Falcate Conidia Research Articles

Cultural and morphological characteristics of Colletotrichum sublineolum isolates infecting sorghum in eastern Ethiopia

Colletotrichum sublineolum is the most destructive pathogen causing sorghum anthracnose worldwide. The fungus is known to have highly variable pathotypes. A characteristic study of pathogen is important to document the change occurring in population as variability in morphology indicates the existence of different pathotypes. Controlled condition experiment was conducted to examine cultural and morphological characteristics of C. sublineolum isolates infecting sorghum in eastern Ethiopia. Sorghum leaves showing symptoms of anthracnose were collected from five districts through survey. To study the characteristics of C. sublineolum, single-spore isolates representing isolate collection districts were selected from the stock cultures and cultivated on potato dextrose agar. Culture growth, colony color, elevations, texture and margin, conidial diameter and shape were used to characterize isolates. The isolates were varied significantly in many aspects. Colony colors were differed from light-gray to gray, purple-gray to cottony-gray, white to salmon-whit, plum-pink to beige and rosy brown on upper side of the petri dishes. The mean culture growth of C. sublineolum isolates showed highly significant (P < 0.01) variations among each other and ranged from 15 to 44 mm eight-days after incubation. Most of the isolates were produced hyaline, smooth walled, falcate conidia but without septa. Conidial diameter of C. sublineolum isolates showed variations with width and length ranged from 2.97 to 6.01 μm and 10.01–27.75 μm, respectively. Most isolates had smooth colony margin and few had undulated margin. This finding revealed that substantial variations were observed among C. sublineolum isolates and the existence of variable characteristic showed the presence of several sub-species of the pathogen infecting sorghum in different agro-ecologies of eastern Ethiopia.

Understanding the Etiology of Chilli Fruit Rot Disease in Tamil Nadu

Background: Fruit rot is an age old destructive disease of chilli caused by complex fungal pathogens resulting in severe yield losses both at pre and post-harvest stages. Hence, this study aims to investigate the occurrence of fruit rot disease in Tamil Nadu and to identify the fungal pathogens associated with fruit rot symptoms based on morpho-molecular characters. Methods: Roving survey was conducted in various districts of Tamil Nadu to determine the prevalence of fruit rot disease and to ascertain its causative agents. The pathogens were identified based on the conidial morphology, cultural characteristics and further confirmed by Polymerase chain reaction (PCR) using ITS 1 and ITS 4 primers. Result: Maximum disease severity was documented in Dharmapuri followed by Namakkal and lowest in Nagapattinam district. Ten isolates representing two genera viz., Colletotrichum and Fusarium were recovered from fruit rot infected chilli fruits and validated by pathogenicity test. Based on the morpho-cultural characters, 2 isolates were identified as Fusarium sp., with oval/ellipsoidal microconidia and straight/curved macroconidia, 6 isolates as Colletotrichum scovillei with fusiform conidia and 2 isolates as Colletotrichum truncatum with falcate conidia. The virulent isolates were further confirmed as C. scovillei based on PCR amplification of ITS region of genomic DNA.

The conidial coin toss: A polarized conidial adhesive in Colletotrichum graminicola

Colletotrichum graminicola is an economically significant fungal pathogen of maize. The primary infective conidia of the fungus, falcate conidia, are splash-dispersed during rain events. The adhesion of the falcate conidia triggers germination and is required for the development of infection structures. Falcate conidia are capable of immediate adhesion upon encountering the substrate. We report that rapid adhesion in C. graminicola is polarized, with a single-sided strip of adhesive material running the length of a single side (or face) of the conidium between the tips. This strip of adhesive is co-localized with dynamic transverse actin cables, and both the adhesive strip and actin cables are formed after liberation of the conidium from its conidiogenous cell but prior to adhesion to the infection court. Orientation of conidia upon contact with substrate determines whether they will rapidly adhere, and those which do not initially adhere can be induced to do so by applying force to reorient or “flip” the conidia. We propose that C. graminicola possesses an adhesive mechanism resulting in an adhesion efficiency of approximately 50% upon initial contact with substrata, and that an increase in adhesion efficiency can be induced by disturbance.

First report of Colletotrichum truncatum causing anthracnose in cassava in Brazil.

