Colletotrichum gloeosporioides, a new causal agent of citrus post-bloom fruit drop

Citrus post-bloom fruit drop (caused by Colletotrichum acutatum) frequently occurs in the southwestern region of São Paulo State, Brazil. A survey of Colletotrichum isolates associated with symptoms of post-bloom fruit drop in São Paulo State showed C. gloeosporioides in addition to C. acutatum. The objectives of this study were to confirm the identification of C. gloeosporioides isolated from symptomatic citrus flowers, to test the pathogenicity of C. gloeosporioides isolates, to compare the development of disease caused by C. gloeosporioides and C. acutatum, and to determine the frequency of C. gloeosporioides in a sample of isolates obtained from symptomatic flowers in different regions of São Paulo State. Through the use of species-specific primers by PCR, 17.3% of 139 isolates were C. gloeosporioides, and the remaining 82.7% were C. acutatum. The pathogenicity tests, carried out in 3-year old potted plants of sweet oranges indicated that both species caused typical symptoms of the disease including blossom blight and persistent calyces. Incubation periods (3.5 and 3.9 days, respectively, for C. acutatum and C. gloeosporioides) and fruit sets (6.7 and 8.5%, respectively for C. acutatum and C. gloeosporioides) were similar for both species. The incidences of blossom blight and persistent calyces were higher on plants inoculated with C. acutatum than in those inoculated with C. gloeosporioides. Conidial germination was similar for both species under different temperatures and wetness periods. Under optimal conditions, appressorium formation and melanisation were higher for C. gloeosporioides than for C. acutatum. These results indicated that Colletotrichum gloeosporioides is a new causal agent of post-bloom fruit drop.     

Molecular identification of Colletotrichum gloeosporioides causing yam anthracnose in Nigeria

Four forms of Colletotrichum representing three distinct virulence phenotypes were found associated with foliar anthracnose of yam in Nigeria: the highly virulent (= severity of disease) slow-growing grey (SGG); the moderately virulent fast-growing salmon (FGS); the weakly virulent fast-growing grey (FGG); and the moderately virulent fast-growing olive (FGO) morphotype. Isolates of the four forms were identified as C. gloeosporioides , based on morphology. The reaction of monoconidial cultures on casein hydrolysis medium (CHM), PCR-RFLP and sequence analysis of the internal transcribed spacer region of the ribosomal DNA (ITS1-5·8S-ITS2) were used to establish the identity of the yam anthracnose pathogen(s). All yam isolates were distinguished from C. acutatum by the absence of protease activity on CHM. On ITS PCR and enzymatic digestion of PCR products, all FGS, FGO and SGG isolates produced RFLP patterns identical to those of C. gloeosporioides reference isolates, while FGG isolates revealed unique ITS RFLP banding patterns. Sequence analysis of the ITS1 region and of the entire ITS region revealed that SGG, FGS and FGO isolates were highly similar (98–99% nucleotide identity) and showed 97–100% identity to C. gloeosporioides . Less than 93% similarity of these fungal isolates to reference C. acutatum and C. lindemuthianum isolates was observed. The molecular study confirmed that foliar anthracnose of yam is caused by C. gloeosporioides . While a high similarity was found among most C. gloeosporioides fungi from yam, isolates of the FGG form did not cluster with any previously described Colletotrichum species, and probably represent a distinct species.     

First report of Colletotrichum queenslandicum causing leaf anthracnose on Dracaena cambodiana in China

In June 2021, a leaf spot was found on Dracaena cambodiana on Yongxing island of Sansha City, Hainan Province, China. The disease mainly occurred at the tips or edges of older leaves. About 50% of leaves were showed necrotic symptoms. Similar fungal isolates were obtained from all sterilized sections incubated on PDA. The fungus was identified as Colletotrichum queenslandicum by morphological characteristics and multi-locus phylogenetic analyses with ITS region of rDNA, GADPH, CHS-1, ACT, GS and TUB-2 gene sequences. This is the first report of Colletotrichum queenslandicum causing leaf anthracnose on Dracaena cambodiana.

