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Ibrahim I. Tahir and Hilde Nybom

A series of pre- and post-harvest experiments were conducted to enhance apple tree productivity and improve fruit quality and storage life by altering production system and post-harvest treatments in an organic orchard. Increasing the light distribution and carbohydrate uptake (summer pruning and covering the orchard ground with reflective textile) improved tree productivity, fruit color, content of anthocyanin, ascorbic acid, and total phenolic compounds and reduced incidence of fungal storage diseases. Optimal harvesting time could be determined from the starch index in some cultivars, whereas the Streif index [firmness (soluble solids concentration × starch hydrolysis score)−1] was more accurate for other cultivars. In yet others, titratable acidity and flesh firmness also produced important information. By contrast, soluble solids concentration and skin color are not useful as a result of their sensitivity to weather conditions and light intensity. Post-harvest fruit treatment with hot water (46 °C for 120 seconds) decreased fungal decay during storage in two cultivars, whereas spraying the fruit with 10% ethanol decreased fungal decay in all investigated cultivars. Optimization of storage conditions [cultivar-specific controlled atmosphere (CA) and ultra-low oxygen (ULO) storage procedures] maintained fruit quality and reduced the amount of fungal decay.

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Yanrong Lv, Ibrahim I. Tahir and Marie E. Olsson

Apples contain substances with health-promoting properties, among them, triterpenes, including oleanolic acid (OA) and ursolic acid (UA), which are thought to have anti-inflammatory activity as well as inhibiting initiation, promotion, and metastasis of cancer. This study evaluated effects of harvest time, rootstock, and storage method on two major triterpenes in apple peel, to enhance the understanding of the relative importance of cultivation and environmental factors influencing triterpene concentration. OA and UA concentrations in the semi-dwarfing ‘MM.106’ rootstock apples were significantly higher than in the dwarfing ‘M.9’ rootstock apples at the majority of harvest times over the 2 years of investigations. In 2012 at harvest time, highest concentrations of OA and UA in ‘MM.106’ rootstock apples were 63.4 and 416.3 μg·cm−2, respectively, while they were 59.7 and 380.9 μg·cm−2, respectively, in ‘M.9’ rootstock apples. UA remained fairly stable in most cases during storage, and no difference was found between regular atmosphere storage and controlled atmospheric (CA) storage. OA concentration decreased after harvest time. Furthermore, OA showed different responses to regular atmosphere storage and CA storage, and year-to-year difference was also observed. The two rootstocks showed only slight differences in the effect on total soluble solids (TSS) and fruit color, while the titratable acidity (TA) in apples from trees on ‘M.9’ rootstock had lower levels in most cases at the third harvest time as compared with apples from trees on ‘MM.106’ rootstock. OA concentration was positively correlated with UA concentration both directly at harvest and after storage. OA and UA concentrations were positively correlated with TA and TSS, while they were negatively correlated with red color.

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Ibrahim I. Tahir, Eva Johansson and Marie E. Olsson

The effects of two nonchemical methods [controlled atmosphere (CA) storage and postharvest heating, alone or combined] on the quality (firmness, taste, color, and skin wax) and storability (losses resulting from bruising and fungal decay) of apples were investigated in a 3-year study. Fruits of two cultivars (cv. Aroma and cv. Ingrid Marie) were mechanically wounded on two opposing sides, inoculated with conidial suspensions of one of three pathogens [Pezicula malicorticis (bull's eye rot), Penicillium expansum (blue mould), and Colletotrichum gloeosporioides (bitter rot)], exposed to 40 °C for four different exposure periods (24, 48, 72, and 96 h), and stored either in air (21.0 kPa O2 + 0.03 kPa CO2) or in CA storage (2.0 kPa O2 + 2.0 kPa CO2) for 4 months. Effect of postharvest heating on bruise susceptibility of air- or CA-stored apples was also investigated. Cultivar Aroma apples generally showed higher bruise susceptibility than cv. Ingrid Marie. The sun-exposed side of apples was less sensitive to bruising than the shaded side and red phenotypes of these two cultivars also showed increased resistance to bruising as compared with standard phenotypes. Heat treatment and CA storage, either alone or in combination, decreased bruise occurrence in both cultivars. Pz. malicorticis was the more aggressive storage pathogen for both apple cultivars followed by P. expansum and C. gloeosporioides. The highest decay severity occurred in inoculated and nonheat-treated apples stored in air. Heat treatment, especially in combination with CA storage, showed an eradicative effect on the pathogens without any negative effects on apple quality. Heat treatment maintained flesh firmness during storage, reduced ethylene production, and caused clearly visible changes in epicuticular wax structure, resulting in a higher resistance to bruising or to natural and artificial infections with the pathogens. The effective exposure period could be reduced to 24 h, because a combination of heat treatment (at 40 °C for 24 h) and CA storage showed the best protective effect against bruising and fungal decay. This combined treatment decreased bull's eye rot by 86% and 60% and bitter rot by 73% and 65% in cv. Aroma and cv. Ingrid Marie, respectively, in comparison with untreated apples.

