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Prevention of Sweet Cherry Fruit Cracking Using SureSeal, an Organic Biofilm C. Kaisera Horticulture Faculty Oregon State University Umatilla County Extension 418 N Main Street Milton-Freewater, OR, 978672 USA M. Meland

Norwegian Institute for Agricultural and Environmental Research Bioforsk Vest Ullensvang N-5781 Lofthus Norway

J.M. Christensen

Pharmacy Faculty College of Pharmacy Oregon State University Corvallis, OR, 97330 USA

E. FallahiU of I Lane Parma University of Idaho 29603 U ID, 83660 USA L.E. Long Horticulture Faculty Oregon State University The Dalles County Extension 400 E. Scenic Dr. #2.278 The Dalles, Oregon, 97058 USA

Keywords: Prunus avium, phospholipid, fruit diameter, fruit firmness, stem-pull force,

TSS, sugar, soluble solids Abstract

Rain-induced fruit cracking in sweet cherries can be a major problem. In the Pacific Northwest United States, due to high labor costs, when fruit cracking exceeds 25% at harvest, fruit are not picked. Oregon State University Horticulture and Pharmacy Faculty have collaborated in producing and patenting a novel, elastic, organic biofilm, SureSeal, which significantly reduced sweet cherry fruit cracking by up to 250% in Milton Freewater, Oregon and Loftus, Norway. Formulations of SureSeal are hydrophobic and consist of a copolymer of complex carbohydrates, phospholipids and calcium. Collaborative research undertaken over three years throughout the Pacific Northwest and overseas found that two applications of 1% SureSeal applied at straw color, and again ten days later, reduced fruit cracking con-sistently when compared to untreated control fruit. In Norway, fruit cracking was reduced from 24.6 to 9.8% when trees were treated with SureSeal in combination with plastic ground covers and a preharvest fungicide (fenhexamid). Furthermore, studies throughout Oregon and Idaho found that SureSeal resulted in significantly (P<0.001) higher total soluble solids (TSS) and increased Stem Pull Force (g) (retention force between the pedicel and the fruit) than untreated control fruit. In 2008, ‘Bing’ fruit had higher TSS both before (18.5°Brix) and after (18.9°Brix) two weeks of regular atmosphere storage at 2°C than untreated control fruit (17.4 and 17.2°Brix, respec-tively). In Norway, 1% Biofilm increased TSS to 21.4°Brix compared to untreated control fruit (18.6°Brix). Two applications of 1% Biofilm applied at straw color and again ten days later has the potential to significantly reduce fruit cracking, accelerate maturity by significantly increasing TSS levels, and increase stem pull force. The concurrent reduction in fruit firmness observed may be a function of maturity but, in all instances, fruit firmness still exceeded the minimum standard of 250 g mm-1. a Email: clive.kaiser@oregonstate.edu.

Proc. VIth Intl. Cherry Symposium Eds.: M. Ayala et al. Acta Hort. 1020, ISHS 2014

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INTRODUCTION Rain-induced fruit cracking in cherries remains a problem internationally and can

cause heavy losses in yields and returns (Pennell and Webster, 1996; Vittrup Christensen, 1996; Lang and Flore, 1999; Sekse, 2005). Cherry fruit cracking is the result of several factors including: morphological, physiological, environmental and genetic factors. Despite many years of research, a lack of understanding of several of the mechanisms involved in fruit cracking persists. Furthermore, different experiments have produced contradictory results leading to further controversy (Webster and Cline, 1994; Sekse, 1995a; Opara et al., 1997). Several advances in the use of different cultural practices, which limit the incidence of fruit splitting have, however, been made. These practices range from exclusion of water from the fruit surface during fruit growth and maturation using plastic rain covers (Meland and Skjervheim, 1998; Børve et al., 2003), to reducing osmotic potential across the fruit skins during rainfall events (Lang et al., 1997; Fernandez and Flore, 1998). Some cherry scion cultivars crack more easily than others (Ystaas and Frøynes, 1998; Cline et al., 1995a; Lane et al., 2000) and the question of why susceptible cultivars were more predisposed to cracking than resistant ones has not been explained satisfactorily. Several causes ranging from fruit morphology, through whole tree physiology, to rootstock effects have been shown to have an effect on fruit cracking (Hovland and Sekse, 2003) and it is most likely that these factors act in conjunction with one another and a holistic approach to reducing fruit cracking is favored by the authors.

