Selection criteria for drought tolerance at the vegetative phase in early maturing maize

Identifying drought tolerant maize (Zea mays L.) at the vegetative stage is a meaningful effort at reducing cost and time of screening large number of maize genotypes for drought tolerance. The primary objectives of this study were to assess the effectiveness of vegetative traits in discriminating between drought tolerant and drought sensitive hybrids and to determine the stage at which the stress should be imposed to achieve maximum difference between hybrids with contrasting responses to drought. A drought tolerant hybrid (TZEI 18 × TZEI 31) and a sensitive hybrid (TZEI 108 × TZEI 87) were evaluated in a pot experiment conducted in a screen house facility and in the field at the Teaching and Research Farm of the Faculty of Agriculture, Obafemi Awolowo University, Ile-Ife in 2011. The experiment was laid out as a randomized complete block design in each of four groups of different water treatments, namely one week of watering for 1, 2, and 3 weeks after planting and withdrawing watering for the rest of the period of experimentation (43 days after planting), along with a treatment involving watering throughout the period of the experiment. Data were collected on root and shoot traits under the four levels of water treatment and the data were subjected to analysis of variance (ANOVA) and orthogonal contrasts. Results of the ANOVA showed significant mean squares for root length, root fresh weight, shoot length, number of root branches, shoot dry weight, root dry weight and number of shed leaves. Withdrawing water a week or two after planting induced large differences between the drought tolerant and drought sensitive genotypes for root length, root dry weight, number of root branches and number of shed leaves. In conclusion, root length, root fresh weight, shoot length, number of root branches, shoot dry weight, root dry weight and number of shed leaves were the most reliable traits for pre-anthesis drought tolerance. Watering for only one or two weeks after planting was the best treatment for identifying drought tolerant maize genotypes at the vegetative growth stage.Key words: Drought, maize, pre-anthesis, seedling stage

Impact of progressive global warming on the global-scale yield of maize and soybean

Global surface temperature is projected to warm over the coming decades, with regional differences expected in temperature change, rainfall and the frequency of extreme events. Temperature is a major determinant of crop growth and development, affecting planting date, growing season length and yield. We investigated the effects of increments of mean global temperature warming from 0.5 °C to 4 °C on soybean and maize development and yield, both globally and for the main producing countries, and simulated adaptation through changing planting date and variety. Increasing temperature resulted in reduced growing season lengths and ultimately reduced yields for both crops. The global yield for maize decreased as temperature increased, although the severity of the decrease was dependent on geographic region. Small temperature increases of 0.5 °C had no effect on soybean yield, although yield decreased as temperature increased. These negative effects, however, were partly compensated for by the implementation of adaptation strategies including planting earlier in the season and changing variety. The degree of compensation was dependent on geographical area and crop, with maize adaptation delaying the negative effects of temperature on yield, compared to soybean adaptation which increased yield in China, India and Korea DPR as well as delaying the effects in the remaining countries. The results of this paper indicate the degree to which farmer-controlled adaptation strategies can alleviate the negative impacts of increasing temperature on two major crop species