Foliar diseases affect the eco-physiological attributes linked with yield and biomass in wheat (Triticum aestivum L.)

Foliar diseases are the main biotic cause of yield loss in wheat crops (Triticum aestivum L.) in Argentina and other regions around the world. Most of the studies on foliar diseases take a phytopathological perspective, but few studies have analyzed the problem with an eco-physiological approach aimed at the understanding of which crop traits are affected by foliar diseases. The present study was designed to determine the effects of a foliar disease complex (including leaf rust, Septoria leaf blotch and tan spot), on (i) grain yield and (ii) the physiological components of biomass production; intercepted radiation (RI) and radiation use efficiency (RUE), in bread wheat crops growing under contrasting agronomic and environmental conditions (i.e. different cultivars, years, location and nitrogen supply). The experiments were carried out during 4 years in different locations (three in the rolling pampas of Argentina and one in northern of France). Five different commercial wheat cultivars were sown on early (E) and late (L) sowing dates (SD); and two contrasting nitrogen availability and two fungicide treatments (protected and unprotected) were applied. Foliar diseases appeared during the grain filling period and affected both, leaf area duration (LAD) and healthy area duration (HAD) during that period. Foliar diseases reduced both, above-ground biomass at harvest (1533 and 1703 g m−2 for unprotected and protected treatments, respectively) and grain yield (646 and 748 g m−2 for unprotected and protected treatments, respectively) without important effects on harvest index. Biomass reductions after anthesis, due to the effects of foliar diseases, were associated with a reduced capacity of the canopy to absorb solar radiation more than any effect on RUE. However, RUE was consistently lower-when leaf rust was the predominant disease in the crop, suggesting that this biotrophic pathogen could affect the photosynthetic activity at the leaf or canopy level.