First Report of Phytophthora sansomeana Causing Wilting and Stunting on Corn in Ohio

Abstract

During the spring of 2004, corn seedlings with symptoms of wilting and stunting were observed in corn fields with emergence problems in Madison and Brown counties, Ohio. Phytophthora isolates were recovered from sections of root tissue of diseased seedlings placed on dilute V8 media amended with pentachloronitrobenzene, iprodione, benlate, neomycin sulfate, and chloramphenicol. Colonies were rosaceous on potato dextrose agar, with a growth rate of 5 mm per day. Homothallic isolates with paragynous antheridia were observed on lima bean agar (LBA); oogonia were 35 to 50 μm in diameter. Sporangia were ovoid to obpyriform, nonpapillate, with an average size of 49 × 30 μm. Pathogenicity was tested on corn seeds using a petri dish assay with 3-day-old cultures on LBA and a sand-cornmeal cup test amended with inoculum from 7-day-old cultures on LBA (1). After 1 week in the petri dish assay, the seeds failed to germinate completely and were covered with white, fungal-like, aerial mycelia and the pathogen was recovered from brown discolored radicle roots. In the cup assay, 2-week-old seedlings developed the same symptoms observed in the field; the pathogen was also isolated from brown discolored roots. In both assays, no symptoms developed in the noninoculated controls. Both pathogenicity tests were repeated two times. Genomic DNA was extracted from mycelia of two isolates and the internal transcribed spacer (ITS) region was amplified and sequenced using ITS6/ITS4 primers (2). Both isolates had identical ITS sequences (GenBank Accession No. GQ853880). A BLAST search of the NCBI database showed 100% homology with the sequence of the haplotype isolate of Phytophthora sansomeana (Accession No. EU925375). P. sansomeana is a new species characterized principally by a large oogonial diameter (37 to 45 μm), rapid growth rate (7 to 10 mm/day), and an ITS sequence falling in Cooke's clade 8 (4). Pathogenicity tests, morphological characteristics, and the ITS sequence analysis indicate that P. samsomena is the causal agent of the symptoms observed on corn seedlings. P. sansomeana has been reported as a pathogen of soybean in Indiana, Douglas-fir in Oregon, and weeds in alfalfa fields in New York (4). To our knowledge, this is the first report of P. sansomeana infecting corn in Ohio, albeit other isolates have previously been recovered from soybean in the state. There are four previous reports of Phytophthora spp. affecting corn in the United States and Mexico (3). Crop rotation will have little effect in management of this pathogen since corn and soybean are produced in the same fields continuously throughout the state. References: (1) K. E. Broders et al. Plant. Dis. 91:727, 2007. (2) D. E. L. Cooke et al. Fungal Genet. Biol. 30:17, 2000. (3) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN. 1989. (4) E. M. Hansen et al. Mycologia 101:129, 2009.

Specific molecular detection of Phytophthora sojae using conventional and real-time PCR

“…Phytophthora sojae is not the only soybean-infecting Phytophthora species. A newly described Phytophthora species, named Phytophthora sansomeana, has been isolated from soybean in Indiana, Ohio, China, and possibly Illinois (Hamm & Hansen 1981;Reeser et al 1991;Malvick & Grunden 2004;Tang et al 2010;Zelaya-Molina et al 2010). The objective of this study was to evaluate PCR methods for specific, rapid, and sensitive detection of P. sojae.…”

Phytophthora sansomeana, an Emerging Threat to Soybean Production

“…In Rosaceous trees, fruit production may be stunted or ceased entirely [35]. On maize P. sansomeana causes wilting and stunting and may be related to emergence problems [38], though interestingly, reports from this host lag behind that of soybean in the U.S. and globally. P. sansomeana was also recently isolated from leaf lesions in taro [42].…”

Transcriptomic and epigenetic responses shed light on soybean resistance toPhytophthora sansomeana

“…Many of these Rps genes belong to the NBS-LRR family, which can directly or indirectly recognize the corresponding effectors from a variety of pathogens (Ngou et al, 2022; Wu et al, 2018). In 2009, Phytophthora sansomeana was differentiated from the Phytophthora megasperma complex as a causal agent of root rot across a broader range of hosts, including soybean, carrot, pea, white clover, gerbera, and maize (Detranaltes et al, 2022; Hansen et al, 2009; Lin et al, 2021; Rojas et al, 2017; Zelaya-Molina et al, 2010). The prevalence of P. sansomeana in soybean, particularly in North America and Northeast Asia, has led to significant agricultural losses (Alejandro Rojas et al, 2017; Lin et al, 2021; Malvick & Grunden, 2004; Rahman et al, 2015; Tang et al, 2010).…”