citrus packing machine

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Lemon Essential Oil—15 ml

Item No. 3578

 Citrus Tristeza Virus in Hawai‘i

Scot Nelson, Michael Melzer, and John Hu

Department of Plant and Environmental Protection Sciences

Citrus tristeza virus (CTV) is the most economically important pathogen of citrus worldwide (Figure 1). CTV is the causal agent of “tristeza” (also known as “quick decline”), which has destroyed over 50 million citrus trees growing on sour  citrus packing machine orange rootstocks globally (Figure 2). CTV is also respon­sible for another viral disease known as stem pitting (Figures 3, 4, 5) which reduces fruit qual­ity and negatively impacts the production of limes, grapefruits, and sweet oranges (Figures 6, 7) (72). Numerous strains of CTV exist. Mild strains that infect sweet orange, mandarins, and many other cultivars sometimes do not cause symptoms and result in less severe crop losses. CTV is vectored by multiple aphid species in Hawai‘i (Figures 8, 9, 10), where it poses a continuing threat to citrus cultivation throughout the state. Here we discuss CTV, the diseases it causes, and some integrated practices for its management.  citrus packing machine

Hawai‘i imported nearly 20 million pounds of fresh citrus fruits in 2008, while producing only a few hundred thousand pounds of fresh citrus for local markets (71) (Table 1). Although Hawai‘i possesses a favorable climate for citrus cultivation, citrus farming ranks relatively low in crop value and total acreage among agricultural com­modities.  citrus packing machineAmong the factors contributing to the paucity of productive citrus farms in Hawai‘i are plant diseases, in particular tristeza and stem pitting caused by CTV. Farmers in Brazil coined the disease name “tristeza,” which means “sadness” in Portu­guese, because of the severity of symptoms and the large crop losses caused there by the virus in the 1930s.

The pathogen, CTV

When, how, or from where CTV first entered Hawai‘i is unknown. However, the first report of tristeza and stem pitting in the Islands was at the University  citrus packing machineof Hawai‘i at Mānoa’s Poamoho Agricul­tural Experiment Station on the island of O‘ahu in 1952 (33) (Table 2). A subsequent survey of citrus trees elsewhere on O‘ahu indicated that disease symptoms caused by CTV were widespread in citrus throughout Hawai‘i.

CTV is a member of the virus family Closteroviri­dae, genus Closterovirus, of which Beet yellows virus (BYV) is the type member. Several review articles and book chapters have focused on this virus family (1, 2, 16, 44) or  citrus packing machine specifically on CTV (29, 49, 58). The closterovi­ruses are positive-strand RNA viruses with long, flexu­ous particles. A typical CTV particle is approximately 2000 nm in length and 12 nm in diameter (Figure 11). CTV is limited to the phloem tissues of infected hosts.  citrus packing machine The natural host range for CTV is confined to members of the plant family Rutaceae, of which citrus species are members (Tables 3, 4). Some Passiflora species are the only known non-rutaceous hosts (66).

Numerous strains of CTV have been described that vary in virulence and the severity of the diseases they cause. Some strains of CTV cause tristeza, but not stem pitting. Similarly, some strains cause stem pitting in oranges, but not in grapefruit.  citrus packing machine The most reliable and through the use of indicator plants (30, 74). Garnsey et al. (30) have developed a standardized bioassay for strain detection using the following indicator plants: ‘Mexican’ lime, sour orange, ‘Duncan’ grapefruit, ‘Madam Vinous’ sweet orange, and navel sweet orange on a sour orange rootstock. Symptom development in citrus packing machine these indicator plants following inoculation with an unknown CTV strain helps to determine whether the strain can cause quick decline or stem pitting, as well as indicating the severity of symptoms. Severe strains of CTV will cause tristeza and/or stem-pitting symptoms, whereas milder strains cause less severe disease or may infect citrus plants asymptomatically. Some strains of CTV may induce symptoms  citrus packing machine differentially in one host but not in another (49).

Based on the wide range of genetic marker patterns, a diverse population of CTV strains exists in Hawai‘i. Mixed infections consisting of various CTV strains also commonly occur in Hawaiian citrus; observed symptoms citrus packing machine are usually caused by the more severe strain in the mixture.

CTV is limited worldwide to tropical and subtropi­cal regions. Currently, CTV is found in North America (35, 73), Central America and the Caribbean (35, 37, 79), South America (35), Australia (6), Oceania (33), Asia (56), Africa (49, 76), and  citrus packing machine some Mediterranean coun­tries (7, 36, 49). CTV and the diseases it causes exist throughout the Hawaiian Islands, where the incidence reported virus incidence of 91% (41 out of 45 plants) on O‘ahu, Maui, and the island of Hawai‘i, although most of the samples tested appear to have spread from the Big Island. A recent and more comprehensive survey (52) found CTV incidence of 74% (298 of 405 plants).