Susceptibility of Fig Cultivars to Thyrostroma parviniae , and Temperature-Dependent Pathogenicity on Potential Alternative Hosts

Abstract

Thyrostroma parviniae has recently been identified as a dieback and bud-necrosis pathogen of fig trees in Iran. The resulting wood diseases pose a substantial challenge, given the current lack of effective and affordable treatment options. This study evaluates fig cultivar susceptibility to T. parviniae (ex-holotype isolate S83-47; CBS 154727), previously identified as the most aggressive isolate, and assesses its temperature-dependent pathogenicity across multiple economically important fruit and ornamental species present in affected areas. Pathogenicity assays using wounded-stem and cut-stem inoculation methods on young saplings in greenhouse conditions revealed pronounced cultivar-specific responses: the wild genotype ‘Gilasi‘ and the commercially important dried-fruit cultivars ‘Payves‘ and ‘Sabz‘ were highly susceptible, whereas the fresh-fruit cultivar ‘Matti‘ exhibited markedly reduced lesion development. Strong correlations among internal lesion traits indicated that rapid vascular colonization is a key determinant of disease severity. Potential host-range experiments under controlled conditions further demonstrated that T. parviniae can infect detached shoots of diverse woody species, including almond, apricot, elm, pomegranate, red mulberry, and walnut, with the most severe symptoms occurring at 25°C compared to 15 and 20°C, suggesting enhanced aggressiveness under warmer conditions. Apple and quince remained asymptomatic, while pistachio displayed temperature-dependent susceptibility. Multivariate analyses indicated that disease severity in fig, pomegranate, and walnut increases substantially at elevated temperatures in this experimental system, pointing to a possible capacity for the pathogen to expand under ongoing climate warming. These findings identify vulnerable fig cultivars, reveal a broader potential host range than previously recognized, and underscore the need for proactive management strategies. Based on this controlled experimental evidence, the results offer a preliminary basis for breeding programs, orchard design, and regional disease-risk forecasting aimed at mitigating the impact of this emerging pathogen in warm and warming agroecosystems.