Host restriction of nodulation by ineffective rhizobia in mungbean (Vigna radiata (L.) Wilczek)
2005
Delfin, E.F.
This research was conducted with the primary aim of improving response to inoculation in mungbean with the desired inoculum strain through the identification of mungbean varieties that can restrict nodulation by ineffective rhizobia. A total of 78 mungbean genotypes was screened for restriction of nodulation by ineffective rhizobia under greenhouse condition. Genotypes that consistently formed more nodules with the effective strain M6 than with the ineffective strains BVr56 and BVr33 were identified. A non restricting genotypes was also identified. Microscopic analysis of root nodule development in restricting and non restricting genotypes suggested that restriction of nodulation by ineffective rhizobia was due to delay in nodule development. Early nodulin gene Enod40 was detected in restricting and non restricting genotypes inoculated with either effective or ineffective rhizobia. Indigenous rhizobia from UPLB [University of the Philippines Los Banos, College, Laguna, Philippines] and Gerona, Tarlac [Philippines] were trapped with Pag-asa 3, a restricting genotype and Acc 638, a non restricting genotype. UPLB isolates differed significantly in terms of nodule number and nodule weight. Cluster analysis of rep -PCR amplified DNA fragments of 23 UPLB isolates and rhizobial strains M6 and BVr56 and BVr33 showed the existence of 5 major cluster groups at approximately 0.6 similarity level with strains M6, BVr56, and BVr 33 occupying the first 3 groups and the native rhizobia from UPLB in the last two groups. The discriminating characteristics of Pag-asa 3 was evident when inoculated with Gerona, Tarlac isolates. With Pag-asa 3 as host, 10 isolates formed higher number of nodules than strain M6. With Acc 638, only 2 isolates formed higher nodule number than M6.
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