• Energy Research

Water use efficiency (WUE) is a quantitative measurement which improvement is a major issue in the context of global warming and restrictions in water availability for agriculture. In this study, we aimed at studying the variation and genetic control of WUE and the respective role of its components (plant biomass and transpiration) in a perennial fruit crop. We explored an INRA apple core collection grown in a phenotyping platform to screen one-year-old scions for their accumulated biomass, transpiration and WUE under optimal growing conditions. Plant biomass was decompose into morphological components related to either growth or organ expansion. For each trait, nine mixed models were evaluated to account for the genetic effect and spatial heterogeneity inside the platform. The Best Linear Unbiased Predictors of genetic values were estimated after model selection. Mean broad-sense heritabilities were calculated from variance estimates. Heritability values indicated that biomass (0.76) and WUE (0.73) were under genetic control. This genetic control was lower in plant transpiration with an heritability of 0.54. Across the collection, biomass accounted for 70% of the WUE variability. A Hierarchical Ascendant Classification of the core collection indicated the existence of six groups of genotypes with contrasting morphology and WUE. Differences between morphotypes were interpreted as resulting from differences in the main processes responsible for plant growth: cell division leading to the generation of new organs and cell elongation leading to organ dimension. Although further studies will be necessary on mature trees with more complex architecture and multiple sinks such as fruits, this study is a first step for improving apple plant material for the use of water.

ABSTRACT This study aimed to characterize the occurrence, duration, and intensity of the flushes of vegetative growth in two peach cultivars of Prunus persica L. Batsch, grown as a pioneer endeavor at a high-altitude tropical climate site in the State of Minas Gerais, Brazil. The observational experiment was carried out in 2017/18 and 2018/19 on the ‘Tropic Beauty’ and ‘BRS Kampai’ cultivars by an evaluation of the number and duration of flushes of vegetative growth during the year over two cycles. The number of fruit-bearing shoots, total number of leaves and shoot length were also assessed. At harvest, fruit load and diameter were determined and grouped into diameter ranges. The number of hours recorded at different temperature ranges, 25.1 °C, were summed separately and divided into daily and nightly periods. The peach tree has an unusual vegetative growth pattern when cultivated in a tropical area, which occurs in two flushes, with the first flush occurring from budbreak to fruit harvest between June and Sept, forming short shoots (less than 10 cm), with early shoot growth cessation, with a limited leaf number that can potentially diminish the supply of carbohydrates to the fruit, leading to smaller growth. The second flush occurs after harvest, between Oct and Dec, when there is an increase in daily temperature and precipitation, and no competition with fruits. Notabily, these second flush shoots grow with greater vigor and regularization of the growth cycle, forming fruit-bearing shoots with abundant leaf and flower buds for the next production cycle.

Fruit production should be adapted to future scenarios that are frequently associated with scarce resources, especially freshwater and fertilizers. New biologically-based fruit production strategies, i.e. taking into account tree growth and water status, are required to optimize irrigation and fertilization under abiotic stress conditions. It was hypothesized that a moderate abiotic stress, here deficit irrigation with or without nitrogen deficit, in the preharvest period, could decrease postharvest losses due to diseases and pruning weights due to reduced vegetative growth, without sacrificing the yield and fruit quality. This study was conducted over two years using the same trees of ‘Moncante’ nectarine cultivar grown in a commercial orchard. Trees were assigned to three treatments: (1) full irrigation at 80% estimated crop evapotranspiration (ETc), (2) deficit irrigation, i.e. at 75% of full irrigation, and (3) deficit irrigation and deficit nitrogen, i.e. at 75% of full irrigation and 75% of usual N-fertilization adopted by the grower in this commercial orchard. Deficit irrigation alone and in combination with deficit nitrogen reduced postharvest diseases and pruning weights without significant yield losses. Our results suggest that ETc-based approaches of reduced water irrigation may be a sustainable way to decrease phytosanitary inputs and workload in the orchard while maintaining the orchard performance.