Improvement of soybean and mungbean in the tropics

• Kasetsart University, Thailand

Among its tropical grain legumes, Thailand has identified soybean (Glycine max) and mungbean (Vigna radiata - green gram; and V. mungo - black gram) as the two with highest priority for improvement. Although important components of Thailand's agricultural production, both at present return yields well below their potential, with large seasonal and regional variability. Grown mainly as human food, they provide important protein in the rice-based diet, while smaller quantities are used as animal feed. Soybean is also a valuable source of oil. Mungbean-widely eaten as bean-sprouts-is also a much-valued source of starch for noodles, and supplies a substantial export market. Both legumes fix nitrogen, making them important in crop rotations. Despite these uses, their low and unpredictable yields have made farmers unwilling to grow them.

All the collaborators in Thailand have current programs on soybean and mungbean improvement and have made useful advances, but a unified research program can be expected to achieve more substantial progress. This collaborative project is designed to conduct research in Australia and Thailand to quantify the environmental and genetic constraints limiting production of these legumes across the range of potential environments. Additionally, as an adjunct to the more applied breeding and agronomy programs in Thailand, assistance will be provided to delineate research goals and expertise in physiological research and breeding methodology, and to identify sources of germplasm for crop improvement.

The project will involve two research approaches: manipulation of germplasm through breeding, genetic and physiological studies to optimise performance in a given environment; and manipulation of environment through agronomic management to permit greater expression of genetic potential. It will facilitate development and exchange of adapted germplasm and apply existing research experience and understanding of the genotype x environment interaction to the solution of continuing problems. Initially it will emphasise climatic adaptation, since factors such as daylength, temperature and water availability have had major importance in conditioning adaptation of these crops in Australia's tropics.

In Thailand, both legumes can be utilised as early- or late-monsoonal or as dry-season crops, with optimal crop duration depending on the season and rotational sequence and on whether irrigated or rainfed. Matching cultivar to cropping niche is therefore the most important single component of the improvement program, which will include cultivars tolerant of cold, drought and/or waterlogging for different regions. The scientists will also take account of non-climatic limiting factors, such as soil acidity and pest- and disease-resistance.

On the plant breeding side, knowledge of the environmental control of adaptation will enable the team to better define breeding aims, identify genotypes with appropriate traits, develop more efficient screening and selection procedures and design more efficient breeding strategies using knowledge of the genetic basis of the desired trait. Specific breeding needs already identified include: appropriate photoperiodic response; increased tolerance of the climatic constraints; resistance to wet-season weather damage in mungbean; physiological and agronomic traits such as synchrony of pod-set in mungbean, seed characteristics and growth habit; and resistance to or tolerance of diseases such as powdery mildew, cercospora leafspot and bacterial blight in mungbean, and bacterial pustule, phytophthora and possibly rust in soybean.

On the agronomic side, the scientists will aim to improve management factors such as sowing dates, spatial arrangement and irrigation practice, to optimise the use of limited resources and minimise environmental constraints.

Most aspects of the research will be undertaken in both countries, although work on the genetic and physiological basis of adaptation and agronomic studies to minimise drought stress will take place in Australia, while studies on genotype x environment interaction, on adaptation and on a range of agronomic questions will be undertaken in various regions of Thailand. Many of the results should prove of mutual benefit to the two countries.