Assessment of forest dieback on the Moroccan Central Plateau using spectral vegetation indices

Cork oak forests in Morocco are rich in resources and services thanks to their great biological diversity,playing an important ecological and socioeconomic role.Considerable degradation of the forests has been accentuated in recent years by signifi cant human pressure and eff ects of climate change;hence,the health of the stands needs to be monitored.In this study,the Google Engine Earth platform was leveraged to extract the normalized diff erence vegetation index(NDVI)and soil-adjusted vegetation index,from Landsat 8 OLI/TIRS satellite images between 2015 and 2017 to assess the health of the Sibara Forest in Morocco.Our results highlight the importance of interannual variations in NDVI in forest monitoring;the variations had a signifi cantly high relationship(p<0.001)with dieback severity.NDVI was positively and negatively correlated with mean annual precipitation and mean annual temperature with respective coeffi cients of 0.49 and−0.67,highlighting its ability to predict phenotypic changes in forest species.Monthly interannual variation in NDVI between 2016 and 2017 seemed to confi rm fi eld observations of cork oak dieback in 2018,with the largest decreases in NDVI(up to−38%)in December in the most-aff ected plots.Analysis of the infl uence of ecological factors on dieback highlighted the role of substrate as a driver of dieback,with the most severely aff ected plots characterized by granite-granodiorite substrates.

Comparative tree-ring anatomy of Fraxinus excelsior with Chalara dieback

We tested the hypothesis that the biometrical characters of wood elements in ash trees(Fraxinus excelsior L.) become modified in response to the progression of disease caused by Chalara fraxinea. Anatomical analyses were performed on wood samples collected at breast height from the trunks of groups of ash trees which contained healthy, weakened and dead trees. We measured(1) treering width,(2) earlywood vessel diameter,(3) earlywood vessel element length,(4) fibre length,(5) fibre diameter,(6) fibre lumen diameter, and(7) fibre wall thickness. We showed that tree-ring width diminished in all analysed groups during disease progression. However, the greatest suppression of growth was observed in dead trees. In both weakened and dead ash trees, the reduction in tree-ring width was accompanied by diminished vessel diameter in the earlywood of the outermost annual rings. The annual rings of dead trees had shorter fibres having greater lumen diameter and thinner cell walls. Consequently, water conduction in the sapwood of dead ash trees was less efficient owing to reduced vessel diameter, and this seems to be one of the greatest disease-induced morphological modifications. All the anatomical modifications might be due to leaf loss and crown dieback triggered by Chalara fraxinea.

Linking morphological and ecophysiological leaf traits to canopy dieback in Persian oak trees from central Zagros

Intraspecific variability in morphological and ecophysiological leaf traits might be theorized to be present in declining populations,since they seem to be exposed to stress and plasticity could be advantageous.Here we focused on declining Persian oaks(Quercus brantii Lindl.var.persica(Jaub and Spach)Zohary)in the Zagros Mountains of western Iran,representing the most important tree species of this region.We selected trees with contrasting crown dieback,from healthy to severely defoliated,to investigate the relationships between canopy dieback and leaf morphology,water content and pigments.We also measured esterase and peroxidase,as enzymatic antioxidants and indicators of contrasting genotypes.Trees showing moderate to severe defoliation showed higher leaf mass area(LMA),reduced relative water content(RWC),and lower stomatal density(SD).Increasing LMA indicates a more sclerophyllic structure,according to drier conditions.We did not find significant differences in leaf pigments(chlorophyll a and b,and carotenoids)among crown dieback classes,suggesting that Persian oak trees are able to maintain accurate photochemical efficiency,while reduced RWC and SD suggest hydraulic limitations.Our results do not provide a consistent pattern as regards enzymatic antioxidant defense in Persian oak.Morphological leaf traits would be important drivers of future adaptive evolution in Persian oak,leading to smaller and thicker leaves,which have fitness benefits in dry environments.Nonetheless,drought responses may be critically affecting carbon uptake,as photosynthetic compounds are less effectively used in leaves with higher sclerophylly.

