Effect of year, sampling month and grape cultivar on noble rot incidence, mycelial growth rate and morphological type of Botrytis cinerea during noble rot development

Abstract

The aims of this three-year study were firstly to investigate the effect of 3 years, three sampling months and two grape cultivars (cvs) on noble rot incidence in the field and on the mycelial growth rate of Botrytis cinerea isolates in vitro under three incubation temperatures, and secondly to show possible effects of years, sampling months and cultivars on eight morphological (four mycelial: M I-IV and four sclerotial: S I-IV) types of B. cinerea isolates incubated at 20 °C. In addition, the relationship between monthly noble rot incidences and morphological types was calculated. Analyses of variance indicated significant differences among years, months and cultivars for noble rot incidence. Noble rot incidences were significantly higher on cv. ‘Turán’ compared to cv. ‘Olaszrizling’ in November in all years. Noble rot incidences were significantly lower in September compared to values in November in all years. Analyses of variance indicated significant differences among years, months, and temperatures for mycelial growth rate but the differences among cultivars were non-significant. Mycelial growth rates at 15 and 25 °C were higher in 2013 compared to 2014 and 2015; however, the rates at 20 °C were higher in 2014 compared to 2013 and 2015. The overall mean growth rate was the highest in 2013 (76 mm) compared to either 2014 or 2015 (65 or 69 mm, respectively). Mycelial growth rates were significantly different between earlier (September) and later (November) sampling months in three cases: i) in 2013 at 15 °C, ii) in 2014 at 20 °C, and iii) in 2015 at 25 °C. Analyses of variance indicated significant differences among years and months for the frequency distribution of the morphological types but the differences among cultivars were non-significant. In general, the most frequent mycelial and sclerotial types were M I-III and S IV (means were 21.5, 16.1, 28.9, and 13.1%, respectively). Isolates of mycelial types were more frequent in 2013 (∑ M-type 82.2%) compared to 2015 (∑ M-type 57.1%). The frequency distributions of morphological types among sampling months showed differences between the earlier (September or/and October) and the later months (November) in 2013 for M I-III, S II and S IV types; in 2014 for M I, M III, M IV, S I, S III and S IV types; and in 2015 for M I, M IV and S I-IV types. Pearson correlation analyses revealed a significant positive relationship between morphological types (∑ S-type and ∑ M-type) and monthly noble rot incidences (r = 0.676 and P = 0.048). In summary, our results showed possible effects of year/sampling month on noble rot incidence in connection with mycelial growth rate and morphological types of B. cinerea strains isolated during noble rot development.