Three graft-transmissible diseases and a variegation disorder of small fruit in New Zealand

Abstract

The presence in New Zealand of the reversion disease ofblack currants was demonstrated by the development oftypical symptoms in susceptible cultivars after graft inoculation. Reversion appears to be responsible for the serious crop losses occurring in Otago and Southland regions. It is not restricted to those areas, but occurs at a low incidence in Canterbury and Nelson regions. Spread has occurred through the use of infected cuttings during propagation, and probably also by the gall mite vector. Red currant vein banding disease was detected in several red currant cultivars by graft inoculation to red currant seedlings, and to the indicator B1385/81, but is of low incidence. The disease boysenberry decline, possibly caused by a mycoplasma-like organism, occurs in the northern half of the North Island. During the 1980s it appeared to be spreading rapidly until the removal of most infected plantings greatly reduced its incidence. The boysenberry leatbopper is a possible vector, but in controlled glasshouse and field trials natural spread of the disease by this agent has notbeen observed. A leaf variegation symptom, widespread in several black currant cultivars in New Zealand, may be a non-transmissible syndrome.

History of Boysenberry and Youngberry in New Zealand in relation to their problems with Boysenberry decline, the association of a fungal pathogen, and possibly a phytoplasma, with this disease

“…Previously, Wood (1991) reported the successful transmission of Boysenberry decline from an infected Kumeu field plant of Boysenberry to a clone of Boysenberry obtained from North America and named 'Boysen-72'. In this trial symptoms had shown on the 'Boysen-72' in the second season after graft inoculation, and possible, but not conclusive transmission had also obtained to several blackberry cultivars.…”

“…It was later concluded that this foliar nemotode was not associated with the decline symptom. Tests for presence of Rubus viruses were also negative (Wood 1991). The disease was shown to be transmissible by grafting from diseased to healthy Boysenberry (Wood 1991), and the possibility of it being caused by a mycoplasma-like organism (or phytoplasma as these organisms are now known) was then considered.…”

“…Tests for presence of Rubus viruses were also negative (Wood 1991). The disease was shown to be transmissible by grafting from diseased to healthy Boysenberry (Wood 1991), and the possibility of it being caused by a mycoplasma-like organism (or phytoplasma as these organisms are now known) was then considered. The disease had some similarities (but also differences) to the phytoplasma disease Rubus stunt, which occurs in Europe (Murant & Roberts 1971;van der Meer 1987).…”

“…The disease had some similarities (but also differences) to the phytoplasma disease Rubus stunt, which occurs in Europe (Murant & Roberts 1971;van der Meer 1987). However, when the cultivar 'Mailing Landmark', a Rubus stunt susceptible red raspberry (R. idaeus L.) was grafted with Boysenberry decline affected material, no symptoms of stunt developed (Wood 1991). Grafting of Boysenberry decline affected material to cultivars sensitive to the blackberry dwarf disease of the western United States (Zeller 1927;Wilhelm 1951;Wagnon & Williams 1970) gave inconclusive results (Wood 1991).…”

“…However, when the cultivar 'Mailing Landmark', a Rubus stunt susceptible red raspberry (R. idaeus L.) was grafted with Boysenberry decline affected material, no symptoms of stunt developed (Wood 1991). Grafting of Boysenberry decline affected material to cultivars sensitive to the blackberry dwarf disease of the western United States (Zeller 1927;Wilhelm 1951;Wagnon & Williams 1970) gave inconclusive results (Wood 1991). The latter disease had been found to be graft-transmissible to Boysenberry and Youngberry in the United States, though the plants were not severely affected (Zeller & Milbrath 1940), and neither were found naturally affected under field conditions (Wilhelm 1951).…”