Dieback intensity but not functional and taxonomic diversity indices predict forest productivity in different management conditions: Evidence from a semi-arid oak forest ecosystem

The relationships between different aspects of diversity(taxonomic,structural and functional)and the aboveground biomass(AGB)as a major component of global carbon balance have been studied extensively but rarely under the simultaneous influence of forest dieback and management.In this study,we investigate the relationships between taxonomic,functional and structural diversity of woody species(trees and shrubs)and AGB along a gradient of dieback intensity(low,moderate,high and no dieback as control)under two contrasted management conditions(protection by central government vs.traditional management by natives)in a semi-arid oak(Quereus brantii Lindl.)forest ecosystem.AGB was estimated and taxonomic diversity,community weighted average(CWM)and functional divergence indices were produced.We found that the aerial biomass was significantly higher in the intensively used area(14.57(±1.60)t/hm^(2))than in the protected area(8.70(±1.05)t/hm^(2))due to persistence of some large trees but with decreasing values along the dieback intensity gradient in both areas.CWM of height(H),leaf nitrogen content(LNC)and leaf dry matter content(LDMC)were also higher in the traditional managed area than in the protected area.In contrast,in the protected area,the woody species diversity was higher and the inter-specific competition was more intense,explaining a reduced H,biomass and LDMC.Contrary to the results of CWM,none of the functional diversity traits(FDvar)was affected by dieback intensity and only FDvar values of LNC,leaf phosphorus content(LPC)and LDMC were influenced by management.We also found significantly positive linear relationships of AGB with CWM and FDvar indices in the protected area,and with taxonomic and structural diversity indices in the traditional managed area.These results emphasize that along a dieback intensity gradient,the leaf functional traits are efficient predictors in estimating the AGB in protected forests,while taxonomic and structural indices provide better results in forests under a high human pressure.Finally,species identity of the dominant species(i.e.,Brant’s oak)proves to be the main driver of AGB,supporting the selection effect hypothesis.

The Relationship of the Sapstreak Fungus, <i>Ceratocystis virescens</i>, to Sugar Maple Dieback and Decay in Northern Michigan

Unusually high levels of dieback have recently been reported in sugar maple, Acer saccharum Marsh., in Upper Michigan, and a network of plots was established to determine the extent and factors associated with the dieback. A possible contributor to this dieback is sapstreak disease caused by Ceratocystis virescens (Davidson) Moreau. Unhealthy trees with considerable crown dieback were evaluated across the western Upper Peninsula, MI to determine the prevalence of the sapstreak fungus using a minimally destructive sampling technique. Approximately 8% of 90 trees sampled were sapstreak positive and approximately 10% of trees were positive at one site that had recently been harvested. While the high levels of maple dieback present in these forests appear not to be directly caused by widespread sapstreak disease, the occurrence of sapstreak may be significantly impacting trees at some locations. However, even when present on a low number of trees, the biointeraction of sapstreak and decay rates from other fungi could be important for future tree mortality and value to the forest industry. Therefore, the effect of two sapstreak fungal isolates on the amount of decay caused by two common maple white rot fungi, Trametes versicolor (L.:Fr.) Pilat. And Irpex lacteus (Fr.:Fr.) Fr. was tested in the laboratory. Sugar maple wood blocks were precolonized by two native isolates of C. virescens followed by inoculation and incubation with decay fungi. Mean percent weight loss of blocks by white rot decay fungi ranged from 39% to 55%, but decay rates were not significantly affected by the presence of the sapstreak fungus.

Morphological and Phylogenetic Resolution of Diplodia neojuniperi Emerging Diplodia Top Dieback of Pinus thunbergii Parl. in China

In Bazhong City,Sichuan Province,China,top dieback symptoms were found on many pine trees(Pinus thunbergii Parl).The tips of old needles first turned grayish-green and then developed into brown bands in the field.Phylogenetic analysis of concatenated ITS and EF1-αindicated the pathogen of this dieback disease as Diplodia neojuniperi.Additionally,effects of temperature,pH and medium on the mycelial growth were also characterized.The most favorable temperature and pH level for mycelial growth are 25°C and 8,respectively.The optimal medium for mycelial growth is PDA medium.To our knowledge,this is the first report of D.neojuniperi causes Diplodia top dieback on Pinus thunbergii.Our results provide fundamental information for monitoring and preventing such disease in the future.

