Diversity of soil-borne fungal pathogens associated to root rot and vine decline of melon in Sardinia (Italy)

Root rot and vine decline of melon (MRRVD) is a destructive disease complex mainly occurring in semiarid cultivation areas. In the last decade, in the melon producing area of Sardinia (Italy), yield reductions up to 100% were recorded due to the occurrence of MRRVD. The aim of the present study was to undertake a two-years survey of fungal pathogens associated with MRRVD grown as a monocrop in two locations in Central Sardinia, Sinis and Sassu, and to investigate the possible role of soil fungal diversity in the disease development. Melon plants were affected by similar symptoms but colonised by a set of soil-borne fungal pathogens different between surveyed sites and cropping seasons, including Plectosphaerella melonis, P. cucumerina, Fusarium solani, Macrophomina phaseolina and Monosporascus cannonballus. Olpidium bornovanus and O. virulentus were isolated using bait plants and detected by NGS analysis. Bait plants had a general decrease in biomass and yellowing of foliage. The presence of most of the isolated pathogens were also confirmed by the NGS analysis of soil microbiome. Our results confirm that among the fungal complex implicated in the occurrence of RRVD in Sardinia, O. bornovanus along with O. virulentus likely assume a key role in the development of the disease alone and possibly in association with other pathogens. Differences in the pathogenic fungal spectrum here recorded in symptomatic roots may be associated with agricultural practices, soil physicochemical characteristics, and fungal community composition and function profile.

甜瓜根腐病与蔓枯病复合病害（MRRVD）是一类主要发生于半干旱种植区域的毁灭性复合病害。近十年来，意大利撒丁岛甜瓜主产区因MRRVD的发生，曾记录到最高达100%的产量损失。本研究旨在对撒丁岛中部两处单作甜瓜种植区（Sinis与Sassu）中与MRRVD相关的病原真菌开展为期两年的调查，并探究土壤真菌多样性在病害发生发展中的潜在作用。受侵染的甜瓜植株表现出相似的症状，但不同调查区域与种植季的土传病原真菌类群组成存在差异，涵盖甜瓜单孢腔菌（Plectosphaerella melonis）、黄瓜单孢腔菌（P. cucumerina）、茄腐镰孢（Fusarium solani）、菜豆壳球孢（Macrophomina phaseolina）以及炮弹单孢囊壳菌（Monosporascus cannonballus）。本研究通过诱捕植物分离得到芸苔油壶菌（Olpidium bornovanus）与有毒油壶菌（O. virulentus），并通过下一代测序（NGS）分析完成了上述病原的检测。诱捕植物的生物量普遍下降，且叶片出现黄化症状。对土壤微生物组的NGS分析也证实了大部分分离得到的病原真菌的存在。本研究结果证实，在撒丁岛与MRRVD相关的真菌复合类群中，芸苔油壶菌与有毒油壶菌单独或与其他病原真菌协同侵染时，可能在病害发生发展中发挥关键作用。本研究中记录的显症根系病原真菌谱差异，可能与种植管理措施、土壤理化特性以及真菌群落组成与功能特征相关。