Bitter pit control in apples cv. Braeburn through foliar sprays of different calcium sources

Between 1995 and 1999, essays were done to determine the effectiveness of foliar Ca sprays from different sources, on bitter pit control and on pre- and post-harvest apple Malus domestica Borkh. quality. Trees cv. Braeburn/seedling were 4 year-old at the start of the experiment, and planted in a clay loam soil. The commercial orchard, planted at 2.5 x 4.5 m, was located in San Clemente, Chile (35° 34’ S; 71° 33’ W). To increase the potential for bitter pit incidence, trees received annually 150-180 kg ha-1 N as urea, and had intense hand fruit thinning early in the season (40 d after full bloom). Plants were furrow irrigated with a frequency determined through an evaporimeter pan class A. Treatments were applied to 120 plants distributed in 5 groups of 24 plants each in a randomized complete block design. In 95/96, Ca sources tested in rates ranging from 1.0 to 18.8 total kg Ca ha-1 were: CaCl2*2 H2O (Cloramon Lab.), Wuxal Ca and Wuxal Aminocal (Aglukon), Stopit (Cyanamid), Nutraphos 28 (Leffingwell), Ca(NO3)2 (NorskHydro), Kamab 26 and Aminoquelant Ca (Astorga Lab.). Besides a control treatment (no Ca), in 97/98 and 98/99 seasons, total Ca applied was 7.6 and 10.0 kg Ca ha-1, respectively. Sources in 97/98 were: Wuxal Ca, CaCl2, Basfoliar Ca, Stopit, Ca(NO3)2 and Wuxal Aminocal. In 98/99 Ca sources were: CaCl2, Ca(NO3)2 , Stopit, and Wuxal Ca. Ca was applied 6 times in each season with a commercial blast sprayer, using 1200-1500 L water ha-1. At harvest, variables measured were: color (ground and surface), weight, pressure and soluble solids (SS), as well as subepidermal Ca levels. After 120 d in cold storage (1 °C, 95% R.H.) plus 10 d at 18° C, bitter pit (internal and external), seed number, pressure and SS were measured. Bitter pit incidence varied greatly among treatments and seasons. Bitter pit control was partially dependent on total Ca applied (r2 = 0.72). For a given year, there was no relationship between natural bitter pit incidence (control treatment), and the degree of reduction of bitter pit incidence. There was high and positive association between internal and external bitter pit incidence (r = 0.83). Bitter pit control by Ca sprays averaged 91.9 and 82.3%, for internal and external incidence, respectively. In 95/96, lowest bitter pit severity was obtained with Wuxal Ca, Wuxal Aminocal and CaCl2. Bitter pit incidence and severity were highly correlated (r = 0.96 and 0.83, for internal and external bitter pit, respectively). After 120 d of storage, subepidermal Ca levels could only explain 53.3% of the variability in external bitter pit incidence, which would not allow to use fruit Ca levels to predict postharvest bitter pit incidence. Ca sources did not significantly alter fruit weight, seed number, surface and ground color of apples at harvest or after storage. The effects on firmness, soluble solids and their changes during storage were inconsistent among treatments and seasons.