Plant Disease
A leading international journal of applied, peer reviewed plant pathology research
A publication of the American Phytopathological Society
Volume 88, Number 7
Abstracts • Interpretive Summaries

FOCUS

The Latest in Plant Pathology and Nematology. Page 687. Publication no. D-2004-0507-01O.

RESEARCH

Long-Term Effect of Biological Soil Disinfestation on Verticillium Wilt
Jan-Kees C. Goud, Aad J. Termorshuizen, Wim J. Blok, and Ariena H. C. van Bruggen. Pages 688-694.
Interpretive Summary
Because of the ban on methyl bromide, growers need alternative measures to control soilborne fungi and nematodes. Biological soil disinfestation (BSD), involving incorporation of grass combined with plastic mulching, eliminates many soilborne pests and diseases through the creation of anaerobic conditions. It is as effective as methyl bromide and has a comparable broad spectrum of activity. BSD was compared with a control treatment at two locations for the control of Verticillium wilt. After the soil treatments, plots were cropped with Acer platanoides and Catalpa bignonioides for 4 years. Soil inoculum levels of Verticillium dahliae were reduced by 85% after BSD and did not increase during the 4-year period. Less Verticillium wilt occurred, and stem infection with V. dahliae was reduced by 80 to 90%. Pratylenchus fallax populations in the soil and in roots were reduced by 95 to 99%. Market value of the plants was up to € 140,000 ha(^–1) higher for A. platanoides and up to € 190,000 ha(^–1) higher for C. bignonioides compared with the control. BSD is an effective, economically profitable, and environmentally friendly control method for tree culture and other high value crops.
Publication no. D-2004-0428-01R.   .

Development of MILIONCAST, an Improved Model for Predicting Downy Mildew Sporulation on Onions
Tijs Gilles, Kath Phelps, John P. Clarkson, and Roy Kennedy. Pages 695-702.
Interpretive Summary
Downy mildew, a common disease of onions, which is caused by the fungus Peronospora destructor, is spread by wind-dispersed spores. These spores are produced only during periods of high humidity at night. A new study was conducted to develop an improved sporulation model, because it was found that existing models frequently failed to predict sporulation. Laboratory studies found that spores are produced most quickly at 8 to 12°C after 5 h of high humidity at night. The largest numbers of spores are produced at 100% relative humidity (RH), and this decreases with decreasing humidity until only a few spores are produced at 93% RH. A model has been developed based on these laboratory findings, which has been named MILIONCAST, an acronym for MILdew on onION foreCAST. MILIONCAST was tested for its accuracy in predicting sporulation on onion plants under outdoor conditions, and 81% of predictions were correct. The existing models DOWNCAST, a version of DOWNCAST modified by de Visser, and ONIMIL gave accurate predictions in only 69, 74, and 67% of cases, respectively. The MILIONCAST sporulation model could become a useful tool in the management of onion downy mildew when it is used in combination with infection models
Publication no. D-2004-0419-01R.  

Occurrence and Impact of a New Leaf Rust Race on Durum Wheat in Northwestern Mexico from 2001 to 2003
R. P. Singh, J. Huerta-Espino, W. Pfeiffer, and P. Figueroa-Lopez. Pages 703-708.
Abstract
Durum wheat (Triticum turgidum var. durum) is the main irrigated winter crop in northwestern Mexico. Historically, leaf rust, caused by Puccinia triticina, had not induced significant losses to durum production in the area until 2001. That year, a new race, designated as BBG/BN, was detected that caused the most widely grown cultivar, Altar C84, which had remained resistant for 16 years, to become susceptible. Other recommended cultivars also became either moderately susceptible or susceptible. Detailed characterization of avirulence/virulence characteristics on Lr genes indicated that this race possibly did not evolve from the older races, but may have been introduced. Rust epidemics during the 2000–2001, 2001–2002, and 2002–2003 crop seasons have caused estimated losses of at least US$32 million. Although a majority of cultivars from 31 different countries, including the United States and Canada, and most of CIMMYT’s durum wheat germ plasm were highly susceptible, diversity for both race-specific resistance and moderate levels of slow rusting resistance were identified. Jupare C2001, a resistant cultivar released in 2001, showed high levels of resistance and negligible losses in grain yield in a trial where Altar C84 suffered over 27% losses. Additional keywords: brown rust.
Publication no. D-2004-0430-02R.

Finger Imprint of Poncirus trifoliata: A Specific Interaction of a Viroid, a Host, and Irrigation.
G. Vidalakis, D. J. Gumpf, J. A. Bash, and J. S. Semancik. Pages 709-713.
Publication no. D-2004-0426-01R.   Interpretive Summary.

AFLP Analysis of Phytophthora cactorum Isolates from Strawberry and Other Hosts: Implications for Identifying the Primary Source of Inoculum.
H. Huang, S. N. Jeffers, D. R. Layne, and G. Schnabel. Pages 714-720.
Publication no. D-2004-0430-01R.

