SURVEY OF “CANDIDATUS LIBERIBACTER SOLANACEARUM” IN CARROT CROPS AFFECTED BY THE PSYLLID TRIOZA APICALIS (HEMIPTERA: TRIOZIDAE) IN NORWAY

Abstract

SUMMARY The carrot psyllid Trioza apicalis Forster (Hemiptera: Triozidae) is a serious insect pest of carrot (Daucus carota L.) in northern Europe, where it can cause up to 100% crop loss. Although it was long believed that T. apicalis causes damage to carrot by injection of toxins into the plant, it was recently established that this psyllid is a vector of the new bacterium “Candidatus Liberibacter solanacearum”, which severely damages carrot crops. This bacterium is also known to severely affect solanaceous crops and is the causal agent of zebra chip, a new and economically important disease of potato in North and Central America and New Zealand. Symptoms in psyllid-affected carrots include leaf curling, yellowish and purplish discoloration of the leaves, stunted growth of both leaves and roots, and proliferation of secondary roots. These plant symptoms resemble those caused by leafhoppertransmitted phytoplasmas and Spiroplasma citri in carrots. Using PCR assays, a survey of “Ca. L. solanacearum” in carrot crops in Norway determined that the bacterium is widespread in several counties in southeastern and eastern Norway, where most of the carrot crops are grown. Liberibacter infection rate ranged from 33.3 to 100% in carrot plants and from 21.2 to 56.3% in T. apicalis. No phytoplasmas or spiroplasmas were detected in carrot or psyllid samples by PCR. Information from this research will help carrot producers reduce damage caused by “Ca. L. solanacearum” to carrot crops by vigorously monitoring and controlling T. apicalis, its insect vector.