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Ibrahim I. Tahir, Eva Johansson and Marie E. Olsson

This 4-year study at the Kivik research station, southeastern Sweden (≈55°N), investigated optimal orchard management procedures to improve tree growth, yield, fruit quality, and storability in the important early season apple cultivar ‘Katja’. Two procedures (one standard, one novel) were applied within pruning, weed control, fertigation, and thinning, yielding a total of 16 different combinations (treatments). Tree vegetative growth, yield, fruit size, fruit color, firmness, soluble solids concentration, malic acid, nitrogen and calcium content, and percentage fruit with storage rot (Pezicula malicorticis) were evaluated for all 16 treatments. Changing to the novel alternative in only one or two of the areas did not produce significant improvements in all investigated parameters. The optimal treatment consisted of radical winter pruning + summer pruning (novel), bark mulching (novel), fertigation with 0.13 g N (standard), and hand thinning after full bloom (novel).

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Ibrahim I. Tahir, Sven-Erik Svensson and David Hansson

In an organic apple orchard, standard mechanical cultivation was compared with four different orchard floor management systems (OFMS): acetic acid (V), living mulch (L), a sandwich system during the growing season (SSS), and a sandwich system during the whole year (SSW). The effects of these OFMS on weed management, soil conditions, tree growth, tree yield, fruit quality, and fruit storage potential in a cool climate were evaluated. Acetic acid treatment showed good weed suppression without any amendatory effect on soil conditions, fruit quality, or tree performance. The L and SSS systems increased soil respiration, decreased tree vigor, and improved fruit quality, but had no sufficient influence on weed competition and thus decreased fruit yield. Only SSW gave better weed control, higher soil respiration, and acceptable tree growth with no yield reduction. Fruit from this system also showed better quality at harvest than fruit from other OFMS and maintained this good quality during storage. A 6-week weed-free period from late May to mid-July gave the highest apple yield in two OFMS (SSW and V).

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Ibrahim I. Tahir, Eva Johansson and Marie E. Olsson

To decrease the unfavorable effects of herbicides on human health and on the environment, new sustainable mulching methods have been developed. These methods aim to impede weed growth and also result in good yield and high fruit quality. The objective of the present study was to investigate the effects of the replacement of conventional methods (chemical treatments or mechanical) with different groundcover material systems (GCMSs) that use aluminum, bark and black polypropylene on 'Aroma' apple (Malus domestica) fruit maturity and quality, and fruit resistance to bruising and decay. The experiment was carried out from 1995 to 2001. Compared with conventional mulching methods, aluminum mulching was found to control annual weeds more effectively, to increase soil temperature, light reflection, yield, and fruit weight, to decrease bruise occurrence, to intensify and saturate the red coloration of apples, and to increase firmness and acid and sugar contents, resistance to storage disorders and decay after storage and shelf life. The other two used GCMSs, bark and black polypropylene also influenced many yield and quality parameters. However, less positive influences on the different parameters were found for bark compared with aluminum, and the use of black propylene was not favorable compared with the conventional mulching methods. Generally, decreased starch content at early picking dates was found for apples grown with GCMSs, indicating an earlier ripening for these apples compared with apples grown with a conventional mulching system. In summary, aluminum mulching was found to be the best alternative mulching method for production of 'Aroma' apples.