Understanding the Genetic Basis of Traits for Rootstock Improvement in Vegetable Crops

根系性状是提高可持续作物生产的重要目标，因为它们控制从土壤中捕获水分和养分，并对作物地上部分的表现有许多其他影响。在园艺中，许多新鲜市场上的一年生作物（如番茄、辣椒、黄瓜和甜瓜）主要是作为砧木栽培品种和接穗（嫩枝）栽培品种之间的嫁接而生产的。这些砧木栽培品种目前用于管理作物活力和对根病的抗性，并且蔬菜砧木种子和嫁接移植物的销售是一个大的和有利可图的业务，因为采用砧木的显著有益效果。仅番茄砧木种子的全球市场就约为1亿英镑。众所周知，增加新鲜水果和蔬菜的消费可以减少慢性病的发病率，慢性病是卫生系统的主要负担;提高我们种植的能力，从而以具有竞争力的价格提供高质量的新鲜农产品，对于刺激消费增长非常重要。目前的研究表明，砧木也可以通过提供改善的根功能或通过向接穗发送信号来赋予对诸如盐、冷和营养限制等胁迫的抗性，但是对这些抗性和活力的遗传基础知之甚少，使得这些性状的育种困难且缓慢。这与土传病害抗性育种形成对比，在土传病害抗性育种中，许多抗性基因是已知的，并且它们常规且容易地组合成新品种以提供多重抗性。提高我们的繁殖能力以获得活力和耐寒性是砧木种子行业的优先事项，因为作物生长在凉爽的早期季节受到限制，并且因为在整个季节保持营养生长和生殖生长之间的正确平衡可以大大提高作物产量。该提案的目的是充分验证，关于基因身份和作用机制，当前和新的基因座，影响砧木性能，包括根系结构，活力和耐冷性番茄，我们的目标作物。我们已经确定了番茄根系结构的位点，从野生番茄种茄pennellii，并获得了几个单基因突变体改变根性状，在这个项目中，我们将充分探讨其遗传基础和作用方式。为了进一步利用野生物种的遗传变异，我们将从两个S. habrochaites亲本系，因为这是最常用于商业砧木的野生物种，它适合生长在安第斯山脉的凉爽山坡上。我们将使用番茄参考基因组，发表于2012年，最新的高通量测序和基因分型技术来定位基因座和测量基因表达;这将允许候选基因被识别。将测试这些候选物，以通过使用遗传修饰改变它们的表达和通过选择在这些基因中具有突变的植物（TILLING）来确定它们是否对观察到的表型负责。我们将使用最先进的方法来测量砧木基因型如何影响枝条的生长和生理，并寻找控制接穗表型的激素信号。该项目小组由根系生物学和番茄遗传学专家组成，他们将与商业种子公司密切合作，提供遗传标记和机制理解，这将提高短期内培育具有更好活力的砧木的能力，并提高我们对所有双子叶作物根系性状遗传控制的理解，以利于中长期作物改良。

Root traits are an important target for improving sustainable crop production as they control capture of water and nutrients from the soil, and have many other influences on the performance of the above ground part of the crop. In horticulture, many annual crops for the fresh market (e.g. tomato, pepper, cucumber and melon) are produced predominantly as grafts between a rootstock cultivar and a scion (shoot) cultivar. These rootstock cultivars are currently used to manage crop vigour and resistance to root diseases, and the sale of vegetable rootstock seed and grafted transplants is a large and profitable business because of the substantial beneficial effects of employing rootstocks. The global market for tomato rootstock seed alone is approximately £100 M. Increased consumption of fresh fruits and vegetables is known to reduce the incidence of debilitating chronic diseases which are a major burden on the health system; improving our ability to grow and therefore deliver high quality fresh produce at competitive prices is important to stimulate increased consumption. Current research indicates that rootstocks can also confer resistance to stresses such as salinity, cold and nutrient limitation by providing improved root functions or by sending signals to the scion, but the genetic basis for these resistances, and of vigour, is poorly understood making breeding for these traits difficult and slow. This contrasts to the breeding of resistance to soil-borne diseases where many resistance genes are known and they are routinely and easily combined into new cultivars to provide multiple resistances. Improving our ability to breed for vigour and cold tolerance are the priorities for the rootstock seed industry because crop growth is limited in the cool early season and because sustaining the correct balance between vegetative and reproductive growth throughout the season can greatly increase crop yield. The aims of this proposal are to fully characterise, with respect to gene identity and mechanism of action, current and novel loci that impact on rootstock performance including root system architecture, vigour and cold tolerance in tomato, our target crop. We have already identified loci for tomato root system architecture from the wild tomato species Solanum pennellii and obtained several monogenic mutants with altered root traits; in this project we will fully explore their genetic basis and mode of action. To further harness wild species genetic variation, we will generate a novel large recombinant inbred line (RIL) population from two S. habrochaites parental lines because this is the wild species most commonly used in commercial rootstocks and it is adapted to grow in the cool slopes of the Andes.We will use the tomato reference genome, published in 2012, and the most recent high-throughput sequencing and genotyping technologies to map loci and to measure gene expression; this will allow candidate genes to be identified. These candidates will be tested to see if they are responsible for the observed phenotypes by altering their expression using genetic modification and by the selection of plants with mutations in these genes (TILLING). We will use state-of-the-art methods to measure how rootstock genotypes influence the growth and physiology of the shoot and to search for hormonal signals that control scion phenotypes. The project team is made up of experts in root biology and tomato genetics who will work closely with a commercial seed company to deliver genetic markers and mechanistic understanding that will improve the ability to breed rootstocks with improved vigour in the short term, and to improve our understanding of the genetic control of root traits in all dicotyledonous crops for the benefit of crop improvement in the medium to long term.