Penetration by Botryosphaeriaceae species in avocado,guava and persimmon fruit during postharvest

Botryosphaeriaceae species have a wide host range and a worldwide distribution. These fungal species can colonize several plant organs, such as the trunk, leaves and fruit. Some Botryosphaeriaceae species cause important diseases on persimmon, avocado and guava fruit. However, there is a lack of information regarding the mechanisms of penetration by Botryosphaeriaceae species on these tropical and subtropical fruits. This study aimed to better understand the mechanisms involved in fungal penetration, host specificity and aggressiveness of Botryosphaeria dothidea, Lasiodiplodia pseudotheobromae and Neofusicoccum parvum on avocado (Persea americana), guava (Psidium guajava) and persimmon (Diospyros kaki) fruit. Scanning electron microscopy (SEM) image analysis showed that in avocado fruit, the three studied Botryosphaeriaceae species penetrated through lenticels. In guava fruit, penetration through stomata was verified for Botryosphaeria dothidea and Neofusicoccum parvum. In persimmon fruit, an appressoria-like structure was observed for B. dothidea, which suggests direct penetration. Disease incidence in wounded fruit was 24% higher than in non-wounded fruit. L. pseudotheobromae and N. parvum showed differences in aggressiveness in guava fruit. The longest incubation period was observed for N. parvum inoculated on guava, with an average of 4.5 days, and the shortest incubation period was verified for B. dothidea inoculated on avocado, with an average of 2.8 days. The area under the disease progress curve (AUDPC) did not differ between Botryosphaeriaceae species on avocado, whereas on guava and persimmon fruit, the AUDPC was lower for B. dothidea. The information regarding penetration mechanisms and aggressiveness is important to improve postharvest disease control strategies.     

Botryosphaeriaceae on Syzygium cordatum across a latitudinal gradient in South Africa

The Botryosphaeriaceae is a family of endophytic fungi, many of which are latent pathogens of woody plants. Although extensively sampled in some parts of the world, little is known regarding their occurrence across different environmental conditions. This study considered the presence of the Botryosphaeriaceae on Syzygium cordatum trees across a latitudinal gradient. We examined the relative importance of different environmental factors on the presence of the Botryosphaeriaceae across this latitudinal gradient. Specifically, Botryosphaeriaceae community composition and species richness were analysed. The optimal growth temperature of the most common Botryosphaeriaceae isolates and its relation to isolate origin was also tested in culture. We identified 14 Botryosphaeriaceae species including seven each of Lasiodiplodia and Neofusicoccum species. The maximum historical temperature emerged as the environmental factor that best predicted the presence of Botryosphaeriaceae species in S. cordatum trees, specifically influencing Botryosphaeriaceae community composition. For all the Botryosphaeriaceae species studied in vitro, temperature strongly influenced mycelial growth and they all had an optimal growth temperature of 25 °C. Contrary to our hypothesis, the optimal growth temperature was not related to isolate origin. These results contribute to understanding the presence of the Botryosphaeriaceae in trees and our ability to detect these latent pathogens.     

一种新发生的油桐叶枯病病原真菌

报道了中国广西田林县油桐主产区一种新的叶片真菌病害,定名为油桐叶枯病。该病主要为害叶片,病菌侵染后叶片呈现灰褐色病斑,后期扩至整个叶片,引起过早脱落,影响油桐产量。从采集的带病标本中分离到16个纯培养物,隶属5个分类单元。依据柯赫法则和致病性测定,证明只有菌株VT-04为油桐叶枯病的病原物。在病斑组织中观察不到有性或无性繁殖结构,而该病原菌在诱导培养（含无菌松针的水琼脂+近紫外照射）条件下可产生子实体。比较培养性状、产孢结构特征并结合分析核糖体rDNA基因转录间隔区（ITS）和RNA聚合酶次大亚基基因（RPB2）序列和系统发育关系,将该病原菌鉴定为葡萄座腔菌科Botryosphaeriaceae中的一种无性型菌物,即小新壳梭孢Neofusicoccum parvum。这是首次在油桐叶片上发现由该病菌引起的病害。     