Indeed, where fruit morphology is concerned, investigations have found that genetic differences in skin morphology (Belmans and Keulemans, 1996), variable cuticle thickness, differences in stomatal density (Beyer and Knoche, 2002; Belmans and Keul-mans, 1996), cutin content (Schreiber et al., 1996; Knoche et al., 2000) and exocarp polar pathways are all implicated. However, all cherry fruit cuticles consist of two distinctly different constituents, namely cutin and wax. Cutin is the largest constituent (90-99%), although it plays a minor role in water exclusion. The lesser occurring wax (1-10%), however, accounts for the water excluding properties of the cuticle. This explains much of the inconsistency of results often found in experiments correlating cuticle thickness with water absorption and fruit cracking (Belmans and Keulemans, 1996). Consequently, it may not be the thickness of the whole cuticle that determines its water diffusion properties but rather the percentage wax, as discussed by Sekse (1995a), Schreiber et al. (1996) and Vittrup Christensen (1996).

Water transport across the cuticular membrane in sweet cherry fruit has been studied in Norway under defined conditions by monitoring fruit transpiration under high and low humidity. Hovland and Sekse (2004a) found that water loss from the fruit skin under low air humidity was linear with time, whereas fruit at high air humidity accumulated water for 4-6 h and this explains why in some cases, fruit cracking can take place following harvest. This also has major implications for harvest when prevailing conditions are cool and overcast, resulting in high relative humidity, and postharvest operations where hydro-cooling is utilized.

An intact cuticle is a prerequisite for the prevention of free water intrusion into the fruit while the fruit surface is wet. Several studies of the fruit skin of sweet cherries have revealed the presence of a network of fine fractures across the cuticle even in the field prior to harvest (Glenn and Poovaiah, 1989; Sekse, 1995b, 1996; Knoche et al., 2000; Hovland and Sekse, 2003). Scanning electron micrographs found that these fractures traversed only the cuticle (Glenn and Poovaiah, 1989). Sweet cherry fruit only develop cuticular fractures during the last two weeks of their growth period and their incidence is greater at high air humidity (Hovland and Sekse, 2004a). Fractures occur in concentric rings around the stem cavity (distal end) and may be observed with a good magnifying glass. Fluorescence microscopy revealed marked differences in percentage of fruit with cuticular fractures among cheek (22%), suture (32%) and stylar end (90%) regions on visually inspected crack-free fruit (Knoche et al., 2002). Dye solution infiltrated these cuticular fractures and indicated that they represented potential pathways for water transport through the sweet cherry fruit surface. Cuticular fractures increased the

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conductance for water uptake (Beyer and Knoche, 2002). Knoche et al. (2002) found an 8% increase of the total conductance for water loss of the cuticle due to fractures. They did not, however, distinguish between the types of cuticular fractures. The number of cuticular fractures on the fruit surface influenced water loss significantly. Indeed, more cuticular fractures resulted in more water loss under low air humidity (Hovland and Sekse, 2004a). This indicated that these fractures represented pathways for water transport through the sweet cherry surface.

Cultivars grown on different rootstocks developed different amounts of cuticular fractures, indicating that there are clear interactions between rootstock and cultivar (Hovland and Sekse, 2003). Cuticular fractures also occurred at high frequency in the stylar region of the fruit (Beyer and Knoche, 2002), and fruit on the northern side of the trees developed fewer cuticular fractures than fruit on the southern side (Hovland and Sekse, 2003). Storage of whole fruit found that fruit with cuticular fractures desiccated faster than fruit with intact cuticles (Glenn and Poovaiah, 1989; Hovland and Sekse, 2004a). A slight increase in the relative weight of the fruit with cuticular fractures was observed during storage at high relative humidity. This could indicate that under high air humidity, fractures represented a pathway for water uptake (Hovland and Sekse, 2004a). Water uptake through the pedicel of fruit in which cuticles were scored to simulate fractures or minor cracks was measured potometrically (Hovland and Sekse, 2004b). These fruit accumulated more water via the pedicel than unscored fruit, implying that the scoring resulted in increased transpiration. The number of cuticular fractures was also important when using the cracking index test, fruit in Class 5 (severe micro-cracking) were much more vulnerable to cracking than intact fruit (no micro-cracking) when the surface was wet (Hovland and Sekse, 2003). This also implied that the fractures are a pathway for water uptake.

