Genetic mechanisms underlying alternate cropping in apple (Malus x domestica)

在欧洲促进环境安全和具有经济竞争力的果树产业是具有挑战性的，因为在全球变暖面前，水果生产是脆弱的，而且容易出现轮作，这被定义为丰产年和低(或零)作物年。到目前为止，通过化学、机械或人工的间伐方法来管理作物的不整齐。但有几个原因(公众舆论、欧洲法律和经济限制)导致了化学品使用量和生产成本的减少，以确保欧洲水果生产的可持续性。水果生产还面临着两大气候威胁：第一，春季霜冻会杀死花朵，随后抑制作物生长，提高轮作；第二，夏季高温和干旱会扰乱开花诱导(FI)。此外，由于果树寿命长，选育新果树的速度很慢。出于所有这些原因，欧洲的粮食安全和果农的生存将需要基于创新和可持续解决方案的新的竞争力。在AlternApp中，我们将探索FI基因和环境控制的新途径，为创新材料的选择开辟新的视角。在苹果树上，FI是分生组织发育成花的时期，是特定年份轮生结果强度的关键发育阶段。长期以来一直被怀疑的遗传决定论的存在，最近在苹果分离群体中得到了证明。第一个候选基因(CG)被发现，它们支持FI激素控制的假设，涉及果实的发育。但也必须考虑生殖和营养生长之间的营养竞争的作用。这两个假设将通过遗传学和基因组学方法进行检验。将研究两个分离群体的FI和生育行为，以确定与常规表型相关的基因组区域。表型以及基因类型、年份和气候影响将通过具体的统计发展情况进行量化。新一代测序技术(NGS)将探索不同结实行为的品种和人工设定的高低种植条件下的转录组，以确定新的CGs和感兴趣的等位基因变异。为了将转录组与分生组织开花行为的异质性联系起来，将顶端分生组织组织收集在具有小气候、形态和生理特征的枝条上。通过这个项目，我们期待着苹果树FI与其轮回结果行为相关的新的和高水平的结果，以及与发现关键基因的等位基因变异相关的更多应用结果，以便在育种计划中使用。

Promoting an environmentally safe and economically competitive fruit tree industry in Europe is challenging because fruit production is fragile in front of global warming and is prone to alternate bearing, which is defined as a high cropping year followed by a low (or nil) cropping. Cropping irregularity is managed so far by thinning methods, chemical, mechanical or manual. But several reasons (public opinion, European laws, and economical constraints) lead to the reduction of chemical use and production costs to ensure the sustainability of fruit production in Europe. Fruit production has also to face two major climatic threats: first frost damage in spring which kills flowers and subsequently suppresses cropping and enhances alternate bearing and second high temperature and drought impacts during summer which can perturb floral induction (FI). Moreover, because of their long life, breeding for new fruit tree selections is slow. For all these reasons, food security and the survival of fruit growers in Europe will require new competiveness based on innovative and sustainable solutions. In AlternApp, we will investigate new avenues on the genetic and environmental control of FI to open perspectives for innovative material selection. In apple tree, FI, the time at which meristems become committed to develop flowers, is the critical developmental stage for the intensity of alternate bearing in a given year. The existence of a genetic determinism, suspected since a long time, has been recently demonstrated in an apple segregating population. First candidate genes (CGs) were revealed which support the assumption of hormonal control of FI, involving developing fruits. But the role of nutritional competition between reproductive and vegetative growth, must also be considered. These two assumptions will be examined by genetic and genomics approaches. Two segregating populations will be studied for FI and bearing behavior, in order to identify genomic regions associated to regular phenotypes. Phenotypes, as well as genotypes, years and climatic effects will be quantified by specific statistical developments. Transcriptome of varieties contrasted in their bearing behavior and artificially set into high or low cropping conditions will be explored by New Generation Sequencing Technology (NGS) to identify new CGs and allelic variation of interest. Apical meristem tissues will be collected on shoots which are micro-climatically, morphologically and physiologically characterized in order to correlate transcriptome with the heterogeneity of meristem flowering behaviors within the trees. By this project, we expect new and high standing results on FI in apple tree in relation to their alternate bearing behavior and more applied results linked to the discovery of allelic variation in key genes that could be used in breeding programs.