Genetic Diversity for Concentration of Sixteen Mineral Elements Among Diverse Rice Germplasm.

Mineral nutrients such as Ca, Fe, and Zn play critical roles in human health, with over 3 billion people suffering from Fe and Zn deficiencies.  Rice provides the major source of nutrition for a large proportion of the world’s population, but unfortunately, rice grain is not a good source of mineral nutrients and can contain toxic elements such as As and Cd.  The first step toward breeding rice lines with improved nutritional value is to understand the genetic diversity available to breeders in germplasm collections.

A core subset of 1700 accessions from among the 17,000+ rice accessions in the USDA National Small Grains Collection was grown over two years, two replications/year in Beaumont, TX, under both flooded and unflooded field conditions to impact soil redox and nutrient availability.  ICP-MS was used to analyze the harvested brown rice for variation in accumulation Mg, P, K, S, Ca, Mn, Fe, Co, Ni, Cu, Zn, As, Rb, Sr, Mo, and Cd.

Fifteen repeated check-plots paired with fifteen soil samples per replication documented that environmental variance within this study was small compared with the genetic variance.  Large (> 5x) ranges in grain content were found for each of the elements, with the unflooded field treatment providing greater phenotypic variance than flooded fields.  Three element x element correlations were found to be significant; P x K (r=0.56), P x Mg (r=0.66), and Zn x Ca (r=0.64).  Both K and Mg were more directly correlated with P than with each other (r=0.35).  For all elements, the grain content histograms were skewed with significantly more accessions having higher-than-average content than those having reduced element content.  Accessions high for particular elements were sometimes found to have similar geographic origins.  For example, four of the five lines highest in Mo content originated from Malaysia.  The common origin of the high-Mo accessions is exciting in that it supports the contention that we identified rice accessions containing heritable gene(s) underlying their elevated Mo content.  Accessions exhibiting extreme mineral content were crossed to develop progeny populations in which genes affecting rice nutritional value can be molecularly tagged.  Spatial location of the accumulated minerals within the rice kernel is also under investigation.