In this section:
Pseudomonas syringae
First Report of Pseudomonas syringae on grapevines (Vitis vinifera) in South Australia
Australasian Plant Pathology (2002), Vol 31 (4) pp 421-2
B. H. HallA, R.L. McMahonA, D NobleB, E.J. CotherB., D McLintockC
A South Australian Research and Development Institute, Plant Research Centre, Box 397, Adelaide, South Australia, 5001.
B NSW Agriculture, Orange Agricultural Institute, Forest Road, Orange, NSW 2800
C Kirribilly Vineyard Management Services, PO Box 205, Birdwood, SA 5234
Abstract
Pseudomonas syringae was recorded on grapes (Vitis vinifera) for the first time in South Australia in November 2000. The bacterium was recovered from angular leaf lesions collected from affected Verdelho vines from a vineyard in the cooler grape growing regions of South Australia. In November 2001, further infections were confirmed on Merlot, Cabernet Sauvignon, Viognier, Sauvignon Blanc and Chardonnay from three of the cooler winegrowing areas close to Adelaide. No crop loss has been recorded.
A bacterial leaf spot of grapevines (Vitis vinifera) was observed in October 2000 in vineyards in the Northern Adelaide Hills area of South Australia, approximately 35 km east of Adelaide., Small dark spots with yellow halos, first observed after heavy rains, developed on the lower leaves of vines, cv Verdelho. The spots developed into angular lesions delineated by veins, occasionally coalescing and causing chlorosis and senescence of infected leaves. Symptoms were only observed on leaves.
Copious quantities of bacterial ooze were observed when necrotic tissue was cut into thin slices and suspended in a drop of sterile distilled water. Loopfuls of the bacterial suspension were streaked onto Kings Medium B and sucrose peptone agar. Bacteria isolated from the lesions were identified as Pseudomonas syringae and representative isolates lodged in the Australian Collection of Plant Pathogenic Bacteria as DAR 73915 and 75241
Pathogenicity tests were conducted by inoculating leaves, petioles and stems of 8-week-old potted vines, cv Chardonnay, with a suspension of P. syringae. Cultures of both isolates (DAR73915 and DAR75241), grown on nutrient agar for 24 h at 24oC, were suspended in sterile water to form a milky suspension of approximately 1012 cfu/ml. Plants were inoculated by either a) pricking the plant with a needle dipped in the inoculum, b) pricking the leaves and stems with a sterile needle and then rubbing the inoculum over the damaged area with a finger or c) rubbing the inoculum on undamaged young leaves with a finger. Five replicate plants were inoculated by each method and two plants per method were used for the control and inoculated with only sterile distilled water. All plants were sealed in a pre-moistened plastic bag for 48 h to provide a humid environment conducive to infection.
After 10 days incubation at 25oC in the greenhouse, small circular dark lesions with a yellow halo were observed on the youngest leaves of two plants inoculated by rubbing. P. syringae was isolated from the lesions and its identity was confirmed by fatty acid methyl ester analysis as identical to the isolate used to inoculate the plant.
After another wet spring in 2001, infection in cv. Verdelho was more severe than in 2000 and bacteria were also recovered from small black spots and elongated lesions on the stem. Bacterial infections confirmed as caused by P. syringae were observed in 10 more vineyards in 2001. Merlot and Cabernet Sauvignon were infected in 3 vineyards in the same district, Merlot and Viognier in 3 vineyards from the Adelaide Hills, approximately 10km south of the original infection site, and Cabernet Sauvignon, Sauvignon Blanc, Chardonnay and Merlot were infected in 4 vineyards from the Southern Vales region, approximately 50km south of Adelaide.
The first record of P. syringae on grapevines was reported as occurring in Argentina in 1968, where it was defined as a weak pathogen (Klingner et al 1976). Other reports of P syringae on grapevines have been of bacteriosis from Azerbaijan (Samedov et al 1988) and a bark necrosis of grapevine in Sardinia (Cugusi et al 1985).
In South Australia, the bacterium appears to be similar to the P. syringae strain found in Argentina (Klingner et al 1976). Work is in progress to further characterise the pathogen.
Although the disease has developed in two consecutive years, P. syringae does not appear to be a serious problem in grapes in south Australia. There was little spread of the bacteria from the initial infection to new leaves, even after further wet weather, but this is likely to be due to the commencement of regular applications of copper-based fungicides in mid-November. Although infection in 2001 was more severe than the previous year, defoliation of affected leaves was uncommon and there was no apparent effect on the fruit set or yield.
References
Cugusi M, Garau R, Prota U, Dore M (1986) A bark necrosis of Grapevine Caused by Pseudomonas syringae V. Hall, in Sardinia. J Phytopathology 116, 176-185
Klingner AE, Palleroni NJ, Pontis RE (1976) Isolation of Psuedomonas syringae from lesions on Vitis vinifera. Phytopath. Z. 86, 107-116
Samedov AN, Mogilevskaya MI, Karagezov TG, Khudaverdieva SR, Aliev LA (1988) Detection of the causal agents of grape bacteriosis in Aspheron (Azebaijan SSR, USSR). Izvestiya Akademii Nauk Azerbaidzhanskoi SSR Seriya Biologicheskikh Nauki. 6, 18-23