Forest Fairy Ring Fungi <i>Clitocybe nebularis</i>, Soil <i>Bacillus</i>spp., and Plant Extracts Exhibit <i>in Vitro</i>Antagonism on Dieback <i>Phytophthora</i>Species

In vitro Kirby-Bauer disc-diffusion assays coupled with bio-imaging software techniques were used to assess native forest dwelling “fairy ring” forming fungi (Clitocybe nebularis) and co-habitant forest tree-root colonising non pathogenic, antibiotic producing bacteria (Bacillus licheniformis, Bacillus pumilis) for their antagonism towards Japanese larch dieback oomycetes phytopathogens which also affects ornamental alternative hosts. The aqueous extracts of C. nebularis exhibited the highest clearance (inhibitory) zone of 21.4 × 105 pixels = 573%) against Phytophthora ramorum than growth/clear zone Cartesian integrates recorded in untreated (control) disc (3.7 × 105 pixels = 100%) over 3-day incubation. The fairy ring fungal extracts also exhibited substantive antagonism against P. kernoviae (147%), P. lateralis (347%) and a solanaceous crop infecting P. infestans (86%). Quite encouragingly, the soil oomycete phytopathogen P. ramorum was inhibited strongly (mean ~ 177%) by both forest bacilli. Aqueous extracts of non-forest antifungal herbaceous plants (garlic and elderberry) expressed similar inhibitory effects (mean ~ 70%). A seaweed fungal elicitor component fucoidan showed moderate levels (mean ~ 85%) of antagonism against P. ramorum, P. kernoviae, P. lateralis and P. infestans. The results in this in vitro study highlight the intensity and vigor of antagonistic forest microflora and non-forest herbaceous antifungal agents such as garlic and other plant extracts as serious candidates for suppression of the oomycete Phytophthora pathogenic fungi in forest soils. This study calls for urgent scoping and impact assessment studies in pot experiments and mini-plot forest trials to gauge the fitness of these natural resources for field level potential biotechnological applications to combat the devastating dieback disease in the native woodlands and horticulture.

First record of Eutypella vitis causing branch dieback on new host trees in Canada

Eutypella vitis is reported for the first time on several new host trees viz.Fagus grandifolia,Fraxinus pennsylvanica and Syringa reticulata with associated branch dieback symptoms in the Niagara Region of Southern Ontario,Canada.Morphological characteristics and phylogenetic analyses of ITS sequence data confirmed the species identification.Eutypella vitis is known as a woody plant pathogen causing dieback of grapevines and other economically important fruit trees widely cultivated in Ontario.The fungus ability to infect several alternate new hosts can promote its faster and wider spread across vineyards and consequently increase a dieback hazard to viticulture in Canada.

First Report of Botryosphaeria dothidea Causing Sweet Osmanthus Leaf Dieback in China

Sweet osmanthus is one of the ten traditional famous flowers in China.The occurrence of the diseases caused by fungi other than Botryosphaeria spp.has been reported mainly from China on sweet osmanthus.A leaf dieback of sweet osmanthus caused by Botryosphaeria sp.was found for the first time in 2007 in Nanning City,Guangxi,China.The objectives of the present study were to isolate and characterize the causal organism of sweet osmanthus leaf dieback.The fungus was isolated from the lesions of affected sweet osmanthus leaves and its pathogenicity to sweet osmanthus was confirmed using a detached-leaf-inoculation method.The identification of the pathogen was carried out mainly based on the morphological characters and molecular analysis of internal transcribed spacer (ITS) sequences.The morphological characters of the pathogenic isolate GHX6 were agreed with that of Botryosphaeria dothidea.The ITS sequence of the isolate was amplified with primers ITS1 and ITS4,and submitted to GenBank (accession no.GQ368251).Molecular analysis based on ITS sequence comparison between the isolate GHX6 and the other related fungi derived from GenBank supported that the causal agent of the sweet osmanthus leaf dieback belonged to Botryosphaeria dothidea.This is the first report of Botryosphaeria dothidea causing leaf dieback on sweet osmanthus in China.

