Perennial O. sativa × O. rufipogon interspecific hybrids: I. Photosynthetic characteristics and their inheritance

A survey of 24 wild Oryza accessions identified Oryza australiensis and Oryza rufipogon as potential sources of enhanced photosynthetic rate for introgression into cultivated rice. Photosynthetic capacity per unit leaf area (CER) was associated with leaf N content but not with leaf chlorophyll concentration, flag leaf area, or specific leaf area. Eight fertile, perennial F1 hybrids between O. sativa and O. rufipogon were grown in non-flooded soil, and CER was measured at flowering under saturating light. Two F1 hybrids had greater CER than the average of 26.1 μmol m2 s−1. The F2 progeny from these hybrids were screened for CER in the field, and segregants with even greater rates of photosynthesis were selected. The basis of high photosynthetic rate in the F2 populations was not leaf thickness or leaf chlorophyll content. One F2 line had exceptionally high CER and stomatal conductance. Broad-sense heritability on an individual plant basis for CER in two F2 populations was 0.44 and 0.37. A highly significant offspring-parent regression of 0.89 for CER was observed in a replicated field evaluation (four blocks, five plants per plot) of 20 vegetatively propagated F2 selections and their F3 seedling progeny. Broad-sense heritability for CER on a plot-mean basis was estimated as 0.74 for both selected F2:3 families and for the selected F2 clones. Genetic resources in the genus Oryza may represent a source of alleles to increase leaf photosynthetic rate in the cultivated species, which we have demonstrated to be a heritable, though environmentally variable, trait in an O. sativa/O. rufipogon population.