Touchdown-PCR based RAPD assay for early diagnosis of gender in Carica papaya L.

Papaya (Carica papaya L.) is a well-known medicinally important nutritive fruit tree cultivated in tropical and subtropical regions of the world. Sex type determination in papaya (Carica papaya L.) is important for optimizing production and productivity. This species has three sex types (male, female and hermaphrodite) determined by a multiallelic locus. Morphological and cytological studies conducted so far have failed to differentiate between the sex forms of papaya. Its dioecious nature, occasional sex-reversal of male flowers and the absence of a heteromorphic pair of sex chromosomes make papaya an interesting system to study sex determination at the molecular level. Present investigation has been carried out to generate gender-specific random amplified polymorphic DNA (RAPD) markers using touchdown-polymerase chain reaction (Td-PCR). Using pooled DNA from male, female and hermaphrodite plants and 35 RAPD primers, a putative male (similar to 900bp) and hermaphrodite specific markers (similar to 550 bp) were identified. This gender diagnostic PCR assay offers a simple and reproducible way for gender determination in papaya genotypes at the seedling phenophase. The RAPD markers developed here could also be used as a starting material towards sequence characterization of sex linked genes for better understanding the developmental as well as evolutionary pathways in sexual dimorphism.