     

Honeybees can spread Colletotrichum acutatum and C. gloeosporioides among citrus plants

Postbloom fruit drop (PFD) is an important citrus disease that causes up to 100% yield losses during years in which conditions are favourable for the occurrence of epidemics. The conidia of Colletotrichum acutatum and C. gloeosporioides, causal agents of PFD, are predominantly dispersed by rain splash. At the beginning of epidemics, the distribution of diseased plants is random and the disease progress rate is very high, which is unusual for pathogens spread by rain splash. As the pathogen produces abundant conidia on diseased petals, pollinating insects may contribute to disease dispersal. This study investigated honeybees (Apis mellifera) as dispersal agents of C. acutatum and C. gloeosporioides among citrus plants. Two experiments were carried out in a screenhouse in which citrus plants were protected (or not) in insect‐proof cages. The source of inoculum was placed on one side of the screenhouse, and a honeybee hive was placed on the opposite side. All uncaged plants showed symptoms of the disease, and none of the caged plants exhibited PFD symptoms. The monomolecular model showed a good fit to disease progress in both experiments. Conidium‐like structures of Colletotrichum spp. were identified attached to the bodies of the honeybees by scanning electron microscopy. These results have revealed that honeybees disperse Colletotrichum among citrus plants.     

Colletotrichum acutatum and Colletotrichum nymphaeae causing blossom blight and fruit anthracnose on olives in southern Brazil

European Journal of Plant Pathology - Olive (O. europaea L.) is an expanding crop in the south of Brazil. Blossom blight and typical anthracnose symptoms on fruit were observed in olive trees in an...     

芒果胶孢炭疽菌漆酶lac1与致病力的相关性分析

为了明确芒果炭疽病病菌(Colletotrichum gloeosporioides)漆酶与该菌侵染相关致病因子之间的关系,本文以愈创木酚为底物筛选获得的高产漆酶菌株A2为材料,测定了漆酶粗提液对芒果炭疽病病菌致病力的影响,并通过半定量RT-PCR法,分析了在不同侵染时段漆酶基因lac1和其他酶基因的表达。结果表明,漆酶粗提液单独不能致病,但能促进该病原菌在寄主中的扩展;在侵染过程中,lac1表达与黑色素合成酶(thd和scd)基因表达相关性更高,与细胞壁降解酶(ecg和pel)基因表达也有一定相关性,但不及前者高。芒果胶孢炭疽菌分泌的漆酶有助于该菌在侵染芒果过程中的扩展,且对侵染相关致病因子黑色素合成酶和细胞壁降解酶基因的表达有一定影响。初步推测,漆酶lac1除了能通过降解芒果组织中的酚类物质、促进病原菌的扩展之外,也可以通过干扰与致病力相关的黑色素合成和细胞壁降解酶的产生来影响芒果胶孢炭疽菌致病力。     

柑橘炭疽病菌的生物学特性及枯草芽胞杆菌对其的抑制作用

近5年来,湖南麻阳苗族自治县的柑橘种植园发生柑橘炭疽病。采集发病柑橘植株,分离其病原菌,从病原菌的培养性状和形态学特征、内转录区(ITS)序列分析和系统发育关系比较等方面对该病原菌进行了鉴定,并探索了枯草芽胞杆菌(Bacillus subtilis)CGMCC 1.354对其的抑制作用。结果表明:该地区柑橘炭疽病菌为盘长孢状刺盘孢(Colletotrichum gloeosporioides)。枯草芽胞杆菌CGMCC 1.354对该病原菌具有较强的抑制作用,其分泌的抑菌物质能抑制柑橘炭疽病菌菌丝生长和孢子萌发。     

Colletotrichum species causing anthracnose on avocado fruit in Mexico: Current status

Colletotrichum species cause anthracnose disease in tropical and subtropical fruit crops worldwide. Mexico is the main producer and exporter of avocado (Persea americana) globally and has yearly outbreaks of anthracnose on this crop. However, which specific Colletotrichum spp. cause these outbreaks in avocado-producing regions remain uncertain; thus, the objective of the present study was to identify the species responsible. A survey performed in six production regions of Mexico yielded 232 isolates, from which a subset of 104 strains was selected based on morphological characteristics and origin. This subset was sequenced and haplotypes were analysed in the gapdh partial gene. Finally, 31 strains were identified through multilocus phylogenetic analyses using the sequences of the internal transcribed spacer region and six loci. This study revealed the presence of two species previously reported in Mexico (C. karsti and C. godetiae), three novel records in Mexico (C. siamense, C. fioriniae, and C. cigarro), four novel records on avocado (C. chrysophilum, C. jiangxiense, C. tropicale, and C. nymphaeae), and two novel lineages (Colletotrichum sp. 1 and Colletotrichum sp. 2). C. siamense was the most prevalent, while the species reported for the first time on avocado, including the novel lineages, were the least prevalent. C. karsti was the most widespread (four regions), followed by C. siamense, C. jiangxiense, and C. chrysophilum (three regions). Pathogenicity tests showed that all species caused anthracnose on avocado fruit. These findings will be useful for improving the management of avocado anthracnose outbreaks in Mexico.     

