Apple fruit (Malus domestics Borkh. cv. Cox's Orange Pippin) were harvested in four orchards from trees growing under the same conditions but differing in crop load. Regardless of fruit size, apples from light-cropping trees had lower Ca and higher K concentrations and more bitter pit than did fruit from trees with heavy crop loads. The inverse relationship between Ca concentration in the fruit and the incidence of bitter pit also varied according to crop load and could affect the ability to predict incidence of bitter pit from Ca measurements. Differences in fruit maturity that would influence bitter pit incidence were not associated with crop load. The enhanced susceptibility to storage disorders, such as bitter pit, in fruit of all sizes from light-cropping trees suggests the need to handle fruit from such trees differently for postharvest storage.
I.B. Ferguson and C.B. Watkins
Adriana Telias*, Emily Hoover, Carl Rosen, and David Bedford
`Honeycrisp', a relatively new apple cultivar, is susceptible to bitter pit, a physiological disorder that develops mainly during storage. Although the cause of bitter pit is unknown, calcium (Ca) content of the fruit is known to be involved. A field experiment was conducted in Chanhassen, Minn. to refine recommendations for use of Ca sprays for reduction of bitter pit in `Honeycrisp' apple. Specific objectives were to determine: 1) Ca concentration and content throughout the fruit growing season; and 2) the association of bitter pit incidence with Ca concentration, crop load, vegetative growth and fruit size. Six treatments tested included: control; Ca(NO3)2 sprays all season; Ca(NO3)2 sprays early in the season; Ca(NO3)2 sprays late in the season; hand-thinning combined with Ca(NO3)2 sprays all season and hand-thinning. Ca concentration in fruits was measured bi-weekly using three different sampling methods: segments, cores and plugs. A randomized block design with four trees as experimental unit and five replications was used. Results suggest lower crop loads increase bitter pit incidence. While fruit from the thinned treatments was larger in size by the end of the experiment, no bitter pit was present at harvest. After 4 months of storage, the hand thinning treatment had 7.4% bitter pit, while thinning plus Ca reduced bitter pit to 2.4%. The other treatments had less than 1% bitter pit. Fruit analyses at the end of the growing season indicate that early and full season sprays resulted in the highest Ca concentration in fruit segments and cores. The lowest values were found for the thinning treatment. No association was found between vegetative growth and bitter pit incidence.
Errol W. Hewett and Christopher B. Watkins
The incidence of external and internal bitter pit in `Cox's Orange Pippin' apple (Malus domestics Borkh.) fruit sprayed with normal therapeutic sprays either with or without Ca salts at 2-week intervals during the growing season was determined after 6 weeks of storage over 7 consecutive years. Following harvest, fruit was either vacuum-infiltrated with CaCI2 or received no further treatment. Although there was a tendency for fruit that had been sprayed and vacuum-infiltrated with Ca to exhibit the greatest degree of bitter pit control, this treatment was not significantly superior to Ca sprays alone. Vacuum infiltration alone reduced the disorder to a lesser extent than Ca sprays and was more effective in reducing external than internal bitter bit. The results suggest that Ca applications over the growing season are superior to postharvest vacuum-infiltration with Ca in the prevention of bitter pit.
Safi S. Korban and John M. Swiader
Inheritance of the bitter pit disorder was determined in the field on fruiting seedlings resulting from crosses between the highly susceptible cultivar ‘Prima’, Coop 11 (a scab-resistant advanced selection), and 3 other scab-resistant selections. Segregation ratios indicated that 2 major genes controlled resistance. Both dominant genes, designated Bp-1 and Bp-2, were required to confer resistance. Analysis of leaf and peeled fruit tissues for Ca, Mg, K, and B indicated the presence of higher levels of Ca and B, and lower levels of Mg and K on a dry weight basis in resistant seedlings. A gradient was observed through the flesh on the fruit for all elements tested. Ca content was elevated at the base, but dropped rapidly towards the apex in susceptible fruits. Mg was reduced at the base and increased towards the apex in all fruits, but its level increased sharply in susceptible fruits.
G. H. Oberly
Spraying ‘Northern Spy’ apple trees with 50 ppm TIBA 2 weeks after petal fall reduced the accumulation of Ca in the fruit and increased the amount of bitter pit. The greatest incidence of bitter pit was associated with the Ca content of the fruit during the middle of the growing season. Calcium accumulated rapidly during the period of cell division and seed development, and again 2 to 3 weeks before harvest. The late influx of Ca may explain the development of less bitter pit in storage in late harvested apples than in apples harvested immature.
