Relationships between susceptibility of field-grown burley tobacco to blue mold and contents of duvatrienediols

Greenhouse studies have suggested a role for alpha- and beta- 4,8,13 duvatriene-1,3-diols (DVT) in the resistance of burley tobacco to blue mold. To test the validity of this relationship in the field, leaf samples from field-grown plants (cv. Ky 14) were assayed for DVT content and tested for susceptibility to Peronospora tabacina under controlled laboratory conditions. The study was conducted in central Kentucky during the 1985 and 1986 growing seasons. In 1985, plants in 11 fields were evaluated six times. Results with leaves from top, middle, and lower stalk positions confirmed the greenhouse findings that susceptibility to blue mold decreases with plant age in both untreated and acetone-dipped leaves, and that dipping leaves in acetone markedly increases susceptibility. There was a significant (P = 0.022) negative correlation between disease severity on untreated leaves and DVT content when leaves from all fields and sampling dates were considered. However, when data from individual sampling dates were analyzed, significant (P = 0.022, 0.026) negative correlations were detected for only two dates. In 1986, intensive sampling was conducted in a single field. Leaves were sampled from 25 plants at approximately 7-day intervals. Results for two stalk positions and two inoculum concentrations were similar to those in 1985. Although there was a highly significant negative correlation (P less than or equal to 0.0001) of disease severity with DVT when all sampling dates were evaluated, no significant (P less than 0.05) correlations were observed within individual sampling dates. Overall, these results indicate that DVT content probably has only a marginal role in the resistance of tobacco to blue mold. The inability to enhance disease in old plants by dipping in acetone suggests the existence of other age-related defense mechanims. The relationship between disease severity and DVT content may be affected by interactions with other mechanisms of resistance and with environmental factors such as rainfall, day/night duration, light intensity, and temperature.