Cherry fruit has a double sigmoid growth pattern (Coombe, 1976), which may contribute to fracture development during the last part of fruit growth and maturation. Here, sweet cherry fruit increase in weight and volume rapidly, causing an increase in cell expansion and water uptake. This probably leads to significant mechanical stress (tension and strain) in the cuticle (Considine and Brown, 1981) and there is no significant forma-tion of new cuticle material that might alleviate the stress (Knoche et al., 2001). Irregular water supply to cherry trees during this period (Sekse, 1995b) increased the number of cuticular fractures. Fracture patterns seemed to be a function of the fruit shape (Yama-moto et al., 1990). Other studies found that fruit susceptibility to cracking was related to fruit size and mostly fruit size within a cultivar, not between cultivars (Vittrup Christen-sen, 1975). Børve et al. (1998, 2000) found that cuticular fractures acted as infection sites for, and promoted, postharvest fruit rot in sweet cherries.

Different theories have been put forward regarding the role that water plays during the cracking process. The traditional opinion is that that water uptake through the fruit surface during and after a rainfall event increases turgor pressure, thus inducing cracking. The water penetrates the wetted fruit cuticle by osmosis due to the difference in osmotic potential between the rainwater and the fruit juice (Vittrup Christensen, 1972; Glenn and Poovaiah, 1989). Since some fruit cracked even under plastic covers, Webster and Cline (1994) developed a model for cherry fruit cracking mechanisms including water uptake through the fruit pedicel. In a review, Sekse (1995a) suggested that this water uptake via the pedicel is followed by a buildup in turgor pressure and that this was the driving force causing cherry fruit cracking. Meanwhile, water uptake over the fruit surface initiated fruit cracking by causing rupturing of the fruit cuticle and the walls of the epidermal cells.

Consequently, the current study was initiated to determine whether a water-dispersible organic, hydrophobic, wax-based biofilm could be produced that would: supplement the wax component of the cherry cuticle; seal off the cuticular fractures; retain elasticity and allow for the normal shrink-swell processes, which take place during fruit growth; be persistent; be safe for human consumption and prevent fruit cracking considerably.

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MATERIALS AND METHODS A unique formulation of complex carbohydrates and phospholipids was

formulated by the two senior authors (Kaiser and Christensen) in the College of Pharmacy, Oregon State University, in late 2006. The formulation was tested for elasticity by coating a flaccid balloon followed by repeated inflating and deflating of the balloon. No cracking or flaking of the Biofilm was observed (data not presented). The base formulation has, however, been further refined using in vitro stress tests and in vivo field tests beginning in May 2007. An international patent was applied for in April, 2009, and the organic biofilm has tentatively been named SureSeal. Postharvest in Vitro Stress Testing (2007)

