Extension plant pathology: strengthening resources to continue serving the public interest.

Extension plant pathologists deliver science-based information that protects the economic value of agricultural and horticultural crops in the United States by educating growers and the general public about plant diseases. Extension plant pathologists diagnose plant diseases and disorders, provide advice, and conduct applied research on local and regional plant disease problems. During the last century, extension plant pathology programs have adjusted to demographic shifts in the U.S. population and to changes in program funding. Extension programs are now more collaborative and more specialized in response to a highly educated clientele. Changes in federal and state budgets and policies have also reduced funding and shifted the source of funding of extension plant pathologists from formula funds towards specialized competitive grants. These competitive grants often favor national over local and regional plant disease issues and typically require a long lead time to secure funding. These changes coupled with a reduction in personnel pose a threat to extension plant pathology programs. Increasing demand for high-quality, unbiased information and the continued reduction in local, state, and federal funds is unsustainable and, if not abated, will lead to a delay in response to emerging diseases, reduce crop yields, increase economic losses, and place U.S. agriculture at a global competitive disadvantage. In this letter, we outline four recommendations to strengthen the role and resources of extension plant pathologists as they guide our nation's food, feed, fuel, fiber, and ornamental producers into an era of increasing technological complexity and global competitiveness.

Isolation and identification of ochratoxin A-producing Aspergillus section Nigri strains from California raisins.

AIMS: To determine incidence and levels of ochratoxin A (OTA) in California raisins and to isolate and characterize OTA-producing fungi from California raisin vineyard populations. METHODS AND RESULTS: Forty raisin clusters sampled from four California vineyards in the San Joaquin Valley were analysed for OTA content using immunoaffinity and HPLC methods. OTA was detected in 93% of the samples, at levels from 0·06 to 11·4 ng g⁻¹. From these raisin samples, a total of 400 strains of Aspergillus were isolated and analysed for OTA production. Twelve isolates (3%), from five raisin samples, produced OTA. These isolates were identified as Aspergillus carbonarius, based on morphological characteristics and multilocus sequence analysis. Levels of OTA produced by these isolates on raisin agar ranged from 0·9 to 15 µg g⁻¹. CONCLUSIONS: OTA is a common contaminant of raisin vineyards, but average levels are much lower than EU regulatory limits for dried fruit. The primary species responsible for OTA contamination in California raisins is A. carbonarius. SIGNIFICANCE AND IMPACT OF THE STUDY: This study illustrates that low-level OTA contamination of raisins occurs in California and that ecological studies of A. carbonarius within the Aspergillus section Nigri population on raisins are warranted to monitor ochratoxigenic potential of the crop.

First Report of Black-Foot Disease, Caused by Cylindrocarpon obtusisporum, of Grapevine in California.

Black-foot disease, caused by Cylindrocarpon obtusisporum (Cook & Harkn.) Wollenweb., impacts young table and wine grape (Vitis vinifera) plantings throughout California. Two- to 5-year-old grapevines showed reduced vigor with small-sized trunks, shortened internodes, uneven wood maturity, sparse foliage, and small leaves with interveinal chlorosis and necrosis. In cross-section, trunks showed dark brown to black streaking in a few to most of the vascular elements. Symptoms included a reduction in root biomass and root hairs with sunken, necrotic root lesions. Pith of affected vines was compacted and discolored. Isolations made from roots, vascular elements, and pith tissue consistently yielded colonies of C. obtusisporum as verified by descriptions in standard texts. Koch's postulates were completed by dipping the roots of cv. Carignane seedlings in a 108 spore per ml suspension for 30 min. Plants were repotted in an artificial soil mix and held in a controlled environment facility at 24°C. Typical black-foot symptoms developed on 92% of the plants within 8 weeks. Control plants dipped in distilled water remained healthy. Cylindrocarpon destructans, a species closely related to C. obtusisporum, was first reported to cause "black-foot disease" on young vines in 1961 (2). In 1975, C. obtusisporum was reported to produce similar "black-foot" symptoms (1). We propose the common name Cylindrocarpon black-foot disease be used with both species. References: (1) S. Grasso et al. Vitis 14:36, 1975. (2) D. R. Maluta and P. Larignon. Viticulture 11:71, 1991.

First Report of Three Phaeoacremonium spp. Causing Young Grapevine Decline in California.

A grapevine decline of unknown etiology is currently under investigation in California. Two- to 5-year-old vines show low vigor with undersized trunks, short internodes, uneven wood maturity, sparse foliage, and stunted, chlorotic leaves with interveinal chlorosis and necrosis. Trunks viewed in cross section show dark streaking in few to most of the vascular elements. Pith is compacted and discolored; the surrounding wood is dry with a silvery sheen. Primary roots also show dark streaking in the vascular elements and total root biomass is reduced. Phaeoacremonium spp. were consistently isolated from the roots, crowns, and lower portions of the rootstocks of declining vines but not from adjacent healthy vines. Phaeoacremonium spp. grew slowly out of infected tissues, but sporulated abundantly in culture. Identification was verified from a published key (1). Phaeoacremonium chlamydosporum and P. inflatipes were isolated throughout the northern and central California production areas, but P. aleophilum was isolated only in Riverside County. Koch's postulates were completed for Phaeoacremonium spp. by dipping roots of 2-month-old Carignane grape seedlings (n = 80) in a 108 spores per ml suspension for 30 min. Plants were potted in an artificial soil mix and held in a growth chamber at 25°C. Over 50% of plants inoculated with Phaeo-acremonium spp. developed root, stem, and vascular symptoms within 8 weeks. Each of the individual pathogen species was reisolated from over 75% of the inoculated plants but never from the controls. Similarly, all three Phaeoacremonium spp. are associated with wilt and decline diseases in grapevines in Africa (1) and Europe (2) but this is the first report in North America. While several names for this disease have been used previously with older grapevines, including Esca, apoplexy, and black measles (3), we propose using Phaeoacremonium grapevine decline to describe the diseases caused by P. aleophilum, P. chlamydosporum, and P. inflatipes on young vines. References: (1) P. W. Crous et al. Mycologia 88:786, 1996. (2) P. Larignon and B. Dubos. Euro. J. Plant Pathol. 103:147, 1997. (3) R. Pearson and A. Goheen. 1988. Compendium of Grape Diseases. American Phytopathological Society, St. Paul, MN.