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Chrislyn A. Drake and James F. Hancock

Black root rot is a widespread disease of strawberry (Fragaria×ananassa Duchnesne) that causes the death of feeder roots and the degradation of structural roots. The major causal organisms of black root rot include Rhizoctonia fragariae Husain and W.E. McKeen, Pythiumspp. and Pratylenchuspenetrans(Cobb) Filipjev and Schuurmans Stekhoven. The current method of control for black root rot is methyl-bromide fumigation; however, methyl bromide is scheduled to be phased out in 2005, and its effects are short-lived in matted-row systems. The objectives of the study were to measure levels of tolerance to black root rot in 20 strawberry genotypes and to determine which pathogens were present in the soil. The genotypes were planted in four blocks each of methyl-bromide fumigated and nonfumigated soil, and were evaluated for crown number, number of flowers per crown, yield, and average berry weight over two years. The results showed that all three pathogens were present in the field, and that there was a significant genotype × fumigation interaction for yield and crown number in both years. The cultivars Bounty, Cabot, and Cavendish, all released from the breeding program in Nova Scotia, displayed tolerance to the pathogens that cause BRR. Greenhouse studies were conducted using a subset of the genotypes to determine if any one pathogen causes more damage than others, and to determine if susceptibility to a particular pathogen varies between genotypes.

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Laura Pickett Pottorff and Karen L. Panter

With the cooperation of six commercial greenhouses (five in Colorado, one out of state), rooted poinsettia cuttings and bedding plant plugs were collected and analyzed for Pythium and Rhizoctonia, two common root rotting pathogens in Colorado greenhouses. Samples of plant, soil, and water debris were taken from four greenhouses, as well as samples of growing media ready for use. These were also analyzed for Pythium and Rhizoctonia. Fungi recovered from the plant, debris, or growing media samples were identified, grown in pure culture, and introduced into susceptible plants (Vinca minor) in pathogenicity studies. Neither pathogen was isolated from the rooted poinsettia cuttings tested. Pythium was not found in any of the plug material or in growing media. Rhizoctonia solani was found in 16% of the plug samples and 7% of the growing media samples tested. Debris from greenhouse floors yielded four species of Pythium as well as Rhizoctonia solani. Isolates of each fungus were able to colonize, but not adversely affect, inoculated plants in pathogenicity studies. It appears that disease causing organisms that have potential to decrease plant quality and growth are already present in the greenhouse. Control of root rotting pathogens can best be carried out by relying heavily on sanitation measures.

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M.A. Chandler, V.A. Fritz, F.L. Pfleger and R.R. Allmaras

Pea root rot is a serious economic threat to pea production in the Great Lakes region. The primary causal organism is Aphanomyces euteiches Drechs., which is responsible for an estimated 10% annual crop loss. A fall oat (Avena sativa) rotation before spring pea planting reduces disease severity. To better understand the beneficial effect of oat on A. euteiches, isolated individual pathogen lifecycle stages of zoospores, mycelium, and oospores were treated in culture with oat extract. Resulting mycelial mats were dried and weighed. Treatment with 90%, 70%, 50%, and 30% oat extract resulted in significant spore germination and mycelial growth of A. euteiches. In the presence of nutrient solution, oat extract concentrations of 90%, 70%, 50%, and 30% significantly enhanced spore germination and mycelial growth of the pathogen. These results demonstrate that the use of oat extract results in dosage dependent germination and growth of A. euteiches.

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Desmond R. Layne and Guido Schnabel

In 2003, a replicated long-term research trial was established on a commercial peach replant site with a history of Armillaria root rot and other soilborne diseases. The objectives of the trial were to determine the short- and long-term effects of preplant fumigation, rootstock, and preplant root dipping with mycorrhizal fungi and beneficial bacteria on tree growth, productivity, and survival. Preplant fumigants included none (control), methyl bromide, Telone II, or Enzone. Rootstocks tested included Guardian, Lovell, and Halford. Root dipping (or not) was with MycorTree. The scion cultivar was Big Red. There were a total of 24 experimental treatment combinations and the trial site comprised more than 1500 trees on 11.5 acres. By 2 years after planting, fumigation with Enzone was disadvantageous when compared with no treatment at all. Enzone-treated blocks had higher tree mortality or were significantly reduced in growth compared to other treatments. Preplant fumigation with Telone II or methyl bromide, however, resulted in reduced tree stunting and phytotoxicity and increased tree growth when compared to the untreated control. After 2 years, 10% of the total trees planted were dead. Half of these were from the Enzone treatment. Enzone does not appear to be a viable preplant fumigation product for South Carolina peach growers, based on this preliminary data. Both Guardian and Halford rootstocks had performance superior to Lovell during the first 2 years. Although Guardian trees were smaller than Halford at the time of planting, by the end of the second growing season, their TCA was not significantly different. There was no benefit to preplant root dipping with MycorTree. Experimental results were not influenced by the location of trees on the site.

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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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Margaret T. Mmbaga, Lucas M. Mackasmiel and Frank A. Mrema

Macrophomina phaseolina is a nonspecialized soil-borne pathogen that can become a problem by causing root rot, charcoal rot, collar rot, damping-off, wilt, leaf blight, and stem blight in both agricultural and natural or landscape environments

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Wendy K. Hoashi-Erhardt, Patrick P. Moore, Gwenyth E. Windom and Peter R. Bristow

red raspberries ( Wilcox et al., 1993 ), although several other soilborne pathogens may contribute to a disease complex affecting raspberries ( Schilder, 2007 ; You et al., 2006 ). Integrated management of root rot in raspberry plantings can include

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Gregory T. Browne, Charles A. Leslie, Joseph A. Grant, Ravindra G. Bhat, Leigh S. Schmidt, Wesley P. Hackett, Daniel A. Kluepfel, Reid Robinson and Gale H. McGranahan

. None of the rootstocks, however, is sufficiently resistant or tolerant to all of the important soilborne pathogens. More than 10 species of Phytophthora have been implicated in Phytophthora crown and root rot on walnut, and among them P. cinnamomi

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John R. Yeo, Jerry E. Weiland, Dan M. Sullivan and David R. Bryla

Phytophthora cinnamomi is a highly virulent root rot pathogen of highbush blueberry and is present in most growing regions worldwide ( Strik and Yarborough, 2005 ; Zentmyer, 1980 ). Symptoms of infection include poor shoot growth, root necrosis

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Ramón A. Arancibia, Jeffrey L. Main and Christopher A. Clark

. In general, postharvest rots reduce pack-out efficiency, which affects profitability, but the internal necrosis associated with tip rot can go unnoticed until consumer use, which affects quality perception, and therefore, diminishes demand. Pathogen