Evidence for Viruslike Agents in Avocado

Publisher Website
Google Scholar
Abstract
Double-stranded RNA (dsRNA), an indicator for the presence of viruses in plants, was detected in all except 22 of > 280 individual avocado plants tested. Three different dsRNA patterns were detected. DsRNA pattern 1 has 3 segments. The smallest segment has a MW of 0.55 .times. 106 daltons. The larger segments are resolved as a doublet by gel electrophoresis with a MW of 6.0-6.5 .times. 106. DsRNA pattern 2 has one major segment with a MW of 3.0 .times. 106. DsRNA pattern 3 has 3 major segments with MW of 2.0, 1.9 and 1.7 .times. 106. The 3 dsRNA patterns were detected both singly and in all possible combinations in different individual plants. Three different viruses (avocado viruses 1, 2 and 3) are proposed to explain the variation in the dsRNA patterns detected. All 3 putative avocado viruses apparently are latent in some cultivars (symptomless carriers). Avocado viruses 1, 2 and 3 are all seed transmitted at a high rate. Avocado viruses 1 and 2 are graft-transmitted across the bud union. Avocado virus 3 is present in all plants of the Hass cultivar tested, both healthy and avocado blackstreak-affected (ABS). Virus 3 alone appears to cause no symptoms. Avocado virus 2 was detected in tissues from ABS-affected ''Hass'' trees, but not in healthy ''Hass'' trees in the field. It is possible, but not proven, that avocado virus 2, either alone or in combination with avocado virus 3, is involved in the ABS disease. Several avocado cultivars had no detectable dsRNA, including the Phytophthora root rot resistent clonal rootstocks ''Duke 6'' and ''Duke 7''. This is the 1st report of the presence of virus-like agents other than tobacco mosaic virus in avocado.