Evaluation of Weeds as Virus Reservoirs in Watermelon Crops

ABSTRACT: Watermelon is one of the most important vegetable crops in Brazil, which is grouped among the greatest producers worldwide. Viruses stand out among the most damaging disease agents, which can drastically reduce fruit production. In this context, weeds present in the field can also interfere in crop production, acting as reservoirs for viruses. Thus, this study aimed to investigate virus occurrence in weeds at the main watermelon-growing regions in the State of Tocantins. Viruses identification (e.g. potyviruses: Watermelon mosaic virus - WMV; Papaya ring spot virus - type watermelon -PRSV-W; Zucchini yellow mosaic virus- ZYMV; the cucumovirus Cucumber mosaic virus - CMV, and the orthotospovirus Zucchini lethal chlorosis virus - ZLCV) infecting weeds was performed by serology and confirmed by RT-PCR tests. Serological and molecular test results indicate that Amaranthus spinosus, Nicandra physaloides, Physalis angulata and Heliotropium indicum were infected by at least one virus species. The highest infection rate was represented by ZYMV (52.7%), followed by PRSV-W (22.2%); CMV, WMV, and ZLCV that showed the same infection rate (8.3%) each. Plants of P. angulata were infected by all five viruses, singly or in mixed infection, and represented 50% of the total number of infected samples. The highest virus infection rates, 50% and 44.4%, occurred in weeds collected at Lagoa da Confusão and Formoso do Araguaia, respectively. The results on occurrence and distribution of viruses infecting weeds in watermelon commercial plantations in the State of Tocantins provide important information about the role of weeds as virus reservoirs contribute to the knowledge of the epidemiology of these diseases, and enable a proper weed management aiming at reducing the secondary spreading control of viruses by insect vectors.

摘要：西瓜是巴西最重要的蔬菜作物之一，巴西亦位列全球西瓜产量第一梯队国家。病毒是危害最严重的植物病原物之一，可大幅降低西瓜果实产量。在此背景下，田间杂草不仅会干扰作物正常生产，还可充当病毒的储存宿主。为此，本研究旨在调查托坎廷斯州主要西瓜种植区杂草的病毒感染情况。

本研究通过血清学方法对感染杂草的病毒进行鉴定，所涉病毒包括马铃薯Y病毒属（potyviruses）的西瓜花叶病毒（Watermelon mosaic virus, WMV）、番木瓜环斑病毒西瓜株系（Papaya ring spot virus - type watermelon, PRSV-W）、西葫芦黄花叶病毒（Zucchini yellow mosaic virus, ZYMV），黄瓜花叶病毒属（cucumovirus）的黄瓜花叶病毒（Cucumber mosaic virus, CMV），以及正番茄斑萎病毒属（orthotospovirus）的西葫芦致死褪绿病毒（Zucchini lethal chlorosis virus, ZLCV），并通过RT-PCR实验对鉴定结果予以验证。

血清学与分子检测结果显示，刺苋（Amaranthus spinosus）、假酸浆（Nicandra physaloides）、洋苦蘵（Physalis angulata）与印度天芥菜（Heliotropium indicum）至少感染了一种目标病毒。其中感染率最高的为西葫芦黄花叶病毒（ZYMV，52.7%），其次为番木瓜环斑病毒西瓜株系（PRSV-W，22.2%）；黄瓜花叶病毒（CMV）、西瓜花叶病毒（WMV）与西葫芦致死褪绿病毒（ZLCV）的感染率均为8.3%。

洋苦蘵（P. angulata）可感染全部5种病毒，涵盖单侵染与复合侵染两种类型，其感染样本数占总感染样本数的50%。病毒感染率最高的两个采样点分别为拉戈阿达孔富桑（Lagoa da Confusão，50%）与阿拉瓜亚河畔福尔莫苏（Formoso do Araguaia，44.4%）。

本研究针对托坎廷斯州商业西瓜种植园中感染杂草的病毒发生与分布情况所获结果，明确了杂草作为病毒储存宿主的关键作用，可为相关病害的流行病学研究提供重要理论参考，同时可为制定合理的杂草管理策略提供依据，以通过阻断昆虫介体传播，实现病毒二次扩散的有效防控。