摘要：

SUMMARY A detailed account is given of the history, aetiology, biology, epidemiology, detection, geographical distribu- tion, and control of huanglongbing (HLB), a destructive disease of citrus that represents a major threat to the world citrus industry, and is slowly invading new citrus- growing areas. HLB, whose name in Chinese means "yellow dragon disease", was first reported from south- ern China in 1919 and is now known to occur in next to 40 different Asian, African, Oceanian, South and North American countries. The agent is a phloem-restricted, non cultured, Gram-negative bacterium causing crip- pling diseases denoted "greening " in South Africa, "mottle leaf" in the Philippines, "dieback" in India, "vein phloem degeneration" in Indonesia. The HLB bacterium belongs to the genus Candidatus Liberibac- ter, three species of which are currently known, Candi- datus Liberibacter asiaticus, occurring in Asian coun- tries and, to a lesser extent, in Brazil and the USA (Florida), Candidatus Liberibacter africanus with its subspecies "capensis", recorded from African countries, and Candidatus Liberibacter americanus present in Brazil. The suggestion is that each liberibacter species has evolved in the continent after which it is named. HLB symptoms are virtually the same wherever the dis- ease occurs. Infected trees show a blotchy mottle condi- tion of the leaves that results in the development of yel- low shoots, the early and very characteristic symptom of the disease. Trees are stunted, declining and bear a few, small-sized, and deformed (lop-sided) fruits, that are poorly coloured (greening) and with coloration starting at the peduncular end (colour inversion). HLB can be transmitted by grafting from citrus to citrus and by dod- der to periwinkle. The psyllids Trioza erytreae and Di- aphorina citri are natural vectors. Two different types of

展开