Targeting virus transmission in a vital crop for African food security

在东非和中非，豆类是一种重要的作物，可以自然地使土壤富含氮，为玉米和木薯等其他重要作物提供天然肥料。在该地区的饮食中，豆类很重要，因为它们富含蛋白质和至关重要的微量营养素。由于豆类主要由妇女种植和交易，这种作物为家庭和儿童提供了重要的直接经济利益。不幸的是，许多病毒攻击豆类植物，造成严重的作物损失。虽然一些豆类品种对这些病毒中的一种具有抗性，但一种广泛存在于撒哈拉以南非洲的密切相关的病毒（豆类常见坏死性花叶病毒）会导致这些“抗性”品系的植物死亡。因此，尽管有作物损失的风险，许多农民更愿意种植易感的豆类品系，制定新的战略来保护这种重要作物是很重要的。这种病毒通过蚜虫的针状口器传播。重要的是，一旦蚜虫以健康的植物为食，病毒颗粒就会被蚜虫甩掉；这是我们可以利用的感染链中的薄弱环节。蚜虫被植物释放的挥发性化学物质吸引。病毒感染可以改变这些植物的“气味”，从而促使蚜虫降落在受感染的植物上，获取病毒颗粒，然后将它们运送到健康的植物上。然而，一些品种的豆类即使在健康的情况下也会散发出对蚜虫更有吸引力的气味。这意味着，如果我们种植包括“有吸引力”品种的豆类植物的混合物，我们可以引诱蚜虫远离作物的其余部分，并减缓疾病的传播。更好的是，如果我们能诱骗携带病毒的蚜虫降落在对病毒有抵抗力的植物上，那么蚜虫一进食就会失去病毒颗粒。这将有效地“消毒”蚜虫，阻止它们传播病毒，并将病毒倾倒到无法生长的植物中。使用含有有限数量抗性植物的混合物的另一个好处是，病毒进化出能够克服抗性的新菌株的压力较小，而且，在病毒感染杀死抗性植物的情况下，只会损失一小部分作物。由于蚜虫和相关昆虫传播大多数植物病毒，该方法可广泛应用于各种作物。在受控条件下，利用拟南芥（Arabidopsis）和黄瓜花叶病毒（cucumber mosaic virus）等多种蚜虫传播病毒进行的实验表明，对蚜虫具有不同吸引力的植物组合可以改变蚜虫和病毒的传播。在乌干达进行的一项试点田间试验使用了对蚜虫具有不同吸引力程度的豆类品种的混合物，结果表明，蚜虫可以被更有吸引力的品种所控制，并在接近收获季节之前阻止蚜虫转移到其他植物上，这表明我们的方法在农场条件下是可行的。我们的跨国团队将：筛豆品种在肯尼亚和卢旺达的豆类种植区很受欢迎，因为它们对蚜虫很有吸引力。我们将确定植物散发的最吸引蚜虫的化学气味。重要的是要与当地品种合作，因为农民更喜欢在当地条件下的耐寒性，烹饪性能和当地适销性的某些豆类类型。我们将特别关注鉴定携带一种或多种病毒抗性基因的吸引蚜虫的品种。B.对吸引/驱避/易感/抗性植物品系的不同排列和混合对田间蚜虫和病毒传播的影响进行数学建模。这不仅可以帮助我们设计现场和实验室实验，还可以分析我们获得的数据。C.在肯尼亚和卢旺达测试我们的模型和实验室实验，以设计最有效和实用的田间设计，最大限度地减少因病毒性疾病造成的作物损失。

In East and Central Africa beans are a vital crop that naturally enriches the soil with nitrogen, providing natural fertilizer for other important crops such as maize and cassava. In the regional diet beans are important because they are rich in protein and critically important micronutrients. Since beans are mostly grown and traded by women, this crop provides important direct economic benefits to families & children. Unfortunately, a number of viruses attack bean plants, causing severe crop losses from disease.Although some bean varieties have resistance to one of these viruses, bean common mosaic virus, a closely related virus that occurs widely in sub-Saharan Africa (bean common necrotic mosaic virus) causes plants of these 'resistant' lines to die. Thus, many farmers prefer to plant susceptible bean lines despite the risk of crop loss and it is important to develop new strategies to defend this vital crop.The viruses are transmitted on the needle-like mouthparts of aphids. Importantly, the virus particles are lost by the aphid as soon as it feeds on a healthy plant; a weak link in the infection chain that we can exploit. Aphids are attracted to volatile chemicals released by plants. Virus infection can change these plants 'odours' so that aphids are encouraged to land on infected plants, acquire virus particles and then transport them to healthy plants. However, some bean varieties emit odours that are more attractive to aphids even when the plants are healthy. This means that if we plant mixtures of bean plants that include 'attractive' varieties we could decoy aphids away from the rest of the crop and slow disease transmission.Even better, if we can decoy virus-bearing aphids to land on plants that are resistant to the virus, then as soon as the aphid feeds it will lose the virus particles. This would effectively 'sanitize' the aphids and stop them spreading the virus, as well as dumping the virus into plants in which it cannot grow. An additional benefit of using a mixture containing a limited number of resistant plants is that viruses will be under less pressure to evolve new strains that can overcome resistance and, in cases where virus infection kills resistant plants, only a small proportion of the crop will be lost. Since aphids and related insects transmit the majority of plant viruses the method could be applied to a wide range of crops. Experiments under controlled conditions using varieties of a plant called Arabidopsis and an aphid transmitted virus called cucumber mosaic virus showed that aphid and virus spread can be altered using combinations of plants with different levels of attractiveness to aphids. A pilot field experiment in Uganda using mixtures of bean varieties with different degrees of attractiveness to aphids showed that aphids can be detained on more attractive varieties and inhibited from moving to other plants until close to harvest time, showing that our approach can work under farm conditions. Our multinational team will:A. Screen bean varieties that are popular in bean-growing regions in Kenya & Rwanda with respect to their attractiveness to aphids. We will identify the chemical odours emitted by plants that are most attractive to aphids. It is important to work with local varieties since farmers prefer certain bean types for hardiness under local conditions, cooking properties and local marketability. We will focus particularly on identifying aphid-attractive varieties carrying one or more virus resistance genes. B. Mathematically model the consequences of different arrangements and mixtures of attractive/repellent/susceptible/resistant plant lines on aphid and virus spread in fields. This will not only help us design our field and lab experiments but also to analyze the data we obtain. C. Test our models and lab experiments in Kenya & Rwanda to devise the most effective & practical field designs that minimize crop losses due to viral diseases.