Severe Defoliation Research Articles

Leafy season length is reduced by a prolonged soil water deficit but not by repeated defoliation in beech trees (Fagus sylvatica L.): comparison of response among regional populations grown in a common garden

Bud-burst and leaf-senescence determine the length of the growing season for deciduous trees and therefore the duration of potential carbon assimilation with consequences on biomass production. In Fagus sylvatica L., leaf phenology depends on both photoperiod and temperature. The future climate is expected to induce more frequent soil water deficits and biotic attacks (possibly resulting in severe defoliation). The aim of the study is to assess whether these constrains may alter leaf phenology. In a common garden, we sowed seeds collected from six beech forests along a small latitudinal gradient (140 km) in North-Eastern France. In 2014, after seven years growth, a rain exclusion was installed above the trees to test how recurrent soil water deficits impacted bud-burst (BB) and leaf-yellowing (LY) over three years. We also analyzed the response of leaf phenology to annual defoliation, aiming at affecting carbon and nitrogen availability in trees. Delayed BB and early LY were observed, reducing the growing season (GS) until 14 days in response to soil water deficit whereas no influence of defoliation was detected. These time lags were not in relation with leaf nitrogen content. In the control treatment, BB occurred earlier and LY later in the northernmost populations than in the southernmost without clear relationships with local climate. A significant treatment x population interaction was observed revealing a plasticity in the leaf phenology response to soil water deficit among populations. These results suggest that beech trees present a genetic differentiation of leaf phenology even within a small latitudinal gradient but that these differentiations could be disrupted by soil water deficit that is predicted to increase in the future.

Defoliation severity is positively related to soil solution nitrogen availability and negatively related to soil nitrogen concentrations following a multi-year invasive insect irruption.

Understanding connections between ecosystem nitrogen (N) cycling and invasive insect defoliation could facilitate the prediction of disturbance impacts across a range of spatial scales. In this study we investigated relationships between ecosystem N cycling and tree defoliation during a recent 2015–18 irruption of invasive gypsy moth caterpillars (Lymantria dispar), which can cause tree stress and sometimes mortality following multiple years of defoliation. Nitrogen is a critical nutrient that limits the growth of caterpillars and plants in temperate forests. In this study, we assessed the associations among N concentrations, soil solution N availability and defoliation intensity by L. dispar at the scale of individual trees and forest plots. We measured leaf and soil N concentrations and soil solution inorganic N availability among individual red oak trees (Quercus rubra) in Amherst, MA and across a network of forest plots in Central Massachusetts. We combined these field data with estimated defoliation severity derived from Landsat imagery to assess relationships between plot-scale defoliation and ecosystem N cycling. We found that trees in soil with lower N concentrations experienced more herbivory than trees in soil with higher N concentrations. Additionally, forest plots with lower N soil were correlated with more severe L. dispar defoliation, which matched the tree-level relationship. The amount of inorganic N in soil solution was strongly positively correlated with defoliation intensity and the number of sequential years of defoliation. These results suggested that higher ecosystem N pools might promote the resistance of oak trees to L. dispar defoliation and that defoliation severity across multiple years is associated with a linear increase in soil solution inorganic N.

Impact of Weather Factors on Coelaenomenodera elaiedis MLK (Coleoptera: Chrysomelidae) in Nigeria

The leaf miner (Coelaenomenodera elaeidis) is a major pest of the oil palm. It breaks out in epidemic proportions periodically, resulting in severe leaf defoliation and consequently low fresh fruit bunch (FFA) yield. This study analyses temperature, rainfall, relative humidity, and leaf miner abundance records sampled in oil palm fields between 1976 and 1980 in the main station of the Nigerian Institute for Oil Palm Research (NIFOR). Data for temperature, rainfall, and relative humidity were obtained from NIFOR meteorological station. Mathematical relationships between the insect stages (larva, pupa, and adult) and weather factors (rainfall and temperature) were developed indicating that pest predictions can be made for different leaf miner stages using their corresponding model equations giving specific values for rainfall and temperature. Variations in the seasonal patterns of temperature and rainfall are of major significance as a cue to timing leaf miner abundance and would help in making better decisions regarding where farmer action can target pest control interventions, thereby contributing to ensure food security. The need for continuous monitoring has great potential for detection and control of insect pests in oil palm growing areas.

