Estimating genetic divergence between peach rootstock cultivars using multivariate techniques based on characteristics associated with seeds
The production of peach rootstocks in Brazil is still performed mainly from seeds of different cultivars, whose endocarps are obtained in peach canning industries. This type of material is not ideal for use as rootstocks, since it is a varietal blend of genotypes with differing in physical and physiological characteristics which can include germination and growth of seedlings. We examined the genetic divergence of peach rootstock based on the relative contribution of 15 seed and endocarp characteristics, using multivariate procedures, in order to help select promising crosses for genetic improvement. Endocarp and seeds from eight rootstock cultivars of Prunus persica suggested as appropriate for cultivation in southern Brazil were evaluated for the biometric characteristics of length, width, thickness and fresh weight, and the seeds were submitted to a germination test. An analysis of variance of the data, principal component analysis and clustering using Tocher's optimization method were carried out. Genetic variability was found among the cultivars for all the characteristics. The characteristics with the greatest contribution to the genetic divergence between rootstocks were endocarp fresh weight, seed width and thickness, and germination percentage. On the basis of principal component analysis, using the variables with the greatest power of discrimination, the cultivars were divided into four groups. For breeding programs we suggest crosses between the cultivars Flordaguard χ Capdeboscq, Capdeboscq χ Tsukuba 1 and Capdeboscq χ Okinawa, aimed at obtaining improved peach rootstock with superior seed and seedling vigour, together with other characteristics of interest for farmers in southern Brazil.