Major constraints on shisham(Dalbergia sissoo) plantations and pathological debate on dieback disease in Punjab,Pakistan

Today,shisham plantations in Punjab,Pakistan face major constraints,especially dieback disease.This article reviews the multidisciplinary team work by forest and plant pathologists and economists to resolve the confusions in the pathology of dieback disease.It is intended to be of practical use to the foresters and plant pathologists reporting on this issue.

国槐枝枯病病原菌鉴定及其生物学特性

近年来,枝枯病在我国南疆的发病率高达50%~70%。为明确国槐枝枯病的致病菌及其生物学特性,采用组织分离法对南疆多地的发病国槐枝条进行病原菌分离,并进行致病性测定、形态学和分子生物学鉴定。结果表明,引起国槐枝枯病的病原菌为新暗色柱节孢(Neoscytalidium dimidiatum)。PDA培养基(pH值5.0)、34℃条件最适宜该菌的菌丝生长;PDA培养基(pH值7.0~9.0)、34℃条件最适宜该菌的分生孢子的形成。较低的相对湿度更有利于该菌的分生孢子萌发和生长。以牛肉膏为氮源、甘露糖为碳源最有利于该菌的菌丝生长,以蛋白胨为氮源最适宜该菌分生孢子的产生;而以木糖、山梨糖为碳源,硝态氮、尿素为氮源时,菌丝生长及产孢速率均有所下降。

Species of Botryosphaeriaceae involved in grapevine dieback in China

Botryosphaeria dieback is a serious disease problem for table and grape wine production worldwide.The disease however,has been less well-studied in China.In this study,we surveyed Botryosphaeria dieback in 72 vineyards of 20 grape-growing regions in China and found that Botryosphaeria dieback occurs in 18 out of 20 provinces.Morphological and multi-gene phylogenetic analyses confirmed that Botryosphaeria dothidea,Diplodia seriata,Lasiodiplodia theobromae and Neofusicoccum parvum are associated with different grapevine dieback symptoms.This study also revealed considerable differences in the geographical distribution of Botryosphaeriaceae species in China with Lasiodiplodia theobromae and Neofusicoccum parvum occurring only in subtropical monsoon climate regions,Diplodia seriata occurring only in temperate monsoon climate regions,and Botryosphaeria dothidea occurring in both temperate and subtropical monsoon climate regions.Analysis of 26 isolates showed that there is little genetic variation within species.Koch’s postulates were satisfied for all species,and pathogenicity testing showed that among the 25 major cultivars growing in China,none was resistant to the four taxa.The current paper represents the first detailed report on Botryosphaeria dieback of grapevines in China.

Identifying marsh dieback events from Landsat image series (1998–2018) with an Autoencoder in the NIWB estuary, South Carolina

This study reports an inventory of marsh dieback events from spatial and temporal perspectives in the North Inlet-Winyah Bay(NIWB)estuary,South Carolina(SC).Past studies in the Gulf/Atlantic coast states have reported acute marsh dieback events in which marsh rapidly browned and thinned,leaving stubble of dead stems or mudflat with damaged ecosystem services.Reported marsh dieback in SC,however,have been limited.This study identified all marsh dieback events in the estuary since 1998.With 20 annually collected Landsat images,the Normalized Difference Vegetation Index(NDVI)series was extracted.A Stacked Denoising Autoencoder neural network was developed to identify the NDVI anomalies on the trajectories.All marsh dieback patches were extracted,and their inter-annual changes were examined.Results showed a continuous,spatially variable multi-year dieback event in 1998–2005,which aligned with the reported dieback in the early 2000s from other states.The identified patches mostly returned to normal within one year while the phenomenon reoccurred in other areas of the estuary during the prolonged dieback period.This study presents the first attempt to explore long-term dieback dynamics in an estuary using satellite time series.It provides valuable information in documenting marsh healthiness and environmental resilience on SC coasts.