Soybean Cultivar and Foliar Fungicide Effects on Phomopsis sp. Seed Infection
J. A. Wrather, J. G. Shannon, W. E. Stevens, D. A. Sleper, and A. P. Arelli. Pages 721-723.
Interpretive Summary
Phomopsis seed decay (PSD) caused by Phomopsis spp. can be severe when soybean seed producers in the southern United States use the early soybean production system (ESPS) to avoid late-July through early-September drought damage to soybean. The usefulness of this production system would be greater if developing seed could be protected from PSD by foliar application of fungicides or by planting Phomopsis spp.-resistant soybean lines. The objective of this research was to determine the affects of the fungicides Benlate and Quadris applied to soybean, at various times, on percent Phomopsis spp. infection of seed in Asgrow 3834, a PSD-susceptible cultivar, and SS93-6012, a PSD-resistant soybean line, planted in mid-April. The percent Phomopsis spp. infection of Asgrow 3834 seed averaged over years was significantly less for the Benlate (8 oz. of formulation/acre) applied at R3 + R5 treatment (48.6% seed infection) than the control (52.8% seed infection) and significantly greater for the Quadris (9.3 fl. oz. of formulation/acre) applied at R3 + R5 treatment (61.6% seed infection) than the control (52.8% seed infection). This method of managing PSD will not be acceptable to soybean growers. The percentage of Phomopsis spp. infection of Asgrow 3834 seed averaged over years (52.8% seed infection) was significantly greater than for line SS93-6012 (2.8% seed infection). There were no differences in percent Phomopsis spp. infection of SS93-6012 seed between the control (2.8% seed infection) and Benlate treatment (4.0% seed infection). The most effective method for PSD management was to plant a resistant soybean line. Line SS93-6012 will be useful in breeding programs focused on developing high-yielding PSD-resistant cultivars.
Publication no. D-2004-0503-01R.  

Survival and Inoculum Production of Gibberella zeae in Wheat Residue
S. A. Pereyra, R. Dill-Macky, and A. L. Sims. Pages 724-730.
Abstract
Survival and inoculum production of Gibberella zeae (Schwein.) Petch (anamorph Fusarium graminearum (Schwabe)), the causal agent of Fusarium head blight of wheat and barley, was related to the rate of wheat (Triticum aestivum L.) residue decomposition. Infested wheat residue, comprising intact nodes, internodes, and leaf sheaths, was placed in fiberglass mesh bags on the soil surface and at 7.5- to 10-cm and 15- to 20-cm depths in chisel-plowed plots and 15 to 20 cm deep in moldboard-plowed plots in October 1997. Residue was sampled monthly from April through November during 1998 and every 2 months through April to October 1999. Buried residue decomposed faster than residue placed on the soil surface. Less than 2% of the dry-matter residue remained in buried treatments after 24 months in the field, while 25% of the residue remained in the soil-surface treatment. Survival of G. zeae on node tissues was inversely related to the residue decomposition rate. Surface residue provided a substrate for G. zeae for a longer period of time than buried residue. Twenty-four months after the initiation of the trial, the level of colonization of nodes in buried residue was half the level of colonization of residue on the soil surface. Colonization of node tissues by G. zeae decreased over time, but increased for other Fusarium spp. Ascospores of G. zeae were still produced on residue pieces after 23 months, and these spores were capable of inducing disease. Data from this research may assist in developing effective management strategies for residues infested with G. zeae.
Publication no. D-2004-0510-02R.

Evaluation of Systems for Timing of Fungicide Sprays for Control of Postbloom Fruit Drop of Citrus in Brazil.
N. A. R. Peres, N. L. Souza, E. L. Furtado, and L. W. Timmer. Pages 731-735.
Publication no. D-2004-0511-02R.   Interpretive Summary.

Management of Tomato Bacterial Spot in the Field by Foliar Applications of Bacteriophages and SAR Inducers
A. Obradovic, J. B. Jones, M. T. Momol, B. Balogh, and S. M. Olson. Pages 736-740.
Publication no. D-2004-0511-01R.

Resistance of Eight Different Clones of the Grape Cultivar Albariño to Plasmopara viticola.
S. Boso, J. L. Santiago, and M. C. Martínez. Pages 741-744.
Publication no. D-2004-0517-01R.

Lack of Control of Citrus Canker by Induced Systemic Resistance Compounds.
J. H. Graham and R. P. Leite, Jr. Pages 745-750.
Publication no. D-2004-0429-01R.

Overwintering of Conidia of Venturia inaequalis and the Contribution to Early Epidemics of Apple Scab.
I. J. Holb, B. Heijne, and M. J. Jeger. Pages 751-757.
Publication no. D-2004-0518-01R.   Interpretive Summary.

Resistance of Eucalyptus Clones to Ceratocystis fimbriata.
E. A. V. Zauza, A. C. Alfenas, T. C. Harrington, E. S. Mizubuti, and J. F. Silva. Pages 758-760.
Publication no. D-2004-0510-01R.

