Impact of Humidity on Temperature‐Induced Grain Sterility in Rice (Oryza sativa L)

Abstract

High temperature‐induced grain sterility in rice is becoming a serious problem in tropical rice‐growing ecosystems. We studied the mechanism of high temperature‐induced grain sterility of different rice (Oryza sativa L) cultivars at two relative humidity (RH) levels. Four varieties of Indica and Japonica rice were exposed to over 85 % RH and 60 % RH at 36/30 °C, 34/30 °C, 32/24 °C and 30/24 °C day/night air temperatures from late booting to maturity inside sunlit phytotrons. Increasing both air temperature and RH significantly increased spikelet sterility while high temperature‐induced sterility decreased significantly with decreasing RH. Neither Indica nor Japonica rice types were superior to the other in the response of their spikelets to increased air temperature and RH. Increased spikelet sterility was due to increased pollen grain sterility which reduced deposition of viable pollen grains on stigma. Reduction in sterility with decreased RH was more due to decreased spikelet temperature than to air temperature. Thus the impact of RH should be considered when interpreting the effect of high temperature on grain sterility. Spikelet fertility was curvilinearly related to spikelet temperature. Grain sterility increased when spikelet temperature increased over 30 °C while it became completely sterile at 36 °C. The ability of a variety to decrease its spikelet temperature with decreasing RH could be considered as avoidance while the variability in spikelet sterility among varieties at a given spikelet temperature could be considered as true tolerance.

Responses of spikelet fertility to air, spikelet, and panicle temperatures and vapor pressure deficit in rice

“…This result was contrary to the previous reports that the increase of vapor pressure deficit reduced high temperature-induced spikelet sterility by increasing transpirational cooling of panicle (Matsui et al, 2007;Jagadish et al, 2007;Weerakoon et al, 2008;Tian et al, 2010;Julia and Dingkuhn, 2013). On the other hands, there was a paucity of studies that low relative humidity under high temperature accelerated rice spikelet sterility induction by desiccating anther and/or pollen.…”

“…Further detailed study is needed to verify the effect of VPD on spikelet sterility. Most of recent studies indicated that decreasing VPD under high temperature conditions decreased spikelet fertility (Abeysiriwardena et al, 2002;Matsui et al, 2007;Yan et al, 2008;Weerakoon et al, 2008;Tian et al, 2010;Yan et al, 2010;Julia and Dingkuhn, 2013;Van Oort et al, 2014). However many of these studies were conducted under high relative humidity conditions above 80% and compared with normal condition of 60% relative humidity.…”

“…However Matsui et al (2007Matsui et al ( , 2014 High relative humidity (>80%) in high-temperature conditions accelerates spikelet sterility induction (Matsui et al, 1999;Abeysiriwardena et al, 2002;Weerakoon et al, 2008;Julia and Dingkuhn, 2013). Tian et al (2010) reported that humid conditions (>80%) and low wind speed (<1m/s) might contribute to induce spikelet sterility, indicating that the two factors led to increase of panicle temperatures.…”

Heterosis analysis in relation to drought tolerance in rice land races and their genotypes

“…Twenty hybrids exhibited better performance than the standard check for plant height. These results are in agreement with those obtained by Weerakoon et al (2008), El-Mouhamady (2009) and El-Mouhamady et al, 2013. Positive heterosis was enviable for rest of the traits viz., Productive tillers per plant, Grains per panicle, Root length, Root dry weight, Root: Shoot ratio, Hundred grain weight, , Chlorophyll stability index, Harvest index, Relative water content, Proline content and grain yield per panicle.…”

The Early-Morning Flowering Trait of Rice Reduces Spikelet Sterility under Windy and Elevated Temperature Conditions at Anthesis

“…Koshihikari) by interspecifi c hybridization with a wild rice, O. offi cinalis Wall ex Watt (CC genome), was considerably more effective in mitigating heat-induced spikelet sterility by fl owering in the early morning when the temperature was cooler (Ishimaru et al, 2010). However, further studies were needed to validate the practical importance of the EMF trait for rice cultivation because the effect of microclimates on spikelet sterility is complicated; humidity, wind velocity and CO 2 concentrations negatively affect spikelet sterility (Kim et al, 1996;Matsui et al, 1997a;Matsui et al, 1997b;Weerakoon et al, 2008). Matsui et al (1997b) reported that a wind velocity above 0.85 m s -1 drastically increased spikelet sterility at 37.5ºC, and relative humidity of 60% in a chamber experiment.…”