Characterization of Lysobacter spp. strains and their potential use as biocontrol agents against pear anthracnose

Colletotrichum fructicola, is an important fungal pathogen that has been reported to cause pear (Pyrus) anthracnose in China, resulting in substantial economic losses due to severe defoliation and decreased fruit quality and yield. In the search for novel strategies to control pear anthracnose, Lysobacter strains have drawn a great deal of attention due to their high-level production of extracellular enzymes and bioactive metabolites. In the present study, we compared four Lysobacter strains including Lysobacter enzymogenes OH11, Lysobacter antibioticus OH13, Lysobacter gummosus OH17 and Lysobacter brunescens OH23 with respect to their characteristics and activity against pear anthracnose caused by C. fructicola. The results showed that the evaluated Lysobacter species presented various colony morphologies when cultured on different media and were proficient in producing protease, chitinase, cellulase and glucanase, with L. enzymogenes OH11 showing typical twitching motility. L. enzymogenes OH11 and L. gummosus OH17 showed potent activity against the tested fungi and oomycetes. L. gummosus OH17 produced HSAF (heat-stable antifungal factor) which was demonstrated to be a major antifungal factor in L. enzymogenes OH11 and C3. Furthermore, L. antibioticus OH13 and L. brunescens OH23 exhibited strong antibacterial activity, especially against Xanthomonas species. Cultures of L. enzymogenes OH11 protected pear against anthracnose caused by C. fructicola, and the in vivo results indicated that treatment with an L. enzymogenes OH11 culture could decrease the diameter of lesions in pears by 35 % and reduce the severity of rot symptoms compared to that observed in the control. In the present study, we systemically compared four Lysobacter strains and demonstrated that they have strong antagonistic activity against a range of pathogens, demonstrating their promise in the development of biological control agents.

Red alder defense mechanisms against western tent caterpillar defoliation

Red alder (Alnus rubra Bong.) is a tree of high economic and ecological importance, yet is subject to severe defoliation during episodic outbreaks of tent caterpillars (Malacosoma spp.). We evaluated variation in western tent caterpillar (Malacosoma californicum Packard, 1864) (WTC) resistance among and within red alder populations and clones and investigated potential defense mechanisms. Bioassay feeding trials were conducted with WTC on 20 red alder clones from 10 provenances (two clones per provenance). Phenology and quality of red alder leaves were analyzed to determine whether bud burst, leaf chemical content, water content, or physical traits are determinants of WTC preference. Alder clones differed in percent leaf area eaten by WTC and in leaf defense traits. The concentrations of total phenolics, condensed tannin, and the diarylheptanoid oregonin were negatively correlated with the percent leaf area eaten by caterpillars. In addition, a potential threshold was observed above which the concentration of each of the chemicals appeared to reduce WTC feeding. In particular, foliar concentrations of oregonin >20% of leaf dry mass were consistently associated with reduced feeding. The effects of oregonin concentration in red alder leaves on tent caterpillar feeding is a novel finding.

Pathogen-induced defoliation impacts on transpiration, leaf gas exchange, and non-structural carbohydrate allocation in eastern white pine (Pinus strobus)

Pathogen-induced defoliation resulted in a reduction in transpiration, an upregulation of photosynthesis in the early growing season, and no change in NSC reserves across stem, root, and foliar tissues. The defoliation of eastern white pine (Pinus strobus L.) by native fungi associated with white pine needle damage (WPND) can substantially reduce foliar area for much of the growing season in the northeastern United States. Chronic defoliations in the region are known to have slowed growth rates in symptomatic stands, but the physiological impacts of WPND as it relates to tree water use and carbon assimilation are largely unresolved. We investigated how the severity of WPND defoliation influences transpiration throughout the course of a growing season. We also assessed leaf-level gas exchange between defoliation severity classes and needle age over time. Finally, we compared concentrations of non-structural carbohydrates (NSC) between defoliation severity classes in five different tissue types over time. We found that trees experiencing a high-severity defoliation had 20% lower sap flux density compared to low-severity individuals. We found that rates of photosynthesis were significantly influenced by the needle age class and time of year, while instantaneous water use efficiency was higher across all needle age classes late in the growing season. Our findings suggest that the residual current-year foliage of high-severity defoliated trees compensated for the loss of mature second- and third-year foliage in the early portion of the growing season. This study found that soluble sugars and starch varied significantly over time and by tissue type, but defoliation severity had little effect on NSC concentrations. Together with reduced basal area increment in high-severity trees relative to low-severity trees, this indicates that WPND-affected trees are prioritizing NSC storage over secondary growth.

