Post-anthesis Drought Stress Research Articles

Effects of Post-Anthesis Drought Stress on the Stem-Reserve Mobilization Supporting Grain Filling of Two-Rowed Barley Cultivars at Different Levels of Nitrogen

Effects of Post-Anthesis Drought Stress on the Stem-Reserve Mobilization Supporting Grain Filling of Two-Rowed Barley Cultivars at Different Levels of Nitrogen

Evaluation of Chlorophyll Content and Fluorescence Parameters as Indicators of Drought Tolerance in Barley

Drought is a major abiotic stress that severely affects food production worldwide. Agronomic and physiological traits associated with drought tolerance are suitable indicators for selection of drought tolerance genotypes to reduce the impact of water deficit on crop yield in breeding program. The objective of this study was to identify indicators related to drought tolerance through analysis of photosynthetic traits in barley ( Hordeum vulgare L.). These traits included chlorophyll content, initial fluorescence (F 0), maximum primary yield of photochemistry of photosystem II (F v/F o) and maximum quantum yield of photosystem II (F v/F m). Four genotypes (Tadmor, Arta, Morocco9-75 and WI2291) variable in drought tolerance were used to investigate the correlation between these traits and drought tolerance. The results reflected that all of these traits were affected negatively in the four genotypes at different levels of post-anthesis drought stress, but the decrease in drought tolerant genotypes was much less than that of drought sensitive genotypes. The results further revealed that the components of the photosynthetic apparatus could be damaged significantly in drought sensitive genotypes, while drought tolerant genotypes were relatively less affected. On the other hand, the values of chlorophyll content, F o, F v/F o and F v/F m in drought tolerance genotypes were significantly higher than those in drought sensitive genotypes under drought stress. It was concluded that chlorophyll content, F o, F v/F o and F v/F m could be considered as reliable indicators in screening barley germplasm for drought tolerance.

Effects of drought stress on growth and yield of barley

Barley (Hordeum vulgare) grown in Mediterranean regions undergoes drought stress during the grain-filling period. A greenhouse experiment was conducted to study the effect of drought stress on grain growth and yield of barley. Plants were exposed to three drought treatments at the beginning of grain filling: (1) well-watered at 100% field capacity, (2) mild drought stress at 60% field capacity, and (3) severe drought stress at 20% field capacity until grain maturity. Grain moisture content and dry weight were determined for grains harvested at 3, 10, 17, 23 and 31 days after the beginning of grain filling. Grain dry weight for severe drought stress plants reached a maximum value earlier than grains from mild drought stress and well-watered plants, indicating that grains from severe drought stress plants had a higher growth rate than those of mild drought stress and well-watered plants. Drought-stressed plants had shorter duration of grain filling than well-watered plants. Drought stress treatments reduced grain yield by reducing the number of tillers, spikes and grains per plant and individual grain weight. In conclusion, postanthesis drought stress was detrimental to grain yield regardless of the stress severity.

Diallel Analysis of Resistance to Macrophomina phaseolina in Sorghum

Charcoal rot of sorghum, caused by the fungus Macrophomina phaseolina, is a severe disease in regions where sorghum encounters post-anthesis drought stress. Previous reports disagree with respect to the narure of the genetic factors that condition resistance to charcoal rot. A diallel cross was made using nine genetically diverse sorghum lines. Parental lines and Fl progenies were evaluated in the field in 1997 and 1998 at two locations. Lines were significantly more resistant than Fls, indicating that heterosis was not affecting resistance. General combining ability (GCA) and specific combining ability (SCA) effects were significant for both locations over both years. However, the magnitudes of SCA effects were much smaller than GCA effects. These observations indicate that resistance to charcoal rot is conditioned by both additive and nonadditive effects.

