For comprehensive information on sorghum diseases and the genus Colletotrichum which causes anthracnose, check out the following books or search the Amazon.com catalogue: 
Plant Pathology 5th edition 
Sorghum and Millet Diseases 
Compendium of Sorghum Diseases 
Colletotrichum : Host Specificity, Pathology and ... 
Colletotrichum : Biology, Pathology and... |
Recent publications by the AuthorAuthor(s): Wharton P. S., and Schilder A. C.Title: Effect of temperature on apothecial longevity and ascospore discharge by apothecia of Monilinia vaccinii-corymbosi. Source: Plant Disease 2005, 89(4):397-403 Abstract: Pseudosclerotia of Monilinia vaccinii-corymbosi with apothecial initials were collected from blueberry (Vaccinium corymbosi cv. Jersey) fields in Grand Junction, MI, in the spring of 2002 and 2003 and monitored during apothecial development and maturation. Apothecia with cup openings as small as 1.2 mm in diameter were able to discharge ascospores. The number of ascospores discharged increased exponentially as the diameter of the cup opening increased, before leveling off at a cup diameter of about 6 mm. Cytological studies showed that ascospore discharge correlated well with the stage of development of asci and ascospores in the apothecium. The effect of temperature on the longevity of apothecia was studied at 10, 15, 20, and 25°C. Initial ascospore discharge was greater for apothecia incubated at higher temperatures (20 and 25°C). However, total discharge was greater in apothecia incubated at lower temperatures (10 and 15°C), as they persisted longer than those incubated at 20 and 25°C. Incubating apothecia at freezing temperatures (–2, –4, –6, and –8°C) for 1 h resulted in a 50 to 98% reduction in the number of ascospores discharged compared with before freezing. However, apothecia incubated down to –6°C were able to recover their ability to discharge ascospores by 2 days after the freezing treatment. Ascospores discharged from apothecia after freezing at –2°C for 1 h remained viable. However, the germination ability of ascospores from apothecia frozen at –4, –6, and –8°C decreased with decreasing temperature such that only 10% of ascospores from apothecia frozen at –8°C germinated successfully. The information obtained in this study may be useful in the development of scouting and management strategies for the control of mummy berry disease. Download this article in .PDF format Author(s): Wharton P. S., and Diéguez-Uribeondo, J. Title: The biology of Colletotrichum acutatum Source: Anales del Jardín Botánico de Madrid 61(1): 3-22 Abstract: Colletotrichum acutatum is major pathogen of fruit crops, causing economically important losses of temperate, subtropical and tropical fruits worldwide. However, few studies have been carried out on key aspects of its biology. This is mainly because traditionally isolates of C. acutatum were often wrongly identified as C. gloeosporioides. Effective separation of the two species was not possible until the introduction of molecular tools for taxonomy. The life cycle of C. acutatum comprises a sexual and an asexual stage and much remains to be resolved regarding the genetics of sexuality and the effects of the sexual stage on population structure. Colletotrichum acutatum exhibits both infection strategies described for Colletotrichum species, i.e. intracellular hemibiotrophy and subcuticular-intramural necrotrophy, and may also undergo a period of quiescence in order to overcome resistance mechanisms in immature fruit such as pre-formed toxic compounds and phytoalexins, or due to the unsuitability of unripe fruit to fulfill the nutritional and energy requirements of the pathogen. Colletotrichum acutatum may overwinter as mycelium and/or appressoria in or on different parts of the host. Conidia are water-born and spread by rain episodes so infections are usually highest during the wettest periods of the growing season. Current management strategies for this fungus comprise the exploitation of cultivar resistance, cultural, chemical, and biological control methods, and preventive strategies such as disease-forecasting models. This review focuses on the current knowledge of biological aspects of C. acutatum and related Colletotrichum species and includes a discussion of the progress towards their control. Download this article in .PDF format Author(s): Wharton P. S., Iezzoni A., Jones, A. L. Title: Screening cherry germplasm for resistance to leaf spot Source: Plant Disease 2003, 87(5):471-477 Abstract: A detached leaf disk assay was developed for screening sour cherry (Prunus cerasus) cultivars for resistance to cherry leaf spot (Blumeriella jaapii). This assay was used to characterize the events occurring in cv. Montmorency (susceptible) and cv. GiSelA 6 [GI 148-1] (resistant) host-pathogen interactions, and to develop a disease scoring scheme to categorize disease severity in sour cherry trees. Forty-three seedlings grown from seeds collected in Russia were screened for resistance using the scoring scheme. Cross infection studies were also carried out with leaf spot isolates from four other Prunus species. These studies were made possible by the development of a new method of culturing B. jaapii isolates, using cherry fruit agar. This method enabled large amounts of inoculum to be produced within 2 weeks rather than a couple of months as required previously. In 'Montmorency', disease symptoms were first observed 4 days postinoculation (dpi), with the appearance of small white spots on the undersides of inoculated leaves. These spots gradually grew, producing erumpent spore masses in acervuli approximately 7 dpi. In 'GI 148-1', disease symptoms were also first observed 4 dpi, with the appearance of small transparent lesions. In the majority of cases, these lesions did not increase in size; however, acervuli occasionally were formed approximately 8 dpi. These contained small cirrhi and were often surrounded by an abscission zone. Of the sour cherry seedlings tested, only 'Almaz' open pollinated (o.p.) R1(1) was rated as resistant. 'Almaz' o.p. R1(1) and 'GI 148-1' were also rated as resistant to leaf spot isolates from other Prunus species. These results and the implications for breeding resistant sour cherry cultivars are discussed. Download this article in .PDF format Author(s): Hutchison, K. A., Green, J. R., Wharton, P. S. and O'Connell, R. J. Title: Identification and localisation of glycoproteins in the extracellular matrices around germ-tubes and appressoria of Colletotrichum species Source: Mycological Research 2002, 106:729-736. Abstract: A monoclonal antibody (MAb), UB31, is described that binds to the extracellular matrix (ECM) surrounding germ-tubes and appressoria, but not conidia, of the bean anthracnose fungus, Colletotrichum lindemuthianum. Comparative localisation studies with MAb UB26, which has the same cell type specificity, suggest that the ECM is heterogeneous in composition. Immunofluorescence showed that UB31 labelled appressoria more intensely than germ-tubes, whereas UB26 labelled these structures to a similar extent. Immunofluorescence and TEM- immunogold labelling showed that UB31 antigens were located close to the appressorial wall, while UB26 antigens extended further away from the wall. MAb UB31 bound to the ECMs of all six Colletotrichum species tested. Western blotting and ELISA indicated that the antibody recognises a high M-r glycoprotein (> 200000) that may be linked to melanin. The glycoprotein recognised by UB31 was not removed from substrata by ultrasonication, suggesting it may contribute to germling adhesion. Download this article in .PDF format Author(s): Wharton, P. S., Julian, A. M. and O'Connell, R. J. Title: Ultrastructure of the Infection of Sorghum bicolor by Colletotrichum sublineolum Source: Phytopathology 2001, 91 (2):149-158. Abstract: Ultrastructural studies of the infection of susceptible and resistant cultivars of Sorghum bicolor by Colletotrichum sublineolum were conducted. Initial penetration events were the same on both susceptible and resistant cultivars. Germ tubes originating from germinated conidia formed globose, melanized appressoria, that penetrated host epidermal cells directly. Appressoria did not produce appressorial cones, but each penetration pore was surrounded by an annular wall thickening. Inward deformation of the cuticle and localized changes in staining properties of the host cell wall around the infection peg suggests that penetration involves both mechanical force and enzymic dissolution. In compatible interactions, penetration was followed by formation of biotrophic globular infection vesicles in epidermal cells. Filamentous primary hyphae developed from the vesicles and went on to colonize many other host cells as an intracellular mycelium. Host cells initially survived penetration The host plasma membrane invaginated around infection vesicles and primary hyphae and was appressed tightly to the fungal cell wall, with no detectable matrix layer at the interface. Necrotrophic secondary hyphae appeared after 66 h and ramified through host tissue both intercellularly and intracellularly, forming