Identification of quantitative trait loci for adaxial and abaxial stomatal frequencies in Oryza sativa

Stomatal frequency is one of the main factors that determine photosynthetic ability and stomatal conductance. However, the genetic basis for stomatal frequency is still poorly understood. The genetic relations between adaxial and abaxial stomatal frequencies have been studied in rice (Oryza sativa L.) with quantitative trait loci (QTL) analysis approach on a population of backcross inbred lines of japonica Nipponbare × indica Kasalath. Four QTLs controlling adaxial and abaxial stomatal frequencies were identified. On chromosome 3 of rice, QTL for adaxial stomatal frequency overlapped that for abaxial stomatal frequency. There was a high correlation (r = 0.660, P < 0.01) between them, and the allele that increases the expression was contributed by Kasalath for both traits. These results suggest that the same gene may pleiotropically control the stomatal frequency on both surfaces of the leaf. QTLs for leaf rolling related to osmotic stress were also mapped. The absence of overlap in QTLs for leaf rolling and stomatal frequency suggests that osmotic tolerance is at least partly independent of stomatal frequency. The genetic relationship between stomatal frequency and yield is also discussed.