Le pommier (Malus Xdomestica Borkh.) cultivé en climat à hiver doux, avec un manque d'une quantité suffisante d'heures de températures froides, présente des anomalies morphologiques et physiologiques. Sur le plan de la phénologie, il s'agit notamment d'un débourrement printanier tardif et désynchronisé entre les différents bourgeons d'un même arbre. Sur le plan agronomique, la floraison et la nouaison sont irrégulières et étalées dans le temps et conduisent à une faible production de fruits. L'objectif de ce travail de thèse est premièrement de mieux caractériser les effets des températures hivernales sur le débourrement et la croissance des bourgeons axillaires en distinguant les effets respectifs des températures hivernales et du génotype. Il s'agit ensuite de vérifier l'hypothèse que les effets des températures sur le débourrement du bourgeon s'effectue via les effets sur son statut hydrique. Les travaux ont été réalisés en France et au Brésil. En France, les expérimentations ont porté sur quatre cultivars à fort besoin (‘Granny Smith', ‘Royal Gala', ‘Starkrimson') ou faible besoin (‘Condessa') en froid, cultivés en hiver froid (conditions extérieures) et doux (serres climatisées). Nous montrons que le débourrement résulte d'une séquence d'évènements où la température hivernale joue un rôle primordial sur les mécanismes de sortie de dormance et donc sur le débourrement proprement dit, durant la période froide. Les caractéristiques propres du cultivar jouent par contre un rôle dans la croissance ultérieure des bourgeons et donc dans l'architecture finale de la pousse du pommier. Par ailleurs, la chute tardive des feuilles, caractéristique du pommier en hiver doux, a peu d'effets sur le débourrement et la croissance des bourgeons. L'analyse du statut hydrique des bourgeons a été réalisée sur le tiers distal des pousses de pommier caractérisé par une forte fréquence de ramification en climat à hiver froid. Nous montrons que, dans la période allant de l'endordormance à la phase de pré-débourrement, la conductance hydraulique à la jonction entre l'axe porteur et le bourgeon varie peu au cours de l'hiver et entre cultivars. Par ailleurs, durant cette même période le potentiel hydrique intra-bourgeon reste négatif, entre -4.35 and -2.24 MPa. Enfin, quel que soit le cultivar, nous ne montrons pas de relation entre les températures hivernales, le potentiel hydrique ou la teneur relative en eau des bourgeons, et l'aptitude au débourrement ultérieur. Ces résultats suggèrent que le bourgeon est hydrauliquement isolé de son axe porteur pendant toute la période hivernale jusqu'à quelques jours précédant le débourrement. Les expérimentations au Brésil ont porté sur le cultivar ‘Eva ‘ à faible besoin en froid, cultivés en conditions naturelles d'hiver doux. Il s'agissait de vérifier les effets possibles de la position du bourgeon le long de l'axe porteur sur sa taille et sa teneur relative en eau. Nous montrons que, tout au long de l'hiver, les bourgeons distaux sont caractérisés par une plus grande taille et une teneur relative en eau plus élevée que les bourgeons proximaux avec une forte augmentation de la teneur relative en eau une semaine avant le débourrement printanier. Le débourrement acrotone semble donc résulter d'une évolution rapide du statut hydrique du bourgeon en fin d'écodormance. L'ensemble des résultats acquis en France et au Brésil, sur des cultivars caractérisés par des besoins variables en froid hivernal, indique que l'aptitude au débourrement printanier des bourgeons de pommier est davantage lié à un « effet rameau entier » qu'au statut hydrique proprement dit des bourgeons individuels, tout au moins jusqu'à quelques jours avant le débourrement effectif. La pousse annuelle de pommier apparait donc comme une unité morphologique et physiologique intégrée qui, dans un contexte climatique donné, conditionne le statut hydrique de chaque bourgeon et son aptitude au débourrement. / The apple tree (Malus Xdomestica Borkh.) presents morphological and physiological anomalies when grown in mild winter climates with insufficient winter chilling to overcome winter dormancy. Symptoms are typically delayed and erratic budburst, entailing desynchronized flowering and fruit-set and poor agronomic performances. This thesis aimed at gaining more insights on the following issues. Firstly, what are the effects of winter temperatures on