|Keywords (Extracted from title, table of contents and abstract of thesis)
macrophomina phaseolina (tassi) gold, m. phaseolina, cotton roots, aspergillus flavipes, trichoderma hamatum, t. harzianum, stachybotrys atra, sp., bacullus sp., vigna sp., sclerotia
A wet-sieving and dilution technique was developed for the isolation and enumeration of sclerotia of M. phaseolina from soil. Used of CaC10 was essential for eliminating faster growing mucorales and other their fungi. PDA containing Penicillin Streptomycin, and Demosan with or without Rose-Bengal gave good results. Of the 154 soil samples analysed from 5 different cotton growing tracts of Pakistan, where root-rot is a problem, 0-29 sclerotial propagules9-1of soil was detected. NO significant different in population of sclerotia between healthy and root-rot infested parts of cotton fields was observed. Frequency of colonization of M. phaseolina was more in upper portions of cotton roots than at the distal portions. Similarly, of M. phaseolina was detected in gram from sub-surface soils.
Antagonists like Aspergillus Flavipes, Trichoderma Hamatum, T. Harzianum, Stachybotrys Atra, sp. and Bacullus sp. previously grown on alfalfa or wheat fragments were more effective in reducing sclerotial number in soil than use of spore suspension, however, complete elimination was not obtained.
In experiments on numerical threshold, infection was directly proportional to the inoculum densities of sclerotia of M. phaseolina in soil and inversely proportional to the soil moisture level. For 50% infection an inoculum level of number of sclerotia 9-1 of soil was 5 for Vigna sp. Okra and guar and 40 for cotton. The appearance of disease was more and rapid in sol kept at 25% moisture levels with less infection at 50 or 100% moisture levels.
An important and useful observations made was that planting of Vigna sp., mustard, clover and wheat increased sclerotial population in soil. This was accompanied with greater colonization of M. phaseolina on host plants. The utilization of these in corporation would appear to increased sclerotial population and root-rot. However of dry or fresh plant residues proved more effective in suppressing sclerotial numbers and root rot. Of the organic amendments, alfalfa, clover and mustard proved better amendments than wheat or cotton in reducing sclerotial numbers; the effect being more pronounced at 3-5% level than at 1% level of amendment. This was accompanied with reduced colonization of M. phaseolina on Vigna used as test plant. Mustard amendment, however was phytotoxic level. Organic amendments like alfalfa, clover or wheat used at 1% and at 50-100% moisture levels reduced the sclerotial numbers by 76-100%. Nitrogen fertilizers at different concentrations also reduced sclerotial population in soil and infection on Vigna plants; the effect being greatly pronounced at higher concentration. Artificially infested soil when subjected to wet conditions reduced sclerotial numbers more than in soils kept dry or under alternate wet and dry treatments. Of the fungicides. Benomy1reduced the sclerotial numbers in soil as compared to Captain and Dithane. Similarly Benomy1 reduced the Macrophomina infection of cotton and chickpea. Mixed cropping of cotton of cotton with moth, organic amendments like wheat straw, alfa-alfa, poultry manure, saw dust did not eliminate the population of sclerotia.
Mulching of soil moist or dry with polyethylene sheets during May-June increased soil temperature from 36 C ambient to 48-52 C and considerably reduced the sclerotial numbers in 1 week, and after 4 week it was possible to eliminate the sclerotia irrespective of amendment with lucern or wheat. Sclerotia at 20 cm depth, however, did not show greater reduction. At another location, where during hot summer months soil temperature after mulching reached a maximum of 52 to 65 C viability of sclerotia was reduced to zero after 1 week. Solar pasteurization can thus be applied to the field to eliminate Macrophomina infection