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，跻身全球西瓜产量前列。病毒是最具破坏性的病害病原之一，可大幅降低果实产量。在此背景下，农田杂草同样会干扰作物生产，并可充当病毒的贮存寄主。本研究旨在调查托坎廷斯州主要西瓜种植区域内杂草的病毒发生状况。针对感染杂草的病毒，采用血清学方法开展鉴定，涉及的病毒包括：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型（Papaya ring spot virus - type watermelon - PRSV-W）、西葫芦黄化花叶病毒（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），并通过逆转录聚合酶链式反应（RT-PCR）试验验证鉴定结果。血清学与分子检测结果表明，刺苋（Amaranthus spinosus）、假酸浆（Nicandra physaloides）、苦蘵（Physalis angulata）与印度天芥菜（Heliotropium indicum）至少被一种病毒侵染。其中侵染率最高的为ZYMV（52.7%），其次为PRSV-W（22.2%）；CMV、WMV及ZLCV的侵染率均为8.3%。苦蘵（P. angulata）可被全部5种病毒单独或混合侵染，其阳性样本数占总阳性样本的50%。在拉戈阿达孔弗桑（Lagoa da Confusão）和阿拉瓜亚河畔福尔莫苏（Formoso do Araguaia）采集的杂草中，病毒侵染率最高，分别达50%与44.4%。本研究针对托坎廷斯州商业西瓜种植园杂草的病毒发生与分布情况开展分析，明确了杂草作为病毒贮存寄主的重要作用，可为这类病害的流行病学研究提供关键数据支撑，同时可为制定针对性杂草管理方案、通过防控昆虫介体以减少病毒二次传播提供科学依据。