axillary burdburst and bud outgrowth, and what are the respective effects of winter temperatures and cultivar?, and secondly, is there a link between the temperature-dependent budburst and bud water status? Works were done in France and Brazil. In France, experiments were carried out in controlled conditions on four apple cultivars characterized by either high chilling (‘Granny Smith', ‘Royal Gala', ‘Starkrimson') or low chilling (‘Condessa') requirements and were submitted to outdoor-cold and greenhouse-mild winter temperatures. We showed that the actual shoot architecture and budburst resulted from an ordered sequence of events with a pivotal role of winter temperatures on the dormancy completion of individual lateral buds. Endogenous factors related to the cultivar branching pattern overtook the temperature effect on the lateral bud outgrowth. Furthermore, the delayed senescence and subsequent leaf persistence during winter, characterizing the apple tree in the mild winter temperature conditions, had only a weak effect on the topological distribution of budburst and lateral outgrowth. The analyses of bud water status were done on distal buds only, characterized by high budburst frequency in cold winter conditions. We showed that, from endodormancy to the pre-budburst stage, xylem conductance at the stem-to-bud junction did not show consistent changes across cultivars and winter temperature treatments. Bud water potential had negative values, between -4.35 and -2.24 MPa, depending on cultivars and winter temperature treatments. Moreover, whatever the cultivar, there were no significant trends across dates for the effects of winter temperatures on bud water potential and relative water content without a consistent relationship with actual spring budburst frequency. These results suggested that lateral buds were hydraulically isolated from the parent stem during winter until a few days before budburst. The other set of experiments was carried out in Brazil, under mild winter conditions, on the low chilling apple cultivar ‘Eva'. The objectives were to gain more insights on the effect of the position of the over-wintering lateral bud along the whole-parent shoot on bud size and water content. Results highlighted that distal buds were larger and had a higher water content than proximal buds with a strong increase of water content a week before spring budburst. It was concluded that the acrotonic pattern of budburst was mainly established during ecodormancy. As a whole, we showed that spring budburst seemed more related to a whole-shoot effect than to the water status of the individual bud during winter dormancy. Our study substantiated the importance of the whole shoot as an integrated morphological and physiological unit in driving budburst and further growth.

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No. of bitstreams: 2 Tese Juliano Dutra Schmitz.pdf: 9582623 bytes, checksum: f579b0458e2ab6f4ae5579715de842ea (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2014-12-03 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / A macieira (Malus X domestica Borkh.) apresenta anomalias fisiológicas quando cultivada em regiões de inverno ameno, onde o frio hibernal é insuficiente para superação da dormência. Assim, na presente tese foram estudados três temas de pesquisa. No tema 1 estudou-se a distribuição e fenologia da brotação e crescimento inicial da ramificação primaveril; No tema 2 estudou-se a brotação primaveril através da determinação do status hídrico de gemas laterais e da condutância hidráulica do xilema. O tema 3 realizou-se a análise do comportamento da brotação primaveril de uma cultivar de baixo exigência em frio cultivada em inverno ameno. Para isso, foram montados dois dispositivos experimentais: Experimento 1: realizado em Montpellier/França, onde foram estudadas quatro cultivares de macieira, com diferentes requerimentos em frio (‘Condessa’, ‘Granny Smith’, ‘Royal Gala’ e ‘Starkrimson’), submetidas a dois regimes térmicos (inverno frio, condições naturais de Montpellier; e inverno ameno, temperatura controlada em casa-de-vegetação). Experimento 2: realizado com a cultivar de baixo requerimento em frio ‘Eva’ sob regime térmico hibernal ameno (condição natural de Capão do leão/Brasil). A partir do experimento 1, dois artigos foram redigidos . Conclui-se a partir dos resultados obtidos (artigos 1 e 