Biology, Epidemiology and Integrated Management Of Diseases Caused By Fusarium In Potted Ornamentals Progress Reports – June 2002
ANNUAL PROGRESS REPORT – JUNE 2002
Project Title: Biology, Epidemiology, And Integrated Management Of Diseases Caused By Fusarium
In Potted Ornamentals
Researcher/Institution Information:
R.J. McGovern, University of Florida, Department of Plant Pathology, Gainesville, Florida, 32611, Phone: 352-392-3631, E-mail: rjm@mail.ifas.ufl.edu
W.H. Elmer, Connecticut Agriculture Experiment Station, P.O. Box 1106, New Haven, Connecticut, 06504, Phone: 203-974-8503, Fax: 203-974-8502, E-mail: wade.elmer@po.state.ct.us
D.M. Geiser, Pennsylvania State University, Department of Plant Pathology, 211 Buckout Lab, University Park, Pennsylvania, 16802, Phone: 814-863-9773, Fax: 814-863-7217, E-mail: dgeiser@psu.edu
B.K. Harbaugh, University of Florida, GCRE, 5007 60th Street East, Bradenton, Florida, Phone: 941-751-7636, Fax: 941-751-7639, E-mail: bkh@mail.ifas.ufl.edu
Industry Needs Addressed And Objectives:
Fusarium species cause common, persistent, and damaging diseases in most major potted and field-grown ornamentals. Severe outbreaks of Fusarium crown and stem rot, Fusarium wilt, and Fusarium root and crown rot caused, respectively, by F. avenaceum, F. oxysporum, and F. solani have caused extensive losses in lisianthus in the US. A decline in caladium production over the past decade that has led to a shortage of tubers for use as potted plants is strongly linked to a high incidence (>90%) of F. solani. Fusarium wilt of cyclamen (F. oxysporum) is highly destructive and economically limiting to the production of quality cyclamens, and its incidence has steadily increased in production facilities across the US. Root rot and vascular wilt caused by F. oxysporum also represents a continuing threat for the production of chrysanthemum. Despite its importance, previous research on Fusarium has been sporadic.
Objective:
This multi-year, interdisciplinary project will generate useful information on the biology, epidemiology, genetics, detection, and integrated management of diseases of ornamentals caused by Fusarium. Model pathosystems to be examined include caladium (F. solani and F. oxysporum), chrysanthemum (F. oxysporum and F. oxysporum), cyclamen (F. oxysporum), and lisianthus (F. avenaceum, F. solani, and F. oxysporum).
Progress Report For FY 2001-2002:
- Biology and Epidemiology of Fusarium
Knowledge of pathogen survival, spread (including insects and other vectors), and the conditions that favor infection is the starting point for effective disease management. We have gained such useful information on the following diseases:Tuber Rot (F. solani) in Caladium
We identified the environmental conditions (high relative humidity, 28o C/82o F) and inoculum density (≥105 conidia of F. solani/ml) that are optimal for Fusarium tuber rot. We screened about 40 F. solani isolates from caladium for their ability to cause tuber rot. Three highly virulent isolates have been selected for use in screening caladium lines and cultivars for resistance to tuber rot (see below). In vitro assays of 70 F. solani isolates from caladium indicated that 47 are sensitive, 10 are moderately resistant, and 2 are highly resistant to thiophanate methyl, the most commonly used fungicide for Fusarium control in ornamentals. This is the first report of such resistance in F. solani.
Fusarium Wilt (F. oxysporum) in Chrysanthemum.
Seven isolates of Fusarium oxysporum f. sp. chrysanthemi were collected from several sources and screened for pathogenicity on two susceptible cultivars of chrysanthemums. One isolate was highly virulent in preliminary tests. The cultivars ‘Hartford’ was selected for all future experiments.
Fusarium Wilt (F. oxysporum) in Cyclamen.
Fungus gnats and shore flies are often implicated as vectors of Fusarium wilt of cyclamen, but data has not been produced that confirms their role in the spread of this disease. In 2001 we demonstrated that fungus gnats transmitted F. oxysporum pathogenic to cyclamen at low levels. In 2002, our transmission experiments were repeated. When fungus gnats were absent, no disease was detected on healthy plants that were caged with diseased plants. Additional studies are underway to confirm insect transmission.
Fusarium Wilt (F. oxysporum) in Lisianthus.
Inoculation of snapdragon and China aster with F.oxysporum from lisianthus caused stunting and yellowing indicating that the fungus may have a broader host-range than previously suspected. These studies are being continued and expanded. In vitro assays of 70 F. oxysporum isolates from lisianthus indicated that 47 are sensitive, 10 are moderately resistant, and 2 are highly resistant to thiophanate methyl, the most commonly used fungicide for Fusarium control in ornamentals. This is the first report of such resistance in F. oxysporum. - Genetic Characterization and Detection of Fusarium
Although Fusarium is commonly isolated from plant tissue, it may or may not be involved with a specific disease. Genetic characterization of Fusarium through DNA sequencing and determination of vegetative compatibility vegetative compatibility grouping (VCG) will allow for identification and detection of pathogenic isolates and aid in understanding their spread within and between countries. This work will also contribute to the much-needed taxonomic revision of the genus Fusarium.Fusarium avenaceum from lisianthus.
Thirty-nine isolates of Fusarium avenaceum have been assayed for vegetative compatibility. Thirty six were isolated from lisianthus. Thirty-four out of 36 isolates were pathogenic on lisianthus including isolates of F. avenaceum that were originally recovered from other host plants. No correlation was seen between host, pathogenicity and origin using vegetative compatibility suggesting a high degree of diversity exist within this pathogen and that there may be many potential crop reservoirs of F. avenaceum.
Fusarium oxysporum from lisianthus.
