MSc

The present study entitled “Development of improved strain in Oyster mushroom (Pleurotus spp.)” was carried out in College of Agriculture, Vellayani during 2017-2019 with the objective to develop improved strain of Pleurotus sp. from native isolates.
Three native isolates used for the study viz., isolate 1 (Pleurotus djamor), isolate 2 (Pleurotus florida) and isolate 3 (a native isolate with 80 per cent similarity to P. florida), were obtained from Mushroom Unit of Instructional Farm, College of Agriculture, Vellayani. Species level confirmation of isolate 3 was done at molecular level ITS sequencing and was confirmed as P. ostreatus.
The morphologic studies of the native isolates revealed that P. florida and P. ostreatus produced comparatively larger sporocarps with long stipe and higher carp weight than P. djamor. P. djamor, P. florida and P. ostreatus produced fruiting bodies with pink, white and greyish white colour respectively. The microscopic characteristics of the isolates were studied. The mycelia were septate and with clamp connections. The basidiospores were cylindrical and produced on tetra-sterigmatic clavate basidia present on the hymenium of the sporocarps.
Strain improvement programme was conducted by spawn mixing, hybridisation through crossing of single spore cultures and gamma irradiation. The experiment was laid out in completely randomised design with required number of replications. Spawn of two different species viz., P. djamor + P. florida and P. djamor + P. ostreatus, were mixed and cultivation trials were conducted. For the given Pleurotus spp., hybridization or crossing of isolates did not take place by spawn mixing, thus did not have any significance in strain improvement. The beds of mixed spawn produced sporocarps of both parents. In addition, the biological efficiency (BE) of P. djamor + P. florida was reduced by 41.95 and 66.49 per cent respectively, compared to their parents. Similarly, BE of P. djamor + P. ostreatus was lower compared to their parents viz., P. djamor and P. ostreatus by 36.41 and 68.81 per cent respectively.
Hybridization was carried out between the compatible single spore cultures of P. djamor with P. florida and P. ostreatus independently by dual culture method. The hybrids were confirmed by the presence of clamp connection in the mycelium from the interaction zone. The BE of the hybrids viz., P. djamor x P. florida and P. djamor x P. ostreatus, was improved by 34.40 and 48.49 per cent respectively over the parent, P. djamor. The days taken for primordial initiation in the hybrids were significantly reduced compared to their parents. The days were reduced in hybrid, P. djamor x P. florida by two and 13 days respectively than the parents; and three and 12 days in hybrid of P. djamor x P. ostreatus, compared to its respective parents. The hybrids showed blended characters of both their parents. Light pink coloured sporocarps with wavy margin and stout stipe was produced by the hybrid, P. djamor x P. florida and light pink coloured sporocarps with slight depression towards the base and increased stipe length was produced in the hybrid, P. djamor x P. ostreatus.
Studies on the effect of gamma irradiation at 20 and 25 Gy in strain improvement revealed that BE of P. djamor increased by 9.25 per cent when irradiated at 20 Gy. The number of days taken for primordial initiation was also reduced by one day compared to P. djamor. Though P. florida irradiated at 25 Gy recorded increase in sporocarp size, there was no significant difference in the BE over P. florida. The BE of P. ostreatus irradiated at 25 Gy was improved by 12.89 per cent and there was earliness in primordial initiation by three days compared to the parent, P. ostreatus.
The improved cultures were evaluated for their relative performance and it was found that BE was higher for the mutant of P. ostreatus irradiated at 25 Gy and increased by 12.3 per cent over the parent. Whereas the hybrids which recorded earliness in primordial formation with pink coloured slightly delicate sporocarps and improved BE were also found to be promising.
Molecular characterisation of improved strains along with parents were analysed by RAPD (Random Amplified Polymorphic DNA). Pairwise comparisons of the strains, based on the presence or absence of unique and shared amplicons, were used to generate similarity coefficient of Jaccard. The results were then analysed using the unweighted pair-group method with arithmetic average (UPGMA). The analysis revealed that the hybrid (P. djamor x P. ostreatus) had 57.1 per cent similarity with P. djamor and 28.6 per cent similarity with P. ostreatus. The hybrid, P. djamor x P. florida had 66.7 and 50 per cent similarity with P. djamor and P. florida respectively. The mutant strain of P. ostreatus at 25 Gy recorded 22 per cent polymorphism with the control.
The present study indicated the exploitability of two promising strains. The hybrid of P. djamor and P. ostreatus can be recommended for the production of slightly delicate, light pink sporocarps with reduced crop period (44.75 days). Whereas P. ostreatus irradiated at 25 Gy produced delicate white sporocarps with increased BE and reduced crop period by one week compared to the parent.