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

在欧洲促进环境安全和经济上有竞争力的果树产业是具有挑战性的，因为水果生产在全球变暖面前是脆弱的，并且容易交替结果，这被定义为一个高种植年，然后是低（或零）种植。到目前为止，通过化学、机械或人工间伐方法来管理作物不规则性。但有几个原因（公众舆论，欧洲法律和经济限制）导致减少化学品的使用和生产成本，以确保欧洲水果生产的可持续性。水果生产还面临两个主要的气候威胁：第一，春季的霜冻会杀死花朵，随后抑制作物生长，促进交替结果;第二，夏季的高温和干旱影响会干扰花卉诱导。此外，由于它们的寿命长，培育新的果树选择是缓慢的。出于所有这些原因，欧洲的粮食安全和水果种植者的生存将需要基于创新和可持续解决方案的新竞争力。在AlternApp中，我们将研究FI遗传和环境控制的新途径，为创新材料选择开辟前景。在苹果树中，FI，即分生组织开始定向发育成花的时间，是决定一年中交替结果强度的关键发育阶段。遗传决定论的存在，怀疑了很长一段时间，最近已被证明在苹果分离群体。第一个候选基因（CG）被发现，支持激素控制FI的假设，涉及发展水果。但也必须考虑生殖生长和营养生长之间营养竞争的作用。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。表型以及基因型、年份和气候影响将通过具体的统计发展加以量化。将通过新一代测序技术（NGS）探索在其生育行为中对比并人工设置为高或低种植条件的品种的转录组，以鉴定新的CG和感兴趣的等位基因变异。将在具有小气候、形态学和生理学特征的嫩枝上收集顶端分生组织，以将转录组与树内分生组织开花行为的异质性相关联。通过本项目，我们期望在苹果树FI与其交替结果行为的关系方面获得新的和高水平的结果，并在发现可用于育种计划的关键基因的等位变异方面获得更多的应用结果。

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.