Heatwaves do not limit recovery following defoliation but alter leaf drought tolerance traits.

As heatwave frequency increases, they are more likely to coincide with other disturbances like insect defoliation. But it is unclear if high temperatures after defoliation impact canopy recovery or leaf traits which may affect response to further stressors like drought. To examine these stressor interactions, we subjected defoliated (DEF) and undefoliated (UNDEF) oak saplings to a simulated spring heatwave of +10°C for 25 days. We measured gas exchange, leaf area recovery, carbohydrate storage, turgor loss point (ΨTLP ), and minimum leaf conductance (gmin ). During the heatwave, stem respiration exhibited stronger thermal acclimation in DEF than UNDEF saplings, while stomatal conductance and net photosynthesis increased. The heatwave did not affect leaf area recovery or carbohydrate storage of DEF saplings, but reflush leaves had higher gmin than UNDEF leaves, and this was amplified by the heatwave. Across all treatments, higher gmin was associated with higher daytime stomatal conductance and a lower ΨTLP . The results suggest defoliation stress may not be exacerbated by higher temperatures. However, reflush leaves are less conservative in their water use, limiting their ability to minimise water loss. While lower ΨTLP could help DEF trees maintain gas exchange under mild drought, they may be more vulnerable to dehydration under severe drought.

Sucrose-Phosphate Synthase and Sucrose Synthase contribute to refoliation in ryegrass, a grassland fructan-accumulating species.

The perennity of grassland species such as Lolium perenne greatly depends on their ability to regrow after cutting or grazing. Refoliation largely relies on the mobilization of fructans in the remaining tissues and on the associated sucrose synthesis and transport towards the basal leaf meristems. However, nothing is known yet about the sucrose synthesis pathway. Sucrose Phosphate Synthase (SPS) and Sucrose Synthase (SuS) activities, together with their transcripts, were monitored during the first hours after defoliation along the leaf axis of mature leaf sheaths and elongating leaf bases (ELB) where the leaf meristems are located. In leaf sheaths, which undergo a sink-source transition, fructan and sucrose contents declined while SPS and SuS activities increased, along with the expression of LpSPSA, LpSPSD.2, LpSuS1, LpSuS2, and LpSuS4. In ELB, which continue to act as a strong carbon sink, SPS and SuS activities increased to varying degrees while the expression of all the LpSPS and LpSuS genes decreased after defoliation. SPS and SuS both contribute to refoliation but are regulated differently depending on the source or sink status of the tissues. Together with fructan metabolism, they represent key determinants of ryegrass perennity and, more generally, of grassland sustainability.

Integration of satellite remote sensing and MaxEnt modeling for improved detection and management of forest pests.

Forest pests pose a major threat to ecosystem services worldwide, requiring effective monitoring and management strategies. Recently, satellite remote sensing has emerged as a valuable tool to detect defoliation caused by these pests. Lymantria dispar, a major forest pest native to Japan, Siberia, and Europe, as well as introduced regions in North America, is of particular concern. In this study, we used Sentinel-2 satellite imagery to estimate the defoliation area and predict the distribution of L. dispar in Toyama Prefecture, central Japan. The primary aim was to understand the spatial distribution of L. dispar. The normalized difference vegetation index (NDVI) difference analysis estimated a defoliation area of 7.89 km2 in Toyama Prefecture for the year 2022. MaxEnt modeling, using defoliation map as occurrence data, identified the deciduous forests between approximately 35° and 50° at elevations of 400 m and 700 m as highly suitable for L. dispar. This predicted suitability was also high for larval locations but low for egg mass locations, likely due to differences in larval habitats and ovipositing sites. This study is the first attempt to utilize NDVI-based estimates as a proxy for MaxEnt. Our results showed higher prediction accuracy than a previous study based on the occurrence records including larvae, adults, and egg masses, indicating better discrimination of the distribution of L. dispar defoliation. Therefore, our approach to integrating satellite data and species distribution models can potentially enhance the assessment of areas affected by pests for effective forest management.

PhenoCaB: a new phenological model based on carbon balance in boreal conifers.