Cassava (Manihot esculenta Crantz) presents significant economic importance in Brazil and other developing countries due to its use in human and animal feeding. In 2019, cassava plants sampled in Pará state (Brazil) presented necrotic and irregular leaf spots, characteristic symptoms of cassava anthracnose. About 90% of the plants were symptomatic, and disease severity was higher during months with high temperature and humidity. Fragments of symptomatic tissues were removed from the lesion transition area, surface disinfested (45 s in 70% ethanol, 1 min in 1% NaOCl, and rinsed twice in sterile water), and plated on potato dextrose agar. Cultures were incubated at 25 °C under continuous light for 7 days. Among the obtained isolates, seven presented grey felt-like mycelium with white sectors, reverse greyish, and hyaline, aseptate, smooth-walled, falcate conidia with average size 20.7-30.7 (26.1 ± 2.1) × 2.4-4.8 (3.5 ± 0.5) μm. Phenotypical features were similar to C. truncatum (Damm et al. 2019). The representative isolate UFT/Coll87 was chosen for further assays. The identity of the isolate was determined by maximum likelihood analysis using sequences of actin (ACT, GenBank accession number MT321653), β-tubulin (TUB2, MT856673) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH, MT800857) partial regions. Colletotrichum isolate from cassava nested with C. truncatum isolates in a clade with 100% support, being confidently assigned to this species. Koch's postulates were fulfilled to confirm the pathogenicity of UFT/Coll87. Inoculation was carried out in three cassava plants by spraying a conidial suspension (106 conida mL-1) on unwounded leaves (three leaves per plant). Plants sprayed with sterile water represented negative control. Inoculated plants were kept in a humid chamber for 48 h, 25 °C, and a 12-h photoperiod. The experiment was repeated 2 times. Typical cassava anthracnose symptoms were observed 10 days after inoculation. No symptoms were observed in negative control. The pathogen was reisolated from symptomatic leaves and was phenotypically identical to the original isolate UFT/Coll87, fulfilling Koch's postulates. Colletotrichum fructicola, C. karstii, C. plurivorum, and C. siamense were reported causing cassava anthracnose in China (Liu et al. 2019). In Brazil, C. chrysophilum, C. fructicola, C. siamense and C. theobromicola were reported in association with cassava (Bragança et al. 2016; Oliveira et al. 2018; Machado et al. 2020). To our knowledge, this is the first report of C. truncatum causing cassava anthracnose worldwide. Our finding is important for disease management due to the high host range of C. truncatum. The pathogen can reduce the cassava yield, and the crop may serve as a potential inoculum source since it is commonly cultivated near to other crops that are also infected by C. truncatum.

First report of quinoa anthracnose caused by Colletotrichum nigrum and C. truncatum in the United States.

