No abstract

Rice, a major food crop, is grown in a wide range of ecological conditions and suffers significant yield losses as it is constantly exposed to a wide range of environmental and biotic stresses. The prevalence of different biotypes/strains has necessitated assembling of numerous resistance genes/QTLs into elite genotypes to confer a broader scale of resistance. The current study reports successful pyramiding of genes/QTLs that confer tolerance/resistance to submergence (Sub1), salinity (Saltol), blast (Pi2, Pi9) and gall midge (Gm1, Gm4) to supplement the four bacterial blight resistance genes (Xa 4, xa5, xa13, Xa21) present in Improved Tapaswini, an elite cultivar. The precise transfer of genes/QTLs was accomplished through effective foreground selection and suitable gene pyramids were identified. Background selection was practiced using morphological and grain quality traits to enhance the recovery of the recurrent parental genome. In the bioassays, the pyramids exhibited higher levels of resistance/ tolerance against the target stresses. The novel feature of the study was successful pyramidization and demonstration of the function of ten genes/QTLs in a new genotype. This success can stimulate several such studies to realize the full potential of molecular plant breeding as the foundation for rice improvement.

Water stress is a serious challenge to rice production. Understanding water stress tolerance is essential for precise trait modification. We identified an EMS induced mutant showing enhanced tolerance to water deficit stress at the vegetative stage. Multiple alterations in physiological behaviour, root morphological and anatomical structure, stomatal response and gene expression in various signalling pathways were found to be responsible for increased tolerance in the mutant. The mutant will be useful for dissecting the water stress tolerance mechanism in rice.

To incorporate durable resistance against bacterial blight, a major disease rice, three resistance genes, xa 5, xa13 and Xa21, from IRBB 60 were transferred through marker-assisted backcrossing using RG 556, RG 136 and pTA248 markers linked to the three genes to supplement the Xa4 gene present in Lalat, a popular rice cultivar. Effective selection enabled the transfer in three back-crosses and a generation of selfing and background selection employing morphological and grain quality traits and molecular markers, led to >90 % recovery of the recurrent parental genome. The gene pyramids exhibited high levels of resistance against the pathogen in multi-location evaluation trials conducted over several locations of bacterial blight in India. IL-2 (CRMAS2621-7-1), a gene pyramid, was identified as being promising for several endemic regions of bacterial blight and was released as Improved Lalat in one of the identified regions. The success of the study demonstrates the vast potential of marker-assisted selection for gene stacking and recovery of the parental genome with high precision.