Bharat Rai

Studies on antagonism betweenFusarium udum Butler and root region microflora of pigeon-pea

AbstractAntagonism betweenFusarium udum Butler causing wilt of pigeon-pea (Cajanus cajan (L.) Millsp.) and the saprophytic microflora of the root region of the host was studied with reference to colony interaction, hyphal interference, volatile and non-volatile metabolites and staling growth products. Studies were extended to screen potential antagonists against the wilt pathogen in soil. Aspergillus flavus, A. niger, A. terreus, Penicillium citrinum andMicromonospora globosa (an actinomycete) were antagonistic againstF. udum, whereas the pathogen parasitized and killedAspergillus luchuensis, Cunninghamella echinulata, Curvularia lunata, Mortierella subtilissima andSyncephalastrum racemosum.The pattern of growth of microorganisms on nutrient agar staled by rhizosphere soil inocula of healthy or wilted pigeon-pea plants was found to be different.F. udum colonized and grew on nutrient agar staled by the rhizosphere inoculum of the wilted plants upto 120h of incubation. However, it could not colonise and grow on the nutrient agar staled by rhizosphere microflora of healthy plants after 48h of incubation because of the presence of antagonists likeA. niger, A. flavus, A. terreus and a few species ofPenicillium in the soil inoculum.When pure cultures in soil ofF. udum was mixed with those of antagonists in different ratios,A. niger, A. flavus andM. globosa significantly suppressed the population ofF. udum, whereasA. terreus markedly reduced the population. When inoculated in soil, the antagonists exhibited a high fungistatic activity againstF. udum.

Biological Control of Fusarium Wilt Disease of Pigeonpea

Biological control of Fusarium udum causing wilt disease of pigeonpea was studied in vitro, as well as, in vivo. Aspergilluspavus, Anergillus niger, Bacilius licheniformis (strain-2042), Gliocladium virens, Peniciliium citrimum, and Trichoderma harzianum, which were found to be the most potent ones in inhibiting the radial colony growth of the test pathogen, were used as biological control by amending their inocula at diffeyent concentrations in pots and in pathogen-infested soil in the fields. Maximum reduction of the wilt disease was observed with G. vireos both in pots and in the fields. The population of E. udum was found to be markedly reduced when the antagonists were applied in the soil. The study establishes that G. virens can be exploited for the biological control of wilt disease at field level.

Antagonistic activity of some leaf surface microfungi against Alternaria brassicae and Drechslera graminea.

The antagonistic effect of some leaf surface fungi against the pathogenic fungi Alternaria brassicae and Drechslera graminea was studied in the field and in the laboratory. Application of spores of the test fungi to leaves, either collectively or individually, inhibited lesion development by the pathogens. Inhibition increased with increasing spore concentration and was highest when a composite spore mixture was used. The most antagonistic fungi were Epicoccum purpurascens, Aureobasidium pullulons and Cladosporium cladosporioides in the case of A. brassicae and E. purpurascens, Alternaria alternata and Aureobasidium pullulans in the case of D. graminea . The metabolites of Acremonium roseogriseum, Aspergillus terreus and C. cladosporioides inhibited A. brassicae . Those of A. pullulans, E. purpurascens and Trichoderma viride reduced the activity of D. graminea . The most pronounced inhibitory effects were caused by a mixture of metabolites of all the test fungi. The most significant effects were observed when the spores of the leaf surface fungi or their metabolites were sprayed on leaves prior to inoculation of the pathogens. Maximum inhibition of A. brassicae in vitro was caused by A. alternata , followed by T. viride and E. purpurascens. D. graminea was not significantly affected in vitro by any of the test fungi.

