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Tomato wild relatives are important sources of resistance to many pests of cultivated tomato [ Solanum lycopersicum L. (syn. Lycopersicon esculentum Mill.)]. Eleven wild tomato accessions previously identified at AVRDC-The World Vegetable Center as resistant to Bemisia tabaci were evaluated for resistance to the two-spotted spider mite [ Tetranychus urticae (Koch.)] based on egg numbers using the leaf disc and Tanglefoot no-choice bioassays, and damage scores in choice bioassays. Highest resistance based on choice and no-choice bioassays was identified in AVRDC S. galapagense accessions VI057400, VI045262, VI037869 and VI037239, and S. cheesmaniae accession VI037240, all of which are new sources of T. urticae resistance. In addition, S. pimpinellifolium accession VI030462 exhibited resistance only in the no-choice bioassay based on egg numbers. Resistance to T. urticae based on the number of eggs from the no-choice bioassays was positively correlated with density of type IV glandular trichomes and negatively correlated with densities of type V trichomes. All resistant accessions accumulated high levels of total acylsugars, which were positively associated with type IV trichomes. There was a significant negative relationship between acylsugar content and T. urticae egg numbers from the no-choice bioassays. There was high correlation between the results from the leaf disc test and the Tanglefoot no-choice bioassay. These findings support the possible presence of broad-based insect and mite resistance in accessions closely related to cultivated tomato. [ABSTRACT FROM AUTHOR]

Numerous agronomical applications of remote sensing have been proposed in recent years, including water stress assessment at field by thermal imagery. The miniaturization of thermal cameras allows carrying them onboard the unmanned aerial vehicles (UAVs), but these systems have no temperature control and, consequently, drifts during data acquisition have to be carefully corrected. This manuscript presents a comprehensive methodology for radiometric correction of UAV remotely-sensed thermal images to obtain (combined with visible and near-infrared data) multispectral ortho-mosaics, as a previous step for further image-based assessment of tree response to water stress. On summer 2013, UAV flights were performed over an apple tree orchard located in Southern France, and 4 dates and 5 h of the day were tested. The 6400 m field plot comprised 520 apple trees, half well-irrigated and half submitted to progressive summer water stress. Temperatures of four different on-ground stable reference targets were continuously measured by thermo-radiometers for radiometric calibration purposes. By using self-developed software, frames were automatically extracted from the thermal video files, and then radiometrically calibrated using the thermal targets data. Once ortho-mosaics were obtained, root mean squared error (RMSE) was calculated. The accuracy obtained allowed multi-temporal mosaic comparison. Results showed a good relationship between calibrated images and on-ground data. Significantly higher canopy temperatures were found in water-stressed trees compared to well-irrigated ones. As high resolution field ortho-mosaics were obtained, comparison between trees opens the possibility of using multispectral data as phenotypic variables for the characterization of individual plant response to drought. [ABSTRACT FROM AUTHOR]

Key message : In drought-stressed apple, leaf area decrease and stem growth cessation increase are key determinants of drought avoidance. Both the genotype and its possible phenotypic plasticity contribute to the variability of responses. Abstract: Under soil water restriction, plant growth is impaired by the indirect negative impact on plant carbon balance of stomata closure and hydraulic failure. The relative contributions of these two phenomena have been scarcely explored in trees under different drought-stress intensities, and even less work is published which accounts for genetic variability and phenotypic plasticity. Working on 21 apple genotypes from the same progeny, we assessed the effects of two consecutive periods of soil drought, moderate and severe, on growth and functional patterns of leaf and stem. Leaf area decreased while temporary stem growth cessation increased under drought with strong variations depending on the genotype. These results suggested that both reduction of transpiring leaf area and leaf organogenesis are key determinants for drought avoidance in the apple. Results also confirmed the pivotal role of stomatal conductance ( g ) in maintaining percent loss of conductivity of the stem xylem (PLC) under values for runaway embolism (ca. 14 % under severe drought). The sorting of genotypes according to their morphological response to drought showed that genotypes with high reduction of growth were characterized by similar g but lower PLC than genotypes with medium and low reduction of growth. This suggests that for a given level of stomatal closure the drought-related reduction of leaf area could also limit the progression of cavitation in stem xylem. As a whole, the variability of morphological responses of apple genotypes to contrasted drought conditions indicated that both genetic variability and phenotypic plasticity are involved in the range of iso-anisohydry documented for this species. [ABSTRACT FROM AUTHOR]

Key message: This study is an important contribution to understanding of the dormancy dynamics of apple buds grown in contrasting climates, highlighting the main factors possibly involved in their control and the key role of rehydration. 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. [ABSTRACT FROM AUTHOR]

Key message: In apple, the overwintering bud appears hydraulically isolated from the parent stem. Spring budburst seems more related to a whole-shoot effect than to the water status of the individual bud during winter dormancy. Abstract: The effects of winter temperatures, i.e., during dormancy, on shoot architecture are well known with budburst preferentially in the distal or the proximal part of the parent shoot in cold and mild winter conditions, respectively. However, the link with the overwintering bud water status is still scarcely documented. Our study was developed on four apple ( Malus domestica Borkh.) cultivars covering a range of chilling requirements from low ('Condessa') to medium ('Granny Smith') and high ('Royal Gala', 'Starkrimson'), and maintained in either cold (1,428 h below 7.2 °C) or mild (99 h below 7.2 °C) fluctuating winter temperatures. Our aim was to analyze xylem conductance at the stem-to-bud junction, and relative water content and water potential of the bud itself, for buds situated in the distal third of one-year-old shoots. From dormancy to the pre-budburst stage, xylem conductance at the stem-to-bud junction increased or decreased or did not show consistent changes depending on the cultivar and the winter temperature treatment. Whatever the cultivar, there were no significant trends across dates for the effects of winter temperatures on bud water potential and relative water content. Water potential had negative values, between −4.35 and −2.24 MPa, across cultivars and winter temperature treatments 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. We discussed that the temperature-related spring budburst was likely more related to a whole-shoot effect mediated by hormonal, hydraulics and/or sugar signaling, than to the individual bud water status during dormancy. [ABSTRACT FROM AUTHOR]

A correction to the article "Genetic variability and phenotypic plasticity of apple morphological responses to soil water restriction in relation with leaf functions and stem xylem conductivity" that was published in the 2016 issue is presented.