A DJ123 allele at the heading date quantitative trait locus qHd7.1 promotes early heading without yield penalties under natural short-day and low fertility conditions in Madagascar

QTL analysis of heading date (Hd) was performed using a recombinant inbred line population derived from a cross between rice cultivars IR64 and DJ123. Phenotypic data was obtained from sites in Japan and Madagascar differing in photoperiod and soil fertility. The Japan site had long-days (LD) and high fertility, while the Madagascar site had short-days (SD) and low fertility conditions. Under LD in Japan, we discovered two Hd QTL on chromosome 7, qHd7.1 and qHd7.2, whereas only one of these (qHd7.1) was detected under SD conditions in Madagascar. RILs carrying DJ123 alleles at both QTLs headed 9.5 days earlier in Japan (LD) compared to IR64 alleles, whereas the effect of DJ123 alleles at qHd7.1 under SD conditions of Madagascar was 4 days and a combined effect of qHd7.1 and qHd7.2 did not exist. In Madagascar, early heading did not carry a yield penalty, whereas it caused reduced grain yield in Japan. These results suggest that RILs harboring the DJ123 allele of qHd7.1 have high yield potential and good adaptation to low fertility conditions in Madagascar and that this can be achieved in a shortened cultivation period, improving resilience to effects of climate change for African rice farmers.