PhD

Survey conducted in different localities to obtain the native flora of Calocybe resulted in the collection of ten isolates of Calocybe, seven from Thiruvananthapuram, two from Kollam and one from Pathanamthitta.
The nature of growth in petridish and spawn substrate of the native isolates varied widely. Of the ten isolates, the most promising isolate OE-349 which gave better yield, shelf life, nutrient status and low mortality was selected for further studies.
Cultural characters studied showed that locally available jackfruit seed kernel broth can be substituted for potato dextrose broth for maximum biomass production. In solid media the Calocybe isolate had fluffy growth in oat meal agar and better radial growth in potato dextrose agar medium.
Calocybe preferred fructose, rather than dextrose, hence can be used for higher biomass production. Least preferred carbon sources were lactose and sucrose. Among the nitrogen sources peptone was the best for maximum biomass production. The inorganic source, ammonium salts were less preferred than nitrate source. Calocybe preferred a pH of 5.5 for maximum biomass production. An increase or decrease in pH resulted in the reduction of biomass.
Among the various substrates subjected to different sterilisation techniques, spent mushroom substrate (SMS) subjected to solarisation out yielded paddy straw and coir pith, compared to boiling and chemical methods. Solarised SMS gave higher biological efficiency and better fruiting body weight. Mortality percentage was minimum in solarised SMS. Solarised beds of SMS and paddy straw were free from contaminants. Coirpith did not prove as a successful substrate for Calocybe cultivation as it was highly contaminated with Trichoderma.
Of the various supplements, rice bran supported higher biological efficiency than others. The application of supplements at four per cent rate gave better yield than two per cent. Rice bran supplementation of solarised SMS out yielded the other supplements neem cake, vermicompost and ferrous sulphate. Neem cake and vermicompost were not suitable for supplementation as there was heavy incidence of Trichoderma on beds.
Casing materials consisting of sand, soil and CaCO3 gave better biological efficiency than coir pith soil mixture, vermicompost-soil mixture and clay-soil mixture. Vermicompost and coir pith when used as an ingredient in casing material there was heavy incidence of Trichoderma. Clay-soil mixture did not support fruiting body production of Calocybe due to crust formation as a result of quick absorption and slow release of water.
Strain improvement was done using UV rays and gamma irradiation. UV irradiation at two distances (5 cm to 10 cm) from source for different periods (10, 15, 20 and 25 minutes) did not produce any significant effect on the yield as well as shelf life and nutrient status of mushroom. But irradiation at 10 cm from source had a positive effect on nature, radial growth of mycelium and yield when compared to irradiation at 5.00 cm.
Irradiation with  rays enhanced yield, nutrient status and shelf life of Calocybe. Irradiation with  ray from 0.5 – 2.5 KR showed an increase in yield upto 1.5 KR followed by a decline.
A hybrid was developed by crossing single spores of two different isolates with dissimilar character. The hybrid (54.88 per cent BE) out yielded the parents in yield, characters, nutrient content and enzyme activity.
Molecular characterisation of hybrid and their parents revealed that hybrid had 44.40 per cent similarity with one parent and 28.57 per cent similarity with other parent. Dendrogram constructed clustered one parent and hybrid into one group and other parent into another group at 0.26 similarity coefficient.