Quinoa (Chenopodium quinoa Willd.) is increasingly produced outside its native Andean range. In September 2019, stem lesions were observed on all six plants of quinoa accessions PI 510547 (25% severity) and PI 596293 (75% severity) in a demonstration plot in Ames, IA. Lesions were bleached, silvery-white to dark gray, slightly sunken, oval to linear with slightly tapered tips and contained setose acervuli. Fungi were isolated from both accessions following disinfestation with 70% ethanol and plating onto ½ acidified potato dextrose agar (APDA) and V8 medium. Isolates were examined morphologically. On V8 medium, isolate CQ1 produced sparse, flat, gray mycelia with profuse sclerotia and hyaline, aseptate, cylindrical conidia (n= 50, mean: 21.0 (range: 19.2-24) by 4.3 (2.4-4.8) µm); isolate CQ2 produced fluffy, gray to dark gray mycelia with profuse sclerotia and acervuli and hyaline, aseptate, falcate conidia (n =50, 26.8 (24-31.2) by 2.4 µm). Direct hyphal PCR was used to amplify ITS (ITS1/ITS4), ACT (ACT-512F/ACT-783R), GAPDH (GDF1/GDR1), CHS-1 (CHS-79F/CHS-234R), and TUB2 (T1/Bt-2b, CQ1 only) (Fu et al. 2019, Liu et al. 2013), and products were sequenced bidirectionally (MT772082-3, MT786524-30). A maximum likelihood tree was generated in MEGA X (Kumar et al. 2018) from a multiple sequence alignment of vouchered CBS isolates (Liu et al. 2013) and CQ1 was identified as Colletotrichum nigrum. CQ2 sequences showed 99-100% similarity to Colletotrichum truncatum sequences in Genbank (MN581860, MK675238, MF682518, MK118057). Koch's postulates were completed once with two isolates of each species grown on V8 medium under 12 hours of near UV light for two weeks. Greenhouse conditions were a 12 hr day/night cycle and temperature range of 26-30° C. Approximately 5 mL of mycelium on agar medium was sterilely removed and macerated in 6 mL of sterile distilled water. Non-inoculated medium was macerated in sterile water as a control. Forty-day old quinoa PI 634920 were inoculated by making three, 2-3 mm incisions between the cotyledons and first true leaves with a sterile razor blade. Next, 500 µL of slurry was placed on 2.54 cm2 of sterile cheesecloth and placed against the wound and wrapped with Parafilm. Six plants were inoculated per isolate and control. After two weeks, sunken, bleached to tan areas extended past wound sites of inoculated plants. No discoloration or sunken tissue was observed on control plants. Plants were tented with plastic film for one week. Acervuli were observed on C. truncatum- and C. nigrum-inoculated stems, and sclerotia were observed on C. nigrum-inoculated stems. Stems were surface disinfested with 10% bleach and plated onto ½ APDA. Colony morphologies of isolated fungi matched those of original inoculum for inoculated plants. Colletotrichum spp. were never isolated from control plants. When stems were inoculated, approximately 100 µL of slurry was also placed on 3-5 detached quinoa leaves in Petri dishes with moistened blotter paper and incubated for 48 hours at 25° C. Brownish, circular lesions developed on leaves inoculated with either species, but no lesions developed on control-slurry leaves. Colletotrichum spp. cause disease in quinoa relatives including spinach (Kurt 2015), beets (Gourley 1966) and amaranth (Wu 2001). This is the first description of Colletotrichum spp. causing stem lesions on quinoa in the United States. This disease may emerge in new quinoa production regions and may cause yield losses due to lodging.

Molecular characterization of &lt;i&gt;Colletotrichum&lt;/i&gt; species causing &lt;i&gt;Begonia&lt;/i&gt; anthracnose in Sri Lanka

Anthracnose disease is known to affect many tropical and subtropical fruits, vegetables and also certain cut-flowers and foliage plants. The disease was known to be caused by Colletotrichum gloeosporioides or C. acutatum which are presently accepted as species complexes. The present study was conducted with the main objective of identifying Colletotrichum species causing begonia anthracnose using morphological and molecular data. Begonia is an ornamental foliage plant grown worldwide. Anthracnose symptoms appear in begonia leaves as brownish, irregular, necrotic lesions. Colletotrichum was isolated from three Begonia species showing anthracnose symptoms, collected from three Provinces of Sri Lanka. Thirty isolates were obtained in the study of which 29 formed oblong conidia and the remainder produced falcate conidia. Six randomly selected isolates forming oblong conidia and the isolate with falcate conidia were sequenced for Internal Transcribed Spacer (ITS) and β-tubulin 2 (TUB2) regions. Considering >98% similarity with NCBI GenBank database for both sequences, the isolates with oblong conidia were identified as C. siamense and the isolate with falcate conidia as C. truncatum. Newly generated sequences were subjected to phylogenetic analysis with the closely related ex-type and authenticated isolates sequences. Phylogenetic analysis confirmed the species as C. siamense and C. truncatum. Koch’s postulates were performed to establish whether the fungi isolated from anthracnose lesions were actually causing anthracnose disease in Begonia leaves. This is the first report of C. siamense causing Begonia anthracnose.

Specialized infection strategies of falcate and oval conidia of Colletotrichum graminicola

