Spikelet sterility of rice observed in the record hot summer of 2007 and the factors associated with its variation

Abstract

Heat-induced spikelet sterility is one of the major threats to rice production from global warming. Previous chamber experiments have shown that even a short exposure to heat can induce spikelet sterility, but actual damage to a crop in the open field has rarely been reported. In the mid-summer of 2007, the Kanto and Tokai regions in Japan experienced record high temperatures above 40°C. We examined whether this extreme heat event induced sterility in open fields. We collected panicle samples from 132 fields in 5 prefectures in the Kanto and Tokai regions. Maximum air temperature averaged over a 5-day period around the heading stage exceeded the threshold for sterility (35°C) in more than 40% of the crops surveyed. Spikelet sterility ranged from 2% to 23%, and was more than 10% in 20% of the crops studied. Spikelet sterility in 2007 was apparently higher than that in the normal summer of 2008 and peaked with the heat wave, which confirms for the first time that extreme heat in midsummer induced sterility under open field conditions in Japan, but to a lesser extent than what was predicted from previous chamber experiments. The lesson from this survey is that air temperature per se is not sufficient to predict the occurrence of heat-induced sterility and that factors influencing the heat budget of the panicles are needed to account for the crop damage. Crop management practices such as selection of tolerant cultivars and optimizing the timing and amount of nitrogen application could moderate the occurrence of heat induced spikelet sterility which can help to develop adaptation measures to climate change.