30Bacterial blight (BB) disease reduces the yield of rice varieties and hybrids considerably in many 31 tropical rice growing countries like India. The present study highlights the development of durable BB 32 resistance into the background of an elite maintainer of rice, DRR17B, by incorporating two major 33 dominant genes, Xa21 and Xa33 through marker-assisted backcross breeding (MABB). Through two sets 34 of backcrosses, the two BB resistance genes were transferred separately to DRR17B. In this process, at 35 each stage of backcrossing, foreground selection was carried out for the target resistance genes and for 36 non-fertility restorer alleles concerning the major fertility restorer genes Rf3 and Rf4, using gene-specific 37 PCR-based markers, while background selection was done using a set of 61 and 64 parental polymorphic

Background Species belonging to the genus Trichoderma are considered as one of the most potential biocontrol agents which can be readily collected from soil and found effective against various fungal and bacterial diseases. In rice-growing areas, the major fungal pathogens affecting rice production include Rhizoctonia solani causing sheath blight and Sclerotium oryzae causing stem rot disease of rice. Due to the lack of resistant varieties and detrimental effects of chemicals, biocontrol gives a good opportunity to manage the diseases efficiently in a sustainable manner. Main body Trichoderma spp. from native rice rhizosphere soil were examined for their antagonistic efficiency to supress the two soil-borne rice pathogens, viz., R. solani and S. oryzae. Morphological, biochemical and molecular characterisation of the isolates led to the identification of species as T. asperellum. The isolates of Trichoderma spp. were found to be positive to IAA release and phosphate solubilisation and were screened against R. solani and S. oryzae in vitro and in vivo in pots under glass house conditions. Regression analysis indicated a positive correlation between the amount of chlamydospores produced by T. asperellum and their antagonistic potential against the two pathogens. Exposure to external stimuli, viz., light, injury and nitrogen sources in culture media triggered increased conidiation in Trichoderma isolates. Among the four isolates studied, Trichoderma asperellum IIRRCK1 (TAIK-1) was found to be the most effective in improving plant growth in rice and highly antagonistic against R. solani and S. oryzae. Sorghum grain was found to be the most suitable among different organic substrates studied to provide better growth and viability of TAIK-1 and improved the efficiency of the seed treatment and soil application. External stimuli in the form of near UV blue light, mechanical injury to the colonies and nitrogen source added to the culture media help in faster conidiation of Trichoderma. Conclusion Strain TAIK-1 showed strong competitive and antagonistic activities against fungal soil-borne pathogens, in addition with promoting healthy growth and development of rice plants. This can be a suitable and safe alternative to chemical management in the rice fields for long-term scenario.

To combat the dreaded diseases in rice like bacterial blight and blast, host plant resistance has been advocated as a sustainable method. Through the present study, we have successfully incorporated three major bacterial blight (BB) resistance genes viz., Xa21, xa13 and xa5 into NLR3449, a high yielding, blast resistant, ne-grain type popular rice variety through marker-assisted backcross breeding. Foreground selection was carried out using PCR based, gene-speci c markers viz., pTA248 (Xa21), xa13prom (xa13) and xa5FM (xa5) at each generation of backcrossing, while 127 polymorphic SSR markers spanning on 12 chromosomes were used for background selection and backcrossing was limited to two rounds. At BC 2 F 1 generation, a single plant (NLR-87-10) with 89.9% recovery and possessing all the three bacterial blight resistance genes was forwarded to BC 2 F 2 generation. A solitary BC 2 F 2 plant viz., NLR-87-10-106 possessing all the three resistance genes and > 90% genome recovery was identi ed and advanced through sel ng till BC 2 F 4 generation by adopting pedigree method. Three best lines at BC 2 F 4 lines, possessing high level of resistance against bacterial blight and blast and equivalent or superior to NLR 34449 in terms of yield, grain quality and agro-morphological traits have been identi ed and advanced for multi-location trials.