LAUSR

AbstractPrevious studies reported the inconsistent results on SPIKE, a quantitative trait locus, that controls the number of spikelets per panicle in rice. SPIKE increased grain yield under tropical conditions but did not increase it under temperate conditions. To reveal the effect of SPIKE on grain yield, we conducted an in-depth study of two varieties, IR64 and the near-isogenic line (NIL) for SPIKE in the IR64 genetic background, grown in research plots at the International Rice Research Institute in the tropics across 11 seasons from 2011 to 2017, and in 2018 with high and low nitrogen (N) fertilizer conditions, where mean yield variation was 417–670 g m−2. In multi-seasonal trials, overall yield performance of NIL-SPIKE was 11% superior to that of IR64. Significant variety × season interaction clarified NIL-SPIKE was superior to IR64 under the lower-yield seasons (< 500 g m−2) but the difference decreased or disappeared completely in the higher-yield seasons (> 500 g m−2). A subsequent N application trial with two levels of N fertilizer (45 and 180 kg N ha−1) confirmed a similar variety × N interaction for SPIKE; NIL-SPIKE tended to be superior to IR64 for grain yield under low-N application (431 g m−2), while the difference disappeared under high-N application (670 g m−2). The advantage of NIL-SPIKE under low-N application was due to more spikelets m−2 compared to IR64 but the difference disappeared under high-N application because there were fewer panicles m−2 in NIL-SPIKE compared to IR64. These results indicate SPIKE is effective for increasing rice yield under low-yield conditions (< 500 g m−2), namely low-N application or low soil fertility. Therefore, SPIKE should be used for breeding programs aimed at regions where soil fertility is poor or farmers cannot purchase adequate fertilizer.