By Jing Luo and Ning Zhang, Rutgers University
Summer patch is an economically important root disease on turfgrasses used on golf courses, sports fields, and lawns. It causes root, crown and stem rot that develop during periods of summer stress. Among the grass hosts, fine fescues are highly susceptible to this disease (Smiley et al., 2005). Magnaporthiopsis poae and M. meyeri-festucae are two commonly found fungi that cause summer patch disease on fine fescues (Landschoot and Jackson, 1989b; Luo et al., 2017).
Both fungal species are capable of causing root discoloration and biomass loss of the host grasses after colonization by producing ectotrophic, dark runner hyphae. However, they are different in morphology, biology and genetics (Luo et al., 2017). Magnaporthiopsis poae has a wide host range and was reported to infect the grass genera Agrostis, Festuca, Poa and Triticum. It is distributed widely in temperate regions of North America (Landschoot et al., 1993). It has a fast growth rate on potato dextrose agar where its colonies reach 6.8 cm diam after 7 days in the dark at 25 C (Luo et al., 2017). By contrast, M. meyeri-festucae is mostly associated with fine fescues. This species has limited distribution and has been only found in Maryland, Massachusetts, and New Jersey in the U.S. It grows slower than M. poae, with 4.5 cm diam colonies on potato dextrose agar after 7 days in the dark at 25 C (Luo et al., 2017).
Several other fungi have also been reported to be associated with summer patch disease on fine fescues and other cool-season grasses (Landschoot and Jackson, 1989a, b; Luo et al., 2017; Vines et al., 2019; Wong et al., 2015). All these species belong to the fungal order Magnaporthales. Their taxonomic, pathogenic, biogeographic and molecular characteristics are well documented in an e-monograph website of Magnaporthales that is being developed at Rutgers University (Luo and Zhang, 2021; Figure 1).
Understanding these summer pathogens will help turfgrass researchers identify control options and develop new summer patch-resistant cultivars.
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