Abstract
Carica papaya L. exhibits monoecious and dioecious plants that usually take six months for phenotypic manifestation. Nursery culling aided by sex-specific DNA markers was envisaged to alleviate the unnecessary cost incurred by farmers for maintaining unproductive male plants that contribute to 40-50% of the population. The mechanism of sex determination in papaya has been described as a tri-allelic single gene system with alleles, M 1 -dominant for maleness, M 2 -dominant for hermaphrodism and m-recessive for femaleness with diploid zygotes; M 1 M 1 , M 2 M 2 and M 1 M 2 being inviable. Bulked DNA samples of male, female and hermaphrodite plants were amplified by Random Amplified Polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR) using 100 random primers. Twenty of most promising of these were analyzed among individual sex types. Two sex-specific fragments, OPC09-1.7 and OPE03-0.4 were associated with maleness and hermaphrodism. The segregation of these two markers was analyzed in the F 1 population obtained by self- pollinating a hermaphrodite plant. A linkage was detected between the RAPD markers, OPC09-1.7 and OPE03-0.4 and the male and hermaphrodite sex of papaya plants. These sex-specific RAPD fragments were cloned and sequenced for converting them to more authentic SCAR markers. The Southern blot hybridization of RAPD-PCR products obtained by amplification of female, male and hermaphrodite papaya DNA amplified by OPC09 primer using radio labeled recombinant plasmid detected a polymorphic fragment in male and hermaphrodite papaya sex types. The nucleotide sequence of OPC09-1.7 fragment showed the possibility of developing more authentic SCAR markers to enhance the accurate sex determination of Carica papaya at the nursery stage.
Highlights
Carica papaya L. (Papaya or Papaw), a native of tropical America, is a widely distributed fruit crop throughout the tropical and warmer subtropical regions
The Southern blot hybridization of Random Amplified Polymorphic DNA (RAPD)-Polymerase chain reactions (PCR) products obtained by amplification of female, male and hermaphrodite papaya DNA amplified by OPC09 primer using radio labeled recombinant plasmid detected a polymorphic fragment in male and hermaphrodite papaya sex types
Among all the polymorphic fragments only two polymorphic fragments amplified by OPC09 and OPE03 primers were found present in all the male and hermaphrodite types of papaya plants
Summary
Carica papaya L. (Papaya or Papaw), a native of tropical America, is a widely distributed fruit crop throughout the tropical and warmer subtropical regions. The consumption of papaya is growing steadily in parallel with the increase in health conscious food consumers, as the fruit is low in calories and sodium, but high in dietary fiber, calcium, potassium and vitamins A and C1,2. Papaya has attractive agronomic features such as easy cultivation, rapid growth, minimum growing space, early production, high yields, multiple uses, prompt returns, and adaptation to diverse (climatic and soil) growing environments[3]. The C. papaya trees exhibit sexual polymorphism as female, male and hermaphrodite plants and discrimination can only be defined in 5 – 8 month old plants. One striking feature is the close association between sex expression and desirable agronomic traits. Hermaphrodite plants produce fleshy fruits of attractive shape, while female plants produce fruits rich in papain. Identification of sex-specific DNA markers would assist in alleviating this problem, if such linked markers are reliable and unaltered by the environment
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