Management options for mid-century maize (Zea mays L.) in Ethiopia.

This simulation study was carried out to assess the impact of climate change and adaptation strategies on maize production across 22 locations in Ethiopia using Decision Support System for Agrotechnology Transfer - Cropping System Model (DSSAT-CSM) CERES-Maize. Three maize varieties, i.e., [BH-660 (late maturing), BH-540 (medium maturing) and Melkasa-1 (short maturing)] along with three planting dates [early (25-Apr), normal (25-May) and late (25-Jun)], four N fertilizer rates (64, 96, 128 and 160 kg N/ha) and three water levels [rainfed (no irrigation), two irrigations (each 30 mm at time of flowering and 5 d after flowering with total = 60 mm) and five irrigations (each 30 mm at time of flowering to early grain-filing, which were applied every five days in total = 150 mm)] were evaluated as the adaptation strategy. The mid-century (2040-2069) temperatures and solar radiation were extracted from multiple model means across the Coordinated Regional Climate Downscaling Experiment (CORDEX) models under the highest Representative Concentration Pathway (RCP8.5). Maize productivity was evaluated assuming that maize was grown on shallow sandy loam soils. Yield of an early, medium and late maturing maize were changed by -13 to -8%, -10 to +4% and + 3 to +13%, respectively, relative to the baseline period (1980-2005). The days to maturity decreased by about 16%. Under rainfed condition, N application up to 64, 128 and 160 kg/ha significantly improved yield for early, medium and late maturing varieties, respectively. Relatively high yield and low inter-seasonal yield variability were simulated for BH-660 and Melkasa-1 when planted on 25-Apr and 25-May, respectively, for most locations. Application of two (60 mm) and five (150 mm) irrigation levels improved yield in drier locations. In conclusion, this study provides potential adaptation options under the future climate in maize producing regions of Ethiopia.

Spatial analysis of the impact of climate change factors and adaptation strategies on productivity of wheat in Ethiopia.

Wheat production is expected to be challenged by future climate change. However, it is unclear how wheat grown in diverse agroecologies will respond to climate change and adaptation management strategies. A geospatial simulation study was conducted to understand the impacts of climate change and adaptation management strategies on wheat (Triticum aestivum L.) production in Ethiopia. Simulation results showed that the average long-term baseline (1980-2005) wheat yield ranged from 1593 to 3356 kg/ha. This wheat yield range is within the national average (2100-2700 kg/ha) for this decade. In regions with cooler temperatures (<21 °C), mid-century temperatures and elevated CO2, along with increased N fertilizer slightly improved attainable yield levels above 3000 kg/ha. Whereas, in regions with heat and drought conditions wheat yield declined regardless the increase of N or CO2 levels. Wheat yield increased at a diminishing rate with increase in N fertilizer rate. However, N fertilizer did not increase yields under low rainfall conditions. Two to five irrigation per season contributed to yield improvement for low rainfall locations, while yield did not substantially improve for locations receiving adequate seasonal rainfall. Therefore, based on this study, improved N fertilizer application in combination with increased CO2 could improve wheat yield under future climate in most wheat producing regions (with adequate rainfall) of Ethiopia. Our results provide valuable information regarding impacts of climate change factors and adaptation strategies for producers, researchers, extension professionals and policy makers.

Quantifying pearl millet response to high temperature stress: thresholds, sensitive stages, genetic variability and relative sensitivity of pollen and pistil.

The objectives were to (1) quantify high temperature (HT) stress impacts at different growth stages (season long, booting to seed-set and booting to maturity) on various yield components; (2) identify the most sensitive stage(s) to short episodes of HT stress during reproductive development; (3) understand the genetic variations for HT stress tolerance based on cardinal temperatures for pollen germination; and (4) determine relative sensitivity of pollen and pistil to HT stress and associated tolerance or susceptible mechanisms in pearl millet. High temperature stress (≥36/26°C) imposed at different stages and durations caused decrease in number of seeds, individual seed weight and seed yield. Two periods (10-12 days and 2-0 days before anthesis) were identified as most sensitive to short episodes of stress, causing maximum decreases in pollen germination percentage and seeds numbers. HT stresses of ≥36/26°C results in floret sterility. Pistils were relatively more sensitive than pollen grains, causing decreased number of seeds and seed yield. HT stress increased the reactive oxygen species contents and decreased the activity of the antioxidant enzymes in both pollen and pistils. Under HT stress, pistils had relatively higher reactive oxygen species and lower antioxidant enzymes activity compared with pollen grains, which explains greater susceptibility of pistils.

Sensitivity of sorghum pollen and pistil to high-temperature stress.

High temperature (HT) decreases seed set percentage in sorghum (Sorghum bicolor [L.] Moench). The relative sensitivity of pollen and particularly pistil and the mechanistic response that induces tolerance or susceptibility to HT are not well known and hence are the major objectives of this research. The male sterile (ATx399) and fertile (RTx430) lines were exposed to 30/20 °C (optimum temperature), 36/26 °C (HT1 ), and 39/29 °C (HT2 ) from the start of booting to seed set in a controlled environment. Similarly, in the field, HT stress was imposed using heat tents. HT stress decreased pollen germination. Relatively high levels of reactive oxygen species and decreased antioxidant enzyme activity and phospholipid unsaturation were observed in pollen compared to pistil under HT. The severe cell organelle damage was observed in pollen and pistil at 36/26 and 39/29 °C, respectively. The seed set percentage was higher in HT-stressed pistil pollinated with optimum-temperature pollen. Direct and reciprocal crosses indicate that pollen was more sensitive with larger decreases in seed set percentage than pistil under HT stress. The negative impact was greater in pollen than pistil at lower temperatures. Overall, pollen was more sensitive than pistil to HT stress because it is more susceptible to oxidative damage than pistil.