hypostromatic acervuli by 114 h. Production of secondary hyphae was accompanied by the appearance of electron-opaque material within infected cells. This was thought to represent the host phytoalexin response. In incompatible interactions, infection vesicles and primary hyphae were formed in epidermal cells by 42 h. However, they were encrusted with electron-opaque material and appeared dead. These observations are discussed in relation to the infection processes of other Colletotrichum spp. and the host phytoalexin response. Download this article in .PDF format Author(s): Wharton, P. S. and Nicholson, R. L. Title: Temporal synthesis and radiolabelling of the sorghum 3- deoxyanthocyanidin phytoalexins and the anthocyanin, cyanidin 3-dimalonyl glucoside Source: New Phytologist 2000, 145 (3):457-469. Abstract: Sorghum (Soughum bicolor) synthesizes a complex mixture of 3- deoxyanthocyanidin phytoalexins in response to inoculation with the non-pathogenic fungus Bipolaris maydis. The anthocyanin cyanidin 3-dimalonyl glucoside, is also synthesized naturally in response to light. To determine the order and time of appearance of these compounds, etiolated sorghum mesocotyls were inoculated with B. maydis and tissue extracts were analysed by photodiode array-HPLC every 2 h for the first 24 h and at 48 h post inoculation (hpi). Uninoculated and inoculated etiolated mesocotyls were also allowed to incorporate L-[U-C- 14] phenylalanine. Apigeninidin appeared at 10 hpi, Followed by luteolinidin and apigeninidin 5-O-arabinoside at 14 hpi. Luteolinidin 5-methylether was not detected until 18 hpi and apigeninidin 7-methylether not until 20 hpi. The concentrations of the primary phytoalexins, apigeninidin, luteolinidin and apigeninidin 5-O-arabinoside, rose steadily between 12 and 24 hpi, and the levels of apigeninidin and luteolinidin were approximately equivalent by 24 hpi. However, between 24 and 48 hpi luteulinidin and luteolinidin 5-methylether accumulated rapidly so that by 48 hpi the amounts of luteolinidin and luteolinidin 5-methylether had increased approximately twofold. Radiolabelling also showed that C-14 was incorporated into the 3-deoxpanthocyanidins and cyanidin 3-dimalonyl glucoside. Several other unidentified phenolic compounds also accumulated radioactivity. Download this article in .PDF format Author(s): Wharton, P. S. and Julian, A. M. Title: A cytological study of compatible and incompatible interactions between Sorghum bicolor and Colletotrichum sublineolum Source: New Phytologist 1996, 134 (1):25-34. Abstract: Cytological and physiological studies were conducted on the infection process of Colletotrichum sublineolum P. Henn. Kabat et Bub. on susceptible and resistant cultivars of Sorghum bicolor (L.) Moench. Compatible interactions were characterized by an early biotrophic phase lasting c. 24 h, during which intracellular infection vesicles and primary hyphae colonized epidermal cells. Thinner secondary hyphae were first observed branching out from primary hyphae after 66 h. These hyphae proliferated throughout the epidermis and into underlying mesophyll cells. Secondary hyphae were associated with host cell death and the onset of a necrotrophic phase. Pigmented cytoplasmic inclusions, thought to represent the host defence response, were also first observed at 66 h, although there was little apparent effect on subsequent fungal colonization of tissue. By 90 h, secondary hyphae had proliferated throughout the leaf sheath, with production of necrotic lesions and acervuli. In incompatible interactions, infection vesicles formed inside epidermal cells within 42 h of inoculation but there was no evidence for a biotrophic interaction as penetrated cells appeared dead and fungal development was restricted to single epidermal cells. Host defence responses were observed earlier than in compatible interactions: heavily pigmented (dark red) cytoplasmic inclusions were distributed throughout penetrated cells at 42 h. By 66 h, these cytoplasmic inclusions had disintegrated and dark red pigment had spread throughout the cell. Concurrent with the disintegration of the cytoplasmic inclusions was the disruption of the cytoplasm of both the host cell and the fungus. Further fungal development was restricted. These observations are discussed in relation to the importance of the initial biotrophic phase in the successful, colonization of S. bicolor by C. sublineolum and the role of the host defence response in preventing colonization. Download this article in .PDF format |
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