For many filamentous fungi with pathogenic lifestyles, the presence of distinct asexual conidia has been described. However, the role of these spore types remains mostly obscure. Colletotrichum graminicola is a hemibiotrophic filamentous fungus, causing anthracnose on maize plants with a high potential of epidemic disease spreading. C. graminicola generates two types of conidia. Falcate shaped conidia formed in necrotic lesions on maize tissues are able to generate appressoria with high efficiency and are considered key disease spreading propagules. The second conidia type, the smaller oval conidia, is formed in the vascular system of the infected plant, probably causing the distribution of the disease in planta. Barely any knowledge exists about how these conidia are able to exhibit their specific functions in the life cycle and pathogenicity of C. graminicola. Here, we show that germlings derived from both falcate and oval conidia differ in the secretion of a germination inhibitor and signals for germling fusion. Germination experiments combined with HPLC and mass spectrometry analyses revealed that germination of falcate conidia is regulated by the self-inhibitor mycosporine-glutamine, whereas this compound is absent from oval conidia cultures. Additionally, germlings derived from oval conidia undergo germling fusions at high frequencies and are able to induce such a fusion when co-incubated with falcate conidia. Falcate conidia germlings alone, however, were never observed to fuse. Plant infection experiments showed a positive correlation between germling fusions and efficient leaf infection by oval conidia. However, this correlation was not observed for infection by falcate conidia. Together, our findings reveal significant differences of two types of conidia derived from the same pathogenic fungus with distinct roles in pathogenesis.

Phialemoniopsis endophytica sp. nov., a new species of endophytic fungi from Luffa cylindrica in Henan, China

During a survey of endophytic fungi in the cucurbit plants collected from Henan, China, a new species, Phialemoniopsis endophytica was isolated from the lower stem of Luffa cylindrica. It differs from other Phialemoniopsis species by its cylindrical to flask-shaped phialides, falcate conidia with blunt ends, ostiolate pycnidium-like conidiomata without marginal setae and ellipsoidal chlamydospores. Multi-locus (ITS, LSU, ACT, and TUB) phylogenetic analysis confirmed that P. endophytica is distinct from other species. A synopsis of the morphological characters of the new species is provided.

Novel insights into the early stages of infection by oval conidia of Colletotrichum sublineolum

Anthracnose, caused by Colletotrichum sublineolum Henn. ex Sacc. & Trotter, is one of the most important sorghum [Sorghum bicolor (L.) Moench] diseases in Brazil. This fungus exhibits conidial dimorphism, producing either falcate or oval conidia on solid and liquid media, respectively. We compared patterns of the initial infection events by these two types of conidia on sorghum leaves using light microscopy and scanning electron microscopy. The infection events during the first 24 h were similar for both oval and falcate conidia. Globose and melanized apressoria were formed at 24 h after inoculation (hai) regardless of the conidia type. Dense mycelium and oval conidia developed from germinated falcate conidia at 32 hai. Hyphal mass displaying acervuli filled with falcate conidia and surrounded by setae, developed from germinated oval conidia at 48 hai. Oval conidia were as capable as falcate conidia of infecting sorghum leaves. The inherent ability to grow faster and the easeness with which oval conidia can be produced in vitro as compared to falcate, make the former a preferred choice for studies on the C. sublineolum-sorghum interaction. It would be instructive to further investigate the potential role of the oval conidia in epidemics.

First Report of Mango Malformation Disease Caused by Fusarium pseudocircinatum in Mexico.