Repeated fall prescribed fire in previously thinned Pinus ponderosa increases growth and resistance to other disturbances

In western North America beginning in the late 19th century, fire suppression and other factors resulted in dense ponderosa pine (Pinus ponderosa) forests that are now prone to high severity wildfire, insect attack, and root diseases. Thinning and prescribed fire are commonly used to remove small trees, fire-intolerant tree species, and shrubs, and to reduce surface and aerial fuels. These treatments can be effective at lowering future fire severity, but prescribed burns must be periodically repeated to maintain favorable conditions and are feasible only outside the historical summer wildfire season. This study examines tree growth and mortality associated with spring and fall burning repeated at five (5 yr) and fifteen-year (15 yr) intervals in six previously thinned ponderosa pine stands in the southern Blue Mountain Ecoregion near Burns, Oregon, USA. Each stand consisted of an unburned control, and four season-by-burn interval treatments: spring 5 yr, spring 15 yr, fall 5 yr, and fall 15 yr. Burning was initiated in fall 1997 and spring 1998. Pine height and diameter growth was evaluated in 2013, 15 years following initial treatment. Mortality was assessed annually from 2002 to 2017, when these stands experienced severe defoliation from pine butterfly (PB, Neophasia menapia), followed by a moderate outbreak of western pine beetle (WPB, Dendroctonus brevicomis), allowing us to examine resistance to these disturbances. Pine in the 5 yr fall treatments added more diameter than spring 15 yr and marginally more than spring 5 yr, while fall 15 yr added marginally more diameter than spring 15 yr. In addition, the fall 5 yr treatments had lower mortality associated with prescribed fire, PB, WPB, Ips spp., red turpentine beetle (RTB, D. valens), and mountain pine beetle (MPB, D. ponderosae), but the effect was not always significant. Annosus root disease (ARD, caused by Heterobasidion irregulare) and black stain root disease (BSRD, caused by Leptographium wagneri var. ponderosum) appear to be unaffected by burning. However, BSRD occurrence dramatically declined in all treatments, probably a result of thinning prior to study initiation. Results from this study demonstrate that repeated fall burning, especially at 5-year intervals, improves ponderosa pine diameter growth and may provide resistance to future biotic and abiotic disturbances while spring burning, regardless of frequency, does not.

Infestation of the invasive exotic moth Hyblaea puera (Lepidoptera: Hyblaeidae) in Avicennia L. (Acanthaceae) in the mangrove of the Mamanguape River, Paraíba, Brazil

Abstract Outbreaks of caterpillars have been recorded in some mangrove forests in Brazil and other countries. This study reports an infestation of Hyblaea puera caterpillars (Cramer, 1777) (Lepidoptera: Hyblaeidae) in the mangrove forest of the Mamanguape River, Paraiba State, Brazil. The attacks occurred between May and July 2020 and affected Avicennia germinans (L.) L. and Avicennia schaueriana Stapf & Leechm. ex Moldenke. During the caterpillar outbreak period, the foliar herbivory rate was > 50 % in both species. Throughout the distribution area of the species in the estuary, there was variation in the intensity of caterpillar infestation: from the absence of attack to the complete defoliation of the trees in mono-specific forests of A. germinans. The consequences of severe defoliation are briefly discussed, emphasizing mangrove conservation.

Variability of radiation use efficiency in mixed pastures under varying resource availability, defoliation and time scale

AbstractForage productivity is the product between incident radiation, the fraction of radiation absorbed by the canopy (fAPAR) and radiation use efficiency (RUE). The extent to which forage productivity may be estimated through remote sensing depends on the relative effects of stress and defoliation on fAPAR and RUE. In a mixed pasture, we determined the relative impact of resource availability and defoliation on forage productivity, fAPAR and RUE, and we evaluated the impact of time scale on fAPAR and RUE under stress conditions. We conducted a one‐year experiment in a temperate‐mixed pasture subjected to different resource availability treatments and defoliation management. We measured RUE and fAPAR with different temporal windows. RUE was less responsive than fAPAR to changes in resource availability and defoliation intensity. However, RUE slightly decreased under water stress and increased under severe defoliation. Additionally, RUE variability during regrowth and among treatments depended on the temporal scale of observation: RUE was more variable for 12‐day periods than 45‐ or 90‐day periods. Our results reinforce the value of fAPAR as an explanatory variable of the variations in forage productivity due to changes in resource availability and management. In addition, the temporal scale of observation affects RUE variability. Thus, most variations of forage productivity may be captured by monitoring systems based on remote sensing of fAPAR provided that the time scale is coarse enough. However, the contrasting response of RUE and fAPAR to defoliation indicates a potential weakness of such a system when situations with contrasting defoliation regime are compared.

