Morphological, biochemical and molecular markers for the genetic analysis of cashew(Anacardium occidentale L.)

Abstract

The research project' Morphological, biochemical and molecular markers for the genetic analysis of cashew' was carried out in the College of Horticulture, Vellanikkara, Thrissur during the period 2000-2002. The major objectives of the study were to fingerprint cashew genotypes based on genetic analysis carried out and the genetic relationship deduced between the morphological, biochemical and molecular parameters studied and also to identify genetically diverse genotypes among those selected for the study to be used in breeding programmes. The study revealed that among the fourteen characters selected i.e., tree height, tree girth, number of primary branches, number of secondary branches, canopy spread, leaf area, number of panicles m", number of nuts m", number of perfect flowers m", apple weight, nut weight, kernel weight, shelling percentage and nut yield, all showed significant variation except number of primary branches. Number of perfect flowers m", number of nuts m", apple weight, nut weight and kernel weight provide a clear seperation of the genotypes. Correlation and path studies revealed tree height and number of nuts m" had significant positive correlation and direct effect on yield. Tree girth showed positive correlation but significant negative direct effect on yield. Number of primary branches showed significant positive direct effect but a significant negative correlation with yield. Apple weight showed significant negative correlation and significant negative direct effect with yield. Genetic divergence studied using Mahalanobis D2 analysis revealed H-1593 to be the most divergent genotype. Cluster' analysis could group them into four clusters. The members of Cluster I (Sulabha, Priyanka and P-3-2) and Cluster II (Mdk-L, AKM-l and K~22-1) were found to be best suited for hybrdisation being the farthest. Biochemical studies on phenol and tannin content could group the twelve genotypes into those with high and low .contents. The genotype H-1593 had the lowest

phenol content. Seed storage protein studies could distinguish K-22-1 from all others by a single unique band. Isozyme analysis in cashew showed only high initial rate of reaction. Further studies to standardise the protocol for isozyme studies needs to be done. Molecular studies involved RAPD analysis using four primers which gave 44 amplification products out of which 30 (68.19 per cent) were found to be polymorphic. Two primers OPP-5 and OPP-IO could distinguish varieties Mdk-2 and Mdk-l with amplicons 22 and 25 respectively. Dendrogram constructed based on the study grouped together Kanaka and Dharasree; Mdk-l and Mdk-2 and H-1600 and P-3-2 with the latter two being the closest of all. On comparative study, H-1600 (Damodar) was tied to Dharasree in biochemical studies and with P-3-2 in molecular studies. In morphological studies also, it was placed close to P-3-2 indicating the proximity of Indian accessions with those of South America. Kanaka and Dharasree were tied together both in morphological and molecular studies but both were diverse by pedigree. Similarly, AKM-l and Dhana were placed close together in the three studies both of which were diverse by pedigree. H-1593 and H-1591 were found to be close in molecular and morphological studies. AKM-l and Mdk-l,Bapatla accessions and early flowering varieties, were closer in both morphological and molecular studies. It can be said that pedigree is not completely answerable to variability. The study had revealed a similar trend for morphological and molecular markers in deducing the genetic divergence. Biochemical markers need more refinement so as to get as precise information as has been obtained for the characterisation of the genotypes through molecular studies.