P-250 - Culture- and molecular-based methods for assessing fungicide resistance to quinone outside inhibitors in Colletotrichum fioriniae

Pre and postharvest fruit rots pose a major threat to blueberry production causing significant economic losses. Colletotrichum fioriniae is one of the primary causal agents, especially in humid climates. Management relies heavily on quinone outside inhibitors (QoI) fungicides (FRAC 11); however, consistent use has led to resistance development in C. fioriniae, limiting management options. Research studies show that two cytochrome b (cytb) amino acid substitutions, F129L and G143A, confer moderate and high levels of resistance, respectively. The objective of this research is to provide insights into the detection of these mutations in C. fioriniae. Three genotypes of C. fioriniae with three isolates per genotype were used (n = 9) for molecular detection of these alleles through conventional PCR and qPCR, followed by sequencing of the cytb gene. Moreover, these isolates were used to confirm that QoI resistance can also be assessed by serial dilution growth assays, discriminatory dose assessments, and spiral gradient fungicide assays. Our results showed that culture-based methods provided consistent results with those from the molecular assays. Lastly, six housekeeping genes were sequenced to confirm that all tested isolates were C. fioriniae. This study found that it was significantly more efficient to use the spiral gradient-based method for culture-based assessment and the qPCR assay for molecular assessment when monitoring QoI fungicide resistance in C. fioriniae populations in fruit crops.