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The heading date is an important trait for determining regional and climatic adaptability in rice. To expand the adaptability of the indica rice cultivar 'IR64', we pyramided multiple early or late heading quantitative trait locus (QTLs) in the 'IR64' genetic background by crossing previously developed near-isogenic lines (NILs) with a single QTL for early or late heading. The effects of pyramiding QTLs were observed in three different climatic zones of the Philippines, Madagascar, and Japan. The early heading pyramiding lines (PYLs) headed 6.2 to 12.8 days earlier than 'IR64' while the late heading PYLs headed 18.8 to 27.1 days later than 'IR64'. The PYLs tended to produce low grain yield compared to 'IR64'. The low yield was not improved by combining SPIKE , which is a QTL that increases the number of spikelets per panicle. Conversely, 'IR64-PYL(7+10)' carrying Hd5 and Hd1 headed earlier, produced more tillers, and more panicles per m 2 than 'IR64', and mitigated the yield decrease in early heading. These results suggest that the effects of pyramided QTLs on heading date were consistent across various environments and PYLs could be used to enhance the adaptation of 'IR64' in other rice growing environments., (Copyright © 2021 by JAPANESE SOCIETY OF BREEDING.)

Applied phosphorus (P) use efficiency is generally low due to the low mobility of P in soil and its affinity to form insoluble complexes. Localized P application nearby the root zone is a potential approach to overcome this issue in crop production. However, the interaction with soil conditions is little understood, which results in less effective application of this approach. Using root-box experiments and changing P-retention capacity of soils, we revealed that applied P use efficiency of rice can be substantially improved by dipping seedlings in P-enriched slurry at transplanting (P-dipping) even in highly P-fixing soils. Spatial analysis of soluble P in soils indicated that P-dipping creates a P hotspot because the P-enriched slurry is transferred with seedling roots. The P hotspot could have induced vigorous surface root and facilitated further P uptake from the spot. In contrast, the effect of conventional P incorporation depended on P-retention capacity of soils; no increases in soluble P content in soils or plant P uptakes were observed when P-retention capacity was high. Our finding of significant interaction between localized P application and a specific soil property should help improving applied P use efficiency and achieving sustainable rice production against depleting P fertilizer resources.