First Report of Phytophthora capsici Infecting Lima Bean (Phaseolus lunatus) in the Mid-Atlantic Region

Abstract

Lima beans are an important crop in Delaware and the Mid-Atlantic Region. In the summer of 2000, five commercial cultivars (3–28, 184–85, C-elite Sel, Butter Bean, and Jackson Wonder) of lima bean in Delaware, Maryland, and New Jersey were observed with white, appressed mycelia on infected pods that appeared distinctly different from signs of downy mildew infection caused by Phytophthora phaseoli. Isolations were made by placing diseased pods between layers of rye media (1). A fungus that produced white mycelia with sporangia was consistently isolated. All Phytophthora isolates from the infected pods were heterothallic, grew at 35°C, had as much as 100 μm long pedicles on varying shapes of caducous sporangia with tapering base and >2 papillae, and were identified as P. capsici (2). Initially, three surface-disinfected pods from cv. Early Thorogreen plants grown in the greenhouse were floated on 20 ml of sterile water in a petri dish, and each was inoculated with a disk of P. capsici. This was repeated for nine isolates obtained from lima bean. After incubation for 7 days at room temperature, all 27 pods were infected, and P. capsici was reisolated from all the pods. A pathogenicity test was performed on the same cultivars from which the original field isolates were collected. Three seedlings and two plants with mature pods were inoculated with a sporangial suspension of each of the nine isolates and placed in a dew chamber for 5 days at 20 to 25°C and 100% relative humidity. White mycelial growth was observed on seedlings and mature pods. One inoculated plant developed brown-to-black stem lesions with white mycelia. All pods on the mature plants showed appressed, white mycelia identical to that observed in the commercial lima bean fields. P. capsici was consistently reisolated from all inoculated plants. In 2000, most infected pods in infested fields were observed low in the plant canopy or touching the soil. However, in 2001, infected pods were mostly in the lower and mid-portion of the plants observed in baby lima bean fields in Kent County, DE. References: (1) C. E. Caten and J. L. Jinks. Can. J. Bot. 46:329, 1967. (2) D. C. Erwin and O. K. Ribeiro. Phytophthora capsici. Page 264 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St Paul, MN, 1996.

Plant-Pathogenic Oomycetes, Escherichia coli Strains, and Salmonella spp. Frequently Found in Surface Water Used for Irrigation of Fruit and Vegetable Crops in New York State

“…Zoospores have been reported to remain viable in surface waters for hours to weeks, depending on the species and environmental factors, such as temperature and pH (11). Phytophthora capsici is the causal agent of phytophthora blight of many vegetables, including tomato, pepper, cucurbits, and snap and lima beans, and has many weed hosts (12,13). The pathogen has been found in surface waters in several agricultural regions of the United States, but its presence in New York State surface waters was previously unknown.…”

A PCR-based Assay for Distinguishing between A1 and A2 Mating Types of Phytophthora capsici

“…The host range of this pathogen subsequently was expanded to include lima bean (Phaseolus lunatus L.), snap bean (Phaseolus vulgaris L.), fraser fir [Abies fraseri (Pursh) Poir. ], and certain weeds (Davidson et al, 2002;Gevens et al, 2008;Quesada-Ocampo et al, 2009).…”

Managing Pod Rot of Lima Bean Caused by Phytophthora capsici with Fungicides in the Mid-Atlantic Region

“…Pod rot, caused by Phytophthora capsici, is a newly described disease of lima bean (Phaseolus lunatus) (Davidson et al 2002). In the mid-Atlantic region, which leads the United States in lima bean acreage (USDA NASS 2014), total crop loss is possible under favorable conditions.…”