|Ochoa, Ronald - Ron|
Submitted to: Experimental and Applied Acarology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2003
Publication Date: 12/1/2003
Citation: Childers, C.C., Rodrigues, J.C., Derrick, K.S., Achor, D.S., French, J.V., Welbourn, W.C., Ochoa, R., Kitajima, E.W. 2003. Citrus leprosis its status in florida and texas: past and present. Experimental and Applied Acarology. 30: 181-202 Interpretive Summary: The citrus leprosis virus causes millions of dollar in damage each year to the citrus industries of Argentina, Brazil, Panama, Paraguay, and Venezuela. There is a strong possibility that the leprosis virus is in Guatemala. This pathogen has been moving northward since 1941 and poses a serious threat to the billion dollar U.S. citrus industry. Three flat mite species in the genus Brevipalpus are vectors of the virus by transmitting the leprosis virus from infected plants to non infected plants. These mite species already occur in the citrus growing areas of the U. S. and could spread the virus rapidly. Although the citrus leprosis virus was recorded from Florida as early as the late 1800's, it has not been reported from the state since the 1960's. This study reports the leprosis situation in the U.S. and related studies on Brevipalpus mites and the leprosis virus. This information will be valuable to policy makers and researchers in establishing strategies for preventing the entry of this deadly virus into the U. S.
Technical Abstract: According to published reports from 1906 to 1968, leprosis nearly destroyed the Florida citrus industry prior to 1925. This was supported with photographs showing typical leprosis symptoms on citrus leaves, fruit, and twigs. Support for the past ocurrence of citrus leprosis in Florida includes: (1) presence of twig lesions in affected orange blocks in addition to lesions on fruit and leaves; (2) yield reduction and die-back on infected trees; and (3) spread of the disease between 1906 and 1925. Transmission electron microscopy (TEM) examination of tissue samples from leprosis-like feeding injuries to orange and grapefruit leaves from Florida and grapefruit and navel orange fruits from Texas were examined using TEM and none contained leprosis-like viral particles or viroplasm inclusions in the samples examined. In contrast, leprosis viroplasm inclusions were readily identified within green non-senescent tissues surrounding leprosis lesions in 2 of every 3 orange leaf samples and half of the the fruit samples examined by TEM from Piracicaba, Brazil. Symptoms of leprosis were not seen in any of the 24,555 orange trees examined across Florida during 2001 and 2002. We concluded that citrus leprosis no longer exists in Florida or occurs in Texas citrus based on: (1) lack of leprosis symptoms on leaves, fruit, and twigs of round orange citrus surveyed in FLorida, (2) failure to find virus particles or viroplasm inclusion bodies in suspect samples examined by TEM from both Florida and Texas or (3) absence of documented reports by others on the presence of characteristic leprosis symptoms in Florida. Non-leprosis damage by Brevipalpus mites on grapefruit and navel orange fruits is found in Texas. Possible contributing factors that led to the disappearance of citrus leprosis in Florida include: (1)several freezes, especially between 1934 and 1962 and (2) widespread and multiple applications of high rates of wettable sulfur applied by handguns in high water volumes to large well spaced trees more than once a season between 1923 and the early 1960s for control of citrus rust mites in combination with (3) management tactics that focused on the elimination of leprosis infected branches by pruning and top-working with resistant citrus cultivares (i.e., grapefruit). These factors contributed to breaking the virus-mite vector cycle of citrus leprosis in Florida. In view of the serious threat to citrus in the U.S., every effort must be taken to quarantine the importation of both citrus and woody ornamental plants that serve as hosts for Brevipalpus phoenicis (Geijskes), B. californicus (Banks), and B. obovatus Donnadieu (ACARI: Tenuipalpidae) from countries where citrus leporsis occurs.