Biennal bearing in apple – Expression patterns of several floral genes revealed by in-situ hybridization

Biennial bearing corresponds to cyclical changes in cropping characterized by “on” and “off” years with “heavy” and “light” fruit loads, respectively. Within the domesticated apple, there is a large variation among cultivars in the amplitude of cycling and tendency to fruitfulness and regular cropping behavior, suggesting genetic control of this phenomenon. A previous study on a segregating population ‘Starkrimson’ x ‘Granny Smith’, using QTL detection and candidate gene mapping, indicated that four main genomic regions that contain floral integrator genes, meristem identity genes, and gibberellin oxidase genes co-located with QTLs [1]. On the consensus map, SOC1 (MdSOC1-like) and GA 20-oxidase (MdGA20ox1a) were located within the QTL interval of annual yields at the bottom of LG1. The flowering gene TERMINAL FLOWER1 (MdTFL1a) do not colocate with any QTL mapped but it has been described as key flowering genes in Malus [2] [3]. GA20ox1 is involved in the later steps of the gibberellin biosynthetic pathway. MdTFL1 is assumed to repress flowering, thus maintaining the apical meristem vegetative. SOC1 integrates multiple flowering signals derived from photoperiod, temperature, hormone, and age-related signals. The aim of this study was to reveal the temporal and spatial expression patterns of these 3 genes during floral bud induction and initiation by in-situ hybridization

Deciphering genetic and physiological determinants of alternate bearing in apple tree

UMR AGAP - équipe AFEF - Architecture et fonctionnement des espèces fruitièresPromoting 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 the collaborative German-French “AlternApp” project, we are investigating 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. Based on previous information on genetic determinism obtained on an apple segregating population and first candidate genes (CGs), we are (i) enlarging the genetic basis considered in genetic studies, (ii) examining the respective role of nutritional competition between reproductive and vegetative growth and hormonal control of FI and (iii) enlarging the list of CGs by RNAseq. New segregating populations are under study for FI and bearing behavior in order to identify genomic regions associated to regular phenotypes. Phenotypes as well as genotypes and years effects are being quantified by specific statistical methods. Apical meristem tissues have been 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. CGs expression profiles, hormonal (especially GA) and carbohydrate contents are also being studied in these tissues. 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

Biochemical and agronomical responses of grapevines to alteration of source-sink ratio by cluster thinning and shoot trimming Respostas bioquímicas e agronômicas de videiras à alteração da razão fonte-dreno pelo desbaste de cachos e desponte de ramos

The control of leaf to fruit ratio by the practice of entire clusters removal from the vine upon berry set has been used in traditional vineyards in order to regulate yield and to improve chemical composition of the berries. Although this practice has been settled in temperate zones, little is known about grapevines behavior in tropical growing areas. The aim of this work was to evaluate the biochemical and agronomical responses of two Vitis vinifera cultivars (Merlot and Cabernet Sauvignon) grown in Caldas, Minas Gerais, Brazil, a new winegrape region. Grapevines were submitted to cluster thinning (0%, 50% and 75% of cluster removal) and trimming treatments (trimmed and untrimmed) imposed at pea size stage. The source-sink alteration by fruit removal and shoot trimming had impact on yield, leaf sugar metabolism and grape composition. Although there was an improvement in color intensity of the berries with reduction of fruit load, the cluster thinning practice should be avoided in vineyards grown in the south of Minas Gerais State without impairment of wine grape quality. On the other hand, shoot trimming practice should be recommended only for Merlot in order to improve sugar grapes from vines with no cluster removal.<br>O controle da razão folhas:frutos pela prática da remoção de cachos inteiros após o estabelecimento das bagas tem sido utilizado nos vinhedos tradicionais, a fim de regular a produção e melhorar as características químicas das bagas. Embora essa prática esteja bem estabelecida em regiões temperadas, pouco se sabe a respeito do comportamento das videiras cultivadas em áreas tropicais. O objetivo deste trabalho foi avaliar as respostas agronômicas e bioquímicas de duas cultivares de Vitis vinifera (Merlot e Cabernet Sauvignon) cultivadas em Caldas, Minas Gerais, Brasil, nova região produtora de uvas finas. As videiras foram submetidas a tratamentos de desbaste de cachos (0%, 50% e 75% de cachos retirados) e desponte (com e sem desponte) realizados no estágio de ervilha. A alteração da fonte-dreno pela remoção dos frutos e desponte afetou a produção, o metabolismo de açúcares nas folhas e a composição das bagas. Embora tenha sido observado um aumento na intensidade de cor das bagas com a redução da carga de frutos, a prática do desbaste de cachos pode ser evitada nos vinhedos do sul de Minas Gerais, sem prejuízo à qualidade das uvas viníferas, enquanto a prática do desponte deve ser recomendada somente para Merlot, a fim de melhorar a concentração de açúcares nas uvas de videiras sem desbaste de cachos