Estimating genetic trends using historical data is an important parameter to check the success of the breeding programs. The estimated genetic trends can act as a guideline to target the appropriate breeding strategies and optimize the breeding program for improved genetic gains. In this study, 17 years of historical data from IRRI’s rice drought breeding program was used to estimate the genetic trends and assess the breeding program's success. We also identified top-performing lines based on grain yield breeding values as an elite panel for implementing future population improvement-based breeding schemes. A two-stage approach of pedigree-based mixed model analysis was used to analyze the data and extract the breeding values and estimate the genetic trends for grain yield under non-stress, drought, and in combined data of non-stress and drought. Lower grain yield values were observed in all the drought trials. Heritability for grain yield estimates ranged between 0.20 and 0.94 under the drought trials and 0.43–0.83 under non-stress trials. Under non-stress conditions, the genetic gain of 0.21% (10.22 kg/ha/year) for genotypes and 0.17% (7.90 kg/ha/year) for checks was observed. The genetic trend under drought conditions exhibited a positive trend with the genetic gain of 0.13% (2.29 kg/ha/year) for genotypes and 0.55% (9.52 kg/ha/year) for checks. For combined analysis showed a genetic gain of 0.27% (8.32 kg/ha/year) for genotypes and 0.60% (13.69 kg/ha/year) for checks was observed. For elite panel selection, 200 promising lines were selected based on higher breeding values for grain yield and prediction accuracy of > 0.40. The breeding values of the 200 genotypes formulating the core panel ranged between 2366.17 and 4622.59 (kg/ha). A positive genetic rate was observed under all the three conditions; however, the rate of increase was lower than the required rate of 1.5% genetic gain. We propose a recurrent selection breeding strategy within the elite population with the integration of modern tools and technologies to boost the genetic gains in IRRI’s drought breeding program. The elite breeding panel identified in this study forms an easily available and highly enriched genetic resource for future recurrent selection programs to boost the genetic gains.

Temperate japonica rice (Oryza sativa) is usually grown in temperate regions. When grown in tropical areas, most temperate japonica rice plants flower prematurely and do not show sufficient vegetative growth. Fourteen japonica rice varieties and lines adapting to tropical environments were developed in the Philippines (tropical Asia) between 2008 and 2014. Their genomes were characterized by genomewide single nucleotide polymorphism genotyping, and their grain yields were examined in the Philippines during the wet and dry seasons and in a high-altitude area of Burundi (tropical Africa). Based on the genotyping, all 14 materials were found to belong to the temperate japonica rice group. Grain yields were more affected by the environment than by the genotypes. Two of the fourteen rice materials showed more stable and higher yields than the check varieties across the three environments, and one of the two has been released as a commercial variety in the Philippines.Together, these results demonstrate that rice plants genetically belonging to the temperate japonica group can be bred to adapt to tropical areas.

Rice is a staple crop for 3.5 billion people in the world. To meet the challenges of the rice production for food security and demand due to population increase, yield improvement due to a rice variety’s genetic characteristics is imperative. Two studies presented in this paper were undertaken at the International Rice Research Institute (IRRI) in the Philippines, to assess genetic gains for yield in rice varieties bred over the past 50 years. These studies are called as “Era” studies as the varieties used for trials were released during long and distinct periods. Due to the differences in time periods of studies, varieties and locations, the studies were treated separately so as to not to compromise the data analyses. The studies demonstrated that IRRI developed varieties have achieved genetic gains and levels of genetic gains were dependent on correction or otherwise for maturities. In Study 1, the highest level of genetic gain was 0.70% at about a 23 kg ha-1 annual yield increase when not corrected for maturity followed by a genetic gain of 0.62% when corrected for maturity. In Study 2, the highest level of genetic gain was 0.74% at about a 19 kg ha-1 annual yield increase when corrected for maturity followed by 0.66% genetic gain when not corrected for maturity. Implications for breeding programs are discussed, however, the studies were not intended to compare genetic gains achieved through different breeding methods nor to compare genetic gains achieved using plot trials versus realized genetic gains for crops grown under farmers’ management.

BackgroundEstimation of genetic trends using historical data is an important parameter to check the success of the breeding programs. The estimated genetic trends can act as a guideline to target the appropriate breeding strategies and optimize the breeding program for improved genetic gains. In this study, 17 years of historical data from IRRI’s rice drought breeding program was used to estimate the genetic trends and assess the success of the breeding program. We also identified top-performing lines based on grain yield breeding values as an elite panel for implementing future population improvement-based breeding schemes.ResultsA two-stage approach of pedigree-based mixed model analysis was used to analyze the data and extract the breeding values and estimate the genetic trends for grain yield under non-stress, drought, and in combined data of non-stress and drought. Lower grain yield values were observed in all the drought trials. Heritability for grain yield estimates ranged between 0.20-0.94 under the drought trials, and 0.43-0.83 under non-stress trials. Under non-stress conditions the genetic gain of 0.44% (21.20 kg/ha/year) for genotypes and 0.17 % (7.90 kg/ha/year) for checks was observed. The genetic trend under the drought conditions exhibited a positive trend with the genetic gain of 0.11% (1.98kg/ha/year) for genotypes and 0.55% (9.52kg/ha/year) for checks. For combined analysis showed a genetic gain of 0.39% (12.13 kg/ha/year) for genotypes and 0.60% (13.69 kg/ha/year) for checks was observed. For elite panel selection, 200 promising lines were selected based on higher breeding values for grain yield and prediction accuracy of >0.40. The breeding values of the 200 genotypes formulating the core panel ranged between 2366.17 and 4622.59 (kg/ha).ConclusionsA positive genetic rate was observed under all the three conditions; however, the rate of increase was lower than the required rate of 1.5% genetic gain. We propose a recurrent selection breeding strategy within the elite population with the integration of modern tools and technologies to boost the genetic gains in IRRI’s drought breeding program. The elite breeding panel identified in this study forms an easily available and highly enriched genetic resource for future recurrent selection programs to boost the genetic gains.