Guanggan (Citrus reticulata) shows strong resistance to Phytophthora nicotianae

Two closely related pathogens of Phytophthora are responsible for stem gummosis and root rot diseases in Citrus worldwide. In this study, a neglected local mandarin called Guanggan (Citrus reticulata) was identified to be strongly resistant to one of the pathogens, P. nicotianae. No visible symptom was seen on all leaf explants within one week or on 50% of in vivo inoculated stems within one month after inoculation with the pathogen. Drenching of the soil with zoosporangial and zoospore suspensions did not cause any reduction in tree growth and leaf chlorophyll content of pot-grown Guanggan seedlings. Quantitative real-time PCR analysis suggested that its resistance to P. nicotianae may be associated with high basal and induced expression of some defense-related genes, particularly the PR3 gene. In conclusion, C. reticulata var. Guanggan is a promising material that can be exploited to improve Phytophthora resistance in Citrus.