Characterization of Colletotrichum acutatum Isolates Causing Anthracnose of Almond and Peach in California

ABSTRACT The causal organism responsible for the recent outbreak of almond and peach anthracnose in California was identified and characterized as Colletotrichum acutatum. Isolates of C. acutatum from almond were found to be similar to California strawberry isolates and South Carolina peach and apple isolates of C. acutatum based on conidial morphology, temperature relationships, fungicide sensitivity, and polymerase chain reaction (PCR) methods using DNA species-specific primers. On almond, blossoms and immature or mature fruit were affected by the disease, causing direct losses of crop. On peach, the disease was observed only on mature fruit. Pathogenicity of almond and peach isolates of C. acutatum was demonstrated on wound- and nonwound-inoculated almond or peach fruit by fulfilling Koch's postulates. Conidial morphology of isolates was variable, depending on the medium or substrate used to culture the isolates. Isolates of C. acutatum from strawberry, almond, and peach were grouped together based on a similar response to temperature, with an optimal growth rate at 25 degrees C (generally less than 10 mm/day), whereas isolates of C. gloeosporioides from citrus and papaya had an optimal growth rate at 30 degrees C (generally greater than 10 mm/day). In fungicide disk assays, isolates of C. acutatum from strawberry, peach, and apple, as well as almond and peach isolates from California, were less sensitive to benomyl at 300, 600, or 1,200 mug/ml. In contrast, C. gloeosporioides isolates from citrus and papaya were very sensitive to benomyl at all concentrations evaluated. All isolates of both species were sensitive to captan (300, 600, or 1,200 mug/ml). Oligonucleotide primers were synthesized for C. acutatum, C. fragariae, or C. gloeosporioides using published DNA sequences from the internal transcribed spacer 1 region of ribosomal DNA. Thirty-two Colletotrichum isolates from almond fruit produced DNA products with a C. acutatum primer (CaInt-2) that matched products and approximate molecular weight of known C. acutatum isolates. No PCR products were produced with primers for C. gloeosporioides or C. fragariae. Isolates from citrus and papaya produced DNA products only with primers from C. gloeosporioides or C. fragariae. Thus, worldwide, anthracnose of almonds may be caused by either C. gloeosporioides, as previously reported, or by C. acutatum, as indicated in this study.     

Colletotrichum acutatum and C. gloeosporioides Cause Anthracnose on Olives

Morphological and cultural features and restriction fragment length polymorphism analysis of ITS regions, including 5.8S rDNA, from 26 isolates of Colletotrichum species revealed that isolates from olive fruits, previously identified as C. gloeosporioides, belong to two taxa: C. acutatum and C. gloeosporioides. Comparison of both ITS sequence data with reference isolates confirmed the presence of both species in olives affected by anthracnose disease.     

Strawberry Anthracnose: Histopathology of Colletotrichum acutatum and C. fragariae

ABSTRACT Ontogeny of the invasion process by Colletotrichum acutatum and C. fragariae was studied on petioles and stolons of the strawberry cultivar Chandler using light and electron microscopy. The invasion of host tissue by each fungal species was similar; however, each invasion event occurred more rapidly with C. fragariae than with C. acutatum. Following cuticular penetration via an appressorium, subsequent steps of invasion involved hyphal growth within the cuticle and within the cell walls of epidermal, subepidermal, and subtending cells. Both species of fungi began invasion with a brief biotrophic phase before entering an extended necrotrophic phase. Acervuli formed once the cortical tissue had been moderately disrupted and began with the development of a stroma just beneath the outer periclinal epidermal walls. Acervuli erupted through the cuticle and released conidia. Invasion of the vascular tissue typically occurred after acervulus maturation and remained minimal. Chitin distribution in walls of C. fragariae was visualized with gold-labeled wheat germ agglutinin. The outer layer of bilayered walls of conidia, germ tubes, and appressoria contained less chitin than unilayered hyphae in planta.     