Jorge B. Retamales, Claudio Valdes, and Verónica Donoso
Bitter pit (BP) is the main physiological disorder of apples in Chile. Its incidence affects pre- and postharvest handling of the fruit and the profitability of this species. Since 1991, its control and prediction have been studied by this research team through field and laboratory trials. The BP incidence is linked to the fruit Ca concentration; however, fruit Ca analysis has not adequately predicted BP incidence in postharvest. Several authors have proposed Ca/Mg antagonism, which has been the basis to develop a predictive method through fruit Mg infiltration (IMG) 40 days before harvest. IMG has been massively used for two seasons in Chile, with 375 samples processed in 1997 and 1170 in 1998. The industry has been increasing its proportion of the samples processed, from 22% in 1997 to 71% in 1998. The most prominent varieties are `Granny Smith' (GS) > `Braeburn' (BR) > `Royal Gala' (RG) > `Red King Oregon' (RKO). The massive use of IMG has obtained predictive capacities (r 2 between BP predicted and BP after 3 months regular cold storage) of 0.8 for `Fuji'; 0.7 for GS, BR, and RG; and 0.58 for RKO. (This reduction in the predictive capacity with regards to the previous research under controlled conditions would, in part, be due to problems in obtaining fruit samples: non-uniform fruit size, inadequate sampling dates, diverse fruit numbers, etc.) Developments are underway to increase the geographical coverage of the service, the predictive capacity of the method for certain cultivars and productive areas and the number of samples processed.
Sergio Lopez-Cuevas and Terence Robinson
A factorial field experiment was conducted at the New York State Agricultural Experimental Station in Geneva, N.Y., during 2004 and 2005 with `Honeycrisp' apple trees on M.9 rootstock. The main plot factors were three levels of applied nitrogen (0 kg/ha, 50 k/ha, and 100 k/ha); three levels of applied K2O (0 k/ha, 100 kg/ha, and 200 kg/ha); ± foliar nutrient sprays containing N, B, Zn, and Mg, ± foliar sprays of CaCl2 and ± trickle irrigation. The subplot factor was cropload (3, 6, 9, 12, and 15 fruits/cm2 TCA). Trees receiving irrigation or potassium had higher yields and the effect was greater as cropload was increased. There was no effect of nitrogen fertilization, foliar Ca, and foliar N, B, Zn, and Mg on yield. Irrigation and increased potassium fertilization rate reduced fruit soluble solids at harvest. Foliar calcium applications, foliar N, B, Zn, and Mg applications, and nitrogen fertilization rate did not affect fruit soluble solids at harvest. No treatment factor had an effect on fruit firmness at harvest, but, after 4 months on cold storage, fruits from irrigated trees had greater firmness. Bitter pit incidence was lower on apples from trees that did not receive irrigation compared to irrigated trees. The difference was constant under all cropload levels. Foliar calcium applications, foliar N, B, Zn, and Mg applications, nitrogen fertilization rate and potassium fertilization rate did not affect bitter pit incidence.
Jorge B. Retamales and Claudio Valdes
Bitter pit is the most important physiological disorders for apples in Chile. During the 1995–96 season, the predictive capacity of bitter pit through magnesium infiltration of the fruit in commercial orchards of three locations in South Central Chile: San Fernando (SF), Curico (CU), and San Javier (SJ) was established. Three orchards were chosen in each location and for each cultivar; fruit were collected 60, 40, and 20 days before commercial harvest. Fruit were infiltrated for 2 min with magnesium chloride at 0.05 M using vacuum levels of 500 or 100 mm Hg for `Granny Smith' and `Braeburn', respectively. The predictive capacity (correlation between predicted and effective bitter pit—after 90 days at 2°C + 10 days at 18°C) increased closer to harvest; with regards to location: SF > CU > SJ. Bitter pit-like symptoms, caused by Mg infiltration stabilized 16 days after infiltration. Bitter pit incidence was better predicted than severity. Bitter pit was better predicted for `Granny Smith' than for `Braeburn'.
Christopher B. Watkins, Jane E. Harman, Ian B. Ferguson, and Michael S. Reid
Addition of 1% lecithin (phosphatidyl choline) to 4% Ca dips increased internal CO2 levels and decreased O2 levels in fruit of apple (Malus domestica Borkh.) stored at 3°C. This effect was greater than that found with lecithin alone. At 18°, respiration and ethylene production by the fruit were reduced slightly by Ca, but to a much greater extent by lecithin. A further reduction of the production of both gases was found with Ca and lecithin. The climacteric rise was also delayed by lecithin treatments. At 3°, ethylene production was both delayed and reduced by lecithin treatments, but no influence on CO2 production was detected. Although differences in Ca concentration of the fruit caused by the addition of lecithin to Ca could not be detected when bulked samples of fruit were analysed, use of 45Ca showed that both the initial rate of Ca uptake and the final Ca content of the fruit flesh after 6 weeks at 3° were increased by lecithin. The beneficial effects of lecithin plus Ca in bitter pit control probably result from rapid modification of gas exchange together with increased Ca uptake.
Raquel Gomez and Lee Kalcsits
premium economic returns for growers ( Gallardo et al., 2015 ). Despite its popularity, ‘Honeycrisp’ is difficult to grow because it is susceptible to physiological disorders like bitter pit and sunburn ( Luby and Bedford, 1992 ). ‘WA 38’ is a new cultivar