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Mycosphaerella blight, caused by Peyronellaea pinodes (Berk. & A. Bloxam) Aveskamp, Gruyter & Verkley (syn. Mycosphaerella pinodes (Berk. et Blox.) Vesterg.), is a destructive foliar pathogen of fi...

Cantaloupe (Cucumis melo var. cantalupo) has become an economically important crop in Thailand and the fruit is popular among consumers. In June 2016, gummy stem blight, an important disease of cucurbits, was found on cantaloupe in Phayao Province, Thailand. The causal fungus was isolated from lesions and identified as Stagonosporopsis cucurbitacearum based on morphological characteristics and phylogenetic analysis of combined sequences of the internal transcribed spacer and large subunit regions of ribosomal DNA, and β-tubulin genes. The isolated fungus caused symptoms of gummy stem blight on inoculated cantaloupe, which were similar to the natural symptoms observed in the field. This is the first report in Thailand of gummy stem blight disease on cantaloupe caused by S. cucurbitacearum.

This review examines how changing fungicide usage in Canada is increasing the risk of fungicide insensitivity in pathogen populations, using examples from field, vegetable and horticultural crops. The current generation of systemic fungicides is selective, effective and has a reduced impact on the environment compared with older contact fungicides. However, many of these new fungicides also have an increased risk of fungicide insensitivity. On the Canadian prairies, a trend towards specialization of production within regions has resulted in limited cropping rotations, or even no rotation, in many fields, and yield targets are increasing. As a result, the frequency and extent of fungicide usage is increasing rapidly and insensitivity to certain fungicides has been identified in several crop pathogens. Case studies of fungicide insensitivity on Ascochyta rabiei on chickpea, Mycosphaerella pinodes on field pea, Fusarium sambucinum and Phytophthora infestans on potato, Pythium violae, P. sulcatum and ...

Mycosphaerella blight (Mycosphaerella pinodes) is the most important disease of field pea (Pisum sativum) in western Canada, occurring in almost every field each year. The objective of the study was to assess the impact of seed infection on epidemics of mycosphaerella blight. In preparation for the trial, seed lots of a susceptible and partially resistant cultivar with different levels of seed infection with M. pinodes were produced at a single site with uniform handling and storage conditions. Field trials were conducted in 2005 and 2006 at three sites in western Canada where levels of external inoculum were high (Vegreville, AB, Saskatoon, SK, Morden, MB), and one site (Bradford, ON) with little external inoculum. For each cultivar, the seed infection treatments were: (i) high seed infection (26–47% of seed infected with M. pinodes); (ii) intermediate seed infection (6–15% of seed infected); (iii) fungicide – intermediate seed lot treated with a fungicide to minimize seed transmission; and (iv)...

The expansion of poplar culture in the north-central and northeastern regions of North America has been limited because many poplar clones are susceptible to the leaf spot and canker disease caused by the fungus Septoria musiva (teleomorph Mycosphaerella populorum). This review provides a brief historical account and summarizes the current state of knowledge focussing on developments in the areas of taxonomy and systematics, host associations and symptomatology. Since selection and deployment of resistant clones is one of the best disease-control strategies against S. musiva, recent advances in our knowledge of epidemiology, genetics and variability in virulence and aggressiveness of the populations of this fungus are also addressed.

Swiss needle cast of Douglas-fir (Pseudotsuga menziesii) is caused by the ascomycete Phaeocryptopus gaeumannii. Symptoms are foliage chlorosis and premature needle abscission due to occlusion of stomata by the ascocarps of the pathogen, resulting in impaired needle gas exchange. Growth losses of 20%-50% due to Swiss needle cast have been reported for approximately 150 000 ha of Douglas-fir plantations in western Oregon since 1996. In the western Coast Range of Oregon and in New Zealand, winter temperature is strongly correlated with pathogen abundance. Models for predicting disease severity based on winter temperature account for 77% and 78% of the variation in 1- and 2-year-old needles, respectively, for western Oregon sites and approximately 80% for New Zealand. A trend of temperatures increasing by 0.2–0.4 °C during the winter months and spring precipitation increasing by 0.7–1.5 cm/decade since 1970 suggests that regional climate trends are influencing the current distribution and severity of...

