Genetic enhancement of phosphorus starvation tolerance through marker assisted introgression of OsPSTOL1 gene in rice genotypes harbouring bacterial blight and blast resistance.

Phosphorus (P), an essential macronutrient, is a prerequisite for various plant-growth mechanisms including root establishment/development, early/late vegetative stage development and reproductive stage development. Rice (Oryza sativa) is very sensitive to P starvation. Most cultivated genotypes have poor tolerance levels to P deficiency and consequently the grain yield is severely affected by P starvation. Since P deficiency of soils is a major concern of rice production areas, it is necessary to develop new cultivars with enhanced P tolerance. This is also an expectation of farmers and the Agriculture ministry of southern states of India where rice cultivation is intensive. Our objective was to introgress the phosphorus starvation tolerance (OsPSTOL1) gene through marker-assisted backcross breeding (MABB) in to two intermediate genetic stocks of popular local-varieties namely, ASD 16 and ADT 43 which harbour bacterial blight and blast resistance (R) genes. To delve into the P starvation phenotypic effect, we have generated a set of four backcross inbred lines (BILs) with enhanced P starvation tolerance. The developed BILs showed altered root architecture pattern and greater root surface area with increased P uptake, confirming their adaptability to P deficient soil conditions. Further, a correlation between root traits and low/high P conditions indicates the function of introgressed OsPSTOL1 in BILs. The enhanced root characteristics, therefore, enabled the plants to access and effectively absorb available nutrients from soil. In summary, the unique features of the OsPSTOL1 BILs with bacterial blight and blast resistance can aid varietal development suitable for cultivation in P deficient soils.

Genetic analysis of fertility restoration under CGMS system in rice (Oryza sativa L.) using three-way test-cross method.

We studied the genetics of fertility restoration by producing three-way test cross (TWTC) hybrids involved different combinations of restorers, maintainers and partial restorers of rice. Pollen and spikelet fertility of 16 TWTC hybrids were studied. Six TWTC involving restorer/restorer combinations as male parents produced progenies with fertility levels ranging from complete to zero. No specific ratio of segregation was observed. The crosses involving maintainer/maintainer combinations as male parents showed fully fertile and partial fertile/sterile plants in their progenies. These could be due to nonallelic gene interactions for fertility restoration between the two restorer or maintainer parents, or due to the influence of some modifying genes in the nuclear genome. TWTC involving partial restorer / restorer and partial restorer/partial restorer as the male parents also produced fully fertile and partial fertile/sterile plants suggesting the complex genetics of fertility restoration in rice. There were no previous results depicting the complementation effects of maintainers for fertility restoration.

The roots of future rice harvests.

Rice production faces the challenge to be enhanced by 50% by year 2030 to meet the growth of the population in rice-eating countries. Whereas yield of cereal crops tend to reach plateaus and a yield is likely to be deeply affected by climate instability and resource scarcity in the coming decades, building rice cultivars harboring root systems that can maintain performance by capturing water and nutrient resources unevenly distributed is a major breeding target. Taking advantage of gathering a community of rice root biologists in a Global Rice Science Partnership workshop held in Montpellier, France, we present here the recent progresses accomplished in this area and focal points where an international network of laboratories should direct their efforts.