Overcoming production constraints to sorghum in rainfed environments in India and Australia

• National Research Centre for Sorghum, India
• University of Queensland, Australia

Sorghum is an important crop in India and in parts of Australia's cropping region. India's Rabi sorghum and dryland sorghum in Australia perform relatively poorly. In both countries yields of sorghum are relatively static, with productivity not having improved over the past two decades. A combination of biotic and abiotic factors have contributed to this lack of improvement. Water and nitrogen deficiencies are the main factors limiting production, both being in short supply. In addition insect damage is also hampering yield improvements. In India shoot fly and stem borer are the major pests, while in Australia midge and Helicoverpa armigera are the problem species. An integrated approach using plant breeding and genetic transformation techniques, along with crop modelling was used to target these insects, and to overcome the constraints of water and nitrogen availability.

The project utilised an integrated approach involving plant breeding and genetic engineering, crop physiology and agronomy, and crop modelling, to: - enhance genetic transformation techniques to aid development of sorghum varieties with high and stable levels of resistance to sorghum shoot fly, - develop methods to improve the efficiency of selection for plant breeding through better analysis and design of multi-environment testing, and - develop improved crop models and climatic and soil databases to be able to simulate water and nitrogen effects on crop production and predict the consequences of management manipulations of the crop.

Each of the three goals were addressed through separate but interacting sub-projects: - improved insect pest resistance by genetic transformation (targeting shoot fly); - improved breeding methods; and - improved management strategies.
The interaction between the sub-projectsallowed the development of shoot fly resistant genotypes to provide more flexibility in sowing date, plant density and nutrition management; flexibility in crop management via sowing dates, density and nutrition would influence multi-environment testing regimes and their optimisation, and modelling and simulation a means of evaluating management strategies outside the practices of farmers because of restrictions on management imposed by shoot fly.

The project developed a sorghum transformation system, allowing transgenic sorghum plants with a gene for stem borer resistance to be developed. This resistance is based on expression of a gene for Baculovirus thuringiensis (BT) toxin that is lethal to many insects. A BT gene produces a toxin harmful to stem borer, creating a resistance in the plant to that insect. Several elements of the process of genetic transformation - microprojectile bombardment and a meristematic-specific promotor - have been developed.
These processes help more stable gene expression. For example meristematic-specific promotion allows the development of specific thin walled tissues (the meristem) which support specific genes to develop as permanent tissues. This stable gene expression is very important as a component in the development of gene transfer technology and utilisation. An important result from this genetic transformation is the potential capability to incorporate different BT genes that are capable of targeting specific insect pest species. A methodology for artificially culturing shoot flies has also been developed, considerably speeding up experiments into the validity of BT toxins.
Improved breeding options have been enhanced through the compilation of a database of yield trials. The trials, for Rabi sorghum, were conducted by the All India Coordinated Sorghum Improvement Program. Ten years of data from across 31 locations was identified. An analysis of the data revealed genotype by environment interactions accounted for more than three quarters of total genetic variance in grain yield. From this data regional adaptation patterns, comprising five near homogenous groups, were identified.
As a result multi-environment trial programs utilising this information for optimal varieties suited to conditions were recommended. This has allowed for accelerated trials by increasing the efficiency at which varieties can be matched to local conditions. Indian scientists involved in the project, along with others, were trained in techniques to analyse adaptation for use in future breeding programs.
A similar database, this for soil and climate data from past sorghum experiments, has also been collated. CROPBAG assembles growth data together with soil and water data from a collection of past, but relevant, sorghum experiments, and those undertaken in project-related trials. The use of a protocol for experiments ensured data collection from project trials was standardised. Through this process the physiological basis of responses of Indian and Australian sorghum varieties to climate-water-nitrogen interactions has been quantified and available for future work.
The APSIM-SORG growth simulation model for Australian conditions has been modified based on the Indian data collected. This is now in use in India. Using the model allowed the identification of problem targets for consideration in further modelling and experiments.
One Indian genotype of sorghum, CSH13R, with higher radiation use efficiency was identified through the project. Another key finding was that average production on deeper soils was substantially higher than that on shallow soils. Some modelling capacity within Indian partner institutions was also developed as a result of the project. This includes the use of simulation modelling, data interpretation and analysis and beyond this in evaluating field trials including genotype by environment trials.
A sorghum biotechnology workshop held in ICRISAT in March, 1999, under the auspices of ACIAR enabled scientists to disseminate results of the advances made in tissue culture and transformation and the future potential of the technology. This resulted in a book, Sorghum Tissue Culture and Transformation (eds. N. Seetharama and I. Godwin, 2004, Science Publishers, New Hampshire, USA)which includes 20 chapters from Australian and Indian collaborators, as well as from the United States (UC Berkeley, Kansas State University, Michigan State University), Belgium (Free University, Brussels) and the Netherlands (AP-Netherlands Biotechnology Project, Wageningen University).