Temporal yield variability in subtropical table grape production

Inconsistent yield between seasons for table grape cultivars grown in subtropical climates in Australia presents a challenge to the industry in terms of marketing and economic sustainability. The pattern of this yield inconsistency has not been described. Marketable fruit yields of three cultivars (Red Globe (RG), Menindee Seedless (MS) and Flame Seedless (FS)) were acquired over 14 seasons, and individual vine yields of MS were collected for a four-season period from a vineyard in the Central Highlands of Queensland, Australia. Cultivars FS and RG did not show an alternate bearing pattern. Yields of MS varied up to four-fold in consecutive seasons. An alternate yielding pattern as measured by the indicators of an alternate bearing index (I) and associated probability calculated using a resampling process was evident in 7 (2009–2015) of the 14 monitored seasons. Individual vine yield over the four-season period 2014–2017 was irregular and 90% variation in vine yields was due to the variation in the number of bunches per vine. The seasonal yield variation of MS was partly explained (R2 = 0.31, P < 0.05) by the mean monthly temperature in October of the year preceding harvest. This result is ascribed to the effect of high temperature during inflorescence initiation and early development which occurs in October in the Central Highlands of Queensland.