Cereals provide more than 50% of human caloric intake internationally, and this project aims to increase sorghum yield by shifting biomass, in the form of seed size increase, from vegetative plant parts to the grain. More grain per unit area without increased demand for water and nutrients will enhance sustainability and food security.

Grain yield is controlled by complex, regulated genetic networks or quantitative trait loci (QTLs) derived from natural variations in many crop plants. Yield is a product of the three major parameters, panicle number, grain number per panicle and grain size. Trade-offs are commonly observed between grain number and size in both natural and domesticated systems. While this overall negative correlation exists there is evidence to suggest it is possible to increase grain size without compromising grain number. Because of the complexity such progress has proven difficult using conventional selective breeding approaches. With the genomic, physiological, and genetic resource tools at hand in sorghum, we can link physiological processes that determine grain size and number to their underpinning genetic control. This will allow manipulation of key loci to generate more biomass in the grain, while minimizing or eliminating the adverse impact on grain and tiller number.

This project aims to study the genetic architecture and physiological control of grain size in cereals, by elucidating the signalling pathways underpinning the grain biomass increase (grain size increase in the absence of grain number diminution) and ascertain whether this link can be extended to other cereal crops.

Our specific objectives are to:

1) Use genomic and crop physiological approaches and association genetics to determine the genetic factors:

• that influence potential grain size in the absence of source limits
• that influence potential grain number per panicle under non-limited conditions
• that break the negative size:number correlation and can be manipulated

2) Evaluate the candidate genes and networks listed in 1 above to:

• Investigate temporal and anatomical expression of candidates and signalling elements in differential genetic contracts
• Use transgenics to ectopically express these genes and modifying elements
• Determine if these genes contribute to racial differentiation that may be associated with adaptation to particular environmental conditions.

• Prof. Ian Goodwin
• Dr Jimmy Botella
• Prof. David Jordan
• Dr Erik Van Oosterom

• Dr Emma Mace
• Geoffrey Morris
• Stephen Kresovich
• Dr Yongfu Tao

• Australian Research Council (ARC)