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Robert J. McGovern*

The Univ. of Florida's College of Agricultural and Life Sciences and Institute of Food and Agricultural Sciences have taken a bold step in teaching crop health management with the creation of the Plant Medicine Program. This innovative program offers students a multidisciplinary approach to solving the challenges of crop production that leads to the Doctor of Plant Medicine (DPM) degree. Extensive coursework in the Plant and Soil Sciences, Entomology, Plant Pathology, and Nematology provides students with the fundamental knowledge needed to be successful problem solvers and decision makers. Students apply their expertise to practical situations during multiple internships with a wide array of professionals. Interns have worked nationally and internationally on a wide variety of crops with private corporations, public institutions, and government and non-government agencies, in research, regulatory, and extension capacities. Students have the opportunity to tailor their program to reflect specific interests while maintaining a strong foundation in the discipline of Plant Medicine through the core courses. Since its inception in 1999, enrollment in the Plant Medicine Program has grown to over 40 students, and beginning in 2003, graduates have become valued members of the global agricultural community.

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Ramona A. Reiser and Robert J. McGovern

Zantedeschia elliotiana `Flame' is a yellow calla with unique rust-colored blush, which is prone to a fungal/bacterial disease complex. Keeping calla rhizomes healthy and free of weakening by the most common fungal organisms Fusarium and Rhizoctonia, which minimizes secondary invasion and toppling by Erwinia carotova soft rot, the most prevalent cause of calla loss in production. Rhizomes were treated by pre-plant bulb dip or post plant drench either with fungicide or bactericide alone or in combination. Pot loss totaled with plants showing a lack of vigor resulted in 8%, 12%, and 14% loss in the most effective three treatments, which were: 1) the common commercial pretreatment (Champ II, Dithane, and Agtrol) 2) control plants and 3) RootShield (Trichoderma harzianum T-22). Upper (leaf and stem) plant fresh weights corresponded having heaviest weights of 47.8, 53.4, and 51.1 g and lower (bulb and root) with 129.5, 135.8, and 127.7 g/plant. The three least-effective treatments were streptomycin sulfate, Kocide 101, and ammonium bicarbonate, which showed losses of 26%, 30%, and 36%. Fresh weights coincided at 30.5, 39.9, and 36.7 g/upper portion and 117.1, 116.5, and 113.1 g/lower portion, lightest of all treatments. The remaining four fungicides with streptomycin sulfate, in order of effectiveness at 16%, 16%, 18%, and 20% loss, were Consyst, Banrot, Medallion, and Heritage. When loss exceeded 20%, flower number/plant also declined. Because plant survival and vigor were not increased with trial chemicals, the common commercial pretreatment or no treatment at all is recommended. Continued research might reveal beneficial optimum rates for other chemicals.

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Brent K. Harbaugh and Robert J. McGovern

Fusarium crown and stem rot, caused by Fusarium avenaceum, is a serious disease of lisianthus, Eustoma grandiflorum Raf. (Shinn.). While more than 80 new cultivars of lisianthus have been released for sale in the United States in the past decade, there is a lack of information on their susceptibility to this pathogen. Forty-six cultivars of lisianthus were evaluated for resistance to F. avenaceum. Cultivars were grouped according to blue/purple, pink, or white colors and evaluated within their color class. Although all cultivars evaluated were susceptible to F. avenaceum, partial resistance was observed as indicated by differences in the length of time to symptom expression and in the frequency of diseased plants. `Ventura Deep Blue' and `Hallelujah Purple' (25%) in the blue group, `Bridal Pink' (23%) in the pink group, and `Heidi Pure White' (53%) in the white group had the lowest frequency of diseased plants at 55 days after inoculation. In 21 of the 46 cultivars, 80% to 100% of the plants expressed symptoms at 55 days after inoculation. Screening cultivars for resistance to F. avenaceum is the first step to breeding and developing resistant cultivars. These results also can be useful to growers who could select cultivars that express some level of resistance as an aid in management of this disease until more resistant cultivars are released.

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Zhanao Deng, Brent K. Harbaugh, Rick O. Kelly, Teresa Seijo and Robert J. McGovern

Caladiums (Caladium ×hortulanum) are popular ornamental plants widely grown for their bright colorful leaves. Pythium root rot, caused by Pythium myriotylum, is one of the few soil-borne diseases in caladium that dramatically reduces plant growth, aesthetic value, and tuber yield. Information on the reaction of caladium cultivars to P. myriotylum is not available, but would be valuable for integrated control of this disease and for breeding new resistant cultivars. Three Pythium isolates obtained from decaying roots of plants collected from a field production site and two greenhouses were evaluated for pathogenicity and potential use in experiments to screen commercial caladium cultivars for resistance. All three isolates were found to be highly virulent; they were able to cause obvious root rotting within 3 to 5 days and severe root rotting and leaf losses on susceptible cultivars within 10 days after inoculation. Nineteen major commercial cultivars were evaluated for their resistance to these isolates. Fifteen of the cultivars were susceptible or highly susceptible to Pythium infection. Four widely grown cultivars, `Candidum', `Candidum Jr.', `Frieda Hemple', and `White Christmas', were found to have a moderate level of resistance (partial resistance) to pythium root rot. Pythium infection also caused leaf discoloration, epinasty, wilting, and collapse. Regression analyses revealed a linear relationship between the root rot and leaf loss severity on Pythium-inoculated plants.

