Abstract
ABSTRACT Rice varietal differences were compared between japonica type (JAT) and indica type (INT) and between panicle number type (PNT) and panicle weight type (PWT) in terms of tiller and panicle development. Rice varieties PNT-JAT Hinohikari, PWT-JAT Akenohoshi, PNT-INT IR36, and PWT-INT Takanari were used in the field experiments. Tiller bud formation and tiller leaf emergence occurred slightly later in the PWT than in the PNT varieties. These parameters occurred slightly earlier in the INT than in the JAT varieties. The maximum number of tillers was greater in IR36 than in Takanari, Hinohikari, and Akenohoshi. The number of panicles per unit area (PN) was greater in IR36 and Hinohikari than in Akenohoshi and Takanari. The widths of the shoot apical meristem (SAM) just before panicle initiation were in the order of Akenohoshi > Hinohikari = Takanari > IR36. The number of spikelets per panicle (SN) was in the order of Takanari = Akenohoshi > IR36 > Hinohikari. In conclusion, the PWT varieties, which had relatively wider SAM, presented with the promotion of main shoot development and the suppression of tiller development. Consequently, PN decreased and SN increased in PWT varieties. INT varieties presented with the promotion of tiller and rachis branch development, which resulted in increases in both PN and SN. These developmental factors may determine varietal differences in the total number of spikelets per unit area. Abbreviations CGR: crop growth rate; DEL: differences between the numbers of emerged leaves in the tiller and those in the main shoot; DIL: differences between the number of initiated leaves in the tiller and those in the main shoot; INT: indica type; JAT: japonica type; MLAI: mean leaf area index; NAR: net assimilation rate; PN: the number of panicles per unit area; SN: the number of spikelets per panicle; PNT: panicle number type; PWT: panicle weight type; SAM: shoot apical meristem; TSN: the total number of spikelets per unit area
Highlights
Rice is a staple food in many Asian countries including Japan
The yield of Takanari in the present study was clearly lower than that for Takanari raised in the temperate region and slightly higher than that for Takanari grown in the cool region
TSN was in the order of IR36 = Takanari ≥ Akenohoshi ≥ Hinohikari and yield was in the order of Takanari ≥ IR36 ≥ Akenohoshi = Hinohikari (Table 3)
Summary
Rice is a staple food in many Asian countries including Japan. Factors determining varietal yield differences must be identified to improve crop productivity. From around 1980, varieties with extremely large panicles have been receiving increasing attention as high yield varieties. These varieties present high yield because of their large sink size (Fukushima et al, 2011). Varieties with extremely large hulls have large sink size and high yield in the cooler region of Japan (Fukushima et al, 2011; Mae et al, 2006). Varieties with standard hull sizes and very high SN were defined as panicle weight type (PWT) varieties. The purpose of this study was to elucidate the factors determining the varietal differences in TSN by comparing
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