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University of Arizona (1971)

ETIOLOGY AND EPIDEMIOLOGY OF VIRUSES OF NATIVE CACTUS SPECIES IN ARIZONA

Milbrath, Gene McCoy

Titre : ETIOLOGY AND EPIDEMIOLOGY OF VIRUSES OF NATIVE CACTUS SPECIES IN ARIZONA

Auteur : Milbrath, Gene McCoy

Université de soutenance : University of Arizona

Grade : Doctor of Philosophy (PhD) 1971

Résumé
The first virus found to infect the saguaro cactus has been isolated. This virus has been designated saguaro virus (SV) and is also the first isometric virus found to infect any of the cacti. It is 35 mp in diameter and contains a single sedimenting component in purified preparations. The virus is widespread in saguaros. Approximately 407o of the saguaros assayed contained SV. It is unknown what long term effect SV may have on the native stands of saguaro. Saguaro virus is easily detected in the floral parts of the saguaro, but it is difficult to detect the virus in the vegetative tissue. A convenient local lesion assay host for SV is Chenopodium amaranticolor. Another species of Chenopodium. C. capitatum, may be infected systemically with SV and eventually killed. Saguaro virus has been characterized by a selected host range, sucrose density gradient centrifugation, analytical ultracentrifugation, and electron microscopy. It sediments as a single band in sucrose density gradient tubes and a single.peak in the analytical ultracentrifuge. Calculated sedimentation coefficients Sw^q of 106, 107, and 112 have been determined from three individual runs. Electron micrographs of purified SV contain uniform isometric particles. Saguaro virus was not found to be serologically related to cucumber mosaic virus, tobacco ringspot virus, rose mosaic virus, apple mosaic virus, cherry necrotic ringspot virus, or plum line pattern virus. Further investigations are needed to establish the identity of SV.
A rod-shaped virus identified as Sammons’ Opuntia virus (SOV) was found to occur in many of the Opuntia cacti. The symptoms on the cactus pads range from faint chlorotic markings to large concentric interlocking rings which sometimes cause depressions in the cactus pad. In addition, the infected cacti have paracrystalline inclusions which are visible in tissue sections in the light microscope. Another type of chlorotic ringspot, initially thought to be a viral symptom, was found to be induced by the Opuntia joint bug (Chelinidea vittiger Uhler).
Sammons’ Opuntia virus was purified directly from infected pads by using either alternate high and low ultracentrifugation or polyethylene glycol precipitation. Purified virus was used for inoculation experiments, electron microscopy, analytical ultracentrifugation, and serology. Electron micrographs of the purified material contained numerous particles with a normal length of 312 + 6.96 mp. A sedimentation co-efficient Sw^q °f 183 was calculated from Schlieren patterns obtained in the analytical ultracentrifuge. Sammons’ Opuntia virus was found serologically related to tobacco mosaic virus. Native Opuntia are exposed to high temperatures (+50 C) for considerable periods of time in the desert climate. The temperature of the interior portion of the pad may range 6-8 C higher than the air temperature. Despite these temperatures the SOV remains infective and is not inactivated. The formation of the paracrystalline inclusions may be helpful in protecting the virus.

Mots clés : Cactus — Diseases and pests. ; Virus diseases of plants.

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Page publiée le 28 février 2016, mise à jour le 22 février 2018