Role of nodD gene product and flavonoid interactions in induction of nodulation genes in Mesorhizobium ciceri.

Mesorhizobium ciceri is a host specific bacterium which nodulates the genus, Cicer. Host specificity is regulated at first step by induction of nodulation (nod) genes in the presence of NodD protein and inducers (flavonoids) of plant origin. The inducer specificity of M. ciceri nodD gene was studied in NodD-mutant strain HN-9 carrying heterologous nodD genes and nodAlacZ fusion. The induction profile of nod promoter in M. ciceri revealed that nodD gene product of M. ciceri is specifically activated by chickpea root exudates only. M. ciceri HN-9 (nodA-lacZ) containing heterologous nodD genes from Rhizobium leguminosarum bv. viciae, R. leguminosarum bv. trifolii and Sinorhizobium meliloti was induced in presence of a number of flavonoids. On the other hand, induction profile of nod promoter showed that heterologous nodD gene products were activated to different levels in NodD(-) mutant of M. ciceri in presence of root exudates from homologous as well as heterologous legume hosts. The transfer of FITA (Flavonoid independent transcription activation) nodD gene in NodD(-) mutant, M. ciceri HN-9, was able to break the inducer specificity barrier and nod promoter was induced to maximum level irrespective of the presence or absence of inducer. It is concluded from the results that host specificity in M. ciceri - chickpea (Cicer arietinum) symbiosis is regulated at first step by the host specific interaction of nodD gene product of M. ciceri and inducers present in the root exudates of chickpea.

Isolation and characterization of mutants of Pseudomonas maltophila PM-4 altered in chitinolytic activity and antagonistic activity against root rot pathogens of clusterbean (Cyamopsis tetragonoloba).

Pseudomonas maltophila PM-4, an antagonist of pathogenic fungi including Rhizoctonia bataticola, R. solani, Fusarium oxysporum and Sclerotinia sclerotiorum associated with root rot of clusterbean (Cyamopsis tetragonoloba) was mutagenized with Tn5. Hyperchitinase producing mutants showing large zone of colloidal chitin dissolution were identified on medium containing calcoflor dye as an indicator. A mutant P-48 producing 137% higher chitinase activity than the parent strain PM-4 was identified. Seed bacterization of clusterbean (Cyamopsis tetragonoloba) with P-48 controlled the root rot upto 40.8% in the presence of conglomerate of all the four fungal pathogens Rhizoctonia bataticola, R. solani, F. oxysporum and Sclerotinia sclerotiorum.