Lower-Than-Expected Floret Sterility of Rice under Extremely Hot Conditions in a Flood-Irrigated Field in New South Wales, Australia

Rice florets are susceptible to high-temperature damage at anthesis, but rice production remains stable in the Riverina region of Australia even when the air temperature during flowering exceeds 40 degrees C. To identify the mechanism that supports rice production under these conditions, we examined sterility and pollination in relation to microclimate and panicle temperature in an extremely hot paddy field in the Riverina region of New South Wales. In windy > 40 degrees C weather, the panicle temperature was > 38 degrees C at the windward edge of the crop but around 35 degrees C inside the crop, probably because of strong transpirational cooling due to the extremely dry wind (15% RH). Pollen from the windward edge of the crop showed extremely poor germination, yet that from inside the crop showed sufficient germination for fertilization. Moreover, sterility inside the crop was significantly lower than that at windward edge. We concluded that the wind with large vapor pressure deficit enabled stable rice production under the extreme heat during flowering.