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.
Highlights
Rice (Oryza sativa L.), is the primary source of food for more than half of the world’s population[1] and is being cultivated under a wide range of environments, from arid highlands to flooded lowlands, high humidity to high temperature climates and in acid, saline and alkaline soils
Parental polymorphism survey revealed distinct polymorphism for the markers tested for the traits to be introgressed into Improved Tapaswini i.e. RG64 (C1O1A51-Pi2), P28 (WHD-1S-75-1-127- Pi9), RM444 (Kavya-Gm1), RM547 (Abhaya-Gm4), SUB1BC2 (FR13A-Sub1QTL) and RM10745 and (FL478-salinity tolerance QTL (Saltol) quantitative traits loci (QTL)) (Fig. 1 and Table 1)
Through utilization of phenotypic selection tied with marker-assisted selection, out of 10 gene pyramids first time we obtained 4 gene pyramids with desired 6 abiotic and biotic tolerance/resistance (Sub[1], Saltol, Pi2, Pi9, Gm1 and Gm4) genes/QTLs along with 4 bacterial blight resistance genes (Xa4, xa[5], xa13, Xa21) in Improved Tapaswini background
Summary
Rice (Oryza sativa L.), is the primary source of food for more than half of the world’s population[1] and is being cultivated under a wide range of environments, from arid highlands to flooded lowlands, high humidity to high temperature climates and in acid, saline and alkaline soils. A range of biotic factors, which can be insect pests such as rice gall midge or diseases like bacterial leaf blight and blast, severely affect rice grown throughout tropical, subtropical and temperate areas of Asia. Oryzae (Xoo), is one of the oldest and most devastating diseases of rice throughout the world[2] and significant yield losses up to 80–100% from bacterial blight infection were known to occur[3] and when infection occurs during panicle initiation or earlier, the grain development will be severely affected. Known as rice fever disease, it was reported in all the rice growing countries of the globe[16,17,18] and it infects panicles, culm and leaves of the rice plants, reducing photosynthetic efficiency and yield of rice grain[19,20] and causes 40–70% loss of rice grain[21,22]. Eight genes (Gm1, Gm2, Gm4, Gm5, Gm6, Gm7, Gm8 and Gm11) have been tagged and mapped[34,35]
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