Grapevine yellow speckle — a newly recognized graft-transmissible disease of Vitis

Abstract

Evidence is presented to show that many grapevines showing leaf symptoms which, particularly when intense, cannot be distinguished from those caused by strains of grapevine fanleaf virus (GFV) or tomato ringspot virus (TRSV) are infected with a previously undescribed disease for which the name grapevine yellow speckle (GYS) is proposed. The causal agent of the disease has not been isolated, but it is graft-transmissible from infected to healthy grapevines. It has not been transmitted by sap inoculation to herbaceous plants. The disease has been detected in some grapevine cultivars grown in Australia for many years, and also in several other cultivars and rootstocks imported from California over the past 10 years. There is no evidence of natural spread or of seed transmission. Attempts to eliminate GYS from plants by heat therapy and propagation of tip cuttings have been unsuccessful. Mataro and LN33, the best indicators for GYS at present, are not entirely satisfactory and there is a need to find an indicator which will detect GYS in a wide range of environments. The disease has not been previously detected, probably because of its similarity to GFV and TRSV and its peculiarity in expressing symptoms only in some environments.

Molecular characterization of grapevine yellow speckle viroid-2 (GYSVd-2)

“…The overall sequence homology within each isolate was high, for example, the homology between the 20 sequence variants of Black Olympia isolate was 98.90-99.72%. Based on the identification of one predominant sequence variant in each of the isolates (i.e., Bv1, Zv1, and Tv1), we hypothesize that all the three GYSVd-2 isolates form a quasispecies with one predominant sequence [11,12,[14][15][16][17].…”

“…Mixed infections involving these viroids in cultivated grapevines is common, and in general, grapevine viroids produce very few, if any, disease symptoms, thereby allowing these viroids to replicate in a host unnoticed. However, of the five types of grapevine viroids identified, GYSVd-1 and GYSVd-2 are associated with disease symptoms such as yellow speckle, which was originally identified under hot greenhouse conditions in Australia [6,7,11].…”

Two Related Viroids Cause Grapevine Yellow Speckle Disease Independently

“…5). A yellowish-green speckling indicative of severe yellow speckle disease (Taylor & Woodham, 1972) was observed along the veins on some of the leaves of this plant (Fig. 4a).…”

“…A second reason for the inconsistencies observed is that indexing for yellow speckle is difficult as the expression of this symptom is erratic (Taylor & Woodham, 1972;Shanmuganathan & Fletcher, 1980). Usually only a few leaves express symptoms on an infected plant and symptom expression in a plant may be non-reproducible from one year to another (Taylor & Woodham, 1972;Shanmuganathan & Fletcher, 1980).…”

“…M. Koltunow & M. A. Rezaian, unpublished results). The existence of sequence variants may explain the differences in the severity of symptoms which have been observed on clonal indicators (Taylor & Woodham, 1972;Shanmuganathan & Fletcher, 1980). The oligonucleotide probe for GYSV would detect GYSV sequence variants provided that significant residue changes did not occur in the region corresponding to probe hybridization.…”