Traditional phenological models use chilling and thermal forcing (temperature sum or degree-days) to predict budbreak. Because of the heightening impact of climate and other related biotic or abiotic stressors, a model with greater biological support is needed to better predict budbreak. Here, we present an original mechanistic model based on the physiological processes taking place before and during budbreak of conifers. As a general principle, we assume that phenology is driven by the carbon status of the plant, which is closely related to environmental variables and the annual cycle of dormancy-activity. The carbon balance of a branch was modelled from autumn to winter with cold acclimation and dormancy and from winter to spring when deacclimation and growth resumption occur. After being calibrated in a field experiment, the model was validated across a large area (> 34 000 km2 ), covering multiple conifers stands in Québec (Canada) and across heated plots for the SPRUCE experiment in Minnesota (USA). The model accurately predicted the observed dates of budbreak in both Québec (±3.98 d) and Minnesota (±7.98 d). The site-independent calibration provides interesting insights on the physiological mechanisms underlying the dynamics of dormancy break and the resumption of vegetative growth in spring.

Topography modulates climate sensitivity of multidecadal trends of holm oak decline.

Forest decline events have increased worldwide over the last decades being holm oak (Quercus ilex L.) one of the tree species with the most worrying trends across Europe. Since this is one of the tree species with the southernmost distribution within the European continent, its vulnerability to climate change is a phenomenon of enormous ecological importance. Previous research identified drought and soil pathogens as the main causes behind holm oak decline. However, despite tree health loss is a multifactorial phenomenon where abiotic and biotic factors interact in time and space, there are some abiotic factors whose influence has been commonly overlooked. Here, we evaluate how land use (forests versus savannas), topography, and climate extremes jointly determine the spatiotemporal patterns of holm oak defoliation trends over almost three decades (1987-2014) in Spain, where holm oak represents the 25% of the national forested area. We found an increasing defoliation trend in 119 out of the total 134 holm oak plots evaluated, being this defoliation trend significantly higher in forests compared with savannas. Moreover, we have detected that the interaction between topography (which covariates with the land use) and summer precipitation anomalies explains trends of holm oak decline across the Mediterranean region. While a higher occurrence of dry summers increases defoliation trends in steeper terrains where forests dominate, an inverse relationship was found in flatter terrains where savannas are mainly located. These opposite relationships suggest different causal mechanisms behind decline. Whereas hydric stress is likely to occur in steeper terrains where soil water holding capacity is limited, soil waterlogging usually occurs in flatter terrains what increases tree vulnerability to soil pathogens. Our results contribute to the growing evidence of the influence of local topography on forest resilience and could assist in the identification of potential tree decline hotspots and its main causes over the Mediterranean region.

Trait-mediated responses of caterpillar communities to spongy moth outbreaks and subsequent tebufenozide treatments.

Outbreaks of the spongy moth Lymantria dispar can have devastating impacts on forest resources and ecosystems. Lepidoptera-specific insecticides, such as Bacillus thuringiensis var. kurstaki (BTK) and tebufenozide, are often deployed to prevent heavy defoliation of the forest canopy. While it has been suggested that using BTK poses less risk to non-target Lepidoptera than leaving an outbreak untreated, in situ testing of this assumption has been impeded by methodological challenges. The trade-offs between insecticide use and outbreaks have yet to be addressed for tebufenozide, which is believed to have stronger side effects than BTK. We investigated the short-term trade-offs between tebufenozide treatments and no-action strategies for the non-target herbivore community in forest canopies. Over 3 years, Lepidoptera and Symphyta larvae were sampled by canopy fogging in 48 oak stands in southeast Germany during and after a spongy moth outbreak. Half of the sites were treated with tebufenozide and changes in canopy cover were monitored. We contrasted the impacts of tebufenozide and defoliator outbreaks on the abundance, diversity, and functional structure of chewing herbivore communities. Tebufenozide treatments strongly reduced Lepidoptera up to 6 weeks after spraying. Populations gradually converged back to control levels after 2 years. Shelter-building species dominated caterpillar assemblages in treated plots in the post-spray weeks, while flight-dimorphic species were slow to recover and remained underrepresented in treated stands 2 years post-treatment. Spongy moth outbreaks had minor effects on leaf chewer communities. Summer Lepidoptera decreased only when severe defoliation occurred, whereas Symphyta declined 1 year after defoliation. Polyphagous species with only partial host plant overlap with the spongy moth were absent from heavily defoliated sites, suggesting greater sensitivity of generalists to defoliation-induced plant responses. These results demonstrate that both tebufenozide treatments and spongy moth outbreaks alter canopy herbivore communities. Tebufenozide had a stronger and longer lasting impact, but it was restricted to Lepidoptera, whereas the outbreak affected both Lepidoptera and Symphyta. These results are tied to the fact that only half of the outbreak sites experienced severe defoliation. This highlights the limited accuracy of current defoliation forecast methods, which are used as the basis for the decision to spray insecticides.