Differences in carbon and nitrogen metabolism between male and female Populus cathayana in response to deficient nitrogen.

Sexual dimorphism occurs regarding carbon and nitrogen metabolic processes in response to nitrogen supply. Differences in fixation and remobilization of carbon and allocation and assimilation of nitrogen between sexes may differ under severe defoliation. The dioecious species Populus cathayana was studied after two defoliation treatments with two N levels. Males had a higher capacity of carbon fixation because of higher gas exchange and fluorescence traits of leaves after severe long-term defoliation under deficient N. Males had higher leaf abscisic acid, stomatal conductance and leaf sucrose phosphate synthase activity increasing transport of sucrose to sinks. Males had a higher carbon sink than females, because under N-deficient conditions, males accumulated >131.10% and 90.65% root starch than males in the control, whereas females accumulated >40.55% and 52.81%, respectively, than females in the control group. Males allocated less non-protein N (NNon-p) to leaves, having higher nitrogen use efficiency (photosynthetic nitrogen use efficiency), higher glutamate dehydrogenase (GDH) and higher leaf GDH expression, even after long-term severe defoliation under deficient N. Females had higher leaf jasmonic acid concentration and NNon-p. The present study suggested that females allocated more carbon and nitrogen to defense chemicals than males after long-term severe defoliation under deficient N.

Distribution and content of calcium and potassium in eucalyptus leaves infected with Calonectria pteridis

AbstractCalonectria leaf spot, caused by Calonectria pteridis, is a serious problem in Eucalyptus crops in both nursery and the field. Under ideal conditions, the disease can cause severe defoliation. It is known that calcium and potassium are directly related to the plant's resistance to pathogens. Thus, the knowledge of how a balanced fertilization of Ca and K interferes in the distribution of these nutrients at the infection site would contribute to elucidate the resistance of the plant related to its nutrition. This study investigated the effect of calcium and potassium fertilizer application on the content and distribution of these nutrients in the symptomatic leaf area, transition zone and asymptomatic leaf area over time. Eucalyptus seedlings were grown in nutrient solution under different Ca and K treatments (6 mmol/L K + 4 mmol/L Ca, 6 mmol/L K + 8 mmol/L Ca and 9 mmol/L K + 12 mmol/L Ca) and inoculated with C. pteridis. Leaves were removed at 24, 48 and 72 hr after inoculation (hai) and evaluated by X‐ray microanalysis. The highest calcium content among the different leaf areas was observed in the symptomatic area, and the levels in this area increased over time, with the highest mean value observed at 72 hai in the 6K + 8Ca treatment. In the other treatments, the mean calcium content peaked at 48 hai and then decreased. A similar pattern in asymptomatic tissue was observed for potassium in the 6K + 8Ca treatment. Fertilization with calcium and potassium directly affected the demand and availability of nutrients at different times during infection. These results demonstrate that plant defence responses and their continuity over time during infection rely on balanced calcium and potassium fertilization because these nutrients are directly involved in plant resistance to the pathogen.

Does defoliation frequency and severity influence plant productivity? The role of grazing management and soil nutrients

Rangeland management approaches, including rotational grazing, rely on assumptions about plant growth responses to the intensity, or severity (sward height) plus frequency, of defoliation. We tested these assumptions at the farm, patch and plant scale using data from a grazing management trial in an Eastern Cape mesic grassland of South Africa along with field plot and glasshouse pot experiments. The grazing trial tested season-long grazing (SLG), four-camp grazing (FCG) and holistic planned grazing (HPG) at equivalent stocking rates over three years. We found that grass growth responses in both potted plants and field plots were reduced under more frequent and severe defoliation but that this was mitigated under elevated soil nutrients, in line with the Compensatory Continuum Hypothesis which predicts that compensatory growth will increase across an increasing fertility gradient. In the farm trial, SLG, which theoretically causes high frequency, low severity defoliation, reduced bare ground cover and increased vegetation greenness with increasing defoliation intensity on nutrient-rich soils. This effect was not present under FCG or HPG and disappeared under very high defoliation intensities and on relatively water- and nutrient-poor soils. Managers are advised to only increase grazing frequency on relatively high nutrient soils, while maximizing recovery on poorer nutrient soils.