Mature ‘Bing’ cherry fruit from California were obtained from the local fresh produce market in Corvallis on 29 May 2007 and treated the same day using four replicates (20 fruit) per treatment. Fruit were dipped in two different formulations of Biofilm (Biofilm A was ~78% hydrophobic whereas Biofilm B was ~85% hydrophobic). Solutions of 5 and 10 g L-1 Biofilm A and B were tested against untreated control fruit. After immersion in the different solutions, fruit were air-dried at room temperature (35% RH) by attaching the stem-end of their pedicels to “crocodile-type” paper clips and hanging them up to allow them to dry overnight. Control fruit were treated similarly. The following morning, the pedicels of all Biofilm coated fruit and an identical number of untreated control fruit were trimmed to approximately 15 mm long. This ensured that the pedicels were not damaged by the force of the jaws of paper clips as well as removing any embolism that may have occurred in the pedicels as a result of being harvested. Each replicate and an identical number of control fruit were then immersed completely in distilled water for 48 h. Fruit were carefully monitored for cracking incidence and this was recorded on a regular basis (0, 12, 24, 36 and 48 h). Cracked fruit were not re-immersed in the distilled water solutions. Results for fruit cracking were recorded and analyzed by General Analysis of Variance using Genstat 11.1 (VSN International Ltd). In Vivo Field Testing (2007) 1. Hood River, Oregon. In a preliminary investigation in Hood River, three separate ‘Bing’ on ‘Mazzard’ trees were selected and treatments randomized accordingly. Each tree was sprayed once only to the point of run-off on 1 June 2007 with 1, 10 or 20 g L-1 Biofilm B using a knapsack sprayer. The percentage fruit cracking for each of four quadrants on each tree and an untreated control was recorded on 25 June and again on 9 July both of which were immediately preceded by rainfall events of 12 mm and 10 mm, respectively. Results were analyzed using Genstat 11.1 and are presented in Figure. 2. 2. Milton-Freewater, Oregon. Another preliminary investigation was undertaken in Milton-Freewater. Sixteen 5-year-old ‘Tieton’ trees with a relatively heavy fruit set were selected for the trial and treatments were randomized accordingly. Four trees each were sprayed to the point of run-off on 11 June 2007 with either 10 g L-1 Biofilm A, 10 g L-1 Biofilm B or 20 g L-1 Biofilm B using a knapsack sprayer and compared against four similar untreated control trees. Between the date of application and harvest, one rainfall event (14 mm) occurred. Fruit were harvested on 7 July and percentage fruit cracking was recorded for four samples of 100 fruit each. Results were analyzed using Genstat 11.1. In Vivo Field Testing (2008) 1. The Dalles, Oregon. In a completely randomized block design, ten eight-year-old ‘Royal Rainier’ on ‘Citation’ interstock trees were sprayed with 1% Biofilm B using a mist blower at an equivalent rate of 2000 L ha-1. The Biofilm treatment consisted of two applications, one at straw color and a second application 10 d later, for comparison against similar untreated control trees. Fruit were harvested according to industry standards. In addition, a sample of 50 fruit was harvested from each replicate. On the day of harvest, 25 fruit were assessed for: fruit diameter (mm) (as a function of Row size) and fruit firmness (g mm-1) using a FirmTech 2 texture instrument (BioWorks, Inc., Wamego,

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Kansas); pedicel-fruit retention force (g) using a Shimpo FGV-5X digital force gauge (Nidec-Shimpo America Corp., Itasca, Illinois); and total soluble solids (TSS, °Brix) using an Atago handheld digital refractometer (Tokyo, Japan). The remaining 25 fruit were stored in cold storage at 2°C for two weeks, removed from the cold room and held at room temperature for 14 h to equilibrate and then subjected to the same assessments as on the day of harvest. Results were analyzed using Genstat 11.1. 2. Milton-Freewater, Oregon. In a completely randomized block design, ten nine-year-old ‘Bing’ on ‘Mazzard’ trees were sprayed with 1% Biofilm B using a mist blower at an equivalent rate of 2000 L ha-1. The treatments were as described for The Dalles. Fruit were harvested according to industry standards. On the day of harvest, the percentage cracked fruit per tree was recorded. In addition, a sample of 50 fruit was harvested from each tree. On the day of harvest 25 fruit were assessed for fruit quality parameters as above. The remaining 25 fruit were stored in cold storage at 2°C for two weeks, removed from the cold room and held at room temperature for 14 h to equilibrate and then subjected to the same assessments as on the day of harvest. Results were analyzed using Genstat 11.1. 3. Sunnyslope, Idaho. In a completely randomized design, twenty 25-year-old ‘Bing’ trees were sprayed with 1% Biofilm B using a mist blower at an equivalent rate of 2,000 L ha-1. The treatments were as described for The Dalles. Ten trees from each of the untreated control and treated sections were sampled for the experiment. Fruit were harvested according to industry standards. On the day of harvest, the percentage cracked fruit per tree was recorded. In addition, a sample of 50 fruit was harvested from each tree and analyzed for fruit weight without stem, fruit firmness, Stem Pull Force and total soluble solids (TSS). Results were analyzed using SAS®. 4. Loftus, Norway. A 5 x 5 completely randomized block design was laid out for 25 seven-year-old ‘Sweetheart’ on ‘Colt’ trees at Bioforsk Ullensvang Research Center (60°N). There were four different treatments and an untreated control. Treatments included a) two applications of 1% Biofilm B (one at straw color and another 10 d later); b) two applications of Biofilm plus the fungicide fenhexamid; c) two applications of Biofilm plus plastic ground covers to exclude rainfall from entering the root zone; d) two applications of Biofilm plus fenhexamid plus plastic ground covers. Fruit were harvested according to industry standards. On the day of harvest, the percentage of cracked fruit on each tree was recorded. In addition, a sample of 50 fruit was harvested from each of the trees and analyzed as above, except fruit firmness was assessed using a digital table penetrometer with a 4 mm probe (Penefel®, CTIFL, France). While both the penetrometer and the Bioworks Firmtech instrument result in fruit firmness output values in (g mm-1), the values between the two instruments are not directly comparable. RESULTS AND DISCUSSION In Vitro Stress Testing (2007)

