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Michael R. Evans and Stephen B. Gaul

Glycine max (soybean) seed were sown in root substrates composed of 80:0:20 or 0:80:20 coconut coir dust (coir):Sphagnum peat (peat):perlite (v/v) amended with dolomitic limestone to a pH of 5.5. Substrates were inoculated with Phytophthora megasperma races 5 and 25 isolated from soybean and grown in dilute liquid V-8 cultures. Uninoculated controls were included. Containers were watered daily to maintain moisture levels at or near container capacity. The experiment was repeated twice. Plants grown in peat-based root substrates inoculated with P. megasperma suffered 50% to 100% mortality. No plants in coir-based root substrates displayed visually apparent infection symptoms. Soybean seed were also sown in root substrates that contained 0:80:20, 20:60:20, 40:40:20, 60:20:20 or 80:0:20 coir:peat:perlite (v/v). Inoculum of P. megasperma races 1, 5, and 25 was grown on water agar and diluted in deionized water. Solution containing 20,000 colony-forming units (oospores) was mixed into the root substrate of each container. Uninoculated controls were included. As the proportion of coir in the substrate increased, the mortality, the number of plants displaying disease symptoms and the severity of disease symptoms decreased. Plants grown in substrates containing at least 60% coir displayed no visually evident disease symptoms.

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Clive Kaiser, Philip B. Hamm, Stacy Gieck, Nicholas David, Lynn Long, Mekjell Meland, and J. Mark Christensen

, and Venturia inaequalis were subcultured and analyzed on Potato Dextrose Agar (PDA) (Becton, Dickinson & Co., Sparks, MD) prepared according to the manufacturer's specifications. Cultures of Phytophthora infestans , Phytophthora megasperma

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Gregory T. Browne

route to further pathogen ingress into a tree ( Browne and Viveros, 1999 ). Phytophthora cactorum (Lebert & Cohn) J. Schöt. and Phytophthora megasperma Drechs. were often associated with root and crown rots and trunk cankers resulting from

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K.E. Maloney, W.F. Wilcox, and J.C. Sanford

`Titan' red raspberry (Rubis idaeus L.), highly susceptible to root rot caused by Phytophthora fragariae Hickman var. rubi Wilcox & Duncan (syns. P. erythroseptica Pethyb., “highly pathogenic” P. megasperma Drechs.), was planted in June 1990 in a silt loam naturally infested with the pathogen. Raked beds (0.36 m high) dramatically reduced disease incidence and severity relative to flatbed treatments. In contrast, metalaxyl at 372 mg·m-1 of row provided little benefit when applied to flat beds and provided consistently moderate but statistically insignificant effects when applied to raised beds. Relative to the flat bed system, primocane vigor was increased in 1992 by 16%, 190%, and 224% in the flat bed plus metalaxyl, raised bed, and raised bed plus metalaxyl treatments, respectively; total yields were increased by 7%, 231%, and 272% with these same respective treatment. The results indicate that raised-bed planting systems can provide substantial control of phytophthora root rot of red raspberries even when highly susceptible varieties are grown on otherwise marginal sites. Metalaxyl appears more effective as a supplement rather than substitute for raised beds under such conditions. Chemical name used: N- (2,6-dimethylphenyl) -N- (methoxyacetyl)alanine methyl ester (metalaxyl).

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W.F. Wilcox

Plants of four apple (Malus ×domestica Borkh.) rootstock clones, M.7, M.26, MM.111, and Ottawa (O.) 3, were grown in unamended potting medium or in the same medium infested with Phytophthora cactorum (Leb. & Cohn) Schroet., P. cambivora (Petri) Buisman, P. cryptogea Pethyb. & Laff., or P. megasperma Drechsler, causal agents of crown and root rots. Plants were flooded for either 0, 24, 48, or 72 h every 7 days for 4 months, then assessed for disease incidence and severity. Averaged across all pathogens and rootstocks, mean crown rot incidences were 2.5%, 6.3%, 19%, and 50% following weekly flooding periods of 0, 24, 48, and 72 h, respectively; when averaged across all rootstocks and flooding treatments, mean incidences of crown rot caused by P. cryptogea, P. cactorum, P. cambivora, and P. megasperma were 36%, 26%, 15%, and 8.8%, respectively; when averaged across all four pathogens, mean crown rot incidences after 72 h of flooding were 40%, 45%, 50%, and 75% for M.26, 0.3, M.7, and MM.111, respectively. In contrast, 72-h flooding periods in the absence of a pathogen were least detrimental to growth of MM.111 clones and most detrimental to shoot growth of M-26. Exceptions to general trends were reflected by statistical interactions among pathogens, rootstocks, and flooding durations, e.g., after 72-h floodings, 0.3 was the rootstock with the greatest amount of root rot caused by P. cryptogea but the least amount caused by P. megasperma. Differential disease susceptibility among rootstocks appeared greatest with respect to P. cactorum and least with respect to P. cryptogea.

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Salvatore Vitale, Laura Luongo, Marzia Scarpari, Lorenza Tizzani, Ivana Garaguso, Massimo Galli, Alessandra Belisario, Michele Scotton, Giovanni Mughini, Maria Gras, and Anita Haegi

. cinnamomi resistance, but also against other common Phytophthora species (e.g., Phytophthora pini , Phytophthora megasperma , Phytophthora gonapodyides ), which are reported as destructive in walnut nurseries and commercial plantations ( Belisario et

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Daren S. Mueller, Mark L. Gleason, Nicholas P. Howell, and Edward M. Moran

: Environmental stewardship program 14 Nov. 2007 < http://earthkind.tamu.edu/ >. Tooley, P.W. Grau, C.R. 1984 Field characterization of rate-reducing resistance to Phytophthora megasperma f. sp. glycinea in soybean Phytopathology 74 1201 1208 Walker, S

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Dong Liu, Ping Li, Jiulong Hu, Kunyuan Li, Zhenyu Zhao, Weiyan Wang, Jinyuan Zhang, Xu Ding, and Zhimou Gao

classification in relation to the other three Phytophthora species ( Phytophthora medicaginis , Phytophthora trifolii , and Phytophthora megasperma ) were evaluated by Hansen and Maxwell (1991) . Researchers observed that their mitochondrial DNA content

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Tina P. Thomas, Madhurababu Kunta, John V. da Graça, Mamadou Sétamou, Mani Skaria, and Apurba Bhattacharya

Phytophthora megasperma f.sp. glycinea Planta 172 101 105 Broers, L.H.M. Jacobs, T.H. 1989 The inheritance of host plant effect on latency period of wheat leaf rust in spring wheat. II. Number of segregating factors and

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Daniel P. Gillespie, Chieri Kubota, and Sally A. Miller

; Ho and Hickman, 1967 ; Kong et al., 2009 ). Ho and Hickman (1967) reported that the average period of motility of Phytophthora megasperma var. sojae zoospores was more than 20 h at pH 6.25 but was reduced to 1 h at pH 4.85. In addition, in a