Biodiversity of rice landraces as a resource for improving grain quality

Introduction
All over Asia, the cultivation of rice landraces has dwindled significantly since the introduction of high yielding varieties (HYV). While HYVs are characterized by a usually much higher yield, especially when combined with the application of inputs such as mineral fertilizer and pesticides, their dominance has led to substantial genetic erosion of cultivated rice. However, the enormous diversity of rice landraces constitutes an important resource, since certain genotypes might be associated with favourable agronomic and especially nutritional traits.

Objectives
–To characterize farming systems in which the cultivation of rice landraces still exists
–To assemble samples of rice landraces from various Asian countries for further chemical characterization of the rice grain
–To assess grain composition and interactions of nutritional components, aiming at identifying varieties which can help to improve the supply of nutrients deficient in the diet in developing countries.

Progress made
Around 100 different varieties of rice were collected from the Philippines, Bangladesh, India, Malaysia, and Vietnam. Farming systems and nutritional habits of farmers cultivating landraces were studies in detail in the Philippines. It was particularly evident that landraces constitute an integral part of rural culture and that market price of landraces can be significantly higher than that of HYVs.
Certain black landraces of rice were found to contain elevated levels of β-carotene, a vitamin-A precursor, which can supply up to 90 percent of vitamin A in plant-based diets. Moreover, β-carotene was found to be closely associated with oleic acid content. As the bioavailability of β-carotene depends on the dietary lipid supply, this association of β-carotene and oleic acid in black rice varieties is particularly interesting and beneficial for the consumers.
Starch properties were analysed in detail in six varieties differing in amylose content. Starch degradability, as measured by the glycemic index, was found to be significantly higher in low-amylose varieties. Cooling of rice after cooking and storing it for one day led to a significant drop in glycemic index due to retrogradation of starch and formation of resistant starch. The drop in glycemic index was particularly pronounced in low-amylose varieties. Therefore, cooling and storing of rice after cooking may be a strategy to slow down starch digestion, thus preventing type II diabetes.
A set of samples from Bangladesh was investigated with a focus on phytochemicals, macro and micro minerals, and protein quality. Phytate level was found to be quite high and positively correlated with a number of mineral constituents, including zinc, potassium and magnesium. This may impede the bioavailability of trace minerals in rice. Samples were also analysed for non-protein nitrogen and available lysine. While available lysine declined with increasing protein content, no significant relation between protein content and non-protein-nitrogen was observed. Red varieties were found to contain significantly more total phenolics than colorless varieties, thus improving antioxidant capacity of ingested red rice.