CSIRO PUBLISHING © Australasian Plant Pathology Society 2003 10.1071/AP02072 0815-3191/03/010105 www.publish.csiro.au/journals/app Australasian Plant Pathology , 2003, 32, 105–107 SHORT RESEARCH NOTE Germination of β conidia of Phomopsis viticola V. Sergeeva A , N. G. Nair B,D , I. Barchia A , M. Priest C and R. Spooner-Hart B A Elizabeth Macarthur Agricultural Institute, Camden, NSW 2570, Australia. B Centre for Horticulture and Plant Sciences, University of Western Sydney, Locked Bag 1797, South Penrith Distribution Centre, NSW 1797, Australia. C Orange Agricultural Research Institute, Orange, NSW 2800, Australia. D Corresponding author; email: n.nair@uws.edu.au Abstract. Germination of β conidia of Phomopsis viticola was recorded in potato-dextrose liquid medium but not in sterile distilled water. Maximum germination of β conidia in vitro occurred within 144 h reaching a plateau around 60–80 h at 26°C, whereas α conidia germinated within 28 h at 30°C. Preliminary bioassays indicated that the β conidia are potentially capable of symptomless infection of grapevine leaves. However, further studies are required to confirm this. AP02072 Phomopsisviti colaβconidi agermi nat ion V.Ser geva etal. Additional keywords: grapevine cv. Chardonnay, α conidium, conidial germination, leaf infection. Cane and leaf blight of grapevines caused by Phomopsis viticola is an important disease in several viticultural regions of the world (Machowicz-Stefaniak et al. 1991; Nair et al. 1994). P . viticola produces dark, eustromatic pycnidia and their exudations (cirrhi) contain two types of conidia that are known as α and β conidia. α conidia are oval and elliptical or fusiform, but β conidia are filiform and mostly curved. The ratio of α:β conidia within a pycnidium can vary significantly although factors responsible for this are unknown (Nitimargi 1935). Pycnidia that form solely α or β conidia are also found (Thate 1966). α conidia are known to germinate and cause infection of grapevine, but β conidia are generally considered to be sterile (Pezet 1974), and their function in disease development remains unknown. We provide evidence in this paper for germination of β conidia of P . viticola and their potential to infect grape leaves. P . viticola (Type 2 of Merrin et al.1995) was isolated from green shoots and leaves of Vitis vinifera (cv. Chardonnay) displaying visible symptoms of Phomopsis cane and leaf blight collected in late October from vineyards in the Hunter Valley, New South Wales. Pieces (5 cm long) of the green shoots and whole leaves were surface sterilised by dipping them in 1% sodium hypochlorite for 1 min followed by rinsing three times in sterile distilled water. They were then placed on potato-dextrose agar (PDA) in Petri dishes (80- mm-diameter) and incubated for 10 days in the dark at 25°C. In all cases, pycnidia developed in 7 days and cirrhi appeared 7–10 days later. Axenic cultures of P . viticola were obtained by transferring conidia from the cirrhi of exuding pycnidia to PDA plates using a sterile needle under aseptic conditions. The plates were incubated at 24°C until pycnidia developed. The cultures were then transferred to a refrigerator at 5–10°C where they were stored until needed. The stock cultures were sub-cultured every 3 months to prevent loss of viability. A representative isolate has been deposited in the culture collection at the Orange Agricultural Institute, Orange, NSW, Australia, as DAR 51225. Pycnidia growing in vitro on PDA and containing α or β conidia exclusively were used to study conidial germination. Cirrhi exuding from ten pycnidia on five replicate Petri dishes were used. Five separate portions of each cirrhus were examined under a binocular compound microscope (magnification ×480) to confirm their contents. Individual suspensions (1 × 10 6 /mL) of each type of conidium were prepared from cirrhi containing these conidial types exclusively. Germination of α and β conidia was studied at different temperatures (8, 20, 26 and 30°C) and durations (2, 4, 6, 8, 24, 28, 30, 32, 48, 50, 52, 56, 72 and 144 h) using different methods: (1) conidial suspensions were made in potato-dextrose liquid medium and these were streaked on PDA in Petri dishes, incubated and germination recorded; (2) conidial suspensions were made in potato-dextrose liquid medium in 25 mL conical flasks, incubated and germination recorded; and (3) conidial suspensions were made in sterile distilled water, incubated and germination recorded. Due to similarity in the results obtained from methods 1 and 2, only data from method 2 (conidial germination in potato-dextrose