Resistance to Brown Stem Rot in Soybean Germ Plasm with Resistance to the Soybean Cyst Nematode
T. J. Hughes, N. C. Kurtzweil, B. W. Diers, and C. R. Grau. Pages 761-768.
Abstract
The soybean cyst nematode (SCN) and Phialophora gregata f. sp. sojae, the causal agent of brown stem rot (BSR), are two pathogens of soybean commonly found in the same field throughout the north-central United States. Field experiments designed to study the role of SCN-resistant germ plasm in soybean production have led to data suggesting that some sources of SCN resistance also may provide resistance to BSR. Soybean germ plasm with resistance to SCN was evaluated in greenhouse and field environments for resistance to BSR development based on the percentage of host tissue symptomatic of BSR. Comparison of SCN-resistant cultivars and plant introductions (PI) to standard BSR-resistant and -susceptible checks were conducted in two greenhouse experiments using a root-dip inoculation with a single isolate of P. gregata. For both greenhouse experiments, PI 209332 was the only source of SCN resistance with resistance to BSR similar to standard BSR-resistant checks. Nine other sources of SCN resistance, including PI 88788 and Peking, expressed BSR symptom severity similar to BSR-susceptible checks. Cultivars derived from most SCN-resistant sources, including PI 209332, also were susceptible to BSR development, while four of the five cultivars derived from PI 88788 were highly resistant to BSR development. SCN-resistant cultivars derived from PI 88788, Peking, and PI 209332 were planted along with standard BSR-resistant and -susceptible checks at two field locations naturally infested with P. gregata and SCN or P. gregata alone. As in greenhouse experiments, four of the five cultivars derived from PI 88788 expressed resistance to BSR development equal to or better than standard BSR-resistant checks at both locations. In contrast, cultivars derived from PI 209332 and Peking expressed varying levels of disease development depending on field environment. Yields observed for PI 88788-derived cultivars were higher than BSR-resistant checks regardless of the presence of SCN. Data from both greenhouse and field experiments suggest that cvs. Williams and Williams 82 may contain a gene or genes for BSR resistance that require one or more modifier genes, possibly located in the genome of PI 88788, for complete expression.
Publication no. D-2004-0517-02R.

DISEASE NOTES

Borage (Borago officinalis) is a New Host of Pseudomonas cichorii in the Ebro Valley of Spain.
M. A. Cambra, A. Palacio-Bielsa, and M. M. López. Page 769.
Publication no. D-2004-0518-01N.

Southern Blight of Jerusalem Artichoke Caused by Sclerotium rolfsii in California
S. T. Koike. Page 769.
Publication no. D-2004-0428-01N.

First Report of Brown Root Rot of Alfalfa Caused by Phoma sclerotioides in Wisconsin
R. C. Larsen, C. R. Grau, G. J. Vandemark, T. J. Hughes, and B. D. Hudelson. Page 769.
Publication no. D-2004-0518-02N.

First Report of Southern Blight of Ruellia brittoniana Caused by Sclerotium rolfsii in Louisiana
G. E. Holcomb. Page 770.
Publication no. D-2004-0430-01N.

First Report of Shining Willow as a Host Plant for Septoria musiva.
N. Feau and L. Bernier. Page 770.
Publication no. D-2004-0504-01N.

First Report of Witches’-Broom Disease of Broussonetia papyrifera and Its Association with a Phytoplasma of Elm Yellows Group (16SrV).
Qingzhong Liu, Tianqi Wu, Robert E. Davis, and Yan Zhao. Page 770.
Publication no. D-2004-0426-02N.

Natural Occurrence of Phytophthora infestans on Black Nightshade (Solanum nigrum) in Wales.
K. L. Deahl, D. S. Shaw, and L. R. Cooke. Page 771.
Publication no. D-2004-0511-01N.

First Report of Yellow Nutsedge (Cyperus esculentus) and Purple Nutsedge (C. rotundus) in Georgia Naturally Infected with Impatiens necrotic spot virus.
N. Martínez-Ochoa, S. W. Mullis, A. S. Csinos, and T. M. Webster. Page 771.
Publication no. D-2004-0505-01N.

First Report of the Pitch Canker Fungus (Fusarium circinatum) in the Sierra Nevada of California.
D. R. Vogler, T. R. Gordon, B. J. Aegerter, S. C. Kirkpatrick, G. A. Lunak, P. Stover, and P. Violett. Page 772.
Publication no. D-2004-0426-01N.

First Report of the White Pine Blister Rust Fungus (Cronartium ribicola) Infecting Whitebark Pine (Pinus albicaulis) and Ribes spp. in the Jarbidge Mountains of Northeastern Nevada.
D. R. Vogler and D. A. Charlet. Page 772.
Publication no. D-2004-0507-01N.

First Report of Black Sigatoka of Banana Caused by Mycosphaerella fijiensis on Grand Bahama Island.
R. C. Ploetz. Page 772.
Publication no. D-2004-0519-01N.