Abstract:
Anthracnose disease in papaya caused by the fungus Colletotrichum
gloeosporioides is a major threat to commercial fruit production in Sri Lanka. The
disease can cause severe losses at the post harvest stage, especially when the fruits
are ready to be consumed. As a viable alternative to highly toxic synthetic
pesticides and relatively inefficient physical control measures, bio control potential
of antagonistic bacteria has to be widely investigated. The objective of the present
study is to screen the presence of potential bacterial antagonists in spent oyster
mushroom substrate against the papaya anthracnose pathogen under in vitro
conditions. An aqueous suspension of four months old oyster mushroom cultivation
media was prepared in sterile distilled water and the serially diluted suspension was
plated on potato dextrose (PDA) media to isolate individual bacterial colonies. The
isolated bacterial colonies were co-cultured on PDA plates with C. gloeosporioides
fungi isolated from an infected papaya fruit. Seven days after culturing (DAC), the
percent inhibition of radial growth (PIRG) relative to an untreated control fungal
colony was recorded for each treatment. Out of 20 different isolates tested,
inhibition of fungal mycelial growth was significant (P< 0.05) with 16 bacterial
isolates of which, the maximum mean inhibition value of 74% shown by the isolate
SMB 4. The overall trend of inhibition remained the same at 11 DAC; however the
degree of inhibition increased in all the effective treatments where the isolate SMB
4 showed 84% mean inhibition. The average length of the inhibition zones between
the fungus and the antagonistic bacterial colonies ranged from 0.60 -2.57 cm. The
results indicate the suitability of spent oyster mushroom substrate as a potential
source of antagonism against anthracnose disease in papaya.