Effect of soil burning on microfungi

SummaryThe qualitative and quantitative nature of microfungi in soil after burning was studied for seven months. The numbers of fungal species and their colonies in soil were reduced immediately after burning but returned to their normal state after about a couple of months. Species of Aspergillus and Penicillium were the first to colonize the burnt soil. Trichoderma viride appeared after two months. Penicillium spp. decreased consistently with time whereas T. viride followed the reverse path. Several other species appeared in due course as and when ecological conditions became suitable for them. re]19760720

Competitive saprophytic colonization of pigeon-pea substrate by Fusarium udum in relation to environmental factors, chemical treatments and microbial antagonism

Abstract The competitive saprophytic colonization (CSC) of pigeon-pea substrates by Fusarium udum was studied in relation to environmental factors, chemical treatments and microbial antagonism. CSC was best at 22°C, good at 30°C, but at 40°C the substrate was vigorously colonized by Coprinus lagopus and Aspergillus nidulans which suppressed colonization by F. udum . High competitive saprophytic ability of F. udum was noted at pH 7 and 9 at soil moisture contents between 5 and 30%. At pH 4 and 5 F. udum was replaced by A. flavus and A. nidulans . The CSC of F. udum decreased in the soil-sand inoculum mixture amended with the fungicides bavistin, dithane Z-78 and difolatan. The herbicides 2,4-D and machete also reduced CSC by F. udum whereas urea promoted it. Colonization of pigeon-pea substrate by F. udum was highly suppressed by antagonism from Penicillium citrinum, A. niger, Micromonospora gtobosa, A.flavus, A. terreus and Trichoderma viride when these were used in inoculum mixtures with F. udum or when substrates had already been colonized by them. Otherwise F. udum was shown to have a high competitive saprophytic ability.

Hyphal parasitism and chlamydospore formation by Fusarium oxysporum on Rhizoctonia solani

Hyphal parasitic behaviour of Fusarium oxysporum on Rhizoctonia solani and consecutive changes during this phenomenon have been investigated and studied. The hyphal parasitism was very commonly recorded between the test fungi. During the course of parasitism coiling, penetration, lysis and formation of chlamydospores by F. oxysporum on R. solani were observed. R. solani is a new host record for the mycoparasite F. oxysporum.

Gibberella indica: the perfect state of Fusarium udum.

(1982). Gibberella Indica: The Perfect State of Fusarium Udum. Mycologia: Vol. 74, No. 2, pp. 343-346.

Microbial decomposition of leaf litter as influenced by pesticides

SummaryThe application of dithane M-45, 2, 4-D and carbofuran at the rates of 1, 5 and 10 mg (active ingredients) per g air-dry litter caused insignificant variations in the microbial populations in decomposing leaf litter. The qualitative nature of mycoflora, was altered, a little, with regard to the total number of species and relative abundance of a few species. The variations in CO2 evolution was significant only in relation to the fungicidal treatment. Percent weight loss of treated and untreated litter differed insignificantly at the end except in the case of fungicidal treatment. The present study infers that the used concentrations of the test pesticides may be recommended in tropical forestry as their application does not pose any potential threat to the process of natural decomposition of the leaf litter.

Trichoderma viride as a mycoparasite ofAspergillus spp.

SummaryTrichoderma viride was found to be parasitic on three species of Aspergillus. The mycoparasitism was characterized by frequent coiling, penetration and hyphal growth of the parasite inside the conidiophores of Aspergillus. The volatile and non-volatile metabolites ofT. viride, more or less, inhibited radial growth of all the testAspergillus spp.

Ecology of Fusarium udum causing wilt disease of pigeon pea: Population dynamics in the root region

The fungi in root regions of healthy and diseased Cajanus cajan differed qualitatively and quantitatively. F. udum was always recorded on the rhizoplane of wilted plants and about 90% of the total fungal population of the rhizosphere of wilted plants was F. udum. Due to such heavy infestation of F. udum the population of actinomycetes was suppressed in rhizosphere of the wilted plants. No definite pattern of increase or decrease in the population of bacteria was observed in root regions of healthy and diseased hosts. However, there were less in non-rhizosphere soil as compared with the rhizospheres. There was, in the beginning, a marked difference in succession of fungi in the rhizosphere and rhizoplane regions of excised healthy and wilted pigeon-pea roots. In early stages the population of F. udum decreased on decaying roots of the wilted plants but increased on that of the healthy ones. The number of fungi g−1 dry soil as well as the population of F. udum decreased on decaying roots of healthy and wilted plants both as natural senescence and decomposition progressed. In advanced stages of root decomposition the pattern of colonization and succession was similar on both types of the roots.