Within 12 h of immersing all fruit in distilled water (Fig. 1), significantly (P<0.001) more untreated ‘Bing’ control fruit (61.3%) were cracked than those coated with 10 g L-1 Biofilm A (40%), 5 g L-1 Biofilm B (43.8%) or 10 g L-1 Biofilm B (17.5%) (P<0.001). After 48 h, the percentage fruit cracking in the untreated control and those coated with 5 g L-1 Biofilm A were the same (80%). Furthermore, this value was not significantly different from those coated with 5 g L-1 Biofilm B (67.5%) nor 10 g L-1 Biofilm A (63.8%). Coating the fruit with 10 g L-1 Biofilm B did, however, result in a highly significant (P<0.001) reduction (51.3%) in fruit cracking after 48 h submersion in distilled water compared to all other treatments. Coating the fruit with 10 g L-1 Biofilm B resulted in the least cracking over the entire duration of the experiment. Based on these results, field applications in 2007 used Biofilm B at 1, 10 and 20 g L-1. In Vivo Field Testing (2007) 1. Hood River, Oregon. Cracking of fruit from ‘Bing’ trees in Hood River was significantly reduced (P<0.001) after fruit were sprayed with three different concentra-

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tions of Biofilm B using a knapsack sprayer (Fig. 2). On 25 June, there was 10% cracking on average in the untreated control fruit, whereas there was only 2, 1 and 6% cracking in those fruit sprayed with 1, 10 and 20 g L-1 Biofilm B, respectively. On 9 July, there was 27% cracking on average in the control fruit, and only 15, 21 and 11% in those fruit sprayed with 1, 10 and 20 g L-1 Biofilm B, respectively. It was interesting to note that fruit sprayed with 10 g L-1 had the least fruit cracking on 25 June and was still less than the control on 9 July whereas fruit coated with twice that concentration, 20 g L-1 Biofilm B, had six times as much cracking on 25 June. This, coupled with the results of the in vitro stress testing, led the authors to conclude that a 10 g L-1 solution of Biofilm B applied twice (once at straw color and again 10 d later) would be better than a single application of 20 g L-1 Biofilm B. 2. Milton-Freewater, Oregon. On average, rain-induced fruit cracking of ‘Tieton’ in the field (Fig. 3) was 23.5% in the untreated control (P<0.001). Those trees treated with 10 g L-1 Biofilm A had 12.7% fruit cracking whereas those trees treated with 10 g L-1 Biofilm B or 20 g L-1 Biofilm B had 7.0 and 20.3% cracked fruit, respectively (Fig. 3). This provided further evidence that the higher concentration of 20 g L-1 Biofilm B was not as effective as coating the fruit with 10 g L-1 Biofilm B. It is possible that the hydrophilic properties may have allowed water to penetrate the cuticle and doubling the concentration over the surface area of the fruit surface may have allowed much more water to pass through. Alternatively, it may have been that the hydrophobic properties prevented transpirational water loss during dry periods and therefore higher internal turgor led to higher cracking with the 20 g.L-1 application. Therefore, the work planned for 2008 was standardized with two sprays of 10 g L-1 Biofilm B, one at straw color and a second application 10 d later. In Vivo Field Testing (2008) 1. Milton-Freewater, Oregon. Only a minor rainfall (<5 mm) event occurred during the two weeks preceding harvest in Milton-Freewater in 2008. This did not result in any significant differences in rain-induced cracking (<3%) in ‘Bing’. However, the control had significantly (P<0.001) firmer fruit (353 g mm-1) than those treated with Biofilm B (319.2 g mm-1) (Table 1), though all fruit were much firmer than the minimum marketable standard set by the Oregon Sweet Cherry Commission (250 g mm-1). In contrast, the Biofilm treatment resulted in fruit with significantly (P=0.032) higher TSS than the untreated controls at harvest (24.4 v. 23.8°Brix, respectively) (Table 1). Neither fruit diameter (mm) nor stem pullforce (g) were affected by Biofilm compared with the untreated control. It did, however, appear that in both The Dalles and Milton-Freewater, Biofilm resulted in fruit that matured faster, as evidenced by the slightly softer fruit (and which may explain the higher TSS). This raises the question as to whether Biofilm-treated fruit could have been harvested sooner and therefore Biofilm also may be useful for advancing fruit maturity. 2. The Dalles, Oregon. A rainfall event did not occur during the three weeks preceding harvest;. consequently, there was less than 1% fruit cracking of ‘Royal Rainier’ fruit at harvest and no significant differences were seen between treatments. In addition, there were no significant differences in fruit diameter or fruit firmness. Biofilm treatment did, however, result in fruit with a significantly (P=0.004) higher stem pullforce at harvest (1,308 g) compared to the untreated control fruit (1,197 g) (Table 2). Furthermore, Biofilm also resulted in significantly (P=0.032) sweeter fruit (18.5 vs. 17.4°Brix) at harvest (Table 2). 3. Sunnyslope, Idaho. A rainfall event did not occur during the three weeks preceding harvest; consequently, no significant rain-induced fruit cracking resulted and total fruit cracking was less than 1% in all treatments. There were no significant differences in fruit diameter, fruit firmness or colour between treatments. In contrast, stem pullforce was significantly higher (P<0.001) for ‘Bing’ fruit treated with Biofilm (950 g) compared to control fruit (711 g) (Table 3) and this was even more noteworthy since the control was close to the minimum marketable standard (700 g) set by the Oregon Sweet Cherry