Elevated heat indices resulting from hurricane-related defoliation: a case study.

Defoliation caused by strong tropical cyclones can modify the partitioning of incident solar radiation between the sensible, latent, and substrate heat fluxes. While previous work has shown hurricane defoliation to warm near-surface air temperature along its track, this study more directly contextualizes the warming to human heat stress and exposure via the heat index (HI). For this case study, the spatial extent and temporal persistence of defoliation produced by Hurricane Laura (2020) in southwestern Louisiana was characterized using the normalized difference vegetation index (NDVI). The defoliated land surface was then assimilated into the Weather Research and Forecasting (WRF) model version 4.2 and compared to a control, normal-foliage simulation for the 30 days following landfall. Over southwest Louisiana, the largest HI increase occurred at 0600 UTC (1:00 AM LT) with an average increase of + 0.25 °C, and the exposure time to HI ≥ 30 °C increased by 8.1% after accounting for the defoliated landscape. Meanwhile, Cameron, Louisiana, the site of Laura's landfall where defoliation was most severe, cumulatively experienced an extra 33 h of HI values exceeding 26 °C, while mean HI increased by 1.2 °C at 0300 UTC. Additional WRF experiments were performed with altered "landfall" years of 2017 and 2018 to determine the sensitivity of defoliation-driven HI changes to the ambient synoptic conditions. While synoptic conditions modulated the magnitude of increase, HIs nonetheless experienced statistically significant increases in both hypothetical "landfall" years. Such findings are valuable for emergency managers and community health officials because overnight minimum temperatures are a strong indicator of heat mortality.

Effects of Temperature and Wetness on Components of the Infection Cycle of Valdensia heterodoxa in Lowbush Blueberry.

Valdensia leaf spot, caused by Valdensia heterodoxa, is a serious disease of lowbush blueberry. The disease may develop rapidly, resulting in extensive defoliation of fields. The purpose of this study was to examine the effects of temperature and wetness duration on various components of the infection cycle to gain a better understanding of epidemic development that might lead to improved management practices. Lesions on leaves appeared 6 h after inoculation at 20°C and were larger on young 3-week-old leaves compared with 8-week-old leaves. Incidence of infection on 3-week-old leaves was lowest at 5°C, highest at 15 and 20°C, and failed to occur at 30°C. Defoliation began 48 h after inoculation at 20 and 25°C but was slower at higher and lower temperatures. Conidia production and release from colonized leaves began 48 h after inoculation at 15 and 19°C. Total conidia production was lowest at 7°C, highest at 15°C, and progressively declined at 19 and 23°C. Production of conidia lasted 2 to 3 days. Sclerotia formed mainly along the midveins and were similar in size at 5 to 15°C, largest at 20°C, and smallest at 25°C. Conidia formed directly on sclerotia that were overwintered outdoors and then incubated on moist filter paper. Conidia production began after 48 h at 10, 15, and 20°C. Total production was lowest at 5°C, highest at 20°C, failed to occur at 25°C, and ceased after 10 days at all temperatures. These data show that at optimal temperatures, relatively short wet periods are required for conidia production on overwintered sclerotia, infection of leaves, and subsequent conidia production on diseased leaves that may account for the sudden and rapid spread of disease in fields. The data will be useful for helping growers identify weather conditions favorable for disease development.

First Report of Alternaria alternata Causing Leaf Spot Diseases of Cotton in Türkiye.

