Allelopathy effect of host root exudates, host rhizosphere bacteria and Heterorhabditis indica on penetration and development of root knot nematode, Meloidogyne incognita (Kofoid & White, 1919) Chitwood 1949
Loading...
Date
2020
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
DIVISION OF NEMATOLOGY ICAR-INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI
Abstract
Root-knot nematode, Meloidogyne incognita from monoculture-tomato rhizosphere
was baited on tomato var. S22 (TSJ2) and cowpea var. Pusa Komal (CSJ2) plants and
single egg-mass lineage was developed for three success generation on their respective
hosts. Three predominant bacteria were isolated and characterized each from the
rhizosphere of tomato viz., Beijerinckia fluminensis, Agrobacterium tumefaciens,
Paenarthrobacter ureafaciens, and cowpea viz., Chryseobacterium rhizosphaerae,
Agrobacterium tumefaciens, Rhizobium pusense, based on the 16S rDNA sequence.
The root exudates profiling by GC/MS analysis resulted in the identification of 38
compounds from tomato and 40 compounds from cowpea, out of which 16 compounds
were common to both. The common compounds consisted of 11 hydrocarbons, 3 fatty
acids and 2 ketones. Tomato contributed 57.89% of the common hydrocarbons
compared to 42.30% in cowpea. Cowpea contributed 66.66% ketones as compared to
33.33% in tomato, while 3 fatty acids showed 100% similarity to both the crops. In
chemotactic attraction studies with host specific root-exudates, TSJ2 showed positive
attraction towards tomato but not cowpea, while CSJ2 showed a neutral response. In
cross-inoculation assay, there was 63.75% reduced penetration of TSJ2 on cowpea,
while 77.20% of CSJ2 on tomato. In pot trials, there was a significant reduction in the
number of galls/plant (57.52%), number of egg-mass/plant (64.41%) and number of
eggs/egg-mass (34.56%) when TSJ2 was inoculated on cowpea. In reverse trial, when
CSJ2 was inoculated on tomato plants, there was a similar reduction in the number of
galls/plant (73.60%), number of egg-mass/plant (70.73%) and number of eggs/eggmass (4.41%). In water agar assay, both TSJ2 and CSJ2 showed neutral chemotaxis
response towards tomato and cowpea root-exudates mixed together in equal
proportions. When exposed to tomato and cowpea roots growing together, the
penetration of TSJ2 and CSJ2 reduced by 80.11% and 83.54%, respectively, compared
to their controls. There was a significant decline in the development and biology of
TSJ2 and CSJ2, with respect to number of galls/plant and number of egg-mass/plant
when inoculated on tomato and cowpea plants raised together in the same pot.
However, the number of eggs/egg-mass significantly reduced only in case of TSJ2.
The three bacteria isolated from tomato rhizosphere significantly repelled TSJ2 but not
CSJ2, while cowpea rhizosphere bacteria repelled both the nematode types. All the six
bacteria were unable to repel Hetrorhabditis indica infective juveniles. When H.
65
indica was applied simultaneously along with TSJ2 and CSJ2 on tomato and cowpea
plants, respectively, the highest dose of 30 IJg-1
showed 61.99% and 58.93% reduction
in the penetration of the two groups of the nematode. In combined allelopathy studies,
involving specific host-root-exudates, specific rhizosphere bacteria and H. indica
(@30 IJg-1
), there was a significant reduction of 59.37% and 46.19% reduction in gall
formation by TSJ2 and CSJ2 on tomato and cowpea plants, respectively. These results
demonstrate for the first time, the existence of metapopulation in clonal M. incognita
species flourishing in monoculture-tomato rhizosphere. Leads can be taken from this
work and utilized for developing novel ecofriendly nematode management strategies
based on crop rotation and intercropping.
Keywords: Meloidogyne incognita, Metapopulation, Allelopathy, Root exudates,
Rhizosphere bacteria, Heterorhabditis indica.
Description
T-10468