Identification and resistance to thiophanate-methyl of Botrytis species on Kansas greenhouse crops and a specialty crops grower survey to assess extension IPM resource needs

Abstract

Gray mold, caused by the fungus Botrytis spp., is a disease that occurs worldwide and infects over 170 plant families, including 200 horticultural commodities such as geraniums, lavender, ornamental peppers, petunias, and other greenhouse commodities. Botrytis cinerea, a necrotrophic generalist, is the major cause of gray mold. However, in recent years, other Botrytis species have been identified on an array of crops using molecular diagnostic techniques. The objective of this study was to identify Botrytis species associated with horticultural crops in Kansas and determine sensitivity to methyl benzimidazole carbamate (MBC) fungicides in Kansas strains. To do this, 80 strains were collected from symptomatic plant parts from greenhouses from 19 sites off 43 different hosts. To determine fungicide sensitivity levels to MBC fungicides, strains were single-spored and tested for sensitivity to 100µg/ml of thiophanate-methyl using fungicide-amended media and control plates. Relative mycelial growth (RMG) was calculated as the average diameter on fungicide-amended media divided by the average diameter on the control x 100. The entire experiment was conducted three times. Of the 80 strains: 63 were highly resistant, RMG ≥ 75%; 9 strains had moderate resistance, RMG ≤50%, but ≥75%; 4 strains had low resistance, RMG between 0 and 50%; and 4 strains were sensitive, RMG=0%. Since the use of morphology has proven to be unreliable for species identification, three nuclear protein-coding genes (RPB2, G3PDH, and HSP60) were used in a phylogenetic analysis that included comparison to known species sequences. 75 strains were identified as Botrytis cinerea and 5 strains were inconclusive. Understanding the species of Botrytis and fungicide sensitivity levels to different active ingredients in Kansas provides growers with science-based information to improve pre- and post-harvest management practices. Many fruit and vegetable producers grow a wide range of crops with a diverse range of pest problems. To understand and prioritize research and extension needs, 107 fruit and vegetable growers were surveyed to gather information about farmer backgrounds, farm systems, quantify top pest problems, current practices, and resource needs. Surveys were distributed at 6 conferences and workshops, as well as online. Nearly half (46%) of farms were less than 5 acres and 33% were novice growers, with farms operated for less than 5 years. Half (51%) of growers said they could identify diseases “usually” or “always” as opposed to “never” or “sometimes”, while 48% never use a disease diagnostic lab. Currently, 73%, 59%, and 46% frequently use online materials, conferences/ workshops, and printed resources, but the most preferred resources were conference/ workshops (23%), online written publications (20%), and online videos (18%). Many growers were smaller-scale and less experienced, and they seek information in diverse formats. Both organic and conventional farmers’ main diagnostic challenge was disease identification, yet many growers did not report using the plant disease diagnostic lab, indicating a need for further training and resources. Our results form a baseline to develop and optimize research and extension projects to better serve growers.