Dual application of Bacillus pumilus and Glomus mosseae for improvement of health status of mandarin plants
2011
Chakraborty, U. | Chakraborty, B.N. | Allay, S. | De, U. | Chakraborty, A.P.
Mandarin (Citrus reticulate) is an ancient commercial crop being cultivated in Darjeeling and Sikkim hills. Decline in general plant health and decreased fruit production as influenced by abiotic and biotic factors is a major threat to the cultivators in the region. Bacillus pumilus TRS 3, a potential plant growth promoting rhizobacterium, isolated from rhizosphere of plantation crop, which showed phosphate solubilization, siderophore production, IAA and volatile production in vitro, when applied to the rhizosphere of nursery grown mandarin seedlings, enhanced growth markedly. Plant growth promotion was determined in terms of increase in height of plants, number of leaves and biomass. B. pumilus also showed antagonism against fungal pathogens in vitro. In addition, screening of arbuscular mycorrhizal fungi from rhizosphere of mandarin plants yielded predominant association of Glomus mosseae, G. fasciculatum, G. intradices, G. versiforme, Gigaspora margarita, G. rosea, G. gigantean along with Acaulospora spinosa, A. bireticulata and Scutellospora sp. Maximum colonization by G. mosseae was evident which was selected for mass multiplication in maize plants. Mandarin roots were inoculated with G. mosseae alone and in combination with B. pumilus which was applied as soil drench. Both microorganisms increased growth of the plants but most significant increase was obtained when both were co-inoculated. Similarly, root rot of mandarin caused by Fusarium oxysporum, was suppressed to certain extent by B. pumilus or G. mosseae, but significant suppression occurred when G. mosseae was co-inoculated with B. pumilus. Three major enzymes involved in defense, chitinase, β-1,3 glucanase and peroxidase showed enhanced activities during disease suppression, which was also confirmed by immunological assays such as PTA-ELISA and Dot-blot. Observed plant health improvement and disease suppression in mandarin plants may be due to a combination of at least three mechanisms- direct inhibition of the pathogen in the soil, induction of resistance in the host or better nutrient availability.
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