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

Abstract

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 investigated 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.