In future climates, greater heat tolerance at anthesis will be required in rice. The effect of high temperature at anthesis on spikelet fertility was studied on IR64 (lowland indica) and Azucena (upland japonica) at 29.6 degrees C (control), 33.7 degrees C, and 36.2 degrees C tissue temperatures. The objectives of the study were to: (i) determine the effect of temperature on flowering pattern; (ii) examine the effect of time of day of spikelet anthesis relative to a high temperature episode on spikelet fertility; and (iii) study the interactions between duration of exposure and temperature on spikelet fertility. Plants were grown at 30/24 degrees C day/night temperature in a greenhouse and transferred to growth cabinets for the temperature treatments. Individual spikelets were marked with paint to relate fertility to the time of exposure to different temperatures and durations. In both genotypes the pattern of flowering was similar, and peak anthesis occurred between 10.30 h and 11.30 h at 29.2 degrees C, and about 45 min earlier at 36.2 degrees C. In IR64, high temperature increased the number of spikelets reaching anthesis, whereas in Azucena numbers were reduced. In both genotypesor=33.7 degrees C at anthesis caused sterility. In IR64, there was no interaction between temperature and duration of exposure, and spikelet fertility was reduced by about 7% per degrees C>29.6 degrees C. In Azucena there was a significant interaction and spikelet fertility was reduced by 2.4% degrees Cd-1 above a threshold of 33 degrees C. Marking individual spikelets is an effective method to phenotype genotypes and lines for heat tolerance that removes any apparent tolerance due to temporal escape.

Episodes of high temperature at anthesis, which in rice is the most sensitive stage to temperature, are expected to occur more frequently in future climates. The morphology of the reproductive organs and pollen number, and changes in anther protein expression, were studied in response to high temperature at anthesis in three rice (Oryza sativa L.) genotypes. Plants were exposed to 6 h of high (38 °C) and control (29 °C) temperature at anthesis and spikelets collected for morphological and proteomic analysis. Moroberekan was the most heat-sensitive genotype (18% spikelet fertility at 38 °C), while IR64 (48%) and N22 (71%) were moderately and highly heat tolerant, respectively. There were significant differences among the genotypes in anther length and width, apical and basal pore lengths, apical pore area, and stigma and pistil length. Temperature also affected some of these traits, increasing anther pore size and reducing stigma length. Nonetheless, variation in the number of pollen on the stigma could not be related to measured morphological traits. Variation in spikelet fertility was highly correlated (r=0.97, n=6) with the proportion of spikelets with ≥20 germinated pollen grains on the stigma. A 2D-gel electrophoresis showed 46 protein spots changing in abundance, of which 13 differentially expressed protein spots were analysed by MS/MALDI-TOF. A cold and a heat shock protein were found significantly up-regulated in N22, and this may have contributed to the greater heat tolerance of N22. The role of differentially expressed proteins and morphology during anther dehiscence and pollination in shaping heat tolerance and susceptibility is discussed.

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1Africa is thought to be the region most vulnerable to the impacts of climate variability 2 and change. Agriculture plays a dominant role in supporting rural livelihoods and 3 economic growth over most of Africa. Three aspects of the vulnerability of food crop 4 systems to climate change in Africa are discussed: the assessment of the sensitivity of 5 crops to variability in climate, the adaptive capacity of farmers, and the role of 6 institutions in adapting to climate change. The magnitude of projected impacts of 7 climate change on food crops in Africa varies widely among different studies. These 8 differences arise from the variety of climate and crop models used, and the different 9 techniques used to match the scale of climate model output to that needed by crop 10 models. Most studies show a negative impact of climate change on crop productivity 11 in Africa. Farmers have proved highly adaptable in the past to short-and long-term 12 variations in climate and in their environment. Key to the ability of farmers to adapt to 13 climate variability and change will be access to relevant knowledge and information. 14

Crop production is inherently sensitive to variability in climate. Temperature is a major determinant of the rate of plant development and, under climate change, warmer temperatures that shorten development stages of determinate crops will most probably reduce the yield of a given variety. Earlier crop flowering and maturity have been observed and documented in recent decades, and these are often associated with warmer (spring) temperatures. However, farm management practices have also changed and the attribution of observed changes in phenology to climate change per se is difficult. Increases in atmospheric [CO(2)] often advance the time of flowering by a few days, but measurements in FACE (free air CO(2) enrichment) field-based experiments suggest that elevated [CO(2)] has little or no effect on the rate of development other than small advances in development associated with a warmer canopy temperature. The rate of development (inverse of the duration from sowing to flowering) is largely determined by responses to temperature and photoperiod, and the effects of temperature and of photoperiod at optimum and suboptimum temperatures can be quantified and predicted. However, responses to temperature, and more particularly photoperiod, at supraoptimal temperature are not well understood. Analysis of a comprehensive data set of time to tassel initiation in maize (Zea mays) with a wide range of photoperiods above and below the optimum suggests that photoperiod modulates the negative effects of temperature above the optimum. A simulation analysis of the effects of prescribed increases in temperature (0-6 degrees C in +1 degree C steps) and temperature variability (0% and +50%) on days to tassel initiation showed that tassel initiation occurs later, and variability was increased, as the temperature exceeds the optimum in models both with and without photoperiod sensitivity. However, the inclusion of photoperiod sensitivity above the optimum temperature resulted in a higher apparent optimum temperature and less variability in the time of tassel initiation. Given the importance of changes in plant development for crop yield under climate change, the effects of photoperiod and temperature on development rates above the optimum temperature clearly merit further research, and some of the knowledge gaps are identified herein.

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Seed set of rice (Oryza sativa L.) is highly sensitive to short episodes of high temperature at anthesis events that are likely to be more frequent in future climates. Breeding for tolerance is therefore an essential component of adaptation to climate variability and change. Experiments were conducted in 2003 and 2004 at optimum (30°C daytime) and high (35 and 38°C) air temperature using parents of some prominent mapping populations (i) to determine whether there were differences in the daily flowering pattern and hence a potential heat avoidance mechanism, and (ii) to identify rice genotypes having true heat tolerance during anthesis, that is, high seed set in spikelets exposed to high temperature. Rice cultivar CG14 (O. glaberrima) reached peak anthesis earlier in the morning (1.5 h after dawn) under both control (30°C) and high (38°C) temperature conditions than O. sativa genotypes (≥3 h after dawn). Exposure to high temperature (centered on the time of peak anthesis) for 6 h reduced spikelet fertility more than exposure for 2 h, and fertility was lower at 38°C than at 35°C. Genotypic ranking for spikelet fertility at 35 and 38°C was highly correlated in both 2003 and 2004. Fertility was also highly correlated across years, suggesting a consistent and reproducible response of spikelet fertility to temperature. The check cultivar N22 was the most heat tolerant genotype (64–86% fertility at 38°C) and cultivars Azucena and Moroberekan the most susceptible (<8%).

Developing crops that are better adapted to abiotic stresses is important for food production in many parts of the world today. Anticipated changes in climate and its variability, particularly extreme temperatures and changes in rainfall, are expected to make crop improvement even more crucial for food production. Here, we review two key biotechnology approaches, molecular breeding and genetic engineering, and their integration with conventional breeding to develop crops that are more tolerant of abiotic stresses. In addition to a multidisciplinary approach, we also examine some constraints that need to be overcome to realize the full potential of agricultural biotechnology for sustainable crop production to meet the demands of a projected world population of nine billion in 2050.