3.2. Comparison between year means
Overall means of grain yield (GY) and quality related traits assessed during both cropping seasons and within both regions are shown in Table 2. Grain yield annual means obtained reflected the environmental conditions’ variations. In 2007 (year of excessive rainfall), no significant difference was observed amongst overall GY means (p > 0.05); however, in 2008 (year of normal rainfall distribution) a significant difference was noted between grain yield means (p < 0.05), where the sub-humid region showed superiority over the semi-arid region with grain yield means of 6748.2 kg/ha and 4584.6 kg/ha, respectively. A significant year effect was mainly noted for protein content, yellow berry and thousand kernel weight. Protein content values were higher during 2008 compared to 2007, in both regions. Thousand kernel weight showed lower values during 2007 (36.33 g and 41.53 g in the sub-humid and semi-arid areas, respectively) compared to the 2008 cropping season (43.03 g and 48.55 g in sub-humid and semi-arid areas, respectively). Water availability received during 2008 might have enhanced nitrogen uptake and the accumulation of nitrogen in the grain despite potential nitrogen leaching associated with excessive rainfall. During severe drought conditions, the grain tends to reduce starch accumulation and the relatively high content of nitrogen observed would be attributed to the composition of teguments (Troccoli et al., 2000). Differences observed for thousand kernel weight appeared to be due to rainfall distribution differences noted in 2007 and 2008 during the grain filling period. A previous study reported that water limitation during the grain filling period resulted in a very low kernel weight (Jia et al., 1996). Yellow berry (YB) rates scored in our study were considered acceptable (ranged from 2.25% to 12.42%). This trait appeared also to be influenced by rainfall during the grain filling period. Excessive rainfall scored during March 2007 (129.4 mm in the SA area and 108 mm in the SH area) was associated with higher rates of YB (12.42% in the sub-humid region and 6.35% in the semi-arid region) than during 2008 (2.85% and 2.25% respectively) where the amount of available water was limited in both regions (40.8 mm in the semi-arid region and 53 mm in the sub-humid one). Regarding Gluten content (Gc) and Gluten index (Gi) a significant year effect was observed in the SH area. During 2007, we noted a mean gluten content of 26.9% and gluten strength tended to be balanced, while in 2008, it was extensible with a mean gluten content scored at 34.7%.