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Results and discussion

Table 1 presents mean, maximum and minimum, standard deviation (SD) and coefficient of variation (CV%) of grain quality traits of durum wheat genotypes grown in two sites and averaged on two years (1998-1999). A combination of heat and drought stress occurred at Abarkoh region during grain filling period where air temperature ranged from 34 to 42C and accompanied with a hot and dry wind. The maximum temperature exceeded 8-10C from the long-term averages in May and June in this area during 1998 and 1999 growing season. Annual precipitation during the two years of experiment (~25mm) was about half of the long term average of this region (5Omm). Plant irrigated in a regular basis of 12d intervals as a common practice of Abarkoh's farmers despite of very low air humidity and low soil moisture content during the grain filling period. Statistical analysis using a paired Student's t test indicated a significant differences (P<0.01) between two regions for all grain quality characteristics and the highest values were recorded where a combination of heat and drought stress occurred at grain filling period in Abarkoh region (Table 1). This result is in agreement with that of Boggini et al. (1997) in durum wheat who reported that mean protein content and SDS sedimentation volume were lower in the environment with higher grain yield. Likewise in bread wheat, grain protein content was drastically increased by water stress, especially stress at anthesis (Jamal et al. 1996).

Coefficient of variation (CM of each grain quality characteristic as the quantitative traits indicates the effect of genetic diversity present in the germplasm. The highest variability was observed for protein content in both locations and for SDS-sedimentation volume in only Isfahan region (Table 1). Protein percentage had a range of 9.7-14.8 and a mean of 11.4 at Isfahan region, whereas these were 10.0-15.3 and 12.1 for Abarkoh region, respectively. A range of 24.3-68.0 with mean of 45.6 in Isfahan and a range of 30.8-68.9 with mean of 47.2 in Abarkoh were obtained for sedimentation volume. Likewise, Blanco et al. (1998) reported significant differences for protein content and SDS-sedimentation volume in the six environments examined. The sedimentation volume was found to be positively correlated (P<0.01) with protein content, wet gluten content, dry gluten content and grain hardiness in both locations. Protein content positively correlated at P<0.01, with wet and dry gluten contents at both environments.

Linear regression of protein content (%) of 15 durum wheat genotypes grown at Abarkoh region and suffered with heat and drought stress on their protein content (%) of non-stressful conditions at Isfahan region was shown in Fig. 1. This result revealed that some genotypes have a similar protein content ranking under both a combination of stressed and optimal environments, while others have a substantially different ranking under optimal and stressed environments. Genotypes Osta/Gata, ICDW 7639 and PI40100 provide a good example of the former response, where their protein contents ranked similarly in both of stressed and optimal environments (Table 2). On the other hands, other genotypes listed in Table 2 provide a good example of the latter response, since their protein contents tend to rank considerably higher in stressed conditions than in optimal conditions.

Under field conditions, temperatures of 35 to 40C are common in many wheat-producing areas of the world (Gusta and Chen 1987), some of which like those of Abarkoh region accompany with a hot and dry wind at grain filling period. The responses of wheat plants to high temperature stress at anthesis and grain filling period differ on at least one major account. Heat stress at anthesis causes both male and female sterility (Gusta and Chen 1987), whereas heat stress at grain filling period causes only grain shriveling (Arzani unpubl).

Acknowledgments

This research was supported by Iranian Scientific Research Funds (NSR Grant No. 1138).

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