First Report of Root Rot Caused by Phytophthora bilorbang on Olea europaea in Italy.

Leaf chlorosis, severe defoliation and wilt associated with root rot were observed on mature olive trees cv. Nera di Gonnos in an experimental orchard at Mirto Crosia (Calabria, southern Italy). An oomycete was consistently isolated from rotten roots of symptomatic olive trees. It was identified as Phytophthora bilorbang by morphological characters and sequencing of Internal Transcribed Spacer (ITS) regions of ribosomal DNA (rDNA). Pathogenicity was verified by inoculating potted two-month-old rooted cuttings of Olea europaea var. Nera di Gonnos in a soil infestation trial. P. bilorbang was re-isolated from roots of symptomatic, artificially inoculated olive cuttings to fulfill Koch’s postulates. This is the first report of P. bilorbang on O. europaea L. and on a species of the Oleaceae family worldwide.

Spatially optimizing vegetation indices integrated with sparse partial least squares regression to detect and map the effects of Gonipterus scutellatus on the chlorophyll content of eucalyptus plantations

ABSTRACT Gonipterus scutellatus is a beetle causing severe defoliation to South Africa’s eucalyptus plantations. This defoliation induced by the beetle inhibits the eucalypts ability to photosynthesize, by affecting its chlorophyll content. Therefore, this study integrates spatially optimized and the single 0.5 m resolution vegetation indices with sparse partial least squares regression (SPLS-R) and partial least squares regression (PLS-R) to detect and map leaf chlorophyll content of defoliated eucalyptus plantations. The optimized vegetation indices were spatially resampled to resolutions that best paralleled varying levels of G. scutellatus defoliation. From the results, the 0.5 m resolution SPLS-R model (R 2 = 0.76; RMSE of 1.50 (2.88% of the mean measured chlorophyll)) outcompeted the 0.5 m resolution PLS-R (R 2 = 0.73; RMSE of 1.54 (2.95% of the mean measured chlorophyll)) model. Furthermore, the spatially optimized SPLS-R (R 2 = 0.81; RMSE of 1.44 (2.76% of the mean measured chlorophyll) model was more superior in detecting and mapping chlorophyll content of defoliated eucalyptus plantations when compared to the 0.5 m resolution SPLS-R model. The most significant variables selected by the optimized SPLS-R model were DMI, ARI, NDRE, GNDVI, and NDVI. In essence, this study has illustrated the significance of the spatial resolution in effectively detecting and mapping chlorophyll content of defoliated eucalyptus plantations.

Assessing potential plants extracts to reduce Leucoptera coffeella (lepidoptera: Lyonetiidae) attack in coffee

Leucoptera coffeella (Guerin-Meneville) (Lepidoptera: Lyonetiidae) is one of the major pests of coffee in South America, causing severe defoliation in plants. The problems involving chemical control and the risks of resistance evolution of the insect, justify the search for alternative methods for manage the species. Plants extracts appears to be a valuable tool for the management of L. coffeella, due to the potential of plants insecticidal properties of them being compatible with the integrated pest management. This study evaluated the effect of nine botanic aqueous extracts on the oviposition and biology of L. coffeella, under laboratory conditions. The extracts of Toona ciliata, Trichilia casaretti and Trichilia pallida decreased the oviposition rate of L. coffeella on coffee leaves. Along with Trichilia catigua, Chenopodium ambrosioides and Melia azedarach, these extracts were classified as deterrent to oviposition by a preference index and the C. ambrosioides, T. casaretti and T. ciliata extracts caused high egg mortality of L. coffeella. Extracts of seeds of A. indica and T. pallida affect negatively the development and survival of L. coffeella, reducing of mined area by the larva. These results elucidate the potential of these plants species for pest control and might be useful in integrated management programs for L. coffeella.

