Developing molecular markers for sex prediction in papaya (Carica papaya L.)

Abstract

The sex of papaya (Carica papaya L.) plants has important agronomic implications, influencing both fruit yield and quality. The sex of individual plants cannot be determined until flowering initiates, however in some breeding and commercial situations it would be advantageous to be able to predict sex-type in seedlings. Despite considerable previous efforts no reliable morphological or biochemical markers capable of predicting sex-type have been developed. Here we describe efforts to identify molecular markers for sex determination in papaya based on PCR approaches. We have compared two techniques, random amplified polymorphic DNA (RAPD) and DNA amplification fingerprinting (DAF) and shown that the DAF procedure has distinct advantages. We have shown DAF reactions produced at least five times more bands than equivalent RAPD reactions, permitting more efficient screening and in our hands DAF reactions were more reliable. Using bulk segregant analysis we were able to define a large number of DAF markers present in only male or hermaphrodite pooled DNAs. Preliminary analyses for linkage associations indicated these markers were reasonably closely linked to the sex- determining alleles. We attempted to convert some DAF markers into more convenient SCAR markers; this proved difficult since DAF bands were difficult to clone.