Isolates of Fusarium oxysporum pathogenic to lisianthus were collected from North America, South America, and Australia. Vegetative compatibility tests thus far have found three VCGs which suggests that geographic divergence may occur. Additional molecular tests will need to be done to determine the degree of diversity within this pathogenic group.
Fusarium solani from caladium.
We have generated DNA sequences from four gene regions: elongation factor, internally transcribed spacer (ITS), nuclear large rRNA, and beta-tubulin in 65 isolates of F. solani from caladium. The results suggest that there are at least two distinct groups of F. solani isolates associated with outbreaks of this disease in Florida. Neither of these lineages was previously identified. Both of these groups are related to isolates of F. solani mostly from North American hosts, suggesting the possibility that there are specific species-like lineages of F. solani that are capable of infecting caladium, and that this might represent a host jump from a different North American host. - Integrated Management of Fusarium
Our goal is to develop an integrated approach to management of diseases caused by Fusarium spp. in the targeted crops through evaluation of cultivar resistance, induced or acquired resistance, biological and chemical control, and cultural practices.Fusarium Tuber Rot in Caladium (F. solani)
Macroexplant Propagation. We finished evaluation of combining macroexplant propagation and fungal soaks in hot water for pathogen-free tuber production. Six of the fungicides, Captan, Heritage, Prochloraz Mn 50 WP, sodium hypochlorite, Spectro 90 WDG, and 3336 WP increased tuber number compared to the non-treated control. Captan, Heritage, Spectro, and 3336 WP also significantly increased tuber weight.
Fungicide Evaluation. Two field trials were conducted to evaluate fungicide efficacy. In an experiment on muck soil, Spectro 90 WDG applied as a tuber soak in combination with hot water increased plant emergence and number of jumbo tubers, while soaking tubers in 3336 WP plus at-planting spray of Medallion+Subdue (Hurricane) decreased Fusarium tuber rot. Spectro also increased caladium emergence and tuber number in raised, mulched beds on sand.
Cultivar Resistance. Various crosses were made between caladium cultivars suspected of being either highly resistant or susceptible to Fusarium tuber rot. Using the pathogenicity assay developed above, we have begun to assess levels of resistance in these crosses.
Fusarium Wilt in Chrysanthemum
Bicontrols , Fungicides. Seven biological products (Actinovate, Companion, Mycostop, Plant Shield, Primastop, SoilGard, and Taegro) delayed the onset of symptoms, but did not provide the level of suppression observed with the chemical fungicides Heritage and Medallion.
Fusarium Wilt in Cyclamen (F. oxysporum)
Induced Resistance, Biocontrols, Fungicides. Experiments conducted in 2001 indicated that benzothiadiazole (Actiguard) could induce disease resistance (delay symptoms) to Fusarium wilt in cyclamen. We obtained the same results with older cyclamens in 2002 but saw no benefit in combining Actiguard with NaCl, which had shown growth-promotion properties in other studies. Such commercial biocontrols as Actinovate Plus/M, Companion, Deny, and RootShield were ineffective against Fusarium wilt. Rotations of 3336 WP and Medallion significantly reduced both Fusarium wilt development and severity.
Fusarium Wilt (F. oxysporum)in Lisianthus
Biocontrols and Fungicides. We reevaluated a number of fungicides and biocontrols tested in 2001 for effectiveness in controlling Fusarium wilt in lisianthus. Among the fungicides, Medallion, Terraguard, Systhane, and 3336 WP were the most effective in reducing plant mortality. Heritage, and Spectro 90 WDG were of intermediate effectiveness. The biocontrols PGA+ and RootShield significantly reduced the rate of plant death and final mortality. Other biocontrol products including CS-20, LS 213, Fusaclean, and SoilGard were ineffective.
Cultivar Resistance. A method was developed to screen lisianthus seedlings (Eustoma grandiflorum) for resistance to Fusarium wilt caused by Fusarium oxysporum in order to determine if any level of resistance is present in commercial germplasm. A very virulent isolate or F. oxysporum was selected from preliminary tests and used to inoculate seedlings. Sixty-one cut flower lisianthus, representing both single- and double-flowering types, were evaluated in two tests. The percentage of dead plants in the single flowering types ranged from as low as 0% to 10 % (‘Tyrol White’, ‘Ballet Purple’, ‘Malibu Deep Purple, Imp, ‘Mellow Pure White’ and ‘Hallelujah Purple’) to 100% (‘Flamenco Blue Rim’, ‘Heidi Blue Rim’, and ‘Mellow Purple Picotee’) in both tests. Of the 15 double flowering types evaluated, only two cultivars had less than 50% dead plants (‘Avila Deep Rose’, 17%; ‘Mariachi White’, 26%) while most cultivars had 80 to 90% dead plants. Thus, the double cultivars appear very susceptible to F. oxysporum. These results will be helpful to growers that may want to avoid using the most susceptible cultivars, and will also be valuable to breeders as a first step in breeding resistant cultivars.
Fusarium Root and Crown Rot (F. solani) in Lisianthus
Cultivar Resistance. Fusarium root and crown rot, caused by F. solani, is a serious problem for dwarf lisianthus grown as pot or bedding plants. We evaluated 17 dwarf cultivars for resistance to Fusarium root and crown rot in two field tests. Seedlings at the 10 to 12 leaf stage were transplanted into four fields with a high inoculum density of F. solani. In the first evaluation, 18% (‘Lisa White’) to 75% (‘Lisa Blue’) of the plants died within 10 weeks from transplanting seedlings in the field. The second test is in progress, and the results after 5 weeks in the field appear very similar to the first test. While there is not the level of resistance that was observed in the cut flowers for F. oxysporum, there is evidence that much needed improvements could be made by selecting for resistance.
