Studies on plant-microbe interaction to improve stress tolerance in plants for sustainable agriculture

Biotic and abiotic stress factors have a major impact on plants and cause extensive losses to crop production. Bacteria that provide growth promotion and prime stress tolerance of plants have great potential to improve crop production and support durable and environmental friendly resource management. Priming refers here to when plants upon appropriate stimulation develop an enhanced capacity to express defense responses to a later stimulus. In this study strains of the beneficial bacterium Bacillus amyloliquefaciens were analysed for their effects on plants. Direct antagonistic effect of B. amyloliquefaciens on several Brassica phytopathogens (Botrytis cinerea, Alternaria brassicae, Alternaria brassicicola, Verticillium longisporum, and Sclerotinia sclerotiorum) was demonstrated by bacteria and exudates in vitro. A bacterial exudate fraction containing lipopeptide antibiotics was analysed and the strongest antagonistic activity was connected with a novel linear form of fengycin identified using mass spectrometry. Growth promotion of Arabidopsis thaliana Col-0, coi1-16, jar1 and npr1 but not in myb72 plants by B. amyloliquefaciens UCMB5113 was demonstrated with increased shoot and root biomass and increased number of lateral roots and root hairs while the primary root growth decreased. Bacillus inoculation resulted in profound effects on various plant hormones that will affect a variety of plant functions. Growth promotion was also demonstrated in split dish experiments where Bacillus strains were sequestered from Arabidopsis plants indicating a role for volatile organic compounds (VOCs). Bacillus VOCs also caused growth suppression of several phytopathogens. GC-MS analysis identified a large number of compounds in the VOC blend and the composition of VOCs was dependent on the medium used for cultivation and the effects on the plant also varied. Thus these Bacillus strains promote growth of plants and improve the survivability of plants exposed to biotic stress challenges by priming of stress tolerance. These findings can be extended to different crops to improve crop productivity under various environmental conditions