of 1. The utility of each molecular marker technique, expressed as marker index, was estimated as a function of average band informativeness and effective multiplex ratio. Marker index was calculated to be more than 10 times higher in AFLP than in RAPD and ISSR. Similarity matrices were determined based on the data generated by molecular and morphometric analyses, and compared for congruency. AFLP displayed no correspondence with RAPD and ISSR. Correlation between ISSR and RAPD similarity matrices was low but significant (r = 0.63; p < 0.005). The similarity matrix based on morphometric markers exhibited no correlation with any of the molecular markers. AFLP, with its superior marker utility, was concluded to be the marker of choice for cashew genetic analysis.

Random amplified polymorphic DNA variation in the eggplant, Solanum melongena L. (Solanaceae).

RAPD analysis was carried out on 52 accessions of Solanum melongena (eggplant) and related weedy forms known as "insanum". Twenty-two primers amplified 130 fragments. Solanum melongena exhibited 117 of the fragments, all of which were also present in insanum. Insanum displayed an additional 13 fragments not found in S. melongena. Overall, the insanum accessions were more diverse than those of S. melongena. The calculated similarity between them was 0.947. The RAPD results were closely concordant with the results of an electrophoretic isozyme survey performed on the same accessions. The concordance of the results shows that even though S. melongena and insanum are highly diverse morphologically, it is no longer appropriate to distinguish them taxonomically.

Allozyme variation in the eggplant, Solanum melongena L. (Solanaceae).

Enzyme electrophoretic studies were made in cultivated Solanum melongena L. (eggplant) and similar wild and weedy forms, several of which have been thought to be different species/taxa. Twenty-nine accessions of S. melongena, 33 accessions of weedy forms (referred to as "insanum") and 2 accessions of wild forms (referred to as "incanum") were surveyed for 29 isozyme loci. In S. melongena, 22 of the 29 loci were monomorphic, and nearly all of its genes were either also monomorphic or in similar frequencies in insanum and incanum. The results demonstrate that the three taxa have a very close genetic relationship. The high genetic identities between them (0.913-0.967) suggests that they are conspecific even though they include extensive morphological diversity.