Screening old and modern wheat varieties for shading tolerance within a specialized poplar plantation for agroforestry farming systems implementation

The sustainability of silvoarable agroforestry systems largely depends on the choice of suitable crop species and varieties for minimizing competitive interactions in the interaction zone with trees. Up to date crop intraspecific variability has been poorly investigated, and mainly in pot trials under artificial shading. Given this framework, a trial was conducted in field conditions in NE Italy to study the response of 10 common wheat varieties cultivated in the 6-m narrow inter-row of a specialized 4-year old poplar plantation (AF, agroforestry) vs. full sun conditions (C, controls). Here it was demonstrated that large genetic variability exists in wheat, as grain yield reductions under shading ranged between 31 and 75% (average − 57%) depending on variety choice. Better tolerance was highlighted in old varieties (− 44% of yield in AF vs. C), that was associated to greater plasticity in delaying leaf senescence, and increased both leaf area index and SPAD (index of chlorophyll content), while achieving the highest grain protein contents (> 17.3% DW). However, under shading modern wheat varieties still remained the highest yielding, particularly in bread-making varieties (469 g m⁻² on average), thanks to larger improvement of the leaf-to-culm biomass ratio and better harvest index. We conclude that there is large scope for identifying wheat varieties suitable for agroforestry systems, while breeding programs can select for specific morpho-physiological adaptation traits to low irradiance.