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Zhanao Deng*, Brent K. Harbaugh, Rick Kelly, Teresa Seijo and Robert J. McGovern

Caladiums (Caladium × hortulanum) are widely grown for their bright colorful leaves. Pythium root rot, caused primarily by P. myriotylum, is one of the most important diseases in caladiums. This disease can dramatically reduce plant growth, impact plant aesthetical value, and lower tuber yield. Pythium infection in the roots may also lead to subsequent entry of Fusarium into tubers resulting in tuber rot. There has been a strong interest in the tuber production and greenhouse plant production industries to identify cultivars that are resistant or tolerant to Pythium. However, few studies have been conducted since the pathogen was identified, and little information is available regarding the existence of any possible resistance in commercial cultivars. Pythium isolates were made from diseased plants collected from different sites; their pathogenicity was confirmed using tissue culture-derived plants. Procedures were developed for oogonia spore production, inoculation, and disease severity assessment. Nineteen major commercial cultivars were inoculated at two spore densities and then maintained in greenhouses under growing conditions favorable for root rotting. Plant appearance, leaf characteristics and severity of root rotting were evaluated 2-3 times after inoculation. Observations indicated that the isolates were highly virulent. They induced visible root rot within 3-5 days, and caused a complete loss of the root system and plant death for some cultivars within 2-3 weeks after inoculation. Several cultivars, including `Candidum' and `Frieda Hemple' which are widely grown cultivars, had much less root rot, higher plant survival, and seemed to have moderate levels of resistance.

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Zhanao Deng, Brent K. Harbaugh, Rick O. Kelly, Teresa Seijo and Robert J. McGovern

Caladiums (Caladium ×hortulanum) are widely grown as pot or landscape plants for their attractive leaves. Pythium root rot (Pythium myriotylum) is one of the most damaging diseases in caladium, severely reducing plant growth, aesthetic value, and tuber yield. Twenty-three commercial cultivars were inoculated with three aggressive isolates of P. myriotylum and evaluated for their resistance to root rot. Three cultivars, `Apple Blossom', `Blizzard', and `Etta Moore', were found to have a moderate level of resistance (partial resistance) to pythium root rot. The rest of these cultivars were susceptible or highly susceptible to Pythium infection, losing up to 94% of their root tissue to rotting within 10 days after inoculation. Data indicated a linear relationship between root rot severity and leaf loss severity on Pythium-inoculated plants and highlight the importance of controlling pythium root rot in caladium pot plant and tuber production. Comparison of some recent releases with their parents for pythium root rot resistance suggests the potential of developing new resistant caladium cultivars using the identified sources of resistance.

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Fahrettin Goktepe, Teresa Seijo, Zhanao Deng, Brent K. Harbaugh, Natalia A. Peres and Robert J. McGovern

Fusarium tuber rot, incited by Fusarium solani, is the major cause of losses of tuber quality and quantity in caladium (Caladium ×hortulanum) during storage and production. To develop a reliable inoculation method for evaluating cultivar susceptibility to Fusarium tuber rot and identifying sources of resistance, the effect of temperature on the mycelial growth of F. solani in vitro and on tuber rot in vivo was examined. The optimal temperature was then used to study the aggressiveness of F. solani isolates. The effect of temperature (13, 18, 23, 28, and 33 °C) on radial mycelial growth of nine F. solani isolates in vitro was determined, and all responded similarly to temperature variables, with optimal growth predicted to be at 30.5 °C. The relationship of these temperatures to disease development was then determined for the most aggressive F. solani isolate 05-20 and it was found that disease development in inoculated tubers was greatest at low temperatures (13 and 18 °C). Cold damage to tubers was observed at 13 °C; therefore, 18 °C was chosen for all future disease screening. The aggressiveness of nine isolates was tested on two caladium cultivars. Significant differences among isolates were observed for the diameter of rotted tissue in both cultivars, indicating that choice of isolate was important for screening. Isolates 05-20 and 05-257 were highly aggressive on both cultivars. Tubers of 17 commercial caladium cultivars were inoculated with three isolates (04-03, 05-20, and 05-527) and incubated at 18 °C. The interaction between isolates and cultivars was highly significant (P < 0.0001), indicating that cultivars were not equally susceptible to different pathogenic isolates of F. solani. Lesion diameters differed significantly (P < 0.0001) among cultivars/isolates and ranged from 9.5 mm (‘Rosebud’ and ‘White Christmas’ for isolate 04-03) to 23.9 mm (‘Carolyn Whorton’ for isolate 05-20). The cultivars were ranked for susceptibility to tuber rot within each isolate and the normalized total rank for the three isolates was used to place cultivars into four categories: resistant (‘Candidum’, ‘Rosebud’, ‘White Christmas’, ‘Florida Sweetheart’, and ‘Aaron’), moderately resistant (‘White Wing’ and ‘Red Flash’), susceptible (‘Candidum Jr.’, ‘White Queen’, ‘Red Frill’, ‘Florida Cardinal’, ‘Miss Muffet’, and ‘Postman Joyner’), and highly susceptible (‘Fannie Munson’, ‘Gingerland’, ‘Frieda Hemple’, and ‘Carolyn Whorton’). The availability of these sources of host plant resistance, aggressive isolates, and resistance assessment techniques will facilitate the development of new Fusarium-resistant caladium cultivars.