Mango (Mangifera indica L.) malformation disease (MMD) is one of the most important diseases affecting this crop worldwide, causing severe economic loss due to reduction of yield. After the first report in India in 1891 (3), MMD has spread worldwide to most mango-growing regions. Several species of Fusarium cause the disease, including F. mangiferae in India, Israel, the USA (Florida), Egypt, South Africa, Oman, and elsewhere; F. sterilihyphosum in South Africa and Brazil; F. proliferatum in China; F. mexicanum in Mexico; and recently, F. tupiense in Brazil (1,2,3,4). Besides F. mexicanum, F. pseudocircinatum, not yet reported as a causal agent of MMD, was isolated in Mexico from affected inflorescences and vegetative malformed tissues (4). Symptoms of vegetative malformation caused by F. pseudocircinatum included hypertrophied, tightly bunched young shoots, with swollen apical and lateral buds producing misshapen terminals with shortened internodes and dwarfed leaves. Infected inflorescences of primary or secondary axes on affected panicles were shortened, thickened, and highly branched, while the peduncles became thick, remained green and fleshy, and branches profusely resembled a cauliflower in shape and size (3). Ten isolates of F. pseudocircinatum were recovered from cultivars Ataulfo, Criollo, Haden, and Tommy Atkins in Guerrero, Campeche, and Chiapas states and characterized. Isolates produced mostly 0-septate but occasionally 1- to 3-septate oval, obovoid, or elliptical aerial conidia (0-septate: 4 to 19 [avg. 8.7] × 1.5 to 4 [avg. 2.6] μm) in false heads in the dark and in short false chains under black light, unbranched or sympodially branched prostrate aerial conidiophores producing mono- and polyphialides, and sporodochia with straight or falcate conidia that were mostly 3- to 5-septate, but sometimes up to 7-septate (3-septate: 25 to 58 [avg. 41] × 2 to 3.3 [avg. 2.9] μm; 5-septate: 33.5 to 76.5 [avg. 56.7] × 2.5 to 6 [avg. 3.5] μm). Circinate sterile hyphae were rarely formed. Two representative isolates, NRRL 53570 and 53573, were subjected to multilocus molecular phylogenetic analyses of portions of five genes: nuclear large subunit 28S ribosomal RNA, β-tubulin, calmodulin, histone H3, and translation elongation factor (TEF)-1α (GenBank GU737456, GU737457, GU737290, GU737291, GU737371, GU737372, GU737425, GU737426, GU737398, and GU737399). Two pathogenicity tests were conducted with NRRL 53570 and 53573 on healthy 2-year-old nucellar seedlings of polyembryonic Criollo; 20 μl conidial suspensions (5 × 106 conidia/ml) of each isolate and water controls were inoculated separately on 15 buds on 3 different trees, as described previously (1). The following conditions were used in experiment 1: 24 to 27°C with light intensity of 16.2 to 19.8 •Mol m-2s-1 in the range of 400 to 700 nm, and photoperiods of 14 h light and 10 h dark. Typical vegetative disease symptoms were discernible in plants inoculated with NRRL 53570 (20%) and 53573 (7%) after 8 months. In experiment 2, after 3 months growth under the above conditions, seedlings were transferred to an outdoor nursery in Iguala, Guerrero. Typical vegetative symptoms of MMD were observed in 86.7 and 13.3% of the buds inoculated with F. pseudocircinatum NRRL 53570 and 53573, respectively, after 9 months. Isolates from typical symptomatic vegetative buds were confirmed as F. pseudocircinatum by sequencing a portion of their TEF-1α gene, thus fulfilling Koch's postulates. This is the first report of F. pseudocircinatum as a causal agent of MMD.

Occurrence of anthracnose on Ardisia crenata caused by genus Colletotrichum having falcate conidia

Occurrence of anthracnose on <I>Ardisia crenata</I> caused by genus <I>Colletotrichum</I> having falcate conidia

Molecular and morphological differentiation of Colletotrichum truncatum from scentless chamomile and selected crop species

The fungal pathogen Colletotrichum truncatum is a potential bioherbicide agent for management of the noxious weed scentless chamomile (Metricaria perforate) in western Canada. Isolates of the potential biocontrol agent from scentless chamomile cannot be separated morphologically from the pathogen that causes anthracnose on lentil and field pea, raising questions about crop safety for its use as a bioherbicide agent in the region. Internal transcribed spacer (ITS) regions of ribosomal DNA (rDNA) of C. truncatum from scentless chamomile and several crop species were examined for genetic differences. ITS-rDNA fragments of 63 isolates were amplified using the universal primers Its4 and Its5 and sequenced. The rDNA fragment was 571 bp in size for isolates from scentless chamomile, 566 bp from lentil, 558 or 559 bp from field pea isolates and 555 bp from soybean. Phylogenetic analysis using parsimony and neighbour-joining methods separated these putative C. truncatum isolates into four groups that coincided with host origin. All of the isolates of scentless chamomile fell within a single cluster regardless of their geographic origins, and were most closely related to C. truncatum isolates from lentil. Morphologically, the isolates from scentless chamomile, lentil and field pea were similar in conidial shape and dimension, whereas soybean isolates had substantially longer and more falcate conidia and slightly bigger appressoria. Based on the sequence information, strain-specific PCR primers were designed for isolates of C. truncatum from each host and used to amplify specific rDNA fragments (markers). This molecular technique was sensitive and strain-specific for detection and differentiation of Colletotrichum isolates from scentless chamomile, lentil, field pea and soybean, and may be used as a tracking and monitoring tool in environmental risk assessment for the bioherbicide agent.