Spotted gums and hybrids: Impact of pests and diseases, ontogeny and climate on tree performance

The increased threat of pests and pathogens in plantations has strengthened the need to understand the factors underlying their occurrence, such as climate and tree ontogenic, and the effect of these pests and diseases on plant performance. Spotted gums (Corymbia citriodora and C. henryi), C. torelliana, and their hybrids are important commercial plantation taxa, because they are suited to a range of environments where traditional commercial eucalypts grow poorly. They have desirable field performance and can produce a range of timber and fibre products. This study investigated field performance, ontogenetic shifts from juvenile to intermediate leaves, and damage by pests and pathogens in pure spotted gum taxa, including C. citriodora subsp. citriodora (CCC), C. citriodora subsp. variegata (CCV) and C. henryi (CH), C. torelliana (CT), and their hybrids over a two year period. The study revealed that higher mean daily rainfall and maximum/minimum temperatures positively influenced tree performance but were also associated with higher levels of defoliation by generalist insects. Necrosis associated with Quambalaria pitereka was not correlated with climatic conditions in most of the taxa. Growth rate and defoliation were positively correlated, while flushing and damage parameters (defoliation and leaf necrosis) were often negatively correlated, suggesting that the taxa studied may have high tolerance to defoliation. Ontogenetic shifts were variable between taxa, occurring earlier in pure spotted gum taxa than in hybrids. The only environmental factor related to the transition from juvenile to intermediate leaves was mean daily rainfall, suggesting that ontogenetic shifts may be associated with an adaptation to water availability. Overall, CCC and CT × CCC displayed the best combination of performance and resistance to pests and pathogens. Severe defoliation was associated with reduced diameter at breast height over bark (DBH) in CCV and CH. Tree interactions with damage and climate parameters were more consistent in the pure species than in the hybrids. These results add important knowledge on plant interactions with biotic and abiotic stress, assisting with strategies of pests and pathogen management and selection of the most appropriate taxa for pest and disease prone sites in southern Queensland.

First report of Diplodia seriata de Not. causing black rot of apple (Malus domestica L. Borkh.) in Meghalaya, North Eastern India

In a survey conducted during Januray-May, 2020, apple trees showing characteristic symptoms of frogeye leaf spots, canker and twig die back that in severe cases causing dead branches and severe defoliation have been observed from apple plantation of Umiam, Meghalaya. Isolation of the associated causal fungal agent was done in selective media and its cultural, morphological as well as microscopical studies were carried out. Furthermore, confirmation of the putative fungus was done by conducting pathogenicity test to prove Koch’s postulate. From the available literature, the fungus associated with the disease symptom have been identified as Diplodia seriata causing black rot of apple. To the best of the knowledge, this is the first report of isolation and pathogenicity confirmation of black rot of apple caused by D. seriata from Meghalaya, India.

First Report of Corynespora cassiicola Causing Leaf Spot on Avocado (Persea americana) in China

