Effects of Cultivar Susceptibility, Branch Age, and Temperature on Infection by Botryosphaeriaceae and Diaporthe Fungi on English Walnut ( Juglans regia ).

Botryosphaeriaceae and fungi have been described as the main causal agents of branch dieback and shoot blight of English walnut ( L.). To date, the effects of biotic and abiotic factors on disease development on this host are still poorly understood. Thus, the main goal of this study was to evaluate the effects of cultivar, shoot-branch age, and temperature on infection by Botryosphaeriaceae and fungi on English walnut. The susceptibility of eight commercial cultivars was evaluated against three Botryosphaeriaceae and two species. For the remaining experiments, shoots or branches of 'Chandler' were used. An initial experiment evaluating two inoculation methods was conducted, with inoculation with a mycelial plug being more consistent and useful than conidial suspension inoculation. Cultivar susceptibility varied depending on the fungal species, with 'Chandler' being among the most tolerant cultivars for shoot infection. One-year-old shoots were significantly more sensitive for both and in comparison with 2- to 4-year-old branches. The effect of temperature on shoot infection was evaluated under 5, 10, 15, 20, 25, 30, and 35°C. Lesion development was significantly higher for isolates than for isolates at all temperatures evaluated, with optimum temperature of shoot infection being ∼26°C for and ∼21°C for .