落叶松枯梢病在中国的适生性

落叶松枯梢病(Neofusicoccum laricinum)是威胁落叶松人工林的检疫性林木病害。明确当前该病在中国的潜在适生区及其在未来对气候变化的响应,揭示影响该病害发生流行的主导环境变量,对落叶松枯梢病的早期预警及防治具有重要意义。基于落叶松枯梢病分布数据和环境数据,利用ENMTools、R和刀切法(Jack knife test)筛选分布点数据和环境因子,通过MaxEnt、ArcGIS、SDMTools等技术预测当前和未来气候条件下落叶松枯梢病在中国的潜在适生区,划分病害适生等级并计算各适生等级面积占比,绘制质心转移轨迹。结果表明:(1)建立的落叶松枯梢病在中国的潜在适生区预测模型具有高精确性和可信度(不同年份和不同气候模式下的AUC值均大于0.9);(2)影响落叶松枯梢病分布的主要环境变量为年平均气温、最暖季度降水量、年降水量和最暖季度平均温度;(3)当前气候模式下落叶松枯梢病在中国的潜在适生区面积占中国国土总面积的18.02%,中高适生区集中分布在中国辽宁东南部、吉林东部、黑龙江大部分地区、内蒙古东北部;(4)在三种不同气候条件下(ssp126、ssp245、ssp585),未来落叶松枯梢病在中国的潜在适生区面积与现代气候条件相比均有所减少,其质心由东北向华北、西南地区转移。落叶松枯梢病一旦发生将会造成不可逆的生态灾难和经济损失,因此本研究对落叶松枯梢病在中国的潜在适生区进行预测和分析,研究结果对合理区划落叶松枯梢病潜在入侵风险地、加强重点地区的检疫监测、及时制定有效的防治手段,以及对于发生区的监测和防治与未发生区的早期预警和监管具有重要意义。     

Genetic and pathogenic diversity of Neofusicoccum parvum in New Zealand vineyards

Genetic diversity of 50 isolates of Neofusicoccum parvum, the predominant species of the Botryosphaeriaceae recovered from grapevines displaying symptoms of dieback and decline in New Zealand, was compared to that of isolates from Australia, South Africa, and California. The eight universally primed polymerase chain reaction (UP-PCR) primers distinguished 56 genotypes, with only four clonal pairs found. Seven main groups were identified in a neighbour-joining (NJ) tree with isolates from different regions and vineyards of New Zealand, Australia, and California distributed in different groups, indicating a high level of intra and intervineyard genetic variation. All of the South African isolates were positioned in a separate UP-PCR group, indicating that these isolates were less related to the other N. parvum isolates. When compared to fungi that reproduce sexually the genetic diversity and Shannon diversity indices were low (0.076-0.249; 0.109-0.367, respectively), genetic identity levels were high (0.76-0.95), and genetic distance levels were low (0.04-0.27). The large number of genotypes and the low number of clones in the New Zealand N. parvum populations may be explained by parasexual recombination as anastomosis was observed between nonself pairings. Pathogenicity tests using isolates from different UP-PCR groups inoculated onto either green shoots or 1-y-old grapevines detected virulence diversity, indicating intra and intervineyard variation between isolates, however, no correlation was detected between UP-PCR group and virulence.     

Identification and Characterization of Fungal Pathogens Associated with Boxwood Diseases in the Republic of Korea

Boxwood is a representative ornamental shrub that is widely used in landscaping horticulture. After pruning, damaged leaves or stems of boxwoods are unavoidably vulnerable to infection by various plant pathogens. Several boxwood diseases caused by fungi, such as Volutella blight and Macrophoma leaf spot, have been reported worldwide including Republic of Korea. In this study, we isolated and identified fungal pathogens of boxwood diseases that occurred in Korea and characterized their morphological and taxonomic characteristics. Boxwood samples showing blight symptoms were collected in Seoul, Republic of Korea, and the putative fungal pathogens Pseudonectria buxi, P. foliicola, and Neofusicoccum buxi were successfully identified. Investigation of the morphological features of the field isolates, including mycelial growth and conidial morphology, and phylogenetic analysis of multiple DNA barcode loci revealed that there were some morphological and genetic variations among isolates, but all of the analyzed isolates were closely related to the corresponding reference strains. We also found that P. foliicola strains were more virulent than P. buxi, and the N. buxi strains isolated in this study were weak pathogens or saprophytes. The results of our study will contribute to the development of control strategies for boxwood diseases caused by fungi and accelerate research on the complex ecology of boxwood diseases.     

Neofusicoccum parvum and Diaporthe foeniculina associated with twig and shoot blight and branch canker of citrus in Greece

In a survey performed in Chania and Aetoloacarnania, Greece in years 2013–2014, fungal isolates causing twig and shoot blight and branch canker of citrus trees were morphologically characterized and identified by multiple gene sequence analysis. By sequencing the ITS‐5.8S rRNA, the elongation factor 1‐α (EF1‐α), the β‐tubulin and the RNA polymerase II subunit (Rpb2) genes, the isolates examined were associated with Diaporthe foeniculina (six isolates) and Neofusicoccum parvum (one isolate). All six D. foeniculina isolates showed slow colony growth rates (7.4 ± 3.2 mm/day), while the N. parvum isolate exhibited fast growth (41.6 mm/day). Koch's criteria were met after re‐isolation of D. foeniculina isolates from all inoculated Citrus spp. and N. parvum from inoculated C. reticulata “Ortanique” and after having developed symptoms similar to those detected on shoots and branches collected from citrus fields. Based on lesion length on detached C. medica “Lia Kritis” shoots, N. parvum caused long necrotic lesions (58 mm in length) in comparison with a length of 12–21 mm lesions caused by D. foeniculina isolates. Pathogenicity trials on nine Citrus spp., which had been inoculated with D. foeniculina and N. parvum, revealed different levels of susceptibility, indicating a host‐dependent infection effect, with Poncirus trifoliate × C. paradisi (“Citrumelo Swingle”) being the most resistant citrus genotype. Lack of host specificity suggests that their pathogen–host association could be attributed to ecological rather to co‐evolutionary factors. This work represents the first report, accompanied with pathogenicity tests, on botryosphaeriaceous and diaporthaceous pathogens associated with twig and shoot blight and branch canker of citrus in Greece.     

Botryosphaeriaceae from tuart (Eucalyptus gomphocephala) woodland, including descriptions of four new species

Eucalyptus gomphocephala (tuart) is a tree native to the southwest coast of Western Australia, where, in some areas, there is a significant decline in the health of tuart. Botryosphaeriaceous taxa have been isolated as endophytes and canker pathogens from numerous hosts in many parts of the world and have been implicated in the decline of E. gomphocephala. In the present study, endophytic fungi were isolated from a wide variety of native woody plant species (Acacia cochlearis, A. rostellifera, Allocasuarina fraseriana, Agonis flexuosa, Banksia grandis, E. gomphocephala, E. marginata and Santalum acuminatum), at two locations in native E. gomphocephala woodland; a site in decline at Yalgorup National Park and a healthy site at Woodman Point Regional Park. Of the 226 isolates obtained, 154 were botryosphaeriaceous taxa, 80 % of which were found to be Neofusicoccum australe, isolated from all hosts at both collection sites. Four new species are described, Dothiorella moneti, Dothiorella santali, Neofusicoccum pennatisporum, and a species belonging to a genus only recently included in the Botryosphaeriaceae, Aplosporella yalgorensis. The other species isolated were Botryosphaeria dothidea on the new hosts A. rostellifera, A. cochlearis and E. marginata and Dichomera eucalypti, on the new host E. marginata. None of the new species formed lesions on excised stems of their host species, E. gomphocephala, or a common plantation species, E. globulus. However, Neofusicoccum australe formed lesions on excised stems of E. globulus and E. gomphocephala.