In rice, there has been very limited research on genetic gain in Asia in general, and in Bangladesh, no studies have been done yet, even though rice is the main staple food. The aim of this study was to estimate the genetic gain for yield from the varieties released over the last 50 years for monsoon and winter rice ecosystems.
Over the last 50 years, the Bangladesh Rice Research Institute (BRRI) has developed and released new varieties and conducted variety trials to assess their performance. Within this period, the yield has increased due to improved management (agronomic trend) and plant breeding efforts (genetic trend). Genetic gain can be defined as the rate of increase in performance over a period of time that is achieved through artificial selection and breeding programs.
Over the last 10 to 15 years, there have been several studies assessing long-term genetic gains in different crop species in different countries. To quantify the increase in performance with time that is due to breeding, agronomic and genetic gain need to be dissected, which can be done using models that regress varietal performance for traits of interest on the year of release, in trials conducted across locations and years.
In “ERA” (method to assess yield improvements) studies, all varieties in the series are included in the same trials. Other models allow the genetic trends to be estimated from ongoing varietal performance trials that do not test all varieties in all years, but that retain a sufficient number of common checks from year to year to allow genetic and non-genetic trends to be estimated. It is to be expected that breeding and varietal selection are not the only relevant factors driving crop yield gains when comparing cultivar performance and genetic advances across several locations and years.
Modern rice research in Bangladesh started in the 1960s, but the long-term genetic gain of rice in the country has not yet been quantified. Therefore, the objective of this study was to use historical yield data from trials of BRRI’s released rice varieties to assess the genetic progress achieved due to rice breeding. The key objective of this study was to estimate the long-term rate of genetic improvement delivered by BRRI breeding efforts.
This is the first time that genetic trend has been estimated for Bangladeshi rice breeding programs, and the estimates are among the few to have been published for South Asia. The results indicate that rice yield gains due to breeding have been very limited since the end of the Green Revolution in the favorable environments in which the experiment was conducted, amounting to 0.28% and 0.18% annually in irrigated winter and rainfed monsoon rice, respectively.
These gains are lower than the non-genetic trend detected (0.54% and 0.64% annually for winter and monsoon rice, respectively) and are less than needed to maintain rice food security in the face of population growth, climate change, and land loss to urbanization.
The low rates of genetic gain observed in this study appear to be broadly representative of those achieved in the favorable rice production environments in South Asia critical to the region’s food security, although there is some evidence that the rate of gain has been higher in drought-prone environments.
Modest continuing gains in non-genetic trend of 0.54% and 0.64% annually in winter and monsoon, respectively, may be due to long-term improvements in crop management, but also may shed light on the impacts to date of climate change on rice productivity in favorable rice production environments in Bangladesh. Increasing temperatures are expected to increase climate risk to yields in monsoon production and decrease them in winter rice production, however, we cannot dissect the effect of agronomic practices and the impact of climate change.
The findings of this study confirm the need to increase the rate of genetic gain delivered by rice breeding programs in Bangladesh. Limiting factors have been carefully analyzed, and a program is designed to transform rice breeding at BRRI by reducing cycle time, increasing selection accuracy, and improving selection for breeding value. This program, technically supported by the International Rice Research Institute, is expected to increase the annual rate of genetic gain for yield to 1.5–2.0% in the near future.
Read the study:
Rahman NMF, Malik WA, Kabir MS et al. (2023) 50 years of rice breeding in Bangladesh: genetic yield trends. Theor Appl Genet 136, 1–13