Biological control of banana wilt disease caused by Fusarium oxyspoum f. sp. Cubense using Streptomyces sp. H4

To evaluate the potential of Actinoplanes campanulatus, Micromonospora chalcea and Streptomyces spiralis endophytic in cucumber roots, to promote plant growth and to protect seedlings and mature plants of cucumber from diseases caused by Pythium aphanidermatum, under greenhouse conditions.

Three endophytic actinomycetes strains recovered from surface sterilized root tissues of Azadirachta indica A. Juss. (Meliaceae), plants were selected through tests for their potential as bio-control and plant growth promoting agents. It was also observed that the seed treated with the spore suspension of three selected strains of Streptomyces, significantly promoted plant growth and antagonized the growth of Alternaria alternata, causal agent of early blight disease in tomato plant. It was observed that the three selected strains prolifically produce IAA and siderophores that play vital role in promotion of plant growth and in suppression of Alternaria alternata. Interestingly, Streptomyces strain AzR-051 produced the highest amount of IAA at 13.73 μmol ml(-1) , compared to strains AzR-049 and AzR-010 9.22 μmol ml(-1) and 10.43 μmol ml(-1) respectively. It also produces siderophores higher than the other two strains. Thus these endophytic isolates have the potential as plant growth promoters as well as a bio-control agent, which is a useful trait for crop production in nutrient deficient soils. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

An endophytic Streptomyces sp. GMKU 3100 isolated from roots of a Thai jasmine rice plant (Oryza sativa L. cv. KDML105) showed the highest siderophore production on CAS agar while phosphate solubilization and IAA production were not detected. A mutant of Streptomyces sp. GMKU 3100 deficient in just one of the plant growth promoting traits, siderophore production, was generated by inactivation of a desD-like gene encoding a key enzyme controlling the final step of siderophore biosynthesis. Pot culture experiments revealed that rice and mungbean plants inoculated with the wild type gave the best enhancement of plant growth and significantly increased root and shoot biomass and lengths compared with untreated controls and siderophore-deficient mutant treatments. Application of the wild type in the presence or absence of ferric citrate significantly promoted plant growth of both plants. The siderophore-deficient mutant clearly showed the effect of this important trait involved in plant-microbe interaction in enhancement of growth in rice and mungbean plants supplied with sequestered iron. Our results highlight the value of a substantial understanding of the relationship of the plant growth promoting properties of endophytic actinomycetes to the plants. Endophytic actinomycetes, therefore, can be applied as potentially safe and environmentally friendly biofertilizers in agriculture.