205 Ann. appl. Biol. (2004), 144:205-218 Printed in UK *Corresponding Author E-mail: fiona_constable@hotmail.com ' 2004 Association of Applied Biologists The incidence, distribution and expression of Australian grapevine yellows, restricted growth and late season leaf curl diseases in selected Australian vineyards By F E CONSTABLE 1 *, J JONES 2 , K S GIBB 3 , Y M CHALMERS 4 and R H SYMONS 1 1 Department of Plant Science, Waite Campus, University of Adelaide, Glen Osmond, South Australia 5064, Australia 2 BiometricsSA, University of Adelaide/South Australian Research and Development Institute, GPO Box 397, Adelaide SA 5001, Australia 3 School of Science, Charles Darwin University, Darwin, NT 0909, Australia 4 Department of Primary Industries, PO Box 905, Mildura, Victoria, 3502, Australia (Accepted 17 October 2003; Revised version received 29 September 2003) Summary Surveys were conducted in four Chardonnay vineyards for 3 to 6 years and one Shiraz vineyard for 3 years to determine the yearly percentage of grapevines affected by Australian grapevine yellows disease (AGYd), restricted growth disease (RGd) and late season leaf curl disease (LSLCd). In each of the Chardonnay vineyards in each year, all three diseases were characterised by remission of disease in some grapevines, recurrence of disease in other grapevines and new observations of disease in previously unaffected grapevines. The pattern of temporal incidence of each disease was different between vineyards for the survey period. Although Kochs postulates have not been fulfilled, phytoplasmas are considered to be the most likely cause of AGYd. While some grapevines exhibited a combination of AGYd and RGd or AGYd and LSLCd, both RGd and LSLCd can occur independently of AGYd. Statistical analyses using log-linear models also indicated that RGd and LSLCd were not always associated with AGYd. Thus, it is possible that phytoplasmas are not the cause of RGd or LSLCd and their association is coincidental. Expression of AGYd in Shiraz grapevines occurred later in the season compared to Chardonnay. Very little recurrence of AGYd was observed in the Shiraz grapevines indicating that the variety Shiraz responds differently to phytoplasma infections, assuming that AGYd in Shiraz is a phytoplasma caused disease. RGd and LSLCd were not observed on any grapevines in the Shiraz vineyard. Key words: Spatial distribution, incidence, Australian grapevine yellows, temporal, restricted growth, late season leaf curl Introduction Surveys have shown that Australian grapevine yellows disease (AGYd) and phytoplasmas are found in most viticultural regions of Australia (Bonfiglioli et al ., 1996; Magarey & Wachtel, 1986b). Electron microscopy (Magarey et al., 1988), antibiotics (Magarey & Wachtel, 1986b) and PCR techniques (Bonfiglioli et al., 1995; Gibb et al., 1999; Padovan et al., 1995; Constable et al., 2003) have confirmed an association between phytoplasmas and AGYd. Three different phytoplasmas have been associated with AGYd and include the Australian grapevine yellows (AGY) phytoplasma, tomato big bud (TBB) phytoplasma and the Buckland Valley grapevine yellows (BVGY) phytoplasma (Constable et al., 1998, 2002; Gibb et al., 1999). The AGY phytoplasma is more frequently detected in AGYd affected grapevines compared to the TBB phytoplasma (Constable et al., 2003, 1998; Gibb et al., 1999). The BVGY phytoplasma has only been found in two vineyards in the Buckland Valley grape growing region of Victoria (Constable et al., 2002; Gibb et al., 1999). AGYd occurs more often in the warmer inland districts of Sunraysia in New South Wales and Victoria, Riverina in New South Wales and the Riverland in South Australia compared to other viticultural regions. Chardonnay and Riesling appear to be affected by AGYd more often than other varieties (Magarey & Wachtel, 1986a). However, AGYd symptoms have been observed and phytoplasmas have been detected in other white and red varieties (Bonfiglioli et al., 1996). Previous research has shown that the incidence of AGYd may be temporarily high in one year in some Chardonnay vineyards (Magarey & Wachtel, 1986b). Restricted growth disease (RGd) also commonly