The goal of our research is to develop environmentally sound disease management strategies that are economically feasible for Indiana growers producing apples. Our research effort is directly tied to our extension work, and focuses on the identification and management of fungicide resistance in Venturia inaequalis, the fungus that causes apple scab. Apple scab is one of the most serious diseases of apple and ornamental flowering crabapple, and affects both leaves and fruit; losses of up to 100% have been known to occur when apple scab is unmanaged. In commercial apple production, foliar infection by the apple scab pathogen results in defoliation that leads to a loss of apple quality, and impacts winter-hardiness. Fruit infections result in blemished and deformed fruit that cannot be sold. In commercial apple production, this disease is primarily managed through the use of fungicides. However, fungicide resistance is an emerging problem. We are currently surveying the V. inaequalis population for the presence of fungicide resistance. Use of these fungicides continues despite decreasing efficacy, and we have identified increasing shifts in resistance in the scab populations in Indiana and Michigan over the past three seasons, culminating in the development of field resistance and fungicide failures in orchards in both states. Combining field and laboratory assessments has allowed us to develop methods to quickly assess fungicide resistance, and anticipate which orchards are at risk of fungicide failure, thereby helping growers adjust their management programs appropriately.

Although fungicide use is the primary means of disease management in commercial apple production, both sustainable apple production and landscape crabapple management relies upon plant disease resistance. However, resistance genes, like some fungicides, have a history of losing their effectiveness over time ("resistance breakdown"). We evaluated 33 years of data on 287 crabapples for long-term scab resistance. Of 287, only 31 had no symptoms of scab for longer than a 10-year period and were identified as resistant to the disease. Of these 31 resistant accessions, 14 eventually displayed symptoms, presumably as a result of infection by one or more newly present races of the pathogen in the trial plot. Notable resistance breakdowns in accessions previously classified as resistant include the development of scab on M. x 'Prairifire', M. x 'Bob White', M. x 'Red Jewel', and M. floribunda. Corresponding to these changes in resistance is the putative development of new V. inaequalis races in North America: Race 5, possessing virulence to the Vm gene in ÔPrairifireÕ and the first identification and report of scab on a M. floribunda population that was previously characterized as durably resistant. The detection of scab on this species suggested the presence of Race 7 in North America for the first time, and led to the identification of scab on Malus floribunda 821, the most important source of monogenic scab resistance (Vf) that has been bred into 90 of 110 scab-resistant cultivars and used for transgenic resistance in popular commercial apple cultivars. Our research focuses on evaluating Vf-resistant cultivars to identify which are most susceptible to infection by the new race of scab, and to help growers properly manage these cultivars to minimize the risk of further resistance breakdown. (Reference: Plant Disease Vol. 93, 4:328-331)

The Indiana Green Industry was valued at $3.01 billion dollars for all sectors combined (2004 dollars) based upon 2002 data according to the National Green Industry Survey. The impact of diseases on ornamental production is estimated at 7.1% of crops (Baker and Lindermann, 1979. Annu. Rev. Phytopathol. 17: 253-277), equal to approximately $11 million dollars per year of total crop production value for 2002. One challenging aspect of ornamental crop production is the diversity of species and cultivars in production. More than 2000 plant varieties are produced commercially, each with their own unique spectrum of disease problems. This results in few major economic losses to any one crop, but reliably regular, small economic impacts when crops do suffer from the inevitable production failures due to disease. Dr. Beckerman assists growers in preventing these crop failures, and by developing the management necessary to minimize future losses in the greenhouse, nursery and landscape.

Crabapples
Crabapples are the most widely cultivated small landscape tree in the northern United States and southern Canada. Most retail nurseries (85%) and a majority of landscaping firms (55%) said they sell crabapples and more than 200 varieties of crabapple are currently available from nursery sources. Unfortunately, with this abundance comes confusion regarding which crabapples consumers should plant. Furthermore, negative attitudes persist towards all crabapples because of the inferior performances of a few widely planted selections. In a survey by Romer et al. 2003 (HortTechnology 13: 522-526), 37% of respondents identified disease resistance as one of three most important traits in crabapple evaluations. Dr. Beckerman reviewed the historical records of 287 crabapple cultivars over 33 years at Secrest Arboretum (Wooster, OH), and evaluated their performance to identify durable apple scab resistance. Of 287, only 31 had no symptoms of scab for longer than a 10-year period and were identified as resistant to the disease. Of these 31 resistant accessions, 14 eventually displayed symptoms, presumably as a result of infection by one or more newly present races of the pathogen in the trial plot. Notable resistance breakdowns in accessions previously classified as resistant include the development of scab on M. x 'Prairifire', M. x 'Bob White', M. x 'Red Jewel', and M. floribunda. (Reference: Hort Science 44:599-608)

The Clean Stock Program and International Extension
Recent and historic introductions of exotic plant pathogens into North America and Europe have caused significant disease problems (Dutch elm disease, chestnut blight, sudden oak death), resulting in significant ecological and economic problems, and demands for more stringent phytosanitary regulations to protect environmental and agricultural production interests. These regulations are of particular importance to the nursery and floriculture industries that use live plant material imported from tropical countries to produce plants for their consumers. Dr. Beckerman has added the much-needed component of plant pathology to the existing Clean Stock Program (CSP) collaboration with Centro Agronomico Tropical de Investigacion y Ensenanza (CATIE), USDA-APHIS, and the Costa Rican Ministry of Agriculture. Dr. Beckerman's focus in this program has been to work out the etiology of "Mal Morado," a significant vascular wilt disease of Dracaena. Dr. Beckerman has identified the pathogen as Fusarium oxysporum. Despite the broad host range of the species as a whole, host specialization of isolates with the same or similar host ranges are assigned to a forma specialis; more than 70 formae speciales have been described. She is currently at work identifying this species to forma speciales through a combination of Koch's postulates and molecular analysis.

Top canker of black walnut
Phytophthora citricola causes both a root rot and trunk canker in over 45 species of plants, but has never been reported as a stem canker in trees. Dr. Beckerman identified this pathogen as causing a canker of black walnut in Indiana using a combination of morphological and molecular diagnostics (Beckerman, J. and Ruhl, G. 2007), and provided growers with the information to better understand the etiology and management of this disease. Indiana Department of Natural Resources (DNR) estimates that black walnut production averages between 500,000-600,000 seedlings between two nurseries. In Indiana and surrounding states, DNR and private nurseries report that in "bad years" up to 30% of inventory died from top dieback. The Indiana DNR estimated a yearly loss in revenue approximating $50,000.00 in Indiana alone. More than 15 states in the Midwest produce black walnut in DNR nurseries, and many private industries are involved in black walnut production for both lumber and nut crops. Growers have reported that by using the fungicide rotation recommended by Dr. Beckerman, they have significantly reduced their losses due to top canker. (Reference: Plant Health Progress, April 2007)