Lowland Rice Apical Development: Stages and Cultivar Differences Detected by Electron Microscopy

Abstract

AbstractIdentification of growth stages and cultivar differences are necessary to develop efficient N fertilizer management for lowland rice (Oryza sativa L.). To help characterize growth stages an electron microscope was used to identify different panicle development stages, cultivar growth differences, and potential yield loss periods. Varieties IR50 (90‐d maturity) and IR42 (120‐d maturity) were grown at the International Rice Research Institute during the 1987 wet season. Thirteen morphologically different development stages up to floral organ development were identified. Between cultivars, duration of each development stage varied. Necknode differentiation was defined as physiological panicle initiation (PI) and observed at growth stage (GS) 1.8 occurring 35 days after seeding (DAS) in IR50 and at GS 1.10 (49 DAS) in IR42. Visual panicle initiation (VPI) was observed at GS 1.9 (42 DAS) in IR50 and at GS 1.11 (64 DAS) in IR42. Panicle development took 15 to 18 d (4–7 d for panicle branches) in IR50 and 24 to 31 d (11‐15 d for panicle branches) in IR42. Therefore the present N management practice of N topdressing 5 to 7 d before VPI coincided with PI for short duration IR50 but not for later maturing IR42. Preflowering and post flowering spikelet abortion reduced the spikelet number in IR50 and more so in IR42 where preflowering spikelet abortion started even before spikelet development was completed. Comprehensive N timing studies based on rice apical development stages are required for improving N efficiency and increasing rice yields.