Optimization of Seed Germinability for Direct Seeding By Stacking QTLs in Rice

Improvement of germinability in soil at low temperature is desirable for direct seeding to reduce costs of rice grain production in Japan. We performed a QTL analysis for germinability in soil, using backcross inbred lines (BILs) derived from crosses between a japonica rice variety, “Koshihikari”, and a tropical japonica rice variety, “Awa-akamai”. BILs carrying “Awa-akamai” segments on chromosome 11 showed high seedling emergence rates in soil at low temperature. We named the responsible locus QTL for emergence of seedling in soil on chromosome 11 b (qESS11b). We developed qESS11b-near-isogenic lines (qESS11b-NILs) to evaluate the effects of qESS11b on various agronomic traits. In fields test, qESS11b-NILs showed higher seedling establishment following direct seeding. However, qESS11b-NILs also exhibited a vivipary phenotype. Therefore we combined seed dormancy QTLs (Sdr1 or Sdr4) and qESS11b by crossing NILs. As a result, the vivipary phenotype was erased; qESS11b/Sdr1-NIL and qESS11b/Sdr4-NIL realized our aim, increased germinability in soil at low temperature compared to Koshihikari, while preventing preharvest sprouting. This work was supported by a grant from the Ministry of Agriclture, Forestry, and Fisheries of Japan. (Genomics-based Technology for Agricultural Improvement RBS-2007, Genomics for Agricultural Innovation IPG-1010)