Assessment of Cork Oak Decline Using Digital Multispectral Imagery in Relation with in Situ Crown Condition

Cork oak in Maamora forest is experiencing the dieback phenomenon. The evaluation of the latter in this forest has gained the importance over time and with the solicitation of managers to objectify its phytosanitary situation. Aiming at prioritizing management actions, remote sensing seems to be an effective tool to inquire about stands’ health conditions and their evolution. To this end, this study aims at mapping and validating health status of cork oak stands in Maamora. Sentinel 2 images in 2015 and 2020 were processed to calculate the differential normalized difference water index (NDWI), revealing vegetation moisture variation caused by drought. A statistical method based on thresholds was used to map cork oak dieback stands, those with no changes and those recovered. Results have shown that 54.63% of cork oak in Maamora forest have not changed in terms of phytosanitary situation between 2015 and 2020, 31.10% of oak stands are afflicted by a slight decline and 12.97% by a severe decline. Areas with slight or strong recovery remain minimal and represent 1.04% and 0.25% respectively. Ground data indicated that the map generated displayed a good distinction between stands severely and slightly declined with a global accuracy of 66.66%. Therefore, further research elaborating an advanced vegetation index reflecting the various factors of dieback would be of much importance.

茶树腐皮镰刀菌拮抗菌株的筛选鉴定及促生防病特性分析

腐皮镰刀菌(Fusariumsolani)是可以引起茶树茎腐和枯萎的致病真菌。为获得对茶树腐皮镰刀菌有拮抗效果的生防菌株,从河南省信阳市新县茶园收集的茶树(Camelliasinensis)健康叶片中采用梯度稀释法分离纯化得到内生细菌56株,通过平板对峙法筛选对腐皮镰刀菌抑制效果较好的菌株,并根据形态特征、生理生化特征和分子生物学技术对其进行鉴定,测定其防病促生指标并进行抑菌谱试验,通过发酵液试验和平板对扣法评估挥发性物质对腐皮镰刀菌菌丝生长的影响。结果显示,筛选得到的菌株YB-1476对腐皮镰刀菌菌丝生长抑制率达到63.31%,拮抗效果最佳,鉴定其为贝莱斯芽孢杆菌(Bacillus velezensis)。该菌株有产铁载体和吲哚乙酸、分泌β-1,3-葡聚糖酶和纤维素酶及溶磷的能力。抑菌谱试验表明,菌株YB-1476对平脐蠕孢菌(Bipolarissorokinana)、禾谷镰刀菌(FusariumgraminearumPH-1)、念珠状镰刀菌(Fusarium moniliforme)、尖孢镰刀菌(Fusariumoxysporumf.sp.niveum)和茄链格孢菌(Alternariasolani)5种病原真菌的菌丝生长抑制率分别达到65.03%、42.32%、51.67%、52.33%和63.22%。发酵液原液、稀释10倍和稀释100倍发酵液对腐皮镰刀菌的菌丝生长抑制率分别为66.67%、51.85%和18.52%。菌株YB-1476产生的挥发性物质对腐皮镰刀菌的菌丝生长抑制率达到53.37%。以上结果表明,菌株YB-1476在防控茶树茎腐和枯萎病方面具有巨大应用潜力。

防治葡萄溃疡病的杀菌剂筛选与评价

采用菌丝生长速率法和孢子萌发法测定了7种杀菌剂对可可毛色二孢CSS-01s的室内生物活性,筛选出3种抑制效果较好的杀菌剂;通过对离体葡萄绿枝条及盆栽葡萄幼苗新梢进行人工接种病原菌,进一步评价杀菌剂的防治效果。结果表明,7种杀菌剂对可可毛色二孢菌丝生长和孢子萌发表现出不同的抑制活性,其中戊唑醇、氯氟醚菌唑、啶酰菌胺和氟啶胺对菌丝生长的抑制作用较强,EC_(50)分别为0.116、0.137、0.109μg/mL和0.119μg/mL;戊唑醇、氯氟醚菌唑、氟啶胺对孢子萌发的抑制作用较强,EC_(50)分别为0.420、0.595μg/mL和1.885μg/mL。CSS-01s接种离体葡萄绿枝条试验中,戊唑醇100、200 mg/L,氯氟醚菌唑100、300 mg/L和氟啶胺100、200 mg/L的防治效果无显著差异,在57.81%~65.31%;CSS-01s接种葡萄幼苗新梢试验中,氟啶胺200 mg/L的防治效果最好,为77.56%,与氟啶胺100 mg/L、氯氟醚菌唑100、300 mg/L和戊唑醇200 mg/L之间无显著差异,但显著高于戊唑醇100 mg/L。研究结果显示,氯氟醚菌唑、戊唑醇和氟啶胺可以作为推荐杀菌剂,经进一步的田间药效评价用于葡萄溃疡病的防治。