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Commission. The same was true (P<0.001) of TSS (22.2 v. 19.5°Brix) (Table 3). As in The Dalles and Milton-Freewater, Biofilm treatment resulted in sweeter fruit with higher stem pullforce. 4. Loftus, Norway. Fruit cracking in Norway is expected every year, given the typical extremely high rainfall (>60 mm during the last three weeks of fruit maturation). Indeed, overhead rain covers are utilized almost inclusively by cherry growers throughout the Fjords. The 2008 season was no exception and fruit cracking in the untreated control averaged 24.6% (Fig. 4). Two applications of 1% Biofilm reduced the average fruit cracking to 17% and further inclusion of a preharvest fungicide (fenhexamid) or plastic ground cover did not improve cracking (18.8 and 18.2%, respectively). However, Biofilm plus both plastic ground covers and fenhexamide resulted in the least cracking 9.8% (P<0.001). Unfortunately, a treatment of fenhexamide plus plastic ground covers alone was not tested to determine whether this best result would have been achieved with or without the Biofilm treatment.

We hypothesize that fruit cracking in the open is partly due to internal (soil-plant) water relations. Under the Norwegian conditions, neither fruit firmness nor fruit colour were affected by the Biofilm treatment (Table 4). In contrast, TSS concentrations were significantly (P<0.001) higher (ranging from 20.4 to 21.4°Brix) for all Biofilm treatments compared to the untreated control (18.6°Brix). Average fruit weight was adversely affected by the use of Biofilm plus ground covers (8.9 g), but not Biofilm plus ground covers plus fungicide (10.2 g) compared to the untreated control (10.6 g),. It is possible that exclusion of rain during the early part of the growing season may have affected fruit size and a drip irrigation system under the plastic covers is implicated. In any event, careful monitoring of the soil moisture content is imperative if fruit cracking as a result of internal water relations is to be avoided. This has major implications for irrigation of cherries, especially where they are grown under dry conditions, and further research should is needed to clarify this. Indeed, cherry fruit still crack in the Pacific Northwest even in the absence of rainfall during the three weeks preceding harvest. CONCLUSIONS

Rain-induced fruit cracking of sweet cherries both in vitro and in the field was significantly reduced by coating the fruit with an organic hydrophobic Biofilm. This unique, patented formulation of complex carbohydrates and phospholipids has been shown to reduce fruit cracking significantly at several sites around the world. Most note-worthy were the results obtained in 2007 in Milton-Freewater where fruit cracking was reduced from 23.5 to 7% compared to untreated control fruit. A similar result was found in Norway in 2008, and was improved when used in conjunction with a preharvest fungi-cide (fenhexamid) and plastic ground covers. Under these conditions, fruit cracking was reduced from