Qualitative and quantitative estimation of phenolic compounds was done through reverse phase-high performance liquid chromatography (RP-HPLC) from different parts (leaf, stem, and root) of rice plants after inoculation with two rhizobial strains, RRE6 (Rhizobium leguminosarum bv. phaseoli) and ANU 843 (R. leguminosarum bv. trifolii) and infection by Rhizoctonia solani. On the basis of their retention time, the major phenolic acids detected in HPLC analysis were gallic, tannic, ferulic, and cinnamic acids. Furthermore, in all Rhizobium-inoculated rice plants, synthesis of phenolic compounds was more consistently enhanced than in control (uninoculated plants), where the maximum accumulation of phenolic compounds was observed in plants inoculated with RRE6 and infection with R. solani. Under pathogenic stress, RRE6 performed better because a relatively higher amount of phenolics was induced as compared with plants treated with ANU 843. Phenolic acids mediate induced systemic resistance and provide bioprotection to plants during pathogenic stresses. In addition, both rhizobial strains promote growth and productivity of rice plants in greenhouse conditions. This report on Rhizobium-mediated defense responses and growth promotion of nonlegume (such as rice) provides a novel paradigm of symbiotic plant-microbe interaction.

Abstract:The experiment was conducted to estimate combining ability and heterosis for yield, yield attributing traits and few grain quality parameters in rice. The crosses were made among three CMS lines i.e., IR58025A, Pusa6A and IR68897A and seven pollen parents viz., Sarjoo-52, Jaya, Sasyashree, Swetha, HUR 5-2, PR-106 and BPT 5204. Twenty one hybrids were generated in line x tester design. The superior hybrids were identified on the basis of combining ability effect and heterosis. Cross combination IR68897A/Jaya and IR68897A/BPT 5204 exhibited good x good parental GCA effects suggesting that there is additive x additive type of gene action. The cross IR68897A/Jaya showed highest positive SCA effect. The higher magnitude of heterosis for all the yield and quality traits were not expressed in a single hybrid combination. It varied from cross to cross due to diverse genetic background of their parents. The two crosses IR68897A/Jaya and IR68897A/BPT 5204 were found to be heterotic for yield and yield traits as well as the grain quality characteristcs.

Three novel endophytic rhizobial strains (RRE3, RRE5, and RRE6) were isolated from naturally growing surface-sterilized rice roots. These isolates had the ability to nodulate common bean (Phaseolus vulgaris). Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and sequencing of 16S rDNA of these isolates revealed that RRE3 and RRE5 are phylogenetically very close to Burkholderia cepacia complex, whereas RRE6 has affinity with Rhizobium leguminosarum bv. phaseoli. Plant infection test using gusA reporter gene-tagged construct of these isolates indicated that bacterial cells can go inside and colonize the rice root interiors. A significant increase in biomass and grain yield was also recorded in greenhouse-grown rice plants inoculated with these isolates.

Three novel endophytic rhizobial strains (RRE3, RRE5, and RRE6) were isolated from naturally growing surface sterilized rice roots. These isolates had the ability to nodulate common bean (Phaseolus vulgaris). Polymerase chain reaction-restriction fragment length polymorphism and sequencing of 16S rDNA of these isolates revealed that RRE3 and RRE5 are phylogenetically very close to Burkholderia cepacia complex, whereas RRE6 has affinity with Rhizobium leguminosarum bv. phaseoli. Plant infection test using gusA reporter gene tagged construct of these isolates indicated that bacterial cells can go inside and colonize the rice root interiors. A significant increase in biomass and grain yield was also recorded in greenhouse-grown rice plants inoculated with these isolates.

Twenty F1 hybrids from three CMS lines and eight pollen parents were evaluated to study the heterosis for various yield and quality traits in rice (Oryza sativa L.). The findings suggested that the magnitude of heterosis differed from character to character and cross to cross. Majority of the hybrids recorded desirable heterosis for grain yield. Among the rice hybrids exhibiting high heterosis for grain yield, IR-68897A x Pusa Sugandh-3, IR-58025A x HUR-JM-59221 and IR-58025A x Pusa Sugandh-5 were top performers. The hybrid, IR-68897A x Pusa Sugandh-3 recorded highest yield per plant, and was among the best three performers for traits, days to 50% flowering, days to maturity and number of effective tillers per plant. Thus, IR-68897A x Pusa Sugandh-3 may be considered as the best heterotic combination for yield and yield traits. Among the three high yielding hybrids, IR-58025A x Pusa Sugandh-5 was found to be relatively better performing for majority of the quality traits. Thus, IR-58025A x Pusa Sugandh-5 may be considered as the best cross combination if both yield and quality traits are taken into consideration.