BIOLOGICAL CONTROL OF DIFFERENT SOIL BORNE FUNGAL DISEASES OF POTATO (SOLANUM TUBEROSUM L.) RAISED THROUGH TISSUE CULTURE BY USING VESICULAR ARBUSCULAR MYCORRHIZA AND OTHER ANTAGONISTIC FUNGI

The present research work presents the use of some fungal biotechnological techniques for biological control of soil borne fungal pathogens of potato (Solanum tuberosum L.) by employing vesicular arbuscular mycorrhiza and other antagonistic fungi i.e. Aspergillus niger (Van) Tiegh, and Trichoderma viride Pers with different soil amendments and variable ranges of pH and temperature under glasshouse, screen house and field conditions.\ud \ud Because of aphid virus vectors, which transmit viruses in potatoes resulting in low yield, a study was conducted to determine the best season to raise healthy potato seed crop by avoiding aphid attack. The vector for the transmission of PLRV in potatoes is the green peach aphid (Myzus persicae Sulz). It was found that the population of Myzus persicae was maximum in the months of March and April. It was concluded that the spring crop in the plains of Punjab province is not fit for seed potato production purposes.\ud \ud The potato planting materials i.e. plants and tubers were raised through tissue culture techniques of apical meristem culture, nodal stem cuttings, layering, micro propagation in in-vitro and in-vivo and micro tuberization in-vitro and multiplication of seed tubers. Plants were grown out under field conditions and under controlled conditions in glass houses through out the course of the study. Murashige and Skoog Medium of inorganic salts with various amendments both in solid and liquid media were used for the commercial production of micro plants and micro tubers in in-vitro propagation. The liquid medium proved most suitable to elucidate the virus problem in the potato crop. Virus free seed tubers and plants used in experiments were screened through Enzyme linked immunosorbent assay (ELISA) to detect the potato viruses i.e. PVX, PVY, PLRV and PVS.\ud \ud An elaborate survey was carried out of endogonaceous spore density. Vesicular arbuscular mycorrhizal fungi status and pathogenic infections. This was done in the root systems and in rhizosphere soil of the four potato varieties approved by the Seed Council of Pakistan i.e. Cardinal, Desiree, (red skin) Diamant and Patrones (white skin), growing in different areas of Pakistan (Plains and Northern Hilly Areas). All major vesicular arbuscular mycorrhiza (V AM) forming fungi genera were found in both potato growing areas. During this study the significance of various potato pathogens was determined in these four potato varieties. The investigations took place in both hilly areas and plains of Pakistan using the potatoes crop raised through tissue culture. A survey was also carried out of mycoflora in the rhizosphere of potato plants and a number of potato pathogens were isolated and identified. Fungi were isolated on malt extract agar (MEA) and potato dextrose agar (PDA) media except for obligate parasites. The potato pathogens identified were Rhizoctonia solani Kuhn (stem canker and black scurf), Verticillium alba-atrum Reinke and Berth, V dahliae (Verticillium wilt), Fusarium oxysporum schlect, Fusarium .spp. (Fusarium wilt), Alternaria solani Soraner (early blight), Phytophthora infestans (Mont) de Bary (late blight), Spongospora subterranea (wallr) Lagerh, (Powdery scab) and Streptomyces scabies (Thaxt.) waks and Henric (common scab).\ud \ud The preparations of culture media and inoculum were carried out on various types of substrata including agricultural byproducts. Amongst these, sorghum seeds and wheat straw were the most successful substrates for inoculum. They were treated with 0.1 normal (N) and 0.2 N concentration of sulfuric acid (H2SO4) before being inoculated with antagonistic fungi.\ud \ud A new method was developed for the sterilization of compost and solid media through direct Sun light (Solarizaiton) at 60-75°C by polythene sheets covering.\ud \ud It was observed that the single and dual inoculations of antagonists of Trichoderma viride and VAM resulted in significant control of R. solani, Fusarium oxysporum and Verticillium albo-atrum. Significant biocontrol of disease severity was also obtained with dual inoculations (VAM + Aspergillus niger) made against R. solani and Verticillium spp.\ud \ud Fusarium oxysporum, the cause of wilting disease of potatoes, was suppressed and controlled biologically by using. T viride and VAM. There was a synergistic interaction of R. solani and F. oxysporum during interaction with each other and the wilt disease control in sterilized compost media.\ud \ud Pre inoculations with VAM of tissue culture raised microplants from test tubes to glass houses showed considerable hardening toward water and light stresses and a reduced mortality rate.\ud \ud Spongospora subterranea, the cause of powdery scab in potatoes, was controlled biologically through pre-inoculation of antagonist Trichoderma viride and by adjusting pH levels (i.e. 5.5 to 7.90) under field conditions by amending rhizosphere soils with Single Super Phosphate (SSP) and 1 N Sulphuric acid I-H2SO4