Floret Sterility in Rice in a Cool Environment1

Abstract

AbstractFloret sterility induced by low temperatures of 15 C or below at meiosis (10 to 15 days before heading) is a major factor in reducing yields of Oryza sativa, var. japonica, L. in California. The objective of this study was to reduce Sterility by manipulating genotypic environmental interactions. Field experiments employing differences in plant height, maturity, and water level were conducted at the Davis Rice Research Facility. Microclimatic studies were also conducted to determine temperature profiles within the canopy. Sterility was compared among nine cultivars with similar genetic origin but differing in plant height and maturity. Those that were short‐statured and/ or early‐maturing exhibited significantly less sterility than tall and late cultivars. All cultivars in a water depth study showed less sterility in deep water (15 to 25 cm) than in shallow water (5 to 15 cm). Mean differences were significant at the 0.05 level. The beneficial effect of earliness in reducing sterility was caused by the weather patterns of the rice‐growing region in the Sacramento Valley. The probability of receiving temperatures below 15 C at meiosis was considerably reduced as maturity was shortened. Increased water depth and decreased plant height reduced sterility by placing the panicle in closer proximity to water. Field water temperature at the coldest part of the night was usually 5 to 6 C warmer than air temperature. The microclimatic study demonstrated that absence of substantial nocturnal wind caused a temperature inversion at night between the mid‐canopy level (50 cm above soil surface) and the top of the canopy. Temperature also increased from mid‐canopy to water level because of the warming effect of the water. Thus mid‐canopy is the coldest part of the vertical profile in a rice field.