Development of sporeless/low spore shedding strains of Pleurotus species

Abstract

Di-mon matings were carried out between monokaryons of commercial Pleurotus species (P.florida and P.sajor-caju) with dikaryotic mycelia of natural sporeless mutant (Psm) yielded 16 (P.florida x Psm) and 18 (P.sajor-caju x Psm) hybrids. Exposure of spore suspension of commercial Pleurotus species (P.florida and P. sajor-caju) to Ultra violet radiation for variable timings resulted in yielding few mutants. Few mutants obtained from P.florida spores even though exhibited spore less character in 1st generation failed to maintain the character (stability) in 2nd generation. The mutant obtained from exposure of spore suspension of P. sajor-caju exhibited sporelessness (low sporing character) with good morphology. The stability of the low sporing character was maintained even after 40th generation. It proved the mutation obtained was permanent. Gill sections of low sporing UV mutant along with its parent P.sajor-caju and commercial species P. florida and sporeless mutant (Psm) observed under microscope, showed P. sajor-caju and P. florida more spore intensity. The biological efficiency of P.florida was 61.09% and P.sajor-caju was 62.02%. Low sporing UV mutant showed lower biological efficiency of 52.67%. Natural sporeless mutant (Psm) showed highest biological efficiency of 70.93%. The shelf life of sporophores of commercial Pleurotus sajor-caju and sporeless strains (Psm and low sporing UV mutant) in pp covers at room temperature was 2 days as compared to only one day in 1.33% ventilation pp cover, commercial perforated cover, pp covers lined with brown paper and air tight container. Whereas sporophores of commercial Pleurotus florida could be stored in good condition only for one day in all the treatments the sporophores of Pleurotus sajor-caju and sporeless mutants (Psm and low sporing UV mutant) showed better shelf life compared to Pleurotus florida. Under cold storage condition (4 ºC) UV mutant and Psm showed 14 days extended shelf life compared to 11 days in Pleurotus florida and 13 days in Pleurotus sajor-caju. As the ventilation increased number of storage days also reduced. The present studies on dehydration of commercial Pleurotus species and two sporeless strains were carried out at room temperature (28-32 ºC) and drier (40 ºC). It took 2-3 days for optimal drying (8- 10% moisture) at room temperature as against 5-6 hours in drier for both commercial Pleurotus and two sporeless strains. RAPD analysis was carried out with random primers to know the polymorphism between the species and strains. The cluster analysis of RAPD markers showed two groups. In first group P. florida and Psm were closely related with 43% similarity, which also reflected in distance measure. Even though P. florida and Psm were closely related, morphological characters of both strains were different. P. florida have white sporophores with high spore content. Whereas Psm have light gray funnel shaped sporophores with no spores. In second group P.sajor-caju and UV mutant were closely related with 64% similarity. However sporophore morphology of both the strains was similar to certain extant. P.sajor-caju having gray sporophores with eccentric stipe and slight wavy margin with high spore content. Whereas UV mutant showed highly lobed (flower type) sporophores with very less spore content. Thus, RFLP and RAPD analysis found to be a suitable technique for observing the polymorphism between the strains.