No abstract

The aim of this study was to compare the dormancy dynamics and the physiological status of vegetative and floral buds of apple cultivars grown during cold and mild winters. Long shoots bearing vegetative buds and short shoots bearing floral buds were regularly collected during two successive cycles at Marsillargues, France (2011/12, 2012/13) and Palmas, Paraná, Brazil (2012, 2013). The dormant state in vegetative buds was evaluated by the single-node cutting test and in floral buds by the Tabuenca’s test. The first approach highlighted important differences in the dormancy dynamics in both sites, clearly showing that: (1) the entry and the maximum level of dormancy are strongly correlated with cold winter temperatures; (2) the three classical phases of dormancy dynamics are difficult to differentiate under a mild winter climate; and (3) endodormancy, if it actually exists, is very weak and lasts only for a short time. Distinct temporal changes between both sites were found for flower primordia fresh and dry weight. The ecodormant state was linked to significant changes in dry weight and the capacity to quickly reach a water content of around 77 % according to the Tabuenca’s test. High temperatures in Brazil allowed a quick transition between endodormancy and ecodormancy compared to France where the rehydration period was long. The weak endodormancy associated with a quasi-absence of ecodormancy could explain the strong spatio-temporal heterogeneity of budburst and flowering under a mild winter climate. This may be useful for understanding the future phenology of trees under global warming conditions and for the selection of adapted cultivars

The responses of flowering phenology to temperature increases in temperate fruit trees have rarely been investigated in contrasting climatic regions. This is an appropriate framework for highlighting varying responses to diverse warming contexts, which would potentially combine chill accumulation (CA) declines and heat accumulation (HA) increases. To examine this issue, a data set was constituted in apple tree from flowering dates collected for two phenological stages of three cultivars in seven climate-contrasting temperate regions of Western Europe and in three mild regions, one in Northern Morocco and two in Southern Brazil. Multiple change-point models were applied to flowering date series, as well as to corresponding series of mean temperature during two successive periods, respectively determining for the fulfillment of chill and heat requirements. A new overview in space and time of flowering date changes was provided in apple tree highlighting not only flowering date advances as in previous studies but also stationary flowering date series. At global scale, differentiated flowering time patterns result from varying interactions between contrasting thermal determinisms of flowering dates and contrasting warming contexts. This may explain flowering date advances in most of European regions and in Morocco vs. stationary flowering date series in the Brazilian regions. A notable exception in Europe was found in the French Mediterranean region where the flowering date series was stationary. While the flowering duration series were stationary whatever the region, the flowering durations were far longer in mild regions compared to temperate regions. Our findings suggest a new warming vulnerability in temperate Mediterranean regions, which could shift toward responding more to chill decline and consequently experience late and extended flowering under future warming scenarios.

Few studies have focused on the characterization of bud dormancy and growth dynamics for temperate fruit species in temperate and mild cropping areas, although this is an appropriate framework to anticipate phenology adaptation facing future warming contexts which would potentially combine chill declines and heat increases. To examine this issue, two experimental approaches and field observations were used for high- and low-chill apple cultivars in temperate climate of southern France and in mild climates of northern Morocco and southern Brazil. Low-chill almond cultivars offered an additional relevant plant material for comparison with apple in northern Morocco. Divergent patterns of dormancy and growth dynamics were clearly found in apple tree between southern France and southern Brazil. Divergences were less pronounced between France and Morocco. A global view outlined main differences in the dormancy chronology and intensity, the transition between endordormancy and ecodormancy and the duration of ecodormancy. A key role of bud rehydration in the transition period was shown. High-chill cultivars would be submitted in mild conditions to heterogeneous rehydration capacities linked to insufficient chill fulfillment and excessive forcing linked to high temperatures. This would favor bud competitions and consequently excessive flowering durations and weak flowering. Low chilling requirements in apple and almond would conversely confer biological capacities to tolerate superficial dormancy and abrupt transition from endordormancy to ecodormancy without important heterogeneous rehydration states within buds. It may also assume that low-chill cultivars can also tolerate high temperatures during ecodormancy as well as extended flowering durations.

Escala diagramática para avaliação de severidade da helmintosporiose comum em milho.Ciência Rural, v.42, n.12, dez, 2012. Ciência Rural, Santa Maria, v.42, n.12, p.2131-2137, dez, 2012 ISSN 0103-8478 0,5; 1,0; 2,5; 6,5; 15,5; 30,0; 54,0%. A validação 0,5; 1,0; 2,5; 6,5; 15,5; 30,0 and 54 Adriana