Search

Winters and early springs are predicted to become warmer in temperate climates under continued global warming, which in turn is expected to promote earlier plant development. By contrast, there is no consensus about the changes in the occurrence and severity of late spring frosts. If the frequency and severity of late spring frosts remain unchanged in the future or change less than spring phenology of plants does, vulnerable plant organs (dehardened buds, young leaves, flowers or young fruits) may be more exposed to frost damage. Here we analyzed long-term temperature data from the period 1975–2016 in 50 locations in Switzerland and used different phenological models calibrated with long-term series of the flowering and leaf-out timing of two fruit trees (apple and cherry) and two forest trees (Norway spruce and European beech) to test whether the risk of frost damage has increased during this period. Overall, despite the substantial increase in temperature during the study period, the risk of frost damage was not reduced because spring phenology has advanced at a faster rate than the date of the last spring frost. In contrast, we found that the risk of frost exposure and subsequent potential damage has increased for all four species at the vast majority of stations located at elevations higher than 800 m while remaining unchanged at lower elevations. The different trends between lower and higher elevations are due to the date of the last spring frost moving less at higher altitudes than at lower altitudes, combined with stronger phenological shifts at higher elevations. This latter trend likely results from a stronger warming during late compared to earlier spring and from the increasing role of other limiting factors at lower elevations (chilling and photoperiod). Our results suggest that frost risk needs to be considered carefully when promoting the introduction of new varieties of fruit trees or exotic forest tree species adapted to warmer and drier climates or when considering new plantations at higher elevations.

The ability of portable Near Infrared Spectroscopy to determine apricot fruit quality has been studied. Calibration models allowing the determination of soluble solids content (SSC), total acidity (TA) and firmness (Fi) of apricots were carried out with variable precisions. Models were built for each variety and global models combining different varieties were attempted. SSC was determined with a root mean square error of cross-validation (RMSECV) comprised between 0.67 and 1.1 °Brix and R -values between 0.88 and 0.96. Concerning Fi, the accuracy of the prediction was variety dependant. These predictions were correct for the varieties Kioto and Harostar with RMSECV-values between 6.2% and 13% ( R -values between 0.85 and 0.92) and unsatisfactory for Bergarouge (RMSECV = 24%). TA was predicted with RMSECV-values between 0.79 and 2.61 g 100 ml −1 and R -values between 0.73 and 0.97. In a second application, near infrared spectra were used to classify apricot fruits according to their variety and colour intensity with correct efficiency. The results obtained in the present study showed that NIRS technology could be applicable to apricot quality and that such portable devices could help to obtain a complete follow-up of the fruits in orchards and during post-harvest.

Esca disease, as well as other trunk diseases of grapevine, is an important wood disease that impedes the water transport in plants by clogging the xylem vessels. This type of effect is not detectable for years, due to the long latency time of the disease. In a field experiment, the susceptibility of Vitis vinifera cv. Cabernet sauvignon and Merlot to esca disease was evaluated by visual assessment of foliar symptoms and by necrosis and white rot indexes. C. sauvignon was highly susceptible and Merlot was tolerant to esca. The characteristics of fast chlorophyll a fluorescence transient were investigated in attached leaves by using the so-called JIP-test. The fluorescence transient was analyzed and plants without visible esca foliar symptoms were compared with those showing symptoms. In C. sauvignon, alteration of the photosynthetic apparatus could be detected 2 months before the appearance of foliar symptoms in autumn. To our knowledge, this is the first report of early detection of esca disease using a nondestructive method. For Merlot, only one JIP-test parameter was affected. However, when both cultivars were compared, the relationship of the performance index (defined by the density of reaction centers (RCs) and by the yields φPo and ψo; PIABS = [RC/ABS][φPo/(1 − φPo)][ψo/(1 − ψo)]) versus the calculated rate of the electron transfer [probability that an absorbed photon moves an electron further than Q A − ; φEo = φPoψo = (TRo/ABS)(ETo/TRo) = ETo/ABS = (1 − F0/FM)(1 − VJ)] permitted us to separate the highest performing cultivar Merlot from the susceptible C. sauvignon. Also, the method used allowed us to detect modification of the photosystem II (PS II) performance in greenhouse-grown Riesling × Sylvaner after a drought stress. Finally, the comparison of the fluorescence transients of esca-affected and drought-stressed grapevines provided information on the differentiated functional-behavior patterns of PS II for the two stress types. These results suggest that esca infection cannot simply be interpreted as a water transport deficit through xylem dysfunction, but that other reaction mechanisms in the plants must be considered. The possibility to use fast chlorophyll a fluorescence monitoring as a wood decay early detection tool is discussed.