iotic stresses made DRR17B (developed by the Indian Institute of Rice Research, formerly called the Directorate of Rice Research, Hyderabad), an obvious choice for improvement through DBT’s Accelerated Crop Improvement Program (ACIP) which aimed at targeted improvement of several elite rice varieties and parents used in hybrid rice breeding for resistance against major rice pests and diseases (involving six centers).
It was decided that improvement would be carried out by transferring major genes conferring resistance against these diseases and pests through the process of marker-assisted breeding. The novel tool of marker-assisted breeding is very helpful when popular, high yielding varieties and parents of hybrid rice, which already possess several desirable features are needed to be improved rapidly, within a few seasons/years to incorporate few traits that they are lacking (like resistance to biotic stresses and abiotic stresses).
The process of marker-assisted breeding to incorporate resistance involves crossing the donor parent [usually an agronomically inferior variety possessing the target resistance gene(s)] and recipient parent [usually an elite variety/parental line lacking the resistance gene(s)], screening the progeny for presence of the resistance gene(s) with the help of PCR-based molecular markers and identifying one or more such plants possessing the resistance genes and advancing such plants for further crossing/selfing.
Two major resistance genes, Xa21 (conferring resistance against bacterial blight disease, sourced from an accession of wild species of rice, named Oryza longistaminata) and Pi54 (conferring resistance against blast disease, sourced from a landrace of rice, named Tetep) were introduced to DRR 17B (which is a high yielding female parent used in hybrid rice development, possessing the highly desirable medium-slender grain type with stable maintenance ability, but is highly susceptible to bacterial blight and blast diseases). Within a short period of six seasons, the two resistance genes were transferred by a team of three scientists under the leadership of Dr R.M. Sundaram and three PhD students to DRR17B through the process of marker-assisted breeding and the improved versions of DRR17B were observed to be similar to the original parent (i.e. DRR17B) in terms of yield, plant type, grain type etc., which possessing high level of field resistance to both bacterial blight and blast diseases.
After development of improved versions of DRR17B possessing bacterial blight and blast resistance through marker-assisted breeding, the next step involved conversion of the improved versions of DRR17B possessing multiple biotic stress resistance genes to its cytoplasmic male sterile counterpart (DRR17A) so that it can be immediately used for developing promising, high yielding, biotic stress resistant hybrids. This activity is now in progress and is expected to be completed in another 2-3 seasons (by the end of 2017).
In addition to improving DRR17B, the team at the Indian Institute of Rice Research has also developed pest (gall midge and brown plant hopper) and disease (bacterial blight and blast) resistant versions of a high yielding variety, Akshaydhan, which possesses good adaptability and an elite restorer line, named RPHR-1005.
The improved versions of Akshayadhan, DRR17B and RPHR1005 possessing multiple biotic stress resistance are under evaluation in the All India Coordinated Rice Improvement Programme at multiple locations (including biotic stress prone areas) in the country. The improvement of RPHR1005 is very important as it is the male parent (technically called restorer line) of the country’s first hybrid possessing high yield along with the highly desirable medium slender grain type, named DRRH3. Improved versions of RPHR1005 along with that of DRRH3 have already been developed and tested for their yield and biotic stress resistance and have been found highly promising as compared to their original parents.
DBT’s programme on ACIP has brought together a network of scientific institutions for targeted improvement of several crops including rice for few agronomically important traits and several breeding lines and improved varieties/hybrid rice parental lines of rice, wheat, maize, soybean etc. have been developed in the last six years. The improved lines are presently being tested under the All India Coordinated varietal/hybrid testing programme of Indian Council of Agricultural Research from the last season. Many promising lines have already been identified and advanced for evaluation and release under the ACIP.