Development ofRhizobia with improved symbiotic properties for diverse legume crops
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Date
2014
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Publisher
CCSHAU
Abstract
Present investigation was undertaken to develop efficient rhizobial strains and to over ride host specific symbiotic nodulation behavior in the process of symbiotic infection in diverse legume crops. Such promiscuous Rhizobium strains with improved efficiency to fix nitrogen might add higher amount of nitrogen to the plants. Towards these efforts 295 rhizobial strains were isolated from nodules of legumes chickpea, pea and lentil grown in different fields. These isolates were then analyzed for their cellulose and pectin utilizing ability by growing them on CMC and pectin media. Best growing strains on CMC medium were selected for gamma irradiation to create genetic variations. These gamma irradiated mutant isolates were screened for their enhanced cellulose and pectin utilizing ability. These mutants were compared with their parents for enhanced cellulose and pectin utilization ability. It was found that percent increase in growth on CMC media over parents was in the range of 8.82 to 422.22%. Rhizobial mutants having contrasting antibiotic profile were electrofused for obtaining cross infective rhizobia. Total five fusants each from the rhizobial cross combination E1, E2, E3, E4 and E5 which had their resistance pattern confirmed were obtainedwith the help of electroporation. Symbiotic infection behaviour and cross infectivity of electrofusants, mutants and wild type rhizobial isolates were analysed on chickpea, pea and lentil plants through plant infection test. It was found that doses of gamma-rays on biofertilizer appeared significant effect on number of nodules, plant weight and shoot N content. Greater number of nodules and promiscuous behavior was observed in mutants followed by electrofusants as compare to their parental rhizobial isolates.Mutant rhizobial strains improved shoot nitrogen content up to 50% inchickpea,45% in pea plant whereas the same trend was also observed on lentil plants. The developed Rhizobium strains with improved symbiotic
association and ability to infect across strict specificity for host legumes would be of great help for the
farming community at large.
Representative strains were selected for the molecular analysis based on PCR amplification.
As a nodulation genes marker, nodA, nodC, nodD, nodE, nodV and nodW genes were selected, which
are common nod genes essential for nodulation in all rhizobial species investigated so far and these are
also determinants of host range. The comparison of the nod genes between symbiotic strains and host
plant groups taken together indicated that lateral transfer of Sym genes and genetic rearrangements are
involved in the genetic modification.Apparently the Nod factors of the strains are quite variable. The
PCR amplification of these factors determined that these factors were considerably altered through
mutation and rearrangements were taken place by electro-poration.
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Keywords
root nodulation, genes, planting, biological phenomena, enzymes, rhizobium, nitrogen, legumes, mutants, biological development