杨梅大棚设施抗逆栽培技术试验

该项目以树龄20 a以上东魁杨梅枯枝病感病严重、树势衰退严重的联片果园为试验对象,采用大棚设施、薄肥多施、功能性元素均衡补给、适度修剪遮阴、全树疏花疏果、病虫害防治及温湿度调控等措施,经过近3年的努力,把从原来严重发病、基本无收成的果园,全面整理成为树势基本恢复、产量渐进增长、果品优质高效的示范性果园。该栽培管理模式已经引起业界的广泛关注,吸引省内外各地同行前来交流考察,使来者感到杨梅的枯枝病防治可防可控可治愈。研究认为,要实践既有目的的技术关键在于专业协同、学科交叉融合,注重实践创新应用的技术集成、因树制宜对症防治。

大米草(Spartina anglica)自然衰退种群对N、P添加的生态响应

通过对外来植物大米草(Spartina anglica)自然衰退种群进行N肥、P肥和N-P复合肥不同梯度水平的添加,分析大米草的生长指标差异及其生理生态响应。结果表明:N、P添加后使大米草种群株高均有不同程度的增加,肥效强弱依次为N肥、P肥、N-P肥;叶片数、主根数及总生物量均显著增加(p<0.05)。除N肥外,其它处理的叶片面积和厚度与对照没有显著差异。3种肥源的添加均显著提高了大米草自然衰退种群的光合速率(p<0.05);N和N-P肥均以高浓度效果最显著,但P肥却以中浓度效果最强;光合速率分别比对照增加19.08μmol·m-2·s-1、11.23μmol·m-2·s-1和15.47μmol·m-2·s-1;14d淡水淹没后,肥源添加使大米草自然衰退种群的SOD和POD酶活性增强;中浓度N和中浓度P添加使SOD活性增加最显著,分别比对照增加320.74unit·g-1和134.54unit·g-1;高浓度N和高浓度N-P肥添加使POD酶活性最显著增加。N肥添加可以显著改善大米草自然衰退种群生长生理特性,可以推断大米草种群的衰退与我国海岸带土壤营养中N素营养的限制有一定的相关性。

多效唑对杨梅枯枝病的影响及防治

检测分析不同剂量多效唑施用后在杨梅叶片、根部、果实的残留情况,以及对叶片色泽、根系、果实品质的影响；综合分析多效唑与杨梅枯枝病发生的因果关系.并针对枯枝病发生特点,利用自主研发的混配药物进行综合防治试验,并对治愈植株果实的农药残留进行随机检测.结果表明,重度、中度、轻度发病树叶片、根部多效唑含量差异显著,分别为叶片439.00,25.60,13.20μg/kg ,根部266.00,3.38,1.20μg/kg ,发病程度越高残留量越大；果实中均未检测到多效唑残留；500 mg/kg 高质量分数的多效唑处理使杨梅叶片气孔密度增大,气孔面积减小；T1（200 mg/kg）,T2（300 mg/kg）,T3（500 mg/kg）3个质量分数的多效唑连续施用与植株枯枝病轻度、中度、重度发生相对应,呈正相关；利用自主研发的混配药物对枯枝病发病植株进行防治效果显著.轻度发病树经3年连续治理后基本恢复正常生长,死树率为0,而作为对照的发病率为74.7％、死树率为21.6％；中度发病树治愈率均分别达90％以上,对照发病率为100％；严重发病树治愈率均在50％以上,对照在4年后全部死亡.经综合防治后恢复正常生长的植株果实的农药残留显著降低,克百威、甲胺磷、氧乐果和溴氰菊酯4个农药残留指标低于国家无公害标准的1～5倍,重金属铅的含量低于国家无公害标准的8倍.总之,多效唑施用后对杨梅可产生不可逆的影响,即多效唑（中高浓度多次施用）—树势早衰—拟盘多毛孢菌寄生侵染—枯枝病出现—枯枝死树—病菌扩大繁殖并加速传播,形成恶性循环,导致枯枝死树连续发生.而利用笔者的专利技术尽早采取综合防治效果明显.