Showing papers by "Wade H. Elmer published in 2001"

Seeds as Vehicles for Pathogen Importation

Abstract: Since the 1900s, consumer demand for new plant products gave opportunity for many plant pathogens to disseminate to new areas on imported seeds. New markets for plant commodities encouraged plant breeders to begin collecting seed stocks from abroad. The birth of new seed companies extend their markets to new area. These events began the global dissemination of many seedborne pathogens. Many seedborne pathogens gained entry and escaped detection by specific traits that favored their dissemination. Three recent case scenarios are presented that illustrate how plant pathogens that passively employ the seed coats of their host achieved global dissemination and permanence in each patho-system. Evidence is presented to show that asparagus (Asparagus officinalis) seed produced in the US acted as a vehicle for disseminating one vegetatively compatible group (VCG) of a pathogenic fungus on asparagus called Fusarium proliferatum throughout new plantings in Australia. Similarly, public demand for Mediterranean cuisine in the US and abroad during the last 20 years led to an increase in the importation of basil (Ocimum basilicum) seed along with an inconspicuous fungus called Fusarium oxysporum. The fungus caused a destructive disease called Fusarium wilt of basil that appeared in over 25 separate locals spanning three continents. The third example demonstrated how new developments in lupine (Lupinus spp.) cultivars and increased public demand led to the global dispersal of a seedborne pathogen called Colletotrichum gloeosporioides. Each case highlights how these pathogens use seeds, humans, and particular traits to disperse globally in short period of time.

Characterization of Colletotrichum gloeosporioides Isolates from Ornamental Lupines in Connecticut.

Abstract: Twenty-six isolates of Colletotrichum gloeosporioides were isolated from diseased ornamental lupines (Lupinus spp. 'Russell Hybrids') in seven different nurseries in Connecticut from 1996 to 1998. Three isolates from New Hampshire, New York, and Utah were also included. All isolates identified were pathogenic on lupine and vegetatively compatible with each other. Representative isolates were compared to lupine isolates from Quebec, Canada and France (COL-1 group), and from Australia and France (COL-2 group). Both groups are responsible for causing anthracnose of ornamental and forage Lupinus spp. in these countries. The Connecticut isolates were vegetatively compatible with the isolates in the COL-2 group and had random amplified polymorphic DNA profiles consistent with isolates in the COL-2 group. Isolates in the COL-1 group were vegetatively compatible only with each other and had random amplified polymorphic DNA profiles that differed from the COL-2 group. Isolates in both COL-1 and COL-2 were sensitive to both benomyl and thiobendazole, but the COL-1 group could be distinguished as slightly more tolerant than the COL-2 group and the Connecticut isolates. These assays provided persuasive evidence that the isolates from Connecticut belong to COL-2 group. The introduction of this homogenous pathogen population in Connecticut is likely due to the importation of infested seeds.

First Report of Fusarium Wilt of Exacum affine Caused by Fusarium oxysporum.

Abstract: Wilting Persian violets (Exacum affine) were observed in a Connecticut retail outlet. Diseased stems developed a dark coloration at the nodes, while the foliage turned papery, whitish tan. The vascular tissue in affected stems was reddish brown and extended from the base of the stem upward in a unilateral pattern. Fusarium grew from the discolored stem tissue when placed on Komada's medium (2). Single spores were cultured on carnation leaf agar and identified as F. oxysporum (2). Koch's postulates were completed by growing 12 2-month-old seedlings of E. affine 'Midget' in potting mix amended with ground dried millet seed (2.0 g/liter of soil) that had been colonized for 2 weeks by the fungus. Symptoms appeared slowly after 8 weeks, and F. oxysporum was re-isolated from the vascular tissue. Plants grown in soil mix with sterile millet remained healthy. Similar tests at different times of the year produced the same results. Other tests examined host specificity with two new isolates on seedlings of Persian violet, carnation, lisianthus, and basil. Both isolates caused symptoms only on Persian violets. Although Haematonectria haematococca (synonym Nectria haematococca, anamorph F. solani) causes Nectria canker of Persian violet (1), this is the first report of F. oxysporum causing Fusarium wilt of Persian violet. We propose the formae specialis be F. oxysporum f. sp. exaci. An isolate has been deposited at the Fusarium Research Center at The Pennsylvania State University, University Park, under Accession No. O-2282. References: (1) M. Daughtrey et al. Compendium of Flowering Potted Plant Diseases. American Phytopathological Society, St. Paul, MN, 1995. (2) Nelson et al. Fusarium species: An Illustrated Manual for Identification. The Pennsylvania State University Press, University Park, PA, 1983.