2) que as temperaturas hibernais têm o principal efeito na distribuição da ramificação ao longo do eixo principal e no tempo para brotação; a presença de folha das plantas submetidas ao regime térmico de inverno ameno não afeta a distribu ição de ramos prolépticos vegetativos; a cultivar exerce efeito no crescimento da ramificação. Com relação ao status hídrico, conclui-se que durante o inverno (período de dormência) as gemas laterais permanecem hidraulicamente isoladas do eixo principal; assim como o potencial de brotação está relacionado a um efeito ramo inteiro (todo eixo principal) do que ao potencial individual de cada gema lateral. Através do experimento 2, um artigo foi elaborado, tendo por objetivo testar a hipótese que a posição em que a gema lateral está localizada sobre o eixo principal têm efeito na brotação primaveril, no conteúdo de água e tamanho das mesmas. Pode-se concluir deste estudo que uma semana antes a brotação, as gemas localizadas na zona distal possuem maior potencial de crescimento (maior frequência de brotação e menor tempo médio para brotação), além de apresentarem maior umidade ponderal e tamanho. / The apple tree (Malus X domestica Borkh.) presents morphological and physiological anomalies when grown in mild winter climates with insufficient winter chilling to overcome winter dormancy. Symptoms are typically delayed and erratic budburst, entailing desynchronized flowering and fruitset and poor agronomic performances. This thesis aimed at gaining more insights on the following issues. Firstly, what are the effects of winter temperatures on axillary burdburst and bud outgrowth, and what are the respective effects of winter temperatures and cultivar?, and secondly, is there a link between the temperature-dependent budburst and bud water status? Works were done in France and Brazil. In France, experiments were carried out in controlled conditions on four apple cultivars characterized by either high chilling (‘Granny Smith’, ‘Royal Gala’, ‘Starkrimson’) or low chilling (‘Condessa’) requirements and were submitted to outdoor-cold and greenhouse-mild winter temperatures. We showed that the actual shoot architecture and budburst resulted from an ordered sequence of events with a pivotal role of winter temperatures on the dormancy completion of individual lateral buds. Endogenous factors related to the cultivar branching pattern overtook the temperature effect on the lateral bud outgrowth. Furthermore, the delayed senescence and subsequent leaf persistence during winter, characterizing the apple tree in the mild winter temperature conditions, had only a weak effect on the topological distribution of budburst and lateral outgrowth. The analyses of bud water status were done on distal buds only, characterized by high budburst frequency in cold winter conditions. We showed that, from endodormancy to the pre-budburst stage, xylem conductance at the stem-to-bud junction did not show consistent changes across cultivars and winter temperature treatments. Bud water potential had negative values, between -4.35 and -2.24 MPa, depending on cultivars and winter temperature treatments. Moreover, whatever the cultivar, there were no significant trends across dates for the effects of winter temperatures on bud water potential and relative water content without a consistent relationship with actual spring budburst frequency. These results suggested that lateral buds were hydraulically isolated from the parent stem during winter until a few days before budburst. The other set of experiments was carried out in Brazil, under mild winter conditions, on the low chilling apple cultivar ‘Eva’. The objectives were to gain more insights on the effect of the position of the over-wintering lateral bud along the whole-parent shoot on bud size and water content. Results highlighted that distal buds were larger and had a higher water content than proximal buds with a strong increase of water content a week before spring budburst. It was concluded that the acrotonic pattern of budburst was mainly established during ecodormancy. As a whole, we showed that spring budburst seemed more related to a whole-shoot effect than to the water status of the individual bud during winter dormancy. Our study substantiated the importance of the whole shoot as an integrated morphological and physiological unit in driving budburst and further growth.