Genetic Diversity Within Colletotrichum acutatum sensu Simmonds

ABSTRACT Isolates of Colletotrichum acutatum from several hosts were characterized by various molecular methods in comparison with morphological identification. Species-specific primer analysis was reliable for grouping C. acutatum isolates to their designated species. Arbitrarily primed polymerase chain reaction and A+T-rich DNA analyses identified four subgroups within C. acutatum. Subgroup I contained U.S. isolates from almond, apple, peach, and pecan, subgroup II contained isolates from anemone, olive, and strawberry, subgroup III contained isolates from almond (Israel) and strawberry (Spain), and subgroup IV contained a single isolate from anemone (the Netherlands). Likewise, sequence analysis of the internal transcribed spacer (ITS) 2 region alone or the complete ITS (ITS 1-5.8S-ITS 2) region grouped the isolates into the same four subgroups. Percent similarity of the complete ITS region within each cluster ranged from 99.6 to 100.0, 99.8 to 100.0, and 98.6% among subgroups I, II, and III, respectively. DNA sequence analysis of the ITS 2 region alone or the entire ITS 1-2 region was more informative than that of the ITS 1 region, which could only group the isolates into two main clusters. The molecular methods employed for studying genetic variation in populations of C. acutatum determined that this species is diverse, indicating that isolates within populations of each subgroup are not host specific.     

Identification of Subpopulations of Colletotrichum acutatum and Epidemiology of Almond Anthracnose in California

ABSTRACT In recent years, almond anthracnose has developed into a major problem for the California almond industry. The identification of the causal pathogen as Colletotrichum acutatum was confirmed using species-specific primers and restriction fragment length polymorphisms of ribosomal DNA in comparative studies with isolates of C. acutatum from strawberry and C. gloeosporioides from citrus. Two distinct clonal subpopulations among the almond isolates of C. acutatum were identified. These two subpopulations differed in their colony appearance (pink versus gray cultures), conidial morphology, virulence in laboratory inoculation studies, temperature relationships for growth, and molecular fingerprints using random and simple-repeat primers in polymerase chain reactions. Both subpopulations were commonly isolated from the same orchard or even the same fruit. In other orchards, one subpopulation predominated over the other subpopulation. Using random, simple-repeat, and species-specific primers, isolates of the almond anthracnose pathogen from Israel were very similar to the California isolates that produce gray colonies. In addition to fruit, the pathogen was isolated from blighted blossoms, water-soaked or necrotic leaf lesions, symptomless peduncles, and spurs and wood from branches showing dieback symptoms, indicating that the amount of tissue that may be infected is more extensive than previously considered. Overwintering fruit mummies were identified as inoculum sources for early spring infections. Growth studies using almond kernels with different moisture contents indicated that postharvest damage of stored kernels likely originates from preharvest field infections.     

Anthracnose on almond in Australia:disease progress and inoculum sources of Colletotrichum acutatum

Anthracnose, caused by Colletotrichum acutatum, is an important disease of almond and has caused significant economic losses in California, Israel and Australia. Anthracnose development was monitored for three growing seasons in an almond orchard in South Australia on two almond cultivars, Price and Nonpareil, with up to 80 % of fruit affected in 2004. Lesions, typical of anthracnose, formed on young developing fruit and symptoms continued to appear until the fruit were ca 20 mm long, after which no further lesions developed. Symptoms were observed on leaves, woody tissue showed signs of dieback, but blossom blight was not observed. Maximum disease incidenceperfor, man and Relative Area Under the Disease Progress Curve (RAUDPC) were significantly larger for Price than Nonpareil for each season, but differences in the apparent rates of infection for both cultivars were insignificant for the three growing seasons. The apparent rates of infection were correlated with rainfall and daily temperature for the three years combined but there was no correlation between maximum disease incidence or RAUDPC and these environmental parameters. Considerably more mummified fruit remained on the trees of cv. Price than Nonpareil each year; however, there was no correlation between the number of mummified fruit in one season and maximum disease incidence, RAUDPC or apparent rate of infection, in the following season. C. acutatum was recovered from mummified fruit, peduncles and bark, from both Price and Nonpareil, every month throughout a year-long sampling period. C. acutatum was also recovered from asymptomatic leaves, fruit, bark, buds and blossom, however, less frequently and at lower rates than from mummified fruit and peduncles. Recovery was consistently greater from Price than from Nonpareil for all tissues.     