The electrophoretic karyotype of the filamentous fungus Mycosphaerella fijiensis was determined using contour-clamped homogenous electric field (CHEF) gel electrophoresis. Among 10 isolates from different geographical areas, the highest variation in the banding profiles was found in the chromosomes with sizes below 1.5 megabases pairs (Mbp). The minimal genome size was estimated to range from 27 to 35 Mbp. Eight to 13 chromosomal bands, ranging approximately from 0.5 to 8.6 Mbp in size, were separated. These results open perspectives for the physical mapping of specific genes, such as those associated with avirulence, pathogenicity, and fungicide resistance, and for the construction of chromosome-specific libraries.

Survival of Mycosphaerella pinodes in leaf and stem residues placed at 0, 5, and 10 cm below the soil surface was examined at Morden and Winnipeg, Manitoba, from October 1999 to October 2000. Survival was measured as production of spores from residue and pathogenicity of residue washings on the susceptible field pea cultivar 'AC Tamor'. Spore production on the residues decreased over the 12-month sample-retrieval period, regardless of residue type and burial depth. Spores were rarely produced from residues after 11 months at Morden and 9 months at Winnipeg. In general, more spores were produced on leaf residues than on stem residues. No or few lesions developed from residue washings after 9 months for leaf residue and 8 months for stem residue at both locations. Residues on the soil surface had greater spore production and subsequently produced greater disease severities on pea plants inoculated with residue washings than those of the buried residues. There was no statistical difference in spore productio...

Plants of field pea, Pisum sativum ‘AC Tamor’, were mechanically injured by sandblasting and inoculated with Mycosphaerella pinodes immediately after this pretreatment and 1, 2, 4, and 8 days later under controlled conditions. A negative linear relationship was observed between disease severity, measured as the area under the disease progress curve over a period of 17 days, and the time elapsed between injury and inoculation. Control plants, without injury, were inoculated parallel to the injured plants and did not show this response. Inoculation up to 24 h after injury resulted in significantly higher disease severity than inoculation after that period or inoculation of control plants, suggesting that injury facilitates infection of the pea plant by M. pinodes prior to the formation of callus. In field experiments, differences between injury and control treatments of nine field pea genotypes (cultivars and germplasm accessions) were apparent only a few weeks after inoculation. Disease severity in the sec...

Seed-borne Mycosphaerella pinocles in field pea, its transmission to seedlings, and control by seed treatments were studied under growth room and field conditions. Seeds harvested from naturally infected plants were separated into visibly poor (VP) seeds with lesions, and healthy looking (HL) seeds without lesions. In a controlled environment seed-to-seedling transmission was 67-70% for the HL seeds and 94-100% for the VP seeds. Under field conditions, the percentage of seeds infected by M. pinocles was negatively correlated with seedling emergence (r = -0.939 in 1996. P < 0.01, and r = -0.944 in 1997, P < 0.01) and yield (r = -0.929 in 1996, P < 0.01, and r = -0.757 in 1997, P < 0.05), but there was no relationship with the frequency of foot rot symptoms. When seeds were treated with thiram fungicide or ACM94I bioagent (Glioclaclium roseum), both VP and HL seeds showed increased emergence compared with nontreated controls. Thiram was more effective than ACM941 in improving the emergence, however, neither...

(1998). Pathogenic variation of western Canadian isolates of Mycosphaerella pinodes on selected Pisum genotypes. Canadian Journal of Plant Pathology: Vol. 20, No. 2, pp. 189-193.

(1996). Genotypic variability in seedborne infection of field pea by Mycosphaerella pinodes and its relation to foliar disease severity. Canadian Journal of Plant Pathology: Vol. 18, No. 4, pp. 370-374.