Avocado (Persea americana Mill.) is an economically important fruit crop in China. In September 2018, symptoms of leaf spots were frequently observed causing severe defoliation in an avocado plantation (19°56′ N; 109°49′ E) in Danzhou (Hainan province) in China. On this plantation (about 2.5 ha), 70% of the trees showed the same symptoms. Initially, symptoms on young leaves appeared as small (1 to 2 mm) yellow circular lesions, which then grew into circular to irregular brown to dark-brown lesions (3 to 5 mm), usually with an obvious yellowish margin and slightly raised on the adaxial side of the leaves. Later on, lesions coalesced and formed large necrotic areas. When mature (old) leaves were infected, the lesion was not raised. For pathogen isolation, 10 symptomatic leaves were sampled from different parts of the field. Leaves with typical symptoms were washed with tap water. Small pieces of tissue (4 × 4 mm) were cut from the border of symptomatic and healthy tissue, surface sterilized in 75% ethanol solution (v/v) for 30 s followed by 2% sodium hypochlorite for 3 min, rinsed three times in sterile distilled water, plated on potato dextrose agar (PDA), and incubated at 28°C in constant light. Twenty samples were plated, and one fungus grew from 95% of the samples after 4 days. Purified strains of this fungus were transferred onto new PDA medium and were incubated for 7 days at 28°C, in constant light. The colony (78 mm in diameter) on PDA had abundant hair-like or fine fuzzy aerial hyphae. And the color of the colony was gray to grayish brown. Conidia were cylindrical, straight to slightly curved, pale brown, 46 to 307 µm (average 180 µm; n = 80) × 5 to 16 µm (average 7 µm; n = 80). These morphological characteristics resemble Corynespora sp. (Berk. & M.A. Curtis) C.T. Wei (Ellis et al. 1971). The ACT, EF-1α, and TUB genes were amplified and sequenced with the primer pairs ACT-512F/ACT-783R, EF1-728F/EF-986R (Carbone and Kohn 1999), and tub-F1/tub-R2 (Blair et al. 2008), respectively. A maximum likelihood phylogenetic analysis based on ACT, EF-1α, and TUB (accession nos. MN956378, MN737730, and MN737729) sequences using MEGA 7.0 revealed that the isolate was placed in the same clade as Corynespora cassiicola with 99% bootstrap support. For the pathogenicity test, the conidial suspension (1 × 10⁵ spores/ml) of YLBB1125 isolate was prepared by harvesting conidia from a 15-day-old culture on PDA. Conidia were sprayed onto young leaves of six potted plants. Two additional trees sprayed with sterile distilled water served as controls. After 7 days, typical symptoms of brown to dark-brown spots were observed on all inoculated leaves. Mature and old leaves of six healthy plants were wound-inoculated with 5-mm-diameter mycelial plugs obtained from 7-day-old cultures. The same number of plants treated with PDA plugs served as controls. After 4 days, the inoculation sites with the mycelium showed brown spots with a yellowish margin and a gray mold layer on the abaxial side of leaves. All leaves on control plants remained asymptomatic. All plants were covered with plastic bags for 4 days to maintain high humidity and then maintained in a greenhouse at 28°C with a 12-h/12-h light/dark cycle. C. cassiicola was specifically reisolated and identified from the inoculated (spores and mycelial plugs) symptomatic leaves, thus confirming Koch’s postulates. This is the first report of C. cassiicola as a pathogen causing leaf spot on avocado, although it has been reported previously as an endophyte (Dingley et al. 1981).

Cold tolerance strategy and cold hardiness of the invasive zigzag elm sawfly Aproceros leucopoda (Hymenoptera: Argidae)

Abstract The invasive sawfly Aproceros leucopoda causes severe defoliation of various elm species and thus can be a major pest in forest stands and urban environments. The overwintering biology of A. leucopoda has not been investigated so far; therefore, the aim of this study was to determine the cold tolerance strategy and cold hardiness of hibernating A. leucopoda eonymphs. The supercooling points (SCPs) of overwintering individuals varied geographically, monthly and interannually and ranged between −12.14 °C and −24.22 °C. As none of the eonymphs survived once the SCP had been reached, A. leucopoda is classified as a freeze‐avoidant species. Survival rates of overwintering eonymphs exposed to different sub‐zero temperatures above the SCP (−1.6 °C and −4.0 °C for 10, 20 and 30 days and −10.5 °C for 9 days) ranged between 89.2% and 100%, suggesting that A. leucopoda is not a chill‐susceptible species. Our results suggest that low winter temperatures may not be expected to be an important limiting factor for the overwintering success of A. leucopoda.

Dynamics of defoliation of associated grasses

The behavior of variables related to defoliation dynamics was evaluated, and their respective oscillations in two intercropping of tropical climate grasses managed under two grazing intensities. We used pastures formed with two intercropping (BRS Zuri, Xaraés and Basilisk; BRS Quênia, Marandu and BRS Paiaguás), managed in two grazing intensities: 40 and 60% of the pre-grazing height. In the consortium between BRS Zuri, Xaraés and Basilisk, the first canonical variable explained 72.1 and 79.2% of the total variation of the defoliation pattern for the grazing intensity levels of 40 and 60%. In the consortium between BRS Quênia, Marandu and BRS Paiaguás, the first canonical variable explained 84.3 and 89.0% of the total variation of the defoliation pattern for the grazing intensity levels of 40 and 60%. The choice of forage species of tropical climate to form the consortium may be decisive in order to perpetuate plant diversity. From the population density of tillers, it is possible to observe that grasses belonging to functional groups A and B (Zuri, Xaraés, BRS Quênia and Marandu) have a higher probability of coexisting in the same area. The choice of forage species for the establishment of intercropped pastures is important to ensure the coexistence between them and the persistence of the consortium. The analysis of canonical variables assists in explaining the dynamics of defoliation of intercropping through the estimates of severity and frequency of defoliation of extended tiller and pseudostem.