Keremane L. Manjunath

ASIAN CITRUS PSYLLIDS (STERNORRHYNCHA: PSYLLIDAE) AND GREENING DISEASE OF CITRUS: A LITERATURE REVIEW AND ASSESSMENT OF RISK IN FLORIDA

Abstract The Asian citrus psyllid, Diaphorina citri Kuwayama, was discovered in Florida in 1998. It can be one of the most serious pests of citrus if the pathogens that cause citrus greening disease (huanglongbing) are present. Citrus greening recently has been reported in Brazil by Fundecitrus, Brazil. The establishment of D. citri in Florida increases the possibility that the disease may become established. Diaphorina citri can be separated from about 13 other species of psyllids reported on citrus. The biology of D. citri makes it ideally suited to the Florida climate. Only two species, D. citri and Trioza erytreae (del Guercio), have been implicated in spread of citrus greening, a disease caused by highly fastidious phloem-inhabiting bacteria. The disease is characterized by blotchy mottle on the leaves, and misshapen, poorly colored off-tasting fruit. In areas where the disease is endemic, citrus trees may live for only 5-8 years and never bear usable fruit. The disease occurs throughout much of Asia and Africa south of the Sahara Desert, on several small islands in the Indian Ocean, and in the Saudi Arabian Peninsula. Transmission of citrus greening occurs primarily via infective citrus psyllids and grafting. It is transmissible experimentally through dodder and might be transmitted by seed from infected plants and transovarially in psyllid vectors. Citrus greening disease is restricted to Citrus and close citrus relatives because of the narrow host range of the psyllid vectors. Management of citrus greening disease is difficult and requires an integrated approach including use of clean stock, elimination of inoculum via voluntary and regulatory means, use of pesticides to control psyllid vectors in the citrus crop, and biological control of psyllid vectors in non-crop reservoirs. There is no place in the world where citrus greening disease occurs that it is under completely successful management. Eradication of citrus greening disease may be possible if it is detected early. Research is needed on rapid and robust diagnosis, disease epidemiology, and psyllid vector control.

Progress on strain differentiation of Citrus tristeza virus and its application to the epidemiology of citrus tristeza disease

Citrus tristeza virus (CTV) occurs in most citrus producing regions of the world, and it is the most serious viral pathogen of citrus. With the recent establishment of the brown citrus aphid, Toxoptera citricida, its most efficient vector, on Madeira Island (Portugal) and in Florida (USA) and the countries of the Caribbean Basin, the impact of CTV is likely to increase in these regions. Since there are many strains of CTV and CTV infections frequently occur as mixtures of several strains, it is necessary to be able to distinguish the strains for regulatory purposes, disease management and epidemiology. We describe the evolution of techniques developed to detect CTV and to differentiate the individual strains, and present the results of tests using these latest methods on CTV isolates from mainland Portugal, Madeira Island and Florida. Mild and decline-inducing strains of CTV were detected in mainland Portugal and mild, decline-inducing and severe stem pitting strains on Madeira Island. In Florida we demonstrated the presence of infections that reacted with probes made against stem pitting strains not previously detected there. It is concluded that CTV presents a significant threat to citrus production in mainland Portugal, on Madeira Island and in the neighbouring countries of the Mediterranean Basin, as well as in Florida, elsewhere in the USA and throughout the Caribbean Basin, especially following the widespread establishment of T. citricida throughout the region.

Distribution and Characterization of Citrus tristeza virus in South Florida Following Establishment of Toxoptera citricida

The incidence of Citrus tristeza virus (CTV) was found to increase significantly in southern Florida within 2 years after the establishment of its most efficient vector, Toxoptera citricida (Kirkaldy). Increased incidence of both mild and severe strains was documented, with the incidence of severe strains increasing more than mild strains. Molecular probes capable of differentiating mild, quick decline and various types of stem-pitting strains demonstrated that trees often were infected with more than one strain of CTV, with trees containing up to five different strains. Some CTV strains detected in the southeast urban corridor of Florida and in commercial groves in southwest Florida were found to react with probes specific for stem-pitting strains known from elsewhere in the world. The implications of the presence of these CTV strains in Florida and their possible presence in citrus budwood scion trees are discussed.

Trailers Transporting Oranges to Processing Plants Move Asian Citrus Psyllids

ABSTRACT Huanglongbing (citrus greening) is one of the most serious diseases of citrus. Movement of the disease occurs as a result of natural transmission by the insect vector and by movement of infected plant material. We demonstrate here that Diaphorina citri Kuwayama, the vector of citrus greening pathogens, can be transported in trailers of unprocessed fruit. Several samples of D. citri collected from trailers of oranges were positive for citrus greening pathogens, indicating that the disease can spread widely with the movement of the mature fruit as a result of moving the vectors. While movement of disease and the vector through plant materials into new areas has been recognized, our findings emphasize the need to evaluate the importance of long distance movement of psyllids on unprocessed fruit, even in the absence of vegetative tissue.

Incidence of Huanglongbing-Associated ‘Candidatus Liberibacter Asiaticus’ in Diaphorina citri (Hemiptera: Psyllidae) Collected from Plants for Sale in Florida

ABSTRACT The Asian citrus psyllid, Diaphorina citri Kuwayama, was reported for the first time in Florida in June 1998, and huanglongbing (HLB, citrus greening), vectored by D. citri, was detected in Florida for the first time in Aug 2005. In Florida, the only known HLB pathogen is ‘Candidatus Liberibacter asiaticus’ (Las). After HLB was known to be established in Florida, the psyllid vectors found in regulatory samples from plants for sale were tested for the pathogen by real-time qPCR. Approximately 1,200 regulatory samples were tested between Aug 2005 and Aug 2009. Samples came from venues in 44 of Floridas 67 counties. Most of the samples came from citrus, but about 11% came from Murraya exotica, a popular ornamental plant and close relative of citrus. Approximately 9.7% of the psyllid samples tested were positive for Las. Numbers of samples and proportion of positive samples varied by year and by county.