Botrytis pseudocinerea Is a Significant Pathogen of Several Crop Plants but Susceptible to Displacement by Fungicide-Resistant B. cinerea Strains

Abstract

Botrytis cinerea is one of the most important pathogens worldwide, causing gray mold on a large variety of crops. Botrytis pseudocinerea has been found previously to occur together with B. cinerea in low abundance in vineyards and strawberry fields. Here, we report B. pseudocinerea to be common and sometimes dominant over B. cinerea on several fruit and vegetable crops in Germany. On apples with calyx end rot and on oilseed rape, it was the major gray mold species. Abundance of B. pseudocinerea was often negatively correlated with fungicide treatments. On cultivated strawberries, it was frequently found in spring but was largely displaced by B. cinerea following fungicide applications. Whereas B. cinerea strains with multiple-fungicide resistance were common in these fields, B. pseudocinerea almost never developed resistance to any fungicide even though resistance mutations occurred at similar frequencies in both species under laboratory conditions. The absence of resistance to quinone outside inhibitors in B. pseudocinerea was correlated with an intron in cytB preventing the major G143A resistance mutation. Our work indicates that B. pseudocinerea has a wide host range similar to that of B. cinerea and that it can become an important gray mold pathogen on cultivated plants.

FIG 1

Genetic diversity and fungicide resistance frequencies of Botrytis species and B. cinerea genotypes isolated from fields or orchards of different host plants. Each diagram shows the isolates from one field or orchard (A, B, C, etc.). Frequencies of resistance (0R, 1R, 2R, etc.) against up to seven fungicides are indicated by different shadings of gray according to the legend on the figure. Detailed information of the strains is provided in Table S1 in the supplemental material. Bps, B. pseudocinerea; BcS, B. cinerea S; BcN, B. cinerea N; Bpae, B. paeoniae; Bfab, B. fabae. R, fungicide resistance not determined. Significantly higher frequencies of B. pseudocinerea among Botrytis isolates from untreated versus fungicide-treated fields are indicated by asterisks (Fisher's exact test, P = 0.01). The “×” values above the panels indicate the frequencies of fungicide sprayings in each of the fields.

FIG 2

Seasonal variations of B. pseudocinerea (Bps), B. cinerea S (BcS), B. cinerea N (BcN), B. cinerea X (BcX), and Botrytis spp. (B.sp.) and fungicide resistance frequencies in five commercial strawberry fields. Fungal isolates were collected in spring 2012, summer 2012, and spring 2013 (fields A to D) and in spring 2013, summer 2013, and spring 2014 (field E). Frequencies of resistance against up to five fungicides (excluding iprodione and carbendazim) are indicated by increasingly dark shading, similar to the scheme used in Fig. 1, according to the legend on the figure. Significantly higher frequencies of B. pseudocinerea among Botrytis isolates in the first spring compared to those of the summer after fungicide treatments (Fisher's exact test, P = 0.01) and significant increases in the accumulation of fungicide resistances in B. cinerea isolates after the treatments (t test, P = 0.01) are indicated by asterisks. ns, not significant. If B. cinerea X (BcX) and Botrytis spp. were not found, they are not shown in the diagrams of the respective fields.

FIG 3

Neighbor-joining tree of B. pseudocinerea group A and group B strains and other Botrytis clade 1 species (B. calthae used as an outgroup), based on the combined sequences of g3pdh, tubA, and ms547, with 1,000 bootstrap replicates. Bootstrap values of >70 are shown. Bps, B. pseudocinerea; S. sclerotiorum, Sclerotinia sclerotiorum.