Grain yield of durum wheat (Triticum turgidum L. var. durum) under Mediterranean conditions is frequently limited by both high temperature and drought during grain growth. Path coefficient analyses, based on an ontogenetic diagram, were conducted to study grain yield formation under different temperature and moisture regimes across Spain. Six ICARDA-CIMMYT inbred lines and four Spanish commercial cultivars were grown during 1998 and 1999 at two temperature regimes (cool and warm) and under both rainfed and irrigated conditions. Path coefficient analysis revealed that grain yield under cooler conditions was mostly determined by kernel weight, whereas the number of spikes per square meter predominantly influenced grain production in the warmer environments. The number of kernels per spike had a significant contribution to grain yield, especially under drought stress conditions. These associations do not clearly appear in the simple correlation analysis. Compensatory effects among yield components were almost absent in the cooler environments, probably due to the relative availability of water and N during the critical phases of plant development. Contrarily, under warmer conditions, negative effects of the number of spikes per square meter were registered on both the number of kernels per spike and kernel weight. Path analysis appears to be a useful tool for understanding grain yield formation and provides valuable additional information for improving grain yield via selection for its yield components.

Evaluation of Grain Yield and Its Components in Durum Wheat under Mediterranean Conditions

High temperature is a major determinant of wheat (Triticum aestivum L.) development and growth, decreasing yields by 3 to 5% per 1°C increase above 15°C in plants under controlled conditions. Even greater yield differences have been reported between favorable and unfavorable temperature conditions in the field. The objective of this study was to identify the yield components of the hard red winter wheat cultivar Karl 92 that are affected by controlled high temperature during maturation of intact plants under simulated field populations. Plants at a final density of 144 m 2 were grown in the greenhouse until anthesis and transferred to growth chambers for temperature treatment. Day/night temperatures of 20/20, 25/20, 30/20, and 35/20°C were imposed from 10 and 15 d after anthesis until ripeness in two experiments, and temperatures of 25/20, 30/20, and 35/20°C were applied from 20 d after anthesis until ripeness in a third experiment. Grain yield was reduced by 78%, kernel number was reduced by 63%, and kernel weight was reduced by 29% at 35/20°C compared with 20/ 20°C from 10 d after anthesis until ripeness. The yield loss from high temperature applied during this period was much greater than for previous controlled-environment studies. Kernel numbers in treatments applied during early reproductive growth in our study were as sensitive to high temperature as wheat plants in previous field studies. High temperature applied 15 d after anthesis until ripening reduced grain yield 18%. Since kernel number was set by this time, the loss was exclusively due to decreased kernel weight. High temperature imposed from 20 d after anthesis decreased kernel weight by 18%.

Yield Components of Wheat Grown under High Temperature Stress during Reproductive Growth

In a 2-years experiment, 30 wheat cultivars and 21 landraces from different countries were tested under near optimum and drought stress conditions. Plant height, number of sterile spikelets per spike, spikelets per spike, number of kernels per spike, kernel weight per spike, 1000 kernel weight and grain yield were evaluated. The number of kernels per spike, 1000 kernel weight and especially yield were more sensitive to drought stress in the cultivars than plant height and number of spikelets per spike, while in the landraces these traits did not differ under drought stress compared to near optimum conditions. The average yield of cultivars was significantly better than the average yield of landraces under near optimum as well as drought stress conditions. Path coefficient analysis showed that for cultivars under near optimum conditions there was no significant direct association of any of the analysed characters with yield, while under drought stress conditions, number of kernels per spike had a significant positive direct effect. Under drought stress conditions, the number of sterile spikelets displayed a negative direct effect, while kernel weight per spike had a positive direct effect on yield. Hierarchical cluster analysis was used as a tool to classify cultivars and landraces according to their yield ability under near optimum and drought stress conditions. Among the cultivars, two groups out of five and among one of three in the landraces were characterised by high yields in both near optimum as well as under drought stress conditions. These genotypes may serve as sources of germplasm for breeding for drought tolerance.

Evaluation of grain yield and its components in wheat cultivars and landraces under near optimal and drought conditions.

Empirical threshold values for quantitative trait mapping.

Comparison of leaf, spike, peduncle and canopy temperature depression in wheat under heat stress.

Agronomic and yield data were collected from two trials each containing 16 bread wheat genotypes, planted two years under late sowing conditions of high temperature (above 30° C) and one year under a normal sowing time environment. The aim was to study the character response and yield correlations with yield components and other characters under high temperature conditions with full irrigation. The results show that yield, seeds per spike, biomass, and plant height are more thermo-sensitive than spike number per square meter, 1000 kernel weight, and test weight. The grain-filling rate was more temperature-sensitive than days to anthesis and duration of grain-filling. Simple phenotypic correlation analysis indicated that yield was highly and positively correlated with seeds per spike, biomass, and harvest index (HI), independent of seasons and genotypes under high temperatures. The seeds per spike accounted for variation of yield ranging from 35.2 to 78.1%. Effect of earliness on the yield under high temperature was highly dependent on the temperature regime during the heading stage. Grains per spike, biomass, HI, and test weight could be considered potential selection criteria for yield under high temperature. Analysis of yields under normal and late sowing conditions failed to reveal any association between the yield potential in normal sowing date and the performance of varieties under high temperature.

Differential responses of bread wheat characters to high temperature

Utilization of 1BL/1RS translocation in wheat breeding in China

The endosperm storage proteins of 205 Chinese bread wheat cultivars and advanced lines were fractionated by SDS-PAGE to determine their high molecular weight (HMW) glutenin subunit composition. Seventeen alleles were identified: three at Glu-A1, eight at Glu-B1, and six at Glu-D1. The most common alleles were Null, 1, 7+8, 7+9, and 2+12. The results indicate that wheats from different regions differ in their frequencies of HMW glutenin subunits, however, none of the subunits could be related to specific environments. The glutenin quality scores of Chinese wheats ranged from 3 to 10, with an average of 6.7. Increasing quality scores have implications in improving steam-bread making quality for Chinese consumers. On the basis of HMW glutenin subunit composition, Chinese wheats are close to European wheats, especially Italian wheats because several Italian introductions are widely distributed in the pedigrees of Chinese wheat.

He Zhonghu

Papers

Differential responses of bread wheat characters to high temperature

Utilization of 1BL/1RS translocation in wheat breeding in China

High molecular weight glutenin subunit composition of Chinese bread wheats

QTL mapping for Kernel yellow pigment content in common wheat

QTL mapping of seedling biomass and root traits under different nitrogen conditions in bread wheat (Triticum aestivum L.)