Cotton (Gossypium hirsutum L.) is a crucial crop for the textile industry. Sanliurfa is the major cotton production area in southeast Türkiye (USDA 2021). In the summers of 2021 and 2022, the mid to late season desiccation of leaves, stems and bolls as well as severe defoliation were observed in different cotton fields and cultivars in a 30-ha area centered around 36°51'15.7"N, 39°07'12.2"E. Approximately 45% of the plants were severely affected or completely desiccated. Initially, symptoms were circular, pinhead, necrotic lesions surrounded by a purple halo, scattered all around the infected leaves. As the disease progressed, it spread to bracts, petioles, stem and bolls. The necrotic lesions continued to expand, and formed irregular shapes by coalescing, occupied the whole tissue . Finally, severe infection resulted in premature defoliation. A secondary host (Prosopis farcta) of the inoculum of A. alternata is found in the field where the symptoms of pathogen was seen. The disease symptoms were similar to those described in cotton by Macauley (1982). Infected leaf samples with mycelia were collected (n=35) from 25 diseased plants. The samples derived from lesions on infected leaves were cut into 4- to 5- mm pieces, treated in 2% sodium hypochlorite, dipped in water, plated on potato dextrose agar (PDA) amended with 30 mg/L of streptomycin sulphate, and kept at 27°C in the dark. All the isolated fungal samples formed dark olive-green colonies. For morphological characterization, the colonies were examined under light microscopy at ×400 magnification. Conidia formed both cross or longitudinal septa, and were obclavate to elliptical and measured 16.2 to 30.5 µm long and 7.5 to 10.6 µm wide (n=14). The morphological characters were consistent with the genus Alternaria using a taxonomic key (Barnett and Hunter 1972). For pathogenicity test, healthy cotton plants were grown at 15 to 29°C in greenhouse. Conidial suspension (10 6 per mL) was sprayed on 30-d old plants (n=16) while control plants were sprayed with water. Then, the plants were covered with plastic bags (28x45 cm) at nights, opened in the morning. The disease symptoms were seen 20 days after artificial inoculation. However, the control group showed no symptoms. The pathogen was re-isolated from infected leaves. To confirm the result, the pathogenicity test was conducted twice. Then, DNA was extracted from conidia and mycelia using CTAB method with slight modification (Doyle and Doyle 1990). The nuclear rDNA internal transcribed spacer (ITS) and plasma membrane ATPase regions were (Lawrence et al. 2014; White et al. 1990) amplified, using primers ITS4/ITS5 and ATPDF1/ATPDR1, respectively. The PCR products were Sanger-sequenced and were uploaded to GenBank (accession nos. ITS: OP615138.1, ATPase: OP612816.1). The sequenced parts of the genes were 554 bp and 1025 bp, and showed 100% (ITS) and 97.99% (ATPase) nucleotide identity with the corresponding sequences (MT446176.1, ON442363.1) of the reference strains of A. alternata. To the best of our knowledge, this is the first report of A. alternata causing leaf blight of cotton in Türkiye. In several cotton-growing regions, A. alternata leaf spot epidemics have caused yield loss from 25% (Israel) to 37% (India) (Padaganur et al. 1989; Rotem et al. 1988). Although yield loss caused by the pathogen depends on environmental conditions, observations in Türkiye cotton fields suggest A. alternata has the potential to cause yield loss up to 30% under severe infection.

Feeding potential of adult Systena frontalis (Coleoptera: Chrysomelidae) on leaves of Hydrangea paniculata (Cornales: Hydrangeaceae).

Systena frontalis (F.) (Coleoptera: Chrysomelidae), also known as the red-headed flea beetle, is a defoliating pest of a variety of crop systems, such as ornamentals and food crops. Leaf consumption by this beetle renders ornamental nursery plants, such as hydrangeas (Hydrangea paniculata Siebold, Hydrangeaceae), unsaleable. In Virginia, this insect has become a major pest at commercial nurseries, and their feeding potential on affected crops has not been quantified. In this study, the extent of their damage to individual leaves and host preference between leaf ages were determined. The rate of defoliation on mature and young hydrangea leaves was measured over 24 and 48 h and between different numbers of adults. A single adult caused up to 10% damage to a young leaf or 5% to a whole mature leaf in 24 h. Without choice, there was a higher percent damage to young leaves. When the size of leaves was controlled by cut-out mature leaves, the area damaged was still higher in young leaves when compared with mature leaves. Adult feeding between mature or young leaves was further investigated by choice assays on a caged plant and within a containerized system. In these choice assays, adults inflicted higher percent damage on mature leaves in both caged plant assays and containerized direct choice assays. The choice assays were more similar to field conditions than the nonchoice assays. This demonstrates that S. frontalis showed a preference for mature leaves over young leaves within hydrangeas.

AI-Driven Validation of Digital Agriculture Models.

