Preliminary genetic studies on cactus pear (Opuntia spp. Cactaceae) germplasm from Central Mexico

Cactus pear is the fruit crop of choice for the semiarid highlands of Central Mexico due to its drought tolerance. Growers completely depend on native varieties which do not have acceptance in the emerging international markets due to their low quality. New cultivars must be developed to meet the demand, therefore sound management of the germplasm base is a primary need. In this study the biological basis, techniques and goals of cactus pear breeding are proposed. In the second stage of the project we used a germplasm base of 32 accessions to study the patterns of phenotypic variability. The analysis of quantitative and categorical traits indicated that the cultivated varieties are about 80% similar and may have originated from a few common progenitors. This similarity was further confirmed by the RAPD technique. We also found several phenotypic traits available during the juvenile vegetative phase, which are correlated with important commercial traits and can be used as selection criteria. This is particularly important regarding the long generation time of cactus pear, estimated from 4–6 years. Prior to the molecular characterization a DNA extraction protocol was specifically adjusted for use in cactus pear. Further data indicate that this protocol is useful to four other cacti species as well. Cactus pear exhibits high frequency of apomicts. Resultant seeds can produce both maternal seedlings and sexual seedlings. The extent of this phenomena was studied in commercial cultivars and breeding populations and it was found that apomixis is a varietal trait that can be influenced by the genetic origin of the seed enhanced by some maternal effects. The apomictic origin of seedlings that showed late emergence was confirmed by RAPD, technique