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Lemon Essential Oil—15 ml
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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).
