ISHS Acta Horticulturae 568: X International Symposium on Virus Diseases of Ornamental Plants
SYMPTOMS OF VIRUS INFECTION IN CACTUS |
| Author: | M. Chessin |
| Keywords: | Cactus virus, external and internal symptoms |
| Abstract:
Work with cactus viruses is now approximately a century old. The first definitive indication came in 1951 in Europe. In 1961 virus was also detected in cultivated cactus in the USA, and in 1965 in wild cactus in Arizona. Some infections are symptomless, but both external and internal symptoms do occur. Externally they consist of chlorotic circles, rings and spots on the pads of prickly pear cactus (Opuntia spp.) to a reddening of the fronds of the Christmas cactus (Zygocactus sp.). Occasionally more extreme symptoms, such as bending, marked yellowing and dieback of stems occur. Cactus viruses characteristically induce the production of large cigar- or spindle-shaped Giemsa-stainable inclusions, mainly in the outer cell layers of infected plants. Such inclusions are readily distinguishable from the crystal clusters and spherical inclusions of calcium oxalate found uniformly in epidermal layers of Opuntia spp. In addition, virus infection may produce interrupted spindles, as well as corkscrews, rings, threads, polyhedra and X-bodies. The stomatal apparatus is particularly sensitive to virus infection in some cactus species. Guard cells are conspicuously spindle-free, they fuse with each other and with accessory cells, and they produce outgrowths or “tumors”. Whether these changes influence stomatal function in general or the unusual diurnal behavior of stomata in cactus and other succulents would be interesting subjects for research. A virus of barrel cactus (Ferrocactus sp.) induces severe deformation and dwarfing in tissues formed after infection. Whether the flange-shaped anomalies (cristae) of this and other cactus are virus-caused is unclear. Although virus-like particles have been found in witches’ broom specimens of Opuntia tuna, a spiroplasma is the probable cause of the excessive shoot formation. | |
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