Browsing by Subject "Spikelet sterility"

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Rice genotypic variation on phenological development and yield performance in cold prone high altitude cropping systems
(2021) Abera, Bayuh Belay; Asch, Folkard
Despite a huge potential for rice intensification, several constraints have been reported as bottlenecks for rice production in the East African high-altitude cropping system. In this system, yield reductions are mainly caused by moisture deficit, which dictates the sowing date of the crops, and cold stress, which can occur either during specific crop growth phases or during the entire cropping period. In order to minimize yield losses, cultivation of suitable genotypes and timely implementation of proved crop management options are implicitly needed. Therefore, the objectives of this study were to investigate the effects of weather during specific development stages on yield and yield components of a large number of rice genotypes contrasting in crop duration; to explore the effects of crop establishment method on the performance of a set of rice genotypes in high altitude; and to identify key data sets required for the adaptation of agricultural decision support tools to new environments: the case of RiceAdvice being introduced to the highlands of East Africa. Field trials were conducted during the cropping seasons of 2016 and 2017 at the Fogera rice research station in Ethiopia. Further, to generate data to be used for the advancement of RiceAdvice, trials were implemented in Madagascar (Ambohibary and Ivory) and Rwanda (Bugarama and Rwasave) at different altitudes. Thirty contrasting genotypes were included in the study to investigate the effects early and late sowing and the related weather variation experienced by the crop. The crop establishment methods (direct seeding and transplanting) were evaluated using nine contrasting genotypes. Daily mean, minimum, and maximum temperature, rainfall, radiation, and relative air humidity were recorded during the experimental period; and the phenological development of each genotype was closely monitored in all trials. Data on grain yield and yield components were recorded and finally subjected to analysis of variance. Results showed that yield was positively correlated with the percentage of filled spikelets and the number of productive tillers, and negatively correlated with the number of tillers per hill. Genotypes differed in duration, yield, and yield components between the two years, which was related to both, differences in sowing date as well as differences in weather conditions. Early sowing in 2017 led to an extended duration until maturity of short-duration genotypes, which was related to low radiation levels as the vegetative phase of short duration genotypes entirely took place during the cloudy rainy season. Contrastingly, the duration to maturity of medium- and long-duration genotypes was shortened after early sowing in 2017, probably related to higher relative air humidity. In 2016, late sowing in combination with the early onset of the cool period led to high spikelet sterility in medium- and long-duration genotypes, as the cold-sensitive booting phase took place during the cold spell. Therefore, effects of sowing date on yield differed between genotype groups with short-duration genotypes suffering and medium- and long-duration genotypes profiting from early sowing and vice versa for late sowing. Similar results were obtained in the experiment conducted in Madagascar and Rwanda. At high altitude in Madagascar, short-duration genotypes performed well after late sowing, whereas medium-duration genotypes performed better after sowing one to two months earlier. Also, in Rwanda, delayed sowing compromised yield because of spikelet sterility related to low-temperature during the reproductive stage. Therefore, it was concluded that the choice of variety should depend on the sowing date, which is dictated by the onset of rains. Further, decisions on management intervention have to consider season-specific constraints. Comparison of transplanted and direct seeded rice showed that, in general, transplanting had a strong advantage over direct seeding. While at high-altitudes, growing medium- and long-duration genotypes with a high yield potential bears the strong risk of yield loss due to cold sterility, transplanting, which resulted in significantly higher yields than direct seeding, can mitigate this risk. As after transplanting, physiological maturity was observed earlier in the season than after direct seeding, rice plants, including medium- and long-duration genotypes, escaped the low temperature stress at the critical reproductive stage, and thus, low spikelet fertility. Thus, with a relatively cold tolerant genotype such as Yun-Keng, sowing a few weeks earlier within an irrigated nursery can make use of the full potential and increase yields. Comparison of the experimental sites in Ethiopia, Madagascar and Rwanda, showed that the mean temperature between sowing and flowering of the four tested genotypes was negatively correlated with altitude. In general, precise knowledge of the duration of the potentially suitable genotypes is required and a crop model that is well-calibrated for the genotypes as well as for the environment, in combination with a smartphone application such as RiceAdvice, would be of great help to support farmers’ decision-making. The data recorded from the three countries field trials can be used as data source to validate RiceAdvice, and thus, increase its applicability.