Digital agriculture employs artificial intelligence (AI) to transform data collected in the field into actionable crop management. Effective digital agriculture models can detect problems early, reducing costs significantly. However, ineffective models can be counterproductive. Farmers often want to validate models by spot checking their fields before expending time and effort on recommended actions. However, in large fields, farmers can spot check too few areas, leading them to wrongly believe that ineffective models are effective. Model validation is especially difficult for models that use neural networks, an AI technology that normally assesses crops health accurately but makes inexplicable recommendations. We present a new approach that trains random forests, an AI modeling approach whose recommendations are easier to explain, to mimic neural network models. Then, using the random forest as an explainable white box, we can (1) gain knowledge about the neural network, (2) assess how well a test set represents possible inputs in a given field, (3) determine when and where a farmer should spot check their field for model validation, and (4) find input data that improve the test set. We tested our approach with data used to assess soybean defoliation. Using information from the four processes above, our approach can reduce spot checks by up to 94%.

Holm oak decline is determined by shifts in fine root phenotypic plasticity in response to belowground stress.

Climate change and pathogen outbreaks are the two major causes of decline in Mediterranean holm oak trees (Quercus ilex L. subsp. ballota (Desf.) Samp.). Crown-level changes in response to these stressful conditions have been widely documented but the responses of the root systems remain unexplored. The effects of environmental stress over roots and its potential role during the declining process need to be evaluated. We aimed to study how key morphological and architectural root parameters and nonstructural carbohydrates of roots are affected along a holm oak health gradient (i.e. within healthy, susceptible and declining trees). Holm oaks with different health statuses had different soil resource-uptake strategies. While healthy and susceptible trees showed a conservative resource-uptake strategy independently of soil nutrient availability, declining trees optimized soil resource acquisition by increasing the phenotypic plasticity of their fine root system. This increase in fine root phenotypic plasticity in declining holm oaks represents an energy-consuming strategy promoted to cope with the stress and at the expense of foliage maintenance. Our study describes a potential feedback loop resulting from strong unprecedented belowground stress that ultimately may lead to poor adaptation and tree death in the Spanish dehesa.

Locations of seed abortion in response to defoliation differ with pollen source in a native perennial legume herb.

PREMISE: In many flowering plants, flowers contain more ovules than fruits have seeds. What determines which ovules become seeds? When photosynthates are limited, as may happen when plants lose leaf area to herbivory, fewer fertilized ovules become seeds. METHODS: Greenhouse-grown ramets of distinct individuals of a perennial herbaceous legume were manually defoliated to various levels determined in the field, then self- or cross-pollinated. For each seed produced, we recorded its position in the fruit and its mass. From a subset of seeds from different treatments and positions in the fruits, we grew seedlings and measured their dry mass. RESULTS: Ovules were aborted more frequently in fruits from flowers that were self-pollinated and from those on plants with higher levels of defoliation. Ovules in the basal portion of the fruits were more likely to be aborted than those at the stigmatic end; this pattern was most pronounced for fruits after self-pollination with high levels of defoliation. Total number of seeds produced and seed mass per pod were greatest in cross-pollinated fruits after no or low levels of defoliation. Mean individual seed mass was greater for fruits with fewer seeds, indicating a trade-off between seed number and seed mass. Seedling dry mass (a measure of vigor) was greatest for seeds in the middle positions of fruit produced by cross-pollination after severe herbivory; no positional differences were seen for seeds from self-pollinated fruits. CONCLUSIONS: Observed locations of seed abortion may have been selected not only by defoliation, but in part by propensity for dispersal, while positional differences in seedling vigor may be related to seed size and differential maternal allocation based on pollination treatment and leaf area lost.

First report of Coniella granati causing leaf spot of pomegranate (Punica granatum L.) in Hungary.

