Effects of cherry leaf spot on photosynthesis in tart cherry 'Montmorency' foliage

Results described here span a total of three field seasons and quantitatively depict the effects of an economically important fungal pathogen (Blumeriella jaapii) on tart cherry (Prunus cerasus 'Montmorency') leaf physiology. For the first time, leaf photosynthesis, stomatal conductance (g(s)), maximum ribulose-1,5-bisphosphate carboxylation rate (V(cmax)), and maximum electron transport (J(max)) were measured as functions of visible cherry leaf spot disease (CLS) severity. Defined as the proportion of chlorotic and necrotic tissue per leaf, CLS severity was estimated from leaves of mature 'Montmorency' trees in 2007, 2008, and 2009. Briefly, as visible disease severity increased, all of the leaf-level physiological parameters decreased significantly (P < 0.01) and disproportionately. Thus, the effects of visible symptoms on leaf photosynthetic metabolic function encroached upon asymptomatic tissue as well. Impairment of photosynthetic metabolism in 'Montmorency' tart cherry leaves due to CLS appears to be mediated through disproportionately large perturbations in g(s), V(cmax), and J(max). These findings offer a new perspective on the amount of damage that this serious disease can inflict.