ABSTRACT
Root-knot nematode, Meloidogyne incognita (Kofoid & White) Chitwood, is a major threat to mungbean cultivation. The pest causes a significant reduction in plant growth parameters that ultimately results in loss of grain yield. The present study was carried out under glass house condition to study the effect of different inoculum load of root-knot nematode M. incognita on plant growth, nodulation and nematode development and nutrients status of Mungbean. The results revealed a progressive decline in plant growth parameters viz., fresh and dry shoot weight and shoot length with respect to increase in inoculum level. However, fresh and dry root weight showed the opposite trend. The fresh and dry shoot weight was decreased by 44% and 66%, respectively at 4 J2s/g soil. The chlorophyll content in the leaves also decreased with the increase of inoculum level from 100-6000 J2s/pot. Nutrients contents of the plant viz. N, P, K, Ca and Mg were significantly reduced in shoots while in roots these was increased with an increase of inoculum levels. Nodulation was affected by 80% at the highest inoculum level i.e. 6000 J2s/pot. Also leghaemoglobin, bacteroid content and nitrogenase activity was reduced progressively with increased levels of nematode inoculum. Thus, the root-knot nematode, M. incognita interferes with the process of symbiotic nitrogen fixation between mungbean host and rhizobium and that can affect the quality of produce.
ABSTRACT
Osmotic stress has a detrimental effect on growth and plant growth promoting activities (PGP) of rhizobacteria. Thus, before exploring the potential of a rhizobacterium as bioinoculant for drought prone areas, it is essential to understand the effect of osmotic stress on their PGP traits. Here, we characterized two osmotolerant bacteria Bacillus sp. and Bacillus cereus for their PGP activities with Brassica sp. under osmotic stress conditions. Osmotic stress did not appear to have any deleterious effect on their growth. Lower level of osmotic stress (20% PEG 6000) in fact improved their growth. Both the rhizobacterial strains possessed multiple PGP activities. Lower level of osmotic stress had beneficial effect on most of the PGP activities, while higher level of osmotic stress (40% PEG 6000) had a detrimental effect on ACC deaminase activity and GA production. Variable effect of osmotic stress on the different PGP activities of the osmotolerant rhizobacteria during plant-microbe association was observed. Lower level of osmotic stress enhanced IAA and exopolysaccharide production while GA production was reduced. Further increase in osmotic stress had a detrimental effect on IAA production, while exopolysaccharide production was enhanced. However, ethylene production by the inoculated plants was reduced under stressed conditions. Inoculation with the osmotolerant rhizobacterial strains enhanced seed germination and seedling fresh weight in mustard under osmotic stress conditions. Thus, these osmotolerant Bacillus sp. and Bacillus cereus strains have potential as bioinoculants for mitigation of water deficit stress in plants in drought affected regions.