Pomegranate (Punica granatum L.), the hystoric fruit and ornamental crop native to Iran and North India is widely planted in the Mediterranean and became popular in the house gardens of northest parts of Europe (Fernandez et al. 2014) including Hungary. In August 2020 necrotic black lesions and serious defoliation were observed on 60% of 1-3 year old pomegranate trees (cv. Wonderful) in a horticultural nursery near Gödöllo, Hungary (47°36'00.9"N 19°21'26.5"E). Symptoms started as small irregular dark brown spots on the leaves, which later increased in size (2.6 ± 0.9 mm). Ultimately, the entire leaf turned yellow, defoliation resulted in damage on (6) - 8 - (15)% of the leaves. Then, black pycnidia with unicelled, elliptical to fusiform, colourless conidia (Avg. 50 conidia: 2.4 - (3.6) - 3.9 × 10.2 - (13,1) - 17.9 µm) developed on the surface. These morphological features matched those described earlier by Van Niekerk et al. (2004) and Alvarez et al. (2016) for C. granati. Conidia from pycnidia were directly transferred to potato dextrose agar (PDA) by sterile needle. The plates were incubated at 24°C in the dark. Light yellow colonies with whitish aerial mycelia and later black globose pycnidia were observed. Mass of conidia oozed from pycnidia after 15 days of incubation. Pathogenicity tests were carried out on 1-year-old potted P. granatum trees (cv. Wonderful) with 5 replicates in the greenhouse. Ten, randomly selected leaves were inoculated per plant. 7-mm mycelial plugs from the edge of 10-day-old colonies were placed directly on disinfested (2% NaOCl solution, than sterile distilled water) leaves. The plants were covered with plastic film for 3 days after inoculation (26±3°C and 87±3% relative humidity). Pathogenicity was also tested on nonwounded, surface-disinfested fruits by mycelial plugs in 3 × 3 replicates. Inoculated fruits were placed in large grass vessels for 15 days (24±2°C and 80±5% relative humidity). Uncolonized, sterile PDA plugs were used as controls in both cases. Dark brown legions developed after 9-12 days on the plants in the greenhouse. On pomegranate fruits, the fungus colonized the fruit after 7-8 days, followed by fruit rot. In some cases, after 2 weeks pycnidia developed on the skin surface. No decay were present on control leaves or fruits. The pathogen was reisolated from all infected tissues and identified as C. granati, thus fulfilling Koch's postulates. For molecular identification, total genomic DNA of the isolate was extracted from the growing margins of colonies on PDA and partial sequence of internal transcribed spacer (ITS) and translation elongation factor 1-alpha (tef1) were amplified by PCR using primers described by Alvarez et al. (2016). Sequence data of the Hungarian isolate of the ITS region (GenBank acc. no. MW581953) showed 99.8% identity (559 bp out of 560 bp) with C. granati sequences deposited in GeneBank (Acc. nos. MH860368, MH855389 and KX833582). Considering tef1 sequence of the Hungarian isolate (OM908764) obtained had complete identity with other published C. granati isolates (KX833676, KX833682). C. granati has been previously reported on pomegranate from Europe (Palou et al. 2010, Pollastro et al. 2016). Based on morphological and molecular studies, this is the first record of C. granati in Hungary. The economic importance of this disease in currently limited in Hungary due to pomegranate is rather an ornamental crop, however, the first cultivation trials have been already started. There is a risk that the spread of the pathogen began with the infected propagating material, as a result the disease may outbreak anywhere in the country.

Effect of RH, Temperature, Light, and Plant Age on Infection of Lowbush Blueberry by Sphaerulina vaccinii.

Leaf spot and stem canker caused by Sphaerulina vaccinii is associated with premature defoliation in lowbush blueberry resulting in reduced yields. In this study, we investigated the impact of free water, RH, temperature, light, and plant age on leaf infection under controlled conditions. On potato dextrose agar, germination of conidia was usually polar. Growth was minimal at 5 and 10°C, increased at 15 and 20°C, was maximal at 25°C and decreased at 30°C. Percentage of germinated conidia on inoculated blueberry leaves incubated in dark controlled-humidity chambers for 3 days (25°C) was 86.0, 90.5, 81.3, and 28.3 in free water, 100, 97.5 or 95% RH, respectively. Germination did not occur at 90 or 85% RH. Infection of inoculated plants, however, was not favored by free water, but rather by high RH (>95%) and a 14-h photoperiod (180 µmol/m2 per second). Infection failed in continuous darkness, continuous light, or continuous darkness followed by 4, 8, or 12 h of light. Light and scanning electron microscopy showed that hyphal penetration into stomata on abaxial leaf surfaces was strongly tropic. When germ tubes grew in close proximity to a stomate, a penetration hypha formed at ∼90° angles to the germ tube and took the closest path to the stomate. Stomatal penetration was usually direct, but occasionally appressorium-like hyphal swellings formed over stomatal openings. When inoculated plants were exposed to high RH (>95%) at various temperatures, infection occurred after 4 days at 10°C, after 3 days at 15°C and after 1 day at 20 and 25°C. Infection failed to occur at 30°C. Disease severity also increased with duration of the humid period. When leaves were examined microscopically, those that had been incubated for 6 days showed a substantially greater network of epiphytic growth with more stomatal penetrations compared with those incubated for 3 days. Infection was substantially reduced when the humid period was interrupted by alternating days of low RH (60%). Two-week-old leaves were 2.7 times more susceptible than 8-week-old leaves.

