ABSTRACT
California is the second largest sweet cherry producer in the United States with annual revenues up to $200 million. The South Australian cherry industry generates about 10% of Australia's overall production with approximately 1,500 metric tons of cherries produced yearly. In California, perennial canker diseases and subsequent branch dieback are responsible for extensive damage throughout sweet cherry orchards, reducing annual yields and tree longevity. Surveys of cherry orchards and isolation work were conducted in California to identify the main canker-causing agents. Calosphaeria pulchella was the main fungus isolated from cankers, followed by Eutypa lata and Leucostoma persoonii, respectively. Preliminary surveys in cherry orchards in South Australia documented C. pulchella and L. persoonii in cankers. The pathogenicity of C. pulchella in sweet cherry was confirmed following field inoculations of 2- to 3-year-old branches. C. pulchella was able to infect healthy wood and produce cankers with as much virulence as E. lata or L. persoonii. Spore trapping studies were conducted in two sweet cherry orchards in California to investigate the seasonal abundance of C. pulchella spores. Experiments showed that rain and sprinkler irrigation were important factors for aerial dissemination. Finally, this study illustrates the symptoms and signs of the new disease Calosphaeria canker.
ABSTRACT
ABSTRACT Foliar symptoms of Eutypa dieback, caused by Eutypa lata, in grapevines, cv. Shiraz, varied from year to year in a 6-year study conducted in South Australia and, although trends were similar for vineyards within geographical regions, differences were observed between regions. We attempted to elucidate the causes underlying this variation and hypothesized that it was influenced by climatic factors. A number of possible relationships were identified between climate and symptom expression: (i) increased symptom expression was related to increased winter rainfall 18 months earlier, (ii) decreased disease incidence and prevalence were related to increased temperature in spring, and (iii) a reduction in disease incidence was related to both very high and very low rainfall in October. Theories for these relationships are proposed and require further investigation. A conceptual model was developed which requires validation and has the potential to predict the incidence of foliar symptoms of Eutypa dieback. Information from this study could lead to an improved integrated pest management system to suppress foliar symptoms and sustain productivity of vines infected with E. lata.
ABSTRACT
Grapevine cultivar (Vitis vinifera) and isolate of Eutypa lata influence wood and foliar symptoms of Eutypa dieback. Foliar symptoms of Eutypa dieback developed within 8 months of inoculating young grapevines (cvs. Grenache, Cabernet Sauvignon, and Merlot) in a shadehouse. Isolates of E. lata from various wine regions in southern Australia varied in their ability to colonize inoculated grapevines and induce wood and foliar symptoms. Grapevine cultivars varied for wood and foliar symptom expression but not for mycelial colonization. However, the severity of foliar symptoms was not related to the rate of spread of the fungus in the grapevine. Furthermore, the staining of wood typically attributed to E. lata did not reflect the presence of the fungus because the fungus was detected up to 80 mm beyond the stain. A field trial with mature grapevines revealed significant differences in the rate of spread of wood staining due to E. lata among eight cultivars, with up to 50 mm/year detected in Cabernet Sauvignon and Shiraz grapevines. In the shadehouse, the maximum growth rate of E. lata was recorded to be 115 mm/year for Grenache rootlings. Information from this study may help to optimize management strategies for maintaining productivity of grapevines with Eutypa dieback, thus reducing the economic impact of the disease.
