Investigation of specific molecular marker and EC50 values of guazatine for Geotrichum citri-aurantii on citrus in China

Geotrichum citri-aurantii is a postharvest fungi disease of citrus which can significantly affect the economy. In this work, two pairs of RPB1 genes primers, 2996-R&F and 4989-R&F, targeting G. citri-aurantii, were successfully developed to distinguish G. citri-aurantii from other Geotrichum species and 27 postharvest pathogens of various horticultural species. In addition, G. citri-aurantii (AY-1, isolated in 2012) used as the positive control, we further isolated 24 G. citri-aurantii isolates (4 from Wuhan, 9 from Guilin and 11 from Ganzhou) in China and investi-gated the median effective concentration (EC50) values of all isolates to guazatine using a colony diameter approach. The results showed that the EC50 values of 22 isolates from the three cities generally increased compared to AY-1. The isolate SF-9 from Ganzhou showed the highest EC50 value to guazatine (EC50 = 32.3578 mg/L) among all the isolates and the average EC50 of isolates from Ganzhou (EC50 = 10.3313 mg/L) was 182 times higher than that of the control. However, the average EC50 values of the G. citri-aurantii isolates from Guilin (EC50 = 0.0826 mg/L) and Wuhan (EC50 = 0.1295 mg/L) were 2.2 times and 1.4 times higher than that of AY-1, respectively. What's important, 13 isolates (AY-5, G12, SF-1, 2 from Guilin city; SF-3, 4, 5, 6, 7, 9, 13, 15, 16 from Ganzhou city) of all still gave rise to disease with 1 mg/L of guazatine treatment in vivo. Above all, an efficient method to afford a rapid identification of G. citri-aurantii was developed and it provided theoretical basis to control guazatine use.

Automated summary

In this study, primers targeting the RPB1 genes of Geotrichum citri-aurantii were developed to differentiate it from other species and postharvest pathogens. Multiple isolates of G. citri-aurantii from different cities in China were investigated for their sensitivity to guazatine. The results showed variations in the EC50 values of the isolates, with some showing significantly higher resistance compared to the control.