Trend in yield and protein content relationship in a historical series of durum wheat varieties under rainfed and irrigated environments

Improving grain yield (GY) is a major goal of durum wheat breeding programs, and a high yield needs to be attained while preserving grain quality. The current study evaluated the changes caused by a breeding program on the association between GY and grain protein content (PC) in Moroccan durum wheat. Field experiments with six leading varieties released over three decades were conducted for three growing seasons under two water regimes. GY and PC were largely controlled by environmental effects, including both the growing season and water regime. The year of release and growing season effects were the predominant sources of variation in total chlorophyll content (TCC). A significant increase in GY with the year of release was observed under irrigated conditions, whereas a significant increase in PC over time was noted under rainfed conditions. In addition, a negative correlation was revealed between GY and PC, which was significant only in the rainfed trials. Similarly, a significant and positive association was noted between PC and TCC within the rainfed trials, but not in the irrigated trials. Based on GGE (genotype main effect plus genotype x environment interaction) biplot analysis, the new varieties 'Marouane' and 'Faraj' were identified as desirable varieties in terms of GY and PC close to the 'ideal genotype'. These results indicated that when grown under current irrigated conditions, new varieties improved by the Moroccan breeding program showed better GY performance than old varieties.