Three new species and a new record of Diplococcium from plant debris in Spain

Diplococcium dimorphosporum sp. nov., D. racemosum sp. nov., D. singulare sp. nov. and D. pulneyense Subram. & Sekar collected from plant debris in natural areas of Spain are described and illustrated. The first species is characterized principally by the production of branched conidiophores and short chains of conidia. Diplococcium singulare has unbranched conidiophores, and conidia produced usually at the tip of conidiophores and from lateral spherical conidiogenous cells. In addition, both species develop a Selenosporella synanamorph with narrow falcate conidia. Diplococcium racemosum produces branched, verrucose conidiophores, and verrucose conidia in long branched chains. Diplococcium pulneyense is the second record, being described for first time on the natural substratum and re-described in pure culture. A key to currently accepted species of Diplococcium is provided.

First Report of Colletotrichum capsici Causing Postharvest Anthracnose on Papaya in South Florida.

Postharvest anthracnose of papaya, Carica papaya, is an important disease in most production areas worldwide (2). Colletotrichum gloeosporioides causes two types of anthracnose symptoms on papaya: (i) circular, sunken lesions with pink sporulation; and (ii) sharply defined, reddish brown and sunken lesions, described as 'chocolate spot' (2). Colletorichum spp. were isolated from lesions of the first type on papaya fruit from the University of Florida Tropical Research and Education Center, Homestead in December 2007 and from fruit imported from Belize in March 2008 (4). Single-spore isolates were identified using colony morphology and internal transcribed spacer (ITS) and mating type (MAT1-2) sequences. Two taxa were identified in both locations: (i) C. gloeosporioides (MAT1-2; GenBank Nos. GQ925065 and GQ925066) with white-to-gray, fluffy colonies with orange sporulation and straight and cylindrical conidia; and (ii) C. capsici (ITS; GenBank Nos. GU045511 to GU045514) with sparse, fluffy, white colonies with setose acervuli and falcate conidia. In addition, in Florida, a Glomerella sp. (ITS; GenBank Nos. GU045518 and GU045520 to GU045522) was recovered with darkly pigmented colonies that produced fertile perithecia after 7 to 10 days on potato dextrose agar (PDA). In each of three experiments, mature fruit (cv. Caribbean Red) were wounded with a sterile needle and inoculated with a 15-μl drop of 0.3% water agar that contained 105 conidia ml-1 of representative isolates of each taxon. The diameters of developing lesions were measured after 7 days of incubation in the dark at 25°C, and the presence of inoculated isolates was confirmed by their recovery from lesion margins on PDA. In all experiments, C. capsici and C. gloeosporioides produced lesions that were significantly larger than those that were caused by the water control and Glomerella sp. (respectively, approximately 12, 17, 0, and <1 mm in diameter). C. gloeosporioides produced sunken lesions with dark gray centers and pink/gray sporulation, which match those previously described for anthracnose on papaya (2). In contrast, C. capsici produced dark lesions due to copious setae of this pathogen; they resembled C. capsici-induced lesions on papaya that were reported previously from the Yucatan Peninsula (3). C. capsici has also been reported to cause papaya anthracnose in Asia (4), but to our knowledge, this is the first time it has been reported to cause this disease in Florida. Since it was also recovered from fruit that were imported from Belize, it probably causes anthracnose of papaya in that country as well. Another falcate-spored species, C. falcatum, was recovered from rotted papaya fruit in Texas (1). The Glomerella sp. was recovered previously from other hosts as an endophyte and causes anthracnose lesions on passionfruit (4). However, its role as a pathogen on papaya is uncertain since it was not pathogenic in the current work; the isolates that were recovered from papaya lesions may have colonized lesions that were caused by C. capsici and C. gloeosporioides.

First Report of Colletotrichum boninense, C. capsici, and a Glomerella sp. as Causes of Postharvest Anthracnose of Passion Fruit in Florida.

