Chemical management in fungicide sensitivity of Mycosphaerella fijiensis collected from banana fields in México

Abstract

The chemical management of the black leaf streak disease in banana caused by Mycosphaerella fijiensis (Morelet) requires numerous applications of fungicides per year. However this has led to fungicide resistance in the field. The present study evaluated the activities of six fungicides against the mycelial growth by determination of EC50 values of strains collected from fields with different fungicide management programs: Rustic management (RM) without applications and Intensive management (IM) more than 25 fungicide application/year. Results showed a decreased sensitivity to all fungicides in isolates collected from IM. Means of EC50 values in mg L(-1) for RM and IM were: 13.25 ± 18.24 and 51.58 ± 46.14 for azoxystrobin, 81.40 ± 56.50 and 1.8575 ± 2.11 for carbendazim, 1.225 ± 0.945 and 10.01 ± 8.55 for propiconazole, 220 ± 67.66 vs. 368 ± 62.76 for vinclozolin, 9.862 ± 3.24 and 54.5 ± 21.08 for fludioxonil, 49.2125 ± 34.11 and 112.25 ± 51.20 for mancozeb. A molecular analysis for β-tubulin revealed a mutation at codon 198 in these strains having an EC50 greater than 10 mg L(-1) for carbendazim. Our data indicate a consistency between fungicide resistance and intensive chemical management in banana fields, however indicative values for resistance were also found in strains collected from rustic fields, suggesting that proximity among fields may be causing a fungus interchange, where rustic fields are breeding grounds for development of resistant strains. Urgent actions are required in order to avoid fungicide resistance in Mexican populations of M. fijiensis due to fungicide management practices.

Keywords: Mycosphaerella fijiensis; Sigatoka; banana; fungicides; sensitivity.

Figure 1

Comparison of effective concentration of six fungicides for EC₅₀ on mycelial growth in Mycophaerella fijiensis collected from banana fields with Rustic and Intensive managements of fungicides. All assays were done in triplicate.

Figure 2

Molecular analysis of β-tubulin (at codon 198) in M. fijiensis strains from Intensive (I) and Rustic (R) banana plantations. The restriction pattern shows the loss of the 360 bp band in those strains collected from intensive management fields with fungicides. mf-1 and C1N are reference strains isolated in 1999 from rustic and intensive management fields respectively. Both strains are sensitivive to carbendazim with EC₅₀ values of 0.2 and 5.0 mg L⁻¹. Note: Figure composed of four runs of individual gels.