Effects of Defoliation Treatments of Babica Grape Variety(Vitis vinifera L.) on Volatile Compounds Content in Wine.

The aim of this study was to determine the effects of defoliation performed in the Babica red grape variety on the volatile compounds in produced wine. Three treatments were performed during 2017 and 2018: the removal of six leaves before flowering (FL) and at the end of veraison (VER), as well as control (C). Volatile compounds were analyzed using a gas chromatograph coupled to a mass spectrophotometric detector. Results were statistically evaluated by analysis of variance (ANOVA at the p = 0.05 level) and principal component analysis (PCA). Defoliation treatments were affected by the concentration of several compounds, but only in one year. The VER2017 treatment significantly increased the concentration of three aliphatic esters up to 8 C atoms and octanoic acid ethyl ester. The FL2017 treatment increased the concentration of three aliphatic alcohols. The FL2018 treatment has significantly enhanced the concentration ethyl cinnamate but decreased the concentrations of eugenol and dihydro-2-methyl-3(2H)-thiophenone. Both defoliation treatments reduced the concentration of γ-decanolactone in 2017. Aldehydes, monoterpenoles, and monoterpenes remained unaffected by the defoliation treatments. Vintage was found to be the largest source of variability for most volatile compounds under investigation, which was confirmed by PCA. The effect of defoliation in the mild-Mediterranean climate was found to mostly depend on seasonal weather conditions.

Crown defoliation decreases reproduction and wood growth in a marginal European beech population.

BACKGROUND AND AIMS: Abiotic and biotic stresses related to climate change have been associated with increased crown defoliation, decreased growth and a higher risk of mortality in many forest tree species, but the impact of stresses on tree reproduction and forest regeneration remains understudied. At the dry, warm margin of species distributions, flowering, pollination and seed maturation are expected to be affected by drought, late frost and other stresses, eventually resulting in reproduction failure. Moreover, inter-individual variation in reproductive performance versus other performance traits (growth, survival) could have important consequences for population dynamics. This study investigated the relationships among individual crown defoliation, growth and reproduction in a drought-prone population of European beech, Fagus sylvatica. METHODS: We used a spatially explicit mating model and marker-based parentage analyses to estimate effective female and male fecundities of 432 reproductive trees, which were also monitored for basal area increment and crown defoliation over 9 years. KEY RESULTS: Female and male fecundities varied markedly between individuals, more than did growth. Both female fecundity and growth decreased with increasing crown defoliation and competition, and increased with size. Moreover, the negative effect of defoliation on female fecundity was size-dependent, with a slower decline in female fecundity with increasing defoliation for the large individuals. Finally, a trade-off between growth and female fecundity was observed in response to defoliation: some large trees maintained significant female fecundity at the expense of reduced growth in response to defoliation, while some other defoliated trees maintained high growth at the expense of reduced female fecundity. CONCLUSIONS: Our results suggest that, while decreasing their growth, some large defoliated trees still contribute to reproduction through seed production and pollination. This non-coordinated decline of growth and fecundity at individual level in response to stress may compromise the evolution of stress-resistance traits at population level, and increase forest tree vulnerability.

Satellite data and machine learning reveal the incidence of late frost defoliations on Iberian beech forests.