Anthracnose is an important foliar and fruit disease of passion fruit, Passiflora spp. (3). In 2008, postharvest anthracnose on purple and yellow passion fruits (P. edulis Sims and P. edulis f. flavicarpa O. Degner, respectively) from a commercial planting in Miami-Dade County, FL was examined. Lesions began as light brown areas that became papery, covered much of the fruit surface, and developed pink-to-dark sporulation. Single-conidium isolates from lesions were examined morphologically and with internal transcribed spacer (ITS) sequences. Four taxa were identified: Colletotrichum boninense (GenBank No. GU045516) with felted cream-to-orange colonies and cylindrical conidia; C. capsici (synonym C. truncatum [2]) (GU045515) with sparse, white mycelia, setose acervuli, and falcate conidia; C. gloeosporioides with fluffy white-to-gray colonies and straight, cylindrical conidia; and a Glomerella sp. (GU045517) with darkly pigmented perithecia. In two experiments, four mature, yellow passion fruit were wounded at a single equatorial site with a sterile needle and inoculated with a 15-μl drop of 0.3% water agar that did not contain (noninoculated control) or contained 105 conidia per ml of representative isolates from each taxon. After 21 days at 25°C without light, anthracnose incidence was recorded and the presence of the isolates was confirmed by their recovery from lesion margins on potato dextrose agar. Anthracnose did not develop on noninoculated control fruit. Mean incidences of anthracnose exceeded 50% for isolates of C. boninense (three from passion fruit), C. capsici (two from passion fruit), and a Glomerella sp. (two from passion fruit and one each from papaya and eugenia). Despite its common indictment as a causal agent of anthracnose on passion fruit (3), symptoms developed on only one fruit that was inoculated with an isolate of C. gloeosporioides from passion fruit (13%) and did not develop after inoculation with an isolate from papaya. Work is needed to determine whether host-specific populations of C. gloeosporioides exist on passion fruit that were not assessed during this study or whether the pathogen was misidentified in previous reports on this host. C. boninense was associated previously with postharvest anthracnose of passion fruit in Japan and Colombia, whereas C. capsici was associated with leaf anthracnose of passion fruit in Florida and Japan (4); both species are reported here for the first time as causes of postharvest anthracnose of passion fruit in Florida. Glomerella sp. caused darkly pigmented lesions and produced the teleomorph on symptomatic passion fruit and in single-ascospore cultures. Isolates with ITS sequences that are 99% homologous to those from passion fruit have been recovered in South Florida from eugenia, papaya, and Piper betle (4) and from other locations on several other hosts (GenBank); they are often nonpathogenic endophytes. Almeida and Coêlho (1) reported in Brazil a Glomerella sp. that formed the teleomorph in culture and caused anthracnose on passion fruit, but did not provide ITS sequences. Additional work is warranted on the identity and ecology of these fungi.

A second species of Neoheteroceras and additional characters of the genus

A coelomycetous fungus occurring on submerged wood in Japan is described and illustrated as a new species of Neoheteroceras. The species is characterized by the large falcate conidia with several tubular appendages, but differs from N. flageoletii, the only other known species of the genus, by its larger conidia and longer appendages. The description of the genus Neoheteroceras should be emended to allow for this second species, N. macrosporum, which differs from the original species by the nature of the disposition of the conidiomata, branched conidiophore, and absence of paraphyses.

Root infection and systemic colonization of maize by Colletotrichum graminicola.

Colletotrichum graminicola is a filamentous ascomycete that causes anthracnose disease of maize. While the fungus can cause devastating foliar leaf blight and stalk rot diseases, little is known about its ability to infect roots. Previously published reports suggest that C. graminicola may infect maize roots and that root infections may contribute to the colonization of aboveground plant tissues, leading to disease. To determine whether C. graminicola can infect maize roots and whether root infections can result in the colonization of aboveground plant tissues, we developed a green fluorescent protein-tagged strain and used it to study the plant root colonization and infection process in vivo. We observed structures produced by other root pathogenic fungi, including runner hyphae, hyphopodia, and microsclerotia. A mosaic pattern of infection resulted from specific epidermal and cortical cells becoming infected by intercellular hyphae while surrounding cells were uninfected, a pattern that is distinctly different from that described for leaves. Interestingly, falcate conidia, normally restricted to acervuli, were also found filling epidermal cells and root hairs. Twenty-eight percent of plants challenged with soilborne inoculum became infected in aboveground plant parts (stem and/or leaves), indicating that root infection can lead to asymptomatic systemic colonization of the plants. Many of the traits observed for C. graminicola have been previously reported for other root-pathogenic fungi, suggesting that these traits are evolutionally conserved in multiple fungal lineages. These observations suggest that root infection may be an important component of the maize anthracnose disease cycle.

