STUDIES ON SOMATIC EMBRYOGENESIS IN PAPAYA CV. SURYA WITH REFERENCE TO ENDOPHYTIC BACTERIAL ASSOCIATION
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Date
40625
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Publisher
University of Agricultural Sciences GKVK, Bangalore
Abstract
Papaya (Carica papaya L.) is an important fruit crop world over. Micro
propagation of shoot buds approach has not been very successful for commercial
propagation purpose. Feasibility of somatic embryogenesis from immature zygotic
embryos is also suggested in papaya. A protocol has now been optimized for somatic
embryogenesis from immature zygotic embryos of papaya cv. Surya. Immature zygotic
embryos were established on half-strength MS medium with supplements (MS vitamins,
6 per cent sucrose, 10 mg l-1 2, 4-D, 400 mg l-1 glutamine and 0.8 per cent agar (pH 5.7)
giving high frequency and repetitive embryogenesis after 3-4 subculture passages.
Continuous proliferation of somatic embryos was achieved on maturation and
regeneration medium containing half-strength MS constituents, 3 per cent sucrose, 400
mg l-1 glutamine, 0.2 mg l-1 BAP and 0.1 mg l-1 NAA and 0.8 per cent agar. Medium
containing a combination of 0.5 mg l-1 IAA and 0.5 mg l-1 IBA was ideal for root
development. Endophytes are generally known to originate from the rhizosphere or
phyllosphere and seeds are generally considered to be free from endophytes. Tissue and
medium indexing on visibly clean embryogenic cultures initiated from immature seeds
showed the association of cultivable bacteria in a small section (1.4 per cent) of cultures
after three subculture passages. One bacterium was isolated from such cultures, which is
identified as Brachybacterium rhamnosum based on 16S rRNA gene sequence homology
analysis. PCR-screening of visibly clean and index negative cultures using universal
bacterial 16S rRNA gene primers indicated the presence of non-cultivable bacteria in
index-negative cultures. This was confirmed by microscopy of tissue homogenate
revealing viable bacteria in considerable number.