Research in the Netherlands has revealed that under sub-otpimal conditions, the best way for rice breeders to improve the rice harvest is to produce varieties whose performance is not fertiliser dependent. However, specifically modified varieties need to be developed for rice growing under saline conditions.

Gambian researcher Baboucarr Manneh investigated variations in the rice yield and the possibilities for increasing this under a variety of environmental circumstances by means of plant breeding. For example, he discovered that in general breeding is best directed towards varieties that are adapted to a wide range of conditions and whose performance is not fertiliser dependent. However for cultivation on silt soils, only varieties with a genetic predisposition for these specific conditions should be used.

Manneh carried out field experiments with rice in salt water and in fresh water in The Gambia in West Africa. He also studied the effect of nitrogen fertilisation on the rice yield.

The researcher could accurately predict the rice yield with the help of DNA markers. This opens up the way for breeders to use DNA fingerprints as a selection criterion. Manneh also found that the crop growth model ORYZA1 accurately predicted the biomass and grain yield of the rice. Using this model he could also assess the possibilities for increasing the yield by manipulating the physiological characteristics of the rice plant.

A high biomass production is necessary for the potential grain yield of a rice plant. However, for the actual grain yield the distribution of the total dry matter over the root, shoot, stem and leaf, as well as the cultivation period are important. The relative importance of these factors seems to change with the environmental circumstances investigated.

Rice cultivation in many former mangrove forests in West Africa, is difficult due to the salinity of the water there. In Asia, where most of the world's rice is produced, most of the land is covered with silt water. The growers in these countries often have to cope with a shortage of fertiliser as well. The rice yield under these sub-optimal conditions can be increased by selecting the appropriate varieties.

The research was funded by the Netherlands Organisation for Scientific Research.