An intron in the cytochrome b gene of Monilinia fructicola mitigates the risk of resistance development to QoI fungicides.

BACKGROUND

The cytochrome b (Cyt b) gene is a key genetic determinant for quinone outside inhibitor (QoI) fungicide resistance in plant pathogenic fungi. A mutation at amino acid position G143 can cause qualitative resistance unless it is part of the recognition site for a self-splicing intron. The objective of this study was to clone and sequence the Cyt b gene from Monilinia fructicola (Wint.) Honey, the causal agent of brown rot of stone fruits, and to assess the risk for the development of a mutation at position 143.

RESULTS

The Cyt b gene of M. fructicola was 11 927 bp in size and contained seven introns located at cDNA positions (5'-3') 204, 395, 430, 491, 507, 780 and 812 with sizes of 1592, 1318, 1166, 1252, 1065, 2131 and 2227 bp respectively. Sequence analysis revealed that the above-mentioned 1166 bp intron, a self-splicing group I intron, was located just downstream of the G143 codon. The Cyt b gene region covering the G143 location and the adjacent 1166 bp intron was PCR amplified and sequenced from Chinese and US isolates, indicating that the intron may be omnipresent in M. fructicola.

CONCLUSION

This is the first complete Cyt b gene sequence published for M. fructicola or any other Monilinia species, forming the basis for molecular analysis of QoI fungicide resistance. Sequence analysis revealed that the G143A mutation responsible for high levels of QoI fungicide resistance in many plant pathogenic fungi may not develop in M. fructicola unless genotypes emerge that lack the 1166 bp intron.