Effect of Strawberry Density on the Spread of Anthracnose Caused by Colletotrichum acutatum

ABSTRACT Spread of strawberry anthracnose, resulting from the rain splash dispersal of Colletotrichum acutatum conidia, was determined in field plots by assessing fruit disease incidence at a range of distances from an introduced point source of infected fruit with sporulating lesions. Four within-row plant densities were established in replicated plots in each of 2 years. A generalized linear model with a logit link function and binomial distribution for incidence was used to quantify the effects of distance and side of the row relative to the inoculum source, plant density treatment, and their interactions on disease incidence. At all assessment times, there was a significant (P 相似文献   

Characterization of three Colletotrichum acutatum isolates from Capsicum spp.

Colletotrichum acutatum causes anthracnose on peppers (Capsicum spp.), resulting in severe yield losses in Taiwan. Fungal isolates Coll-153, Coll-365 and Coll-524 collected from diseased peppers were found to differ in pathogenicity. Pathogenicity assays on various index plants revealed that Coll-524 was highly virulent and Coll-153 was moderately virulent to three commercially available pepper cultivars. Both isolates induced anthracnose lesions and produced abundant conidia. Coll-365 was only weakly virulent on pepper fruit, where it caused small lesions and hardly produced conidia on pepper fruit. However, Coll-365 was highly pathogenic to tomato fruit and mango leaves, where it caused anthracnose lesions and formed acervuli and conidia. All three isolates showed similar abilities in the attachment and germination of conidia, formation of highly branched hyphae and appressoria, penetration of cuticles, and infection of epidermal cells on chili peppers. Coll-365 accumulated less turgor pressure in appressoria but produced higher levels of cutinase and protease activity than Coll-153 and Coll-524 did. All three isolates invaded the neighbouring cells through plasmodesmata in chili peppers and showed similar pectinase or cellulase activities in culture. However, the most virulent strain Coll-524 expressed stronger laccase activity and was more resistant to capsaicin compared to Coll-153 and Coll-365. The three isolates are different in numbers and sizes of double-stranded RNAs. Depending on the cultivar genotypes, cellular resistance of chili pepper to C. acutatum might rely on the ability to restrict penetration, colonization, or conidiation of the pathogen. We conclude that the differences in pathogenicity among the three C. acutatum isolates of pepper are attributed to their ability to colonize the host plant.     

PCR-based detection of Colletotrichum acutatum on strawberry

An oligonucleotide primer ( Ca Int 2) was synthesized from the variable internal transcribed spacer (ITS) 1 region of ribosomal DNA (rDNA) from Colletotrichum acutatum . PCR with primers Ca Int2 and ITS4 (from a conserved sequence of the rDNA) amplified a 490 bp fragment from several isolates of C. acutatum but not from other members of the genus Colletotrichum . Amplification of this fragment was achieved from 100 fg of fungal DNA. These primers amplified a fragment of the same size from DNA extracted from strawberry tissues infected by C. acutatum . Southern hybridization analysis confirmed the 490 bp fragment from C. acutatum DNA and infected strawberry to be identical. The species-specific primer ( Ca Int2) developed in this work could be used for the accurate identification of C. acutatum and its detection on other host plants.     

Infection of citrus pollen grains by Colletotrichum acutatum

Postbloom fruit drop (PFD), an important disease caused by Colletotrichum spp., affects citrus yields in Brazil. PFD is characterised by the presence of necrotic lesions on the petals and stigmas of citrus flowers and by the subsequent abscission of young fruit. PFD epidemics have high disease progress rates, which is unusual for a pathogen that produces acervuli and is dispersed by rain. It is possible that other dispersal agents, such as insects and pollen, are involved in the spread of this disease. The objective of this work was to test whether citrus pollen grains can be colonised by Colletotrichum acutatum. Studies using light and electron microscopy showed that the pollen of Citrus sinensis can be infected by C. acutatum. This pathogen can penetrate and colonise citrus pollen grains 24 h after inoculation with the pathogen. The germ tube of conidia either penetrates the pollen sporodermis directly or passes through pollen germ pores. A single hypha can colonise more than one pollen grain. On the surface of the stigma, conidium formation can be observed. This study shows that Citrus sinensis pollen may, in fact, play a role in the spread of C. acutatum in citrus orchards.     