Methodology for Evaluation of Chemical Desiccation Tolerance in Winter Wheat

Postanthesis drought stress is a persistent problem for winter wheat (Triticum aestivum L.) production throughout much of the Great Plains of the USA. Chemical desiccation has been proposed as a method for improving postanthesis drought stress tolerance by identifying genotypes that support grain growth from nonstructural carbohydrates stored in the stems. The objectives of this study were to define cultivar responses to different chemical desiccants and dates of desiccant application and examine grain filling and stem dry weight loss patterns to assess the suitability of chemical desiccation as a screening method for postanthesis drought stress tolerance. In the first year of the study, 10 field-grown winter wheat cultivars were subjected to chemical desiccation with 2% sodium chlorate (NaClO3), 0.15% potassium iodide (KI), and 0.30% KI at 10 and 15 days postanthesis (DPA). Chemical desiccation 10 DPA induced significantly (P≤0.01) greater desiccation injury (for grain yield and its components) than chemical desiccation 15 DPA. Levels of desiccation injury were similar for NaClO3 and 0.30% KI, whereas the 0.15% KI treatment did not induce yield or yield component reduction. The second year of the study included evaluation of stem and grain dry weight changes following chemical desiccation. Chemical desiccation resulted in apparent reduction in grain filling rates and increased stem dry weight losses during grain filling. Cultivars that were more tolerant of chemical desiccation demonstrated increased stem dry weight immediately after anthesis and subsequent increased rates and amounts of stem dry weight loss during grain filling.

Early‐Generation Selection for Chemical Desiccation Tolerance in Winter Wheat

Post‐anthesis drought stress is a common problem in winter wheat (Triticum aestivum L.) production throughout the west‐central and southern Great Plains of the USA. Contact chemical desiccants have been proposed to simulate postanthesis drought stress in the field and to enable selection for postanthesis drought stress tolerance. This study was conducted to determine if early‐generation among‐cross selection for chemical desiccation tolerance is possible and if chemical desiccation tolerance of early‐generation bulks could be altered using mechanical mass selection for kernel weight. The chemical desiccation tolerance of four winter wheat single‐cross populations was evaluated in 1991 at two locations in Colorado, each location consisting of replicated F4‐bulk trials of populations that had been subjected to chemical desiccation [2% (w/v) NaCIO3 applied 10 d postanthesis] and divergent mechanical mass selection for kernel weight in the F2 and F3 generations. At both locations, a cross between tolerant parents showed lower (P ≤ 0.01) chemical desiccation injury (for grain yield, kernel weight, and test weight) than crosses between sensitive parents or between contrasting parents. Separation of F2 populations into selected‐bulks of differing height and maturity showed that selectedbulks from randomly‐selected and tall F2 plants suffered significantly (P ≤ 0.01) lower chemical desiccation injury (at one location only) than selected‐bulks from short plants or plants with similar anthesis dates. Mechanical mass selection within populations advanced with two cycles of chemical desiccation produced F4‐bulk populations with significantly (P ≤ 0.01) lower chemical desiccation injury. The potential for selective improvement of chemical desiccation tolerance of bulk populations was indicated by several instances of reduced chemical desiccation injury for populations advanced to the F4 with desiccant application and mechanical mass selection for high kernel weight. Our results provide evidence that crosses tolerant of chemical desiccation can be identified using early‐generation evaluation of bulk‐populations, prior to extensive line extraction and evaluation.

Chemical desiccation of wheat plants as a simulator of post-anthesis stress

Chemical desiccation (with magnesium chlorate) of wheat, applied 14 days after anthesis, was evaluated as a screen for post-anthesis drought tolerance, in terms of sustained translocation-based kernel growth in the absence of photosynthesis. Thirty-eight and 26 wheat varieties were tested in 1979/1980 and 1980/1981, respectively. In each year the effect of chemical desiccation was studied in a non-stress environment as compared with the effect of post-anthesis drought stress in a drought environment. In both years, the extent of injury to kernell weight by drought stress was significantly and positively correlated, across varieties, with the extent of injury to kernel weight by chemical desiccation. Of the plant attributes studies, the main one associated across varieties with tolerance in kernel growth to post-anthesis stress was small kernel size. The significant negative association found between the extent of injury to kernel weight by chemical dessication or by drought stress and kernel number per spike or days to anthesis, was also mediated, at least partly, through kernel size. A significant positive association was found across varieties between the extent of injury to kernel weight by stress and the extent of compensation in kernel growth for the reduction (by excision) of kernel number per spike. This association seemed also to be mediated partly by kernel size, with a larger compensation observed in small-kernelled varieties. Kernel weight was negatively correlated across varieties with the number of kernels per spike. No correlation was revealed between the extent of injury by stress to kernel weight and non-stress kernel weight per spike. It was therefore concluded that the selection for smaller kernel weight as a post-anthesis stress-adaptive trait is not necessarily antagonistic to the maintenance of a large since size and high potential yield.