USE OF RHIZOBIA IN THE CONTROL OF SOILBRONE PLANT DISEASE CAUSED BY ROOT INFECTING FUNGI

During a survey of cultivated fields of Karachi, Thatta, Hyderabad, Pandora, Tharparker, Tando Qaiser, Islamabad, Naran, Shugran, Kalam, Khanspur and Madyan more than 600 plant specimens belonging to 36 plant species showing symptoms of wilting and root rot disease were collected, Fungi associated with roots were isolated and identified. Macro-phomina phaseolina, Rhizoctonia solani, Fusarium oxysporum and F. solani alone or mixed together were found predominantly associated with infected plants. In the present study Drechslera australiensis on Lens culinaris, Solanum tuberosum, Trifolium alexandrianum and Zea mays; D. halodes on Leas culinaris; F. oxysporum on Brassica napus;p Macrophomina phaseolina on lens culinaris and pisum sativum and verticillium alboatrum on vigna radiate are new host records from Pakistan.\ud \ud Thirty rhizobial strains either isolated from root nodules of leguminous plants or obtained from NifTAL, USDA, NIAB, NAEC, ICARDA or ICRISAT were used to study their interaction with m. phaseolina, R. solani, F. oxysporum and F. solani. Rhizobium meliloti (KUMH 139 & KUMH 555) , Rhizobium sp., (KUMH 770) and Bradyrhizobium sp., (KUMH 560) produced zones of inhibition against all the 4 test fungi whereas R. meliloti (KUMH 653) ingibitedinhibited M. phaseolina, R. solani and F.phaseolina and R. solani.\ud \ud In field experiments, R. meliloti (KUMH 139 & KUMH 555), B japonicum (KUMH 569) and R. leguminosarum (KUMH 551) used as seed dressing and or as soil drench significantly controlled the infection of M. phaseolina, R. solani and Fusarium spp., on leguminous plants like soybean and mungbean as will as non leguminous plants like sunflower and okra. Reduction in root rot disease resulted in increased plant height and fresh weight of shoots, of the three strains of B. japonicum used, TAL- 102 was found more effective in reducing the root rot disease of soybean, lentil, fenugreek and mustard as compared to TAL-379 and a local isolate. \ud \ud Use of rhizobia with other biocontrol agents like Trichoderma spp., Paecilomyces lilacinus, Gliocladium virens and Stachybotrys atra were found more effective in reducing the root rot disease of lentil, mustard, okra, fenugreek, soybean and mungbean in 60 day old plants than their separate use, Greatr grain yield in soybean was recrded where B. japonicum was used with T. hamatum. Use of rhizobia with P. lilacinus significantly increased nodulation in mungbean.\ud \ud Of the fungicides used, vitavax was found, vitavax was found inhibitory to B. japonicum with bavistin was found more effective in controlling the infection of M. phaseolina and Fusarium spp., on both sunflower and soybean and against R.solani in sunflower than their separate use. Highest number of nodules per plant was produced on soybean where B. japonicum was used with bavistin @ 2500 ppm a.i. Soil amendment with cotton or neem cake significantly controlled the infection of M. phaseolina, R. solani and Fusarium spp., on mungbean and okra, however, oil cakes were slightly inhibitory to root nodulation. Greater plant height was observed where cotton cake @ 3% was used with P. lilacinus followed by P. lilacinus mixed with Bradyrhizobia. Although use of potash, supper phosphate and urea controlled the infection of root infection fungi, use of potash was found to reduce the efficacy of P. lilacinus, B. japonicum and R. meliloti in disease control. Use of rhizobia with urea was found more effective in controlling infection of M. phaseolina and F. solani on okra than their separate use.\ud \ud In studies on mass multiplication of rhizobia, wheat bran showed more rhizobial population per gm of substrate as compared to saw dust or rice husk. Soil amendment with wheat bran or rice husk inoculum of rhizobia also showed better control of M. phaseolina and Fusarium infection on okra under field condition than use of rhizobia as seed dressing. Multiplication of rhizobia on sugarcane filter mud amended with 1% sugar yielded upto 1011 cfu/gm of substrate where rhizobia were found viable upto one year with 109 cfu/gm. A six month old inoculum of R. leguminosarum and B. japonicum produced nodules respectively on pea and soybean while 1 year old inoculum of R. meliloti produced nodules on Lucerne. Use of rhizobial inoculum multiplied on sugarcane factory mud was effective for 1 year in controlling R. solani and Fusarium infection and upto 6 month M. phaseolina infecting on okra used as test plant. Rhizobia applied to soil were found ineffective in reducing the infection of root infection fungi on succeeding non leguminous crop like okra but were found effective on their original host like Lucerne and soybean