Anthracnose of bacopa caused by Colletotrichum destructivum

Severe spotting and blighting of leaves were found on bacopa (Sutera cordata), a scrophulariaceous ornamental, in greenhouses in Gunma Prefecture, Japan, from January through February 2007. After we isolated and identified the causal fungus as Colletotrichum destructivum and inoculated host plants with the isolate to confirm pathogenicity, we named this new disease anthracnose of bacopa.     

Occurrence and development of Colletotrichum acutatum on symptomless blueberry bushes

The anthracnose fungus Colletotrichum acutatum was detected in symptomless blueberry bushes ( Vaccinium spp.) in a Japanese blueberry field. Naturally diseased bushes and their apparently healthy neighbours were selected, and C. acutatum was isolated from the symptomless tissues of each bush from February 2000 to January 2002. Analysis of the diseased bushes during the dormant period revealed that the fungus was able to survive on symptomless tissues, such as shoot bark and bud scales. Furthermore, C. acutatum was consistently isolated from symptomless leaves and shoots of several surrounding symptomless bushes. Arbitrarily primed PCR (ap-PCR) analyses of the fungal isolates obtained from the diseased and symptomless bushes revealed that most C. acutatum isolates were genotypically identical, regardless of their origins. Inoculation tests using leaves of various blueberry cultivars suggested that the presence or absence of symptoms on each bush can not always be explained by differences in cultivar susceptibility, and other factors may be associated with the appearance of symptoms.     

Germination and Sporulation of Colletotrichum acutatum on Symptomless Strawberry Leaves

ABSTRACT The germination and sporulation of Colletotrichum acutatum were characterized over time on strawberry leaves (cv. Tristar) and plastic coverslips incubated at 26 degrees C under continuous wetness. Conidia germinated within 3 h after inoculation and formed melanized appressoria with pores by 9 h after inoculation. Host penetration was not observed up to 7 days after inoculation. Production of secondary conidia on conidial and hyphal phialides began within 6 h after inoculation. Secondary conidiation was responsible for up to a threefold increase in the total number of conidia within 7 days after inoculation. Primary conidia and hyphae began to collapse 48 h after inoculation, whereas melanized appressoria remained intact. These findings suggest that appressoria and secondary conidia of C. acutatum produced on symptomless strawberry foliage may be significant sources of inoculum for fruit infections.     

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...     

Tracing Latent Infection of Colletotrichum acutatum on Strawberry by PCR

Colletotrichum acutatum, a quarantine organism on strawberries in the EU, was found in Finland for the first time in 2000. Concern about rapid, unnoticeable spread of this pathogen has necessitated studies to find methods with which the quiescent fungus infection can be detected in imported, cold-stored strawberry plant material. Successful detection of C. acutatum in strawberry tissues by polymerase chain reaction (PCR) is dependent on the method of DNA extraction used. Good-quality nucleic acid, free of PCR inhibitors, was successfully prepared by slightly modifying the DNA extraction method of a commercially available kit. Species-specific primers, previously described in the literature, were successfully used in the PCR reaction. C. acutatum was detected by PCR both on symptomatic and asymptomatic plant parts and in artificially and naturally infected strawberry tissues. Positive PCR results were obtained from ripe and unripe berries, runners, petioles and different parts of crowns. The data demonstrate that the PCR technique can be used to detect C. acutatum in strawberry tissue even in plant parts that do not show visible symptoms.     

