Contribution to the study of adaptation of durum wheat cultivars (Triticum durum Desf.) to organic farming: grain yield,stability and technological and nutritional quality

The objective of this study is to investigate the potential of different durum wheat varieties that could be adapted for organic farming. In this context, four experimental years studies (2001, 2002, 2003 and 2004) were carried out in order to assess fourteen durum wheat varieties including nine old and five improved varieties conducted under organic and conventional cultivation methods and in two cereal growing locations : Kef "Boulifa" : low semi-arid and Bousalem “El Kodia” : higher semi-arid. Studied parameters included (i) grain yield, (ii) yield stability using coefficient of variation, linear regression coefficient, deviations from regression, ecovalence of Wricke, ecovalence of Shukla, ecovalence of Plaisted and Peterson and superiority index of Lin and Binns, (iii) technological and nutritional quality of the whole grain, dry matter, specific weight, proteins, amino acids, mineral content, gluten, amylasic activity and baking strength. Results of the agronomic traits indicated that grain yield is on the average lower under organic cultivation compared to conventional methods (23.2 and 29.8 qx/ha SEM=0.18 qx/ha respectively). However, varieties performance under this environment changed in dry year as was the case in 2001. Data analysis indicated high production potential of some varieties such as Khiar, Ben Bechir and INRAT69 (24.7, 24.6 and 24.4 qx/ha respectively) under organic farming method. INRAT69 was found stable for grain yield under organic farming with low coefficient of variation (33 %) and a linear regression coefficient close to one (bi=0.94). Khiar and Ben Bechir varieties, identified for organic cultivation, were unstable. Results of the technological and nutritional quality were influenced by the cultivation method. The organic method affected positively specific grain weight (80.3 vs 78.3 kg/hl, SEM=0.03 kg/hl), proline contents (1.154 vs 1.146 g/100g of FM) and cystéine (0.216 vs 0.186 g/100g of FM), gluten index which is responsible for the rheological properties of dough (64.73 vs 61.46 %) and amylasic activity (406.7 vs 442.6 s, SEM=1.78 s). Contrary to the organic method, grain protein content is better in the conventional method (13.9 vs 13.5 %/MF, ESM=0.008 %/MF). Organic cultivation of INRAT69 variety was found to be associated with high nutritional and technological quality parameters such us grain weight, dry matter, total amino acids content, gluten index and amylasic activity. Regardless of the cultivation method, results showed that old varieties Badri, Jnah Khortifa and Hamira have high protein and total amino acids content (> 16 %/FM and > 14.5 g/100g FM, respectively). These varieties should be considered by breeders in selection and breeding programs of durum wheat for organic farming. Based on these results, only INRAT69 variety could be potentially used in organic agriculture not only because its stable yield, but also because of its higher technological and nutritional quality. This variety could also be adapted for manufacturing organic pasta and couscous