Plant Disease magazine, December 2004 issue, Volume 88, Number 12
Selection of interpretive summaries of articles relevant to seed professionals

Adding hairy vetch to soil helps manage Fusarium Wilt of watermelon

Suppression of Fusarium Wilt of Watermelon by Soil Amendment with Hairy Vetch
X. G. Zhou, University of Maryland, Lower Eastern Shore Research and Education Center, Salisbury 21801; and K. L. Everts, University of Maryland, Lower Eastern Shore Research and Education Center, Salisbury 21801, with joint appointment with the University of Delaware, Georgetown 19947. Plant Dis. D-2004-1014-02R, 2004 (online). Accepted for publication 17 July 2004.
Fusarium wilt, caused by Fusarium oxysporum f. sp. niveum, is a highly destructive soilborne disease and is a yield-limiting factor in watermelon production worldwide. Few effective, economically feasible, and environmentally benign management options are available for the disease. The objective of this study was to develop a novel soil management approach for Fusarium wilt of watermelon. We evaluated hairy vetch (Vicia villosa Roth) and 12 other organic amendments in the greenhouse, and hairy vetch as a soil amendment in microplots and field condi­tions, for suppression of Fusarium wilt in watermelon and im­pact on the population of F. oxysporum f. sp. niveum in soil. When mixed into a loamy sand soil artificially or naturally infested with race 2 of F. oxysporum f. sp. niveum, pulverized hairy vetch, crab shell, and urea provided the best suppression of Fusarium wilt on watermelon seedlings in greenhouse trials. Hairy vetch amendment in microplots significantly decreased wilt incidence and promoted plant growth. Hairy vetch winter cover crop incorporated into field plots as a green manure and covered with black plastic provided a significant reduction of wilt incidence, a stimulation of plant growth, and an increase in weight of fruit, comparable to improvements achieved by the preplant soil fumigants methyl bromide or 1,3-dichloropropene plus 35% chloropicrin. Hairy vetch also increased the sugar content of watermelon fruit. Significant reductions in the populations of F. oxysporum f. sp. niveum were not observed in hairy vetch-amended soil in microplots and field plots. Incorporating hairy vetch into soil as a green manure may provide an alternative or supplement to cultivar resistance and crop rotation for management of Fusarium wilt of watermelon.

Corncobs a source of the fungus that causes toxic chemicals in South Texas cotton

Aspergillus flavus in Soils and Corncobs in South Texas: Im­plications for Management of Aflatoxins in Corn-Cotton Rotations
Ramon Jaime-Garcia and Peter J. Cotty, United States Department of Agriculture–Agricultural Research Service and Division of Plant Pathology and Microbiology, University of Arizona, Tucson 85721. Plant Dis. D-2004-1018-01R, 2004 (online). Accepted for publication 20 July 2004.
Aflatoxins are dangerous toxic chemicals that contaminate many crops. The fungus Aspergillus flavus causes aflatoxin contamination of both cottonseed and corn. Farmers commonly rotate corn and cotton crops in South Texas, where reduced tillage frequently results in long-term residence of corncobs on soil surfaces. A. flavus can grow and survive on corncobs. We studied the potential of corncobs as sources of A. flavus in cotton and corn crops in South Texas from 2001 to 2003 in order to gain insights into potential methods for preventing contamination. The results indicate that corncobs are an important source of crop exposure to A. flavus. Corncobs from the previous sea­son contained, on average, over 192 times more A. flavus propagules than soil from the same field, and 2-year old corncobs still retained 45 times more propagules than soil. The quantity of A. flavus in corncobs decreased with corncob age. The results suggest that aflatoxin management should include prompt harvest and techniques to reduce the period corncobs remain in the field, such as incorporation under the soil.

New procedure developed to test for soybean sudden death syndrome

Detection and Quantification of Fusarium solani f. sp. glycines in Soybean Roots with Real-Time Quantitative Polymerase Chain Reaction
X. Gao, T. A. Jackson, K. N. Lambert, and S. Li, Department of Crop Sciences, University of Illinois at Urbana and Champaign, Urbana 61801-4798; G. L. Hartman, United States Department of Agriculture–Agricultural Research Service, Urbana, IL 61801-4723, and Department of Crop Sciences, University of Illinois at Urbana and Champaign; and T. L. Niblack, Department of Crop Sciences, University of Illinois at Urbana and Champaign. Plant Dis. D-2004-1018-02R, 2004 (online). Accepted for publication 17 August 2004.
Soybean sudden death syndrome (SDS) is a major disease of soybean caused by the fungus Fusarium solani f. sp. glycines. The organism is difficult to detect and measure because it is a slow-growing fungus with variable characteristics. Reliable and fast procedures are important for detection of this soybean pathogen. Procedures for extracting DNA from pure fungal cultures and fresh or dry roots were optimized. A new procedure to test purity of DNA extracts was described. Real-time quantitative polymerase chain reaction (QPCR) assays were developed for both absolute and relative measurement of F. solani f. sp. glycines. The fungus was measured based on detection of a pathogen gene relative to a host plant gene. DNA of F. solani f. sp. glycines was detected in soybean plants both with and without SDS foliar symptoms. The QPCR protocols were specific and sensitive. The relative QPCR assay is reliable if care is taken to avoid reaction inhibition and it may be used to further study the fungus–host interaction in the development of SDS or screen for resistance to the fungus.

For a full list of contents and access to the articles, visit http://www.apsnet.org/pd/+toc/2004/dde04tp.asp .

Plant Disease is a leading international journal of applied plant pathology, published by The American Phytopathological Society. It publishes original research articles focusing on practical aspects of plant disease diagnosis and control. Each issue also includes a monthly feature article summarizing a significant topic in plant pathology. The Disease Notes section contains timely reports of new diseases, outbreaks, and other pertinent observations.