Date of Award

12-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Division of Agriculture (SAFES)

Committee Member

Dr. James E. Faust, Committee Chair

Committee Member

Dr. Guido Schnabel

Committee Member

Dr. Paula Agudelo

Abstract

Botrytis cinerea Pers. is a necrotrophic fungal pathogen that infects over 235 different plant species around the world. In cut flower roses, B. cinerea causes gray mold disease which leads to large economic losses during greenhouse production and in the post-harvest environment. Disease symptoms are often not visible during the production stage but are observed after storage and/or transportation. Fungicide applications are the primary strategy for gray mold management. However, fungicide resistance has been observed in several crops around the world, resulting in lack fungicide efficacy. Cultural practices such as plant nutrient management, cultivar selection, and crop sanitation are also important aspects of the disease management program. Despite the extensive efforts to control this pathogen, gray mold disease remains a persistent threat for cut rose production. In the first part of this research project, Botrytis cinerea Pers. sensu stricto was confirmed as the unique causal agent of gray mold in cut roses from Colombia. Other pathogenic fungi were identified, e.g., Alternaria alternata, Cladosporium cladosporoides, Epicoccum nigrum, Penicillium citrinum, Aspergillus brasiliensis and Diplodia sp. These fungi may become problematic in the future. Gray mold incidence and severity were evaluated in different rose tissue from the Botrytis susceptible cultivar ‘Orange Crush’. Six commercial shipments from two different greenhouses at the same farm in Colombia were evaluated. The petals showed the highest disease incidence and severity. A total of 49 B. cinerea isolates were collected during the severity and incidence evaluation. Fungicide resistance profiling was performed using ten fungicides. The isolates showed high occurrence of resistance to boscalid, cyprodinil, iprodione and thiophanate-methyl; moderate frequency of resistance to isofetamid, fenhexamid, fluopyram, and penthiopyrad, low resistance to fludioxonil, and no resistance to pidiflumetophen. Variation in the fungicide resistance profiles were observed between greenhouses and shipments. Isolates with simultaneous resistance to different chemical classes were also observed. In the second part of this research project, B. cinerea spore count was recorded using two spore collectors installed in commercial cut flower greenhouses. The relationship between different production activities and conidia count was also evaluated via hierarchical cluster analysis. From the total 26 activities evaluated, 14 of them were related with a high spore count. A higher spore count was observed during the week days compared to the weekend, which coincided with the days with 50.5% more activities in the greenhouse. Possible relationships between spore count and disease incidence were also evaluated; however, no correlation was observed. The results of this research suggest: 1) fungicide resistance management practices should be implemented to improve the effective life of different fungicides and their efficacy against B. cinerea infection, 2) timely removal of plant debris from the production greenhouses may reduce inoculum proliferation, and 3) avoidance of free water in the greenhouse may reduce inoculum dispersal and germination.

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