Durum wheat selection under zero tillage increases early vigor and is neutral to yield

The combination of zero tillage (ZT) and crop residue retention can substantially improve soil structure and reduce the risk of erosion. Growing conditions for crops are substantially altered in such systems and the question whether specific varieties adapted to ZT conditions need to be developed is not answered. Most published research assessed Genotype by Tillage interactions, which are rarely significant, using genotypes generally developed under CT conditions. CIMMYT's durum wheat breeding program went beyond this approach and performed parallel early generation selection within 16 crosses both in conventional tilled (CT) and ZT soils with the aim of comparing the effect of selection environment (either CT or ZT) on the performance of selected progenies. From 16 initial crosses, 234 lines were selected under CT and 250 under ZT. All 484 lines were subsequently tested for yield and growth traits during three seasons near Ciudad Obregon, Sonora, Mexico in three different testing environments. Those included ZT and CT with full irrigation and CT with reduced irrigation. Early vegetative growth was slightly improved with selection under ZT in all testing environments. Grain yield was highest in ZT testing environment, with a very small average difference in 2013 (0.11 t ha(-1)) and larger differences in 2014 (0.65 t ha(-1)) and 2015 (0.42 t ha(-1)). The differences between selection streams observed for yield were marginal and in most cases not significant. We conclude that, within the germplasm pool handled in CIMMYT's durum wheat breeding program, selection can be conducted under either tillage conditions without affecting negatively the performance of resulting progenies. The neutrality of selection under ZT in relation to performance of progenies is a likely hypothesis that should be tested in other ZT conditions and germplasm pool combinations.