Climate warming is driving an advance of leaf unfolding date in temperate deciduous forests, promoting longer growing seasons and higher carbon gains. However, an earlier leaf phenology also increases the risk of late frost defoliation (LFD) events. Compiling the spatiotemporal patterns of defoliations caused by spring frost events is critical to unveil whether the balance between the current advance in leaf unfolding dates and the frequency of LFD occurrence is changing and represents a threaten for the future viability and persistence of deciduous forests. We combined satellite imagery with machine learning techniques to reconstruct the spatiotemporal patterns of LFD events for the 2003-2018 period in the Iberian range of European beech (Fagus sylvatica), at the drier distribution edge of the species. We used MODIS Vegetation Index Products to generate a Normalized Difference Vegetation Index (NDVI) time series for each 250 × 250 m pixel in a total area of 1,013 km2 (16,218 pixels). A semi-supervised approach was used to train a machine learning model, in which a binary classifier called Support Vector Machine with Global Alignment Kernel was used to differentiate between late frost and non-late frost pixels. We verified the obtained estimates with photointerpretation and existing beech tree-ring chronologies to iteratively improve the model. Then, we used the model output to identify topographical and climatic factors that determined the spatial incidence of LFD. During the study period, LFD was a low recurrence phenomenon that occurred every 15.2 yr on average and showed high spatiotemporal heterogeneity. Most LFD events were condensed in 5 yr and clustered in western forests (86.5% in one-fifth of the pixels) located at high elevation with lower than average precipitation. Elevation and longitude were the major LFD risk factors, followed by annual precipitation. The synergistic effects of increasing drought intensity and rising temperature combined with more frequent late frost events may determine the future performance and distribution of beech forests. This interaction might be critical at the beech drier range edge, where the concentration of LFD at high elevations could constrain beech altitudinal shifts and/or favor species with higher resistance to late frosts.

The functional roles of psyllid abundance and assemblage on bird-associated forest defoliation.

Fluctuations in the abundance of insect herbivores and the severity of damage they cause to their hosts are key factors affecting tree health and trophic interactions. Bell miner associated dieback (BMAD) is a trophic cascade involving eucalypt trees, psyllids and bell miners. Bell miners are a territorial species of bird that reduce insectivorous bird diversity, thereby increasing psyllid abundances. The role of psyllids in BMAD is debated, primarily because psyllid host specificity, genus, defoliation potential and/or lerp composition have been conflated or unexplored. This study documented psyllid communities and canopy structure of four eucalypt hosts (Eucalyptus bridgesiana, E. caliginosa, E. propinqua and E. siderophloia) in BMAD and non-BMAD-affected forests in northern New South Wales. Psyllid abundances were significantly higher in BMAD-affected forests. However, psyllid assemblages did not differ between forest types which contrasts with an influential hypothesis concerning bell miner farming of psyllids that produce sugary lerps (Glycaspis species). Importantly, psyllid communities differed among species of eucalypt host. Hosts supporting higher abundances of Cardiaspina tended to have a stronger negative relationship between canopy health and psyllid abundances than other host trees. Cardiaspina were also found on older leaves and associated with more leaf damage than other psyllids. Unlike most other psyllid genera, Cardiaspina initiate premature foliar senescence leading to defoliation which ultimately changes the age structure of leaves of the canopies of affected trees. Our study supports the functional linkage between psyllid assemblages, their relative abundances and defoliation potential to bottom-up mechanisms behind a bird-associated trophic cascade.

Root Secondary Metabolites in Populus tremuloides: Effects of Simulated Climate Warming, Defoliation, and Genotype.

Climate warming can influence interactions between plants and associated organisms by altering levels of plant secondary metabolites. In contrast to studies of elevated temperature on aboveground phytochemistry, the consequences of warming on root chemistry have received little attention. Herein, we investigated the effects of elevated temperature, defoliation, and genotype on root biomass and phenolic compounds in trembling aspen (Populus tremuloides). We grew saplings of three aspen genotypes under ambient or elevated temperatures (+4-6 °C), and defoliated (by 75%) half of the trees in each treatment. After 4 months, we harvested roots and determined their condensed tannin and salicinoid (phenolic glycoside) concentrations. Defoliation reduced root biomass, with a slightly larger impact under elevated, relative to ambient, temperature. Elevated temperature decreased condensed tannin concentrations by 21-43% across the various treatment combinations. Warming alone did not alter salicinoid concentrations but eliminated a small negative impact of defoliation on those compounds. Graphical vector analysis suggests that effects of warming and defoliation on condensed tannins and salicinoids were predominantly due to reduced biosynthesis of these metabolites in roots, rather than to changes in root biomass. In general, genotypes did not differ in their responses to temperature or temperature by defoliation interactions. Collectively, our results suggest that future climate warming will alter root phytochemistry, and that effects will vary among different classes of secondary metabolites and be influenced by concurrent ecological interactions such as herbivory. Temperature- and herbivory-mediated changes in root chemistry have the potential to influence belowground trophic interactions and soil nutrient dynamics.