In vitro propagation and rapid analysis of selected varieties of papaya (carica papaya L)

Abstract

A study was carried out at the Department of Pomology and Floriculture, College of Agriculture, Vellayani during 2003-2006 for refining existing tissue culture protocol with respect to selected varieties and hybrids of papaya. Molecular characterization of papaya hybrids was also carried out using Random Amplified Polymorphic DNA (RAPD) technique. Papaya varieties and hybrids selected for the study were Pusa Nanha, CO-5, Washington, Pusa Nanha x Coorg Honeydew, Pusa Dwarf x Coorg Honeydew, Solo x Coorg Honeydew and Pusa Nanha x Solo. Apical buds and lateral buds from seedlings and mature plants were used as explant for in vitro propagation. The present study revealed that full strength MS medium supplemented with sucrose 30.00 g l-1 and agar 6.00 g l-1 under light condition produced highest shoot number and longest shoot in papaya varieties and hybrids. Application of BA 0.50 mg l-1 along with NAA 0.10 mgl-1 was found to be better for initial culture establishment and proliferation of papaya varieties and hybrids. Application of amino acid, arginine 50.00 mg l-1 resulted in highest shoot proliferation rate, while highest shoot length was obtained from arginine 100.00 mg l-1. Addition of activated charcoal 0.05 per cent and Cobalt chloride 10.00 mg l-1 increased shoot proliferation rate and shoot length in papaya varieties and hybrids. In vitro rooting was best in full strength MS medium supplemented with IBA 3.00 mg l-1, sucrose 30.00 g l-1and activated charcoal 0.05 per cent. Earliest planting out of in vitro propagated plants in potting media was carried out in papaya variety Pusa Nanha and late planting out in papaya hybrid Pusa Nanha x Coorg Honeydew. Highest plant height of in vitro propagated plants, at time of planting out in potting media was recorded by papaya variety Washington and lowest by papaya hybrid Pusa Nanha x Coorg Honeydew, while hsighest leaf number was reported from papaya variety CO-5 and lowest from Pusa Nanha. But longest root was noticed in papaya hybrid Pusa Nanha x Coorg Honeydew and shortest root from CO-5. No significant difference was noticed in the number of roots produced at the time of planting out in potting media. In vitro propagated plants of papaya had better establishment in the potting mixture containing sand : soil : cowdung (1 : 1 : 1) + Mycorrhiza (1.00 g plant -1). After field establishment, highest plant height and plant girth was noticed in papaya variety Washington and lowest in papaya hybrid Pusa Dwarf x Coorg Honeydew. While highest leaf number upto six weeks after planting was shown by papaya variety CO-5 and thereafter by papaya variety Washington. Lowest leaf number upto eight weeks after planting was noticed in papaya hybrid Solo x Coorg Honeydew and thereafter by papaya hybrid Pusa Dwarf x Coorg Honeydew. Early flowering was reported in papaya hybrid Pusa Dwarf x Coorg Honeydew and late flowering in papaya variety Washington. Most of the papaya varieties and hybrids selected for the present study exhibited only dioecious nature, but papaya hybrid Solo x Coorg Honeydew showed gynodioecious nature. Highest field establishment of in vitro propagated plants was shown by papaya varieties CO-5 and Washington and lowest by papaya hybrid Solo x Coorg Honeydew. Genomic DNA was successfully isolated from four papaya hybrids using CTAB method. All the ten primers (six primers from OPA and four primers from OPB series) yielded amplification products with isolated DNA. A total of 39 RAPDs were obtained from ten primers of which 36 bands were polymorphic. Primers OPA-03, OPA-04, OPA-12, OPB-04 and OPB-17 gave 40 scorable bands, with an average of 8.0 bands per primer. The largest cluster in dendrogram was formed by three hybrids - Pusa Nanha x Coorg Honeydew, Pusa Dwarf x Coorg Honeydew and Pusa Nanha x Solo. The second cluster contained only one hybrid - Solo x Coorg Honeydew. The minimum similarity coefficient detected in the present study was 0.389, suggesting a genetic differentiation among the papaya hybrids.