Novel infection strategies of Colletotrichum acutatum on ripe blueberry fruit

The infection and colonization process of Colletotrichum acutatum on ripe blueberry fruit from two cultivars with different susceptibility to anthracnose were examined using light and confocal laser scanning microscopy. Ripe fruit from susceptible cv. Jersey and resistant cv. Elliott were drop-inoculated with a conidial suspension of C. acutatum, and epidermal peels were evaluated at selected times after inoculation and incubation. Results from pre-penetration studies demonstrated that there were significant differences in the rate of formation of melanized appressoria between the two cultivars, with the rate of formation being faster in the susceptible one. In both cultivars, penetration by the pathogen occurred via appressoria 48 h post-inoculation (hpi). However, in the susceptible cv. Jersey, C. acutatum then adopted an intracellular hemibiotrophic-like infection strategy, whereas in the resistant cv. Elliott subcuticular intramural-like infection occurred. In cv. Jersey by 108 hpi, intracellular growth of the pathogen led to the formation of numerous acervuli, with orange conidial masses. By 120 hpi, the conidial masses had coalesced covering the entire inoculated area. In cv. Elliott, acervuli were not seen until 144 hpi and contained few conidia. These results demonstrate for the first time the ability of C. acutatum to adopt a different infection and colonization strategy depending on the susceptibility of the host tissue being colonized.     

Anthracnose of Japanese radish caused by Colletotrichum dematium

Anthracnose of Japanese radish found in Kagoshima and Miyazaki prefectures was demonstrated to be caused by Colletotrichum dematium based on inoculation experiments and morphological and molecular identification of the pathogenic fungus. Although symptoms of Japanese radish anthracnose caused by Colletotrichum higginsianum were similar to those caused by C. dematium, damage by the latter pathogen was more severe than that by C. higginsianum.     

Anthracnose of Nemesia strumosa Caused by Colletotrichum fuscum

Severe wilt with spots and/or leaf and stem blight were found on a scrophulariaceous flowering plant, Nemesia strumosa, grown in Kagawa Prefecture, Japan, in February 1999. Wilted plants had numerous lesions and died early. A mitosporic fungus isolated repeatedly from the diseased plants was identified as Colletotrichum fuscum and was demonstrated to cause the disease. N. strumosa is a new host for C. fuscum, which has been known to attack foxglove (Digitalis spp.). The present disease was named “anthracnose of N. strumosa” as a new disease. Received 10 October 2000/ Accepted in revised form 11 January 2001     

Subcuticular-Intracellular Hemibiotrophic and Intercellular Necrotrophic Development of Colletotrichum acutatum on Almond

ABSTRACT The early infection and colonization processes of Colletotrichum acutatum on leaves and petals of two almond cultivars with different susceptibility to anthracnose (i.e., cvs. Carmel and Nonpareil) were examined using digital image analysis of light micrographs and histological techniques. Inoculated tissue surfaces were evaluated at selected times after inoculation and incubation at 20 degrees C. Depth maps and line profiles of the digital image analysis allowed rapid depth quantification of fungal colonization in numerous tissue samples. The results showed that the early development of C. acutatum on petals was different from that on leaf tissue. On petals, conidia germinated more rapidly, germ tubes were longer, and fewer appressoria developed than on leaves. On both tissues, penetration by the pathogen occurred from appressoria and host colonization was first subcuticular and then intracellular. On petals, colonizing hyphae were first observed 24 h after inoculation and incubation at 20 degrees C, whereas on leaves they were seen 48 to 72 h after inoculation. Intercellular hyphae were formed before host cells became necrotic and macroscopic lesions developed on petals >/=48 h and on leaves >/=96 h after inoculation. Histological studies complemented data obtained by digital image analysis and showed that the fungus produced infection vesicles and broad hyphae below the cuticle and in epidermal cells. In both tissues, during the first 24 to 48 h after penetration fungal colonization was biotrophic based on the presence of healthy host cells adjacent to fungal hyphae. Later, during intercellular growth, the host-pathogen interaction became necrotrophic with collapsed host cells. Quantitative differences in appressorium formation and host colonization were found between the two almond cultivars studied. Thus, on the less susceptible cv. Nonpareil fewer appressoria developed and host colonization was reduced compared with that on cv. Carmel.     

Anthracnose of centipede grass caused by Colletotrichum caudatum

Anthracnose disease was found on centipede grass [Eremochloa ophiuroides (Munro) Hack.] planted as a ground cover on paddy field levees in Shiga Prefecture in 2004. The symptoms were ear blight, stalk blight, and leaf spots. The causal fungus was morphologically identified as Colletotrichum caudatum (Sacc.) Peck. This is the first report of centipede grass anthracnose caused by C. caudatum.