Fruit Quality Response to Irrigation of ‘Royal Gala' Apple In Semi-Arid Climate

Australia and the state of Victoria in particular, are experiencing a prolonged drought (>10years) that has drastically reduced irrigation allocation. Irrigation is an obligatory practice for apple growing in northern Victoria so growers have purchased ‘temporary’ irrigation at substantial cost from other agricultural users. Understanding the correct irrigation volumes to continue producing a high quality crop is fundamental for orchards to remain viable. The aim of this experiment was to determine the optimal irrigation volumes to produce apples of high quality and high health properties. A commercial orchard of ‘Royal Gala’ in the Goulburn Valley near Shepparton, Victoria, Australia, was selected in 2008 and five irrigation treatments, ranging from 160 mm to 690 mm per season, were applied in a randomized block design by using drippers with different emission volumes on the existing irrigation line. The amount used for commercial irrigation in the 2008-09 growing season was approximately 425 mm. Shoot and fruit growth during the season and trunk circumference were measured. Crops were harvested twice based on fruit color. Fruit number and total yield per tree were recorded for each harvest. A sample of 20 fruit per tree for each harvest was collected. Fruit background and blush color, dimensions, weight, total soluble solid content (SSC), firmness, starch index, ferrox reducing action potential (FRAP), and total polyphenols (TPP) were measured to determine fruit quality and health properties. There were no appreciable differences between the two harvests for the measured variables, therefore data were pooled. Average fruit weight and fruit diameter were significantly depressed at the two lowest irrigation volumes, but no differences were recorded under the other treatments. There was a noticeable trend observed among most of the variables measured that separated the data into two distinct groups depending on irrigation volumes. Groups could be defined as low volume, between 160 and 210 mm and high volume, between 315 and 690 mm. Low volumes resulted in reduced fruit size, weight and seasonal growth, compared to high volumes. There were no clear trends and distinctions between irrigation volumes for firmness and starch, while SSC showed an inversely proportional trend to irrigation volume. Antioxidant status of the fruit is currently being analyzed, but appears to increase with decreasing fruit size. This experiment showed that it is possible to reduce the current irrigation volume in Victoria and potentially increase ‘Royal gala’ fruit quality and health attributes.