Tubeufia asiana, the teleomorph of Aquaphila albicans in the Tubeufiaceae, Pleosporales, based on cultural and molecular data

The teleomorph of Aquaphila albicans was discovered on submerged wood collected in Thailand. Its black, soft-textured, setose ascomata, bitunicate asci and hyaline to pale brown, multiseptate ascospores indicated an affinity to Tubeufiaceae (Dothideomycetes). After morphological or molecular comparisons with related species in Tubeufia, Acanthostigma and Taphrophila, it is described and illustrated as a new species, T. asiana Sivichai & K.M. Tsui, sp. nov. Finding this Tubeufia teleomorph was surprising, given the falcate conidia of its A. albicans anamorph, which superficially resemble the conidia of Fusarium and not the coiled, helicosporous conidia of other species in Tubeufiaceae. We assessed the phylogenetic relationships of A. albicans-T. asiana with ribosomal sequences from SSU and ITS and partial LSU regions by parsimony and Bayesian analysis. An initial set of 40 taxa representing a wide range of ascomycete families and their SSU sequences from GenBank showed A. albicans-T. asiana to be nested within the Tubeufiaceae with 100% bootstrap support. Their placement was inferred with ITS and partial LSU ribosomal sequences. The nearly identical ITS sequences of two isolates of A. albicans and one isolate of Tubeufia asiana united these fungi as a monophyletic group with 100% bootstrap support and further nested them, with 88% bootstrap support, in a clade containing Helicoon gigantisporum and Helicoma chlamydosporum. This is the first molecular phylogenetic study to place a nonhelicosporous species within the Tubeufiaceae and to show that helical conidia were lost at least once within the family.

Tubeufia asiana, the teleomorph of Aquaphila albicans in the Tubeufiaceae, Pleosporales, based on cultural and molecular data

The teleomorph of Aquaphila albicans was discovered on submerged wood collected in Thailand. Its black, soft-textured, setose ascomata, bitunicate asci and hyaline to pale brown, multiseptate ascospores indicated an affinity to Tubeufiaceae (Dothideomycetes). After morphological or molecular comparisons with related species in Tubeufia, Acanthostigma and Taphrophila, it is described and illustrated as a new species, T. asiana Sivichai & K.M. Tsui, sp. nov. Finding this Tubeufia teleomorph was surprising, given the falcate conidia of its A. albicans anamorph, which superficially resemble the conidia of Fusarium and not the coiled, helicosporous conidia of other species in Tubeufiaceae. We assessed the phylogenetic relationships of A. albicans-T. asiana with ribosomal sequences from SSU and ITS and partial LSU regions by parsimony and Bayesian analysis. An initial set of 40 taxa representing a wide range of ascomycete families and their SSU sequences from GenBank showed A. albicans-T. asiana to be nested within the Tubeufiaceae with 100% bootstrap support. Their placement was inferred with ITS and partial LSU ribosomal sequences. The nearly identical ITS sequences of two isolates of A. albicans and one isolate of Tubeufia asiana united these fungi as a monophyletic group with 100% bootstrap support and further nested them, with 88% bootstrap support, in a clade containing Helicoon gigantisporum and Helicoma chlamydosporum. This is the first molecular phylogenetic study to place a nonhelicosporous species within the Tubeufiaceae and to show that helical conidia were lost at least once within the family.

The SOD2 gene, encoding a manganese-type superoxide dismutase, is up-regulated during conidiogenesis in the plant-pathogenic fungus Colletotrichum graminicola

The SOD2 gene, encoding a manganese-type superoxide dismutase (MnSOD), was identified from Colletotrichum graminicola among a collection of cDNAs representing genes that are up-regulated during conidiogenesis. The SOD2 gene consists of a 797-bp open reading frame that is interrupted by three introns and is predicted to encode a polypeptide of 208 amino acids. All conserved residues of the MnSOD protein family, including four consensus metal binding domains, are present in the predicted SOD2 protein. However, the predicted protein does not appear to contain a signal peptide that would target it to the mitochondria. Northern hybridizations revealed that expression of the ∼900-bp SOD2 transcript is closely associated with differentiation of both oval and falcate conidia. Southern analysis indicated that there is only a single copy of the gene. SOD2 disruption strains were morphologically and pathogenically indistinguishable from wild-type strains. The dispensability of the MnSOD enzyme may be due to the activities of two other SOD enzymes, a highly expressed iron-type superoxide dismutase and a much less abundant copper/zinc type, that were also detected in C. graminicola.