Histopathology of postbloom fruit drop caused by Colletotrichum acutatum in citrus flowers

Postbloom fruit drop (PFD) is caused by both Colletotrichum acutatum and C. gloeosporioides and is a potentially serious disease in citrus that occurs when flowering coincides with rainfall. The fungus incites necrotic lesions in petals and stigmas leading to premature fruit drop and reduced yield. The mechanisms of infection and survival of the causal agents remain to be fully elucidated. In the present study, we investigated the histopathology of PFD caused by C. acutatum in the petals and stigmas of sweet oranges using electron and light microscopy. In the petals, pathogen penetration occurred intra and intercellularly and also through the stomata, with intercellular penetration occurring most frequently. The distinct tissues of the petals were colonised, including the vascular system, particularly the xylem. Acervuli were observed on both sides of the petals. Although the fungus did not penetrate through the epidermal cells of the stigma, C. acutatum caused necrosis and an increase of phenolics in this tissue. A protective layer rich in lipophilic and phenolic compounds was formed under the necrotic area and crystals of oxalate were associated with the sites where the pathogen was present.     

First report of Pythium diclinum in Morocco

Pythium diclinum was isolated from a reservoir near the city of Rabat (Morocco). This is the first report of its presence in this country. Taxonomic and morphological details of the fungus are presented. The isolate grew on potato carrot agar (PCA) containing various concentrations of NaCl, up to 700 m m . Pathogenicity of the Moroccan isolate was demonstrated in vitro on lucerne seeds and seedlings.     

柑橘果实壳梭孢腐烂病的鉴定

 柑橘果实腐烂病引起伦晚脐橙果皮褐化、坚硬、缩水,严重影响果实商品价值。2017年对湖北宜昌采集的伦晚脐橙病果进行了组织分离、柯赫氏法则验证和病原菌鉴定,明确病原菌为小新壳梭孢Neofusicoccum parvum,该病菌也可侵染柑橘叶片、枝干和果实,引起腐烂。这是关于小新壳梭孢N. parvum侵染柑橘果实的首次报道。     

First report of Pseudomonas oryzihabitans causing fruit black rot in prickly ash in China

Journal of Plant Diseases and Protection - Since the summer of 2017, bacterial fruit black rot disease was observed on prickly ash (Zanthoxylum armatum DC., Yongqing No. 1) in three counties...     

火把对柑桔炭疽病菌的室内毒力试验

采用菌丝生长速率法,用杀菌剂火把对柑桔炭疽病菌进行了室内毒力测定,测得火把对柑桔炭疽病的EC50值为0.8110μg/mL,EC98值为10.5435μg/mL,确定了其在室内有效抑菌浓度。本试验有利于指导进一步的室外药效试验以确定实际应用中的最佳施用浓度。     

First report of Rhizopus stolonifer causing inflorescence and fruit rot of Rauvolfia serpentina in India

Inflorescence and fruit rot caused by Rhizopus stolonifer has appeared for the first time on Rauvolfia serpentina (sarpgandha) in North Indian plains during July–September, 2003. Disease incidence was very high under high humidity and moderate temperature and posing threat to the commercial cultivation of the crop. The initial disease symptoms appear in the form of water-soaked lesions on the flowers and flower buds which later produce slimy wet rot symptoms leading to premature death and drying of infected parts including the leaves. Pathogenicity of R. stolonifer was established artificially under glasshouse conditions.     

Blackening on yam in response to Colletotrichum gloeosporioides

A blackening confined to the cuticle and/or outer epidermal cell walls of mature leaves of Dioscorea alata was found to be associated with the appressoria of the fungus Colletotrichum gloeosporioides on plants subjected to high levels of inoculum in the field and to dense spore suspensions in controlled tests. The blackening occurred with little evidence of fungal penetration into the host cells. Preliminary analyses of the nature of the blackening detected melanin-like compounds and suggest the involvement of phenolic compounds and water-soluble chemicals, possibly enzymes, in the blackening process.     

Laboratory and field evaluation of fungicides to control anthracnose stain of citrus fruit

Anthracnose stain on Clementine tangerine and grapefruit, caused byColletotrichum gloeosporioides, is described. Among the fungicides bioassayed against this organism Bordeaux mixture was the most effective copper compound; potent organic compounds were captafol, captan, chlorothalonil, maneb and mancozeb. Bioassay evaluation of fruit treated in the grove revealed that the protection and lasting effect of captafol and Bordeaux mixture were superior to those of chlorothalonil and maneb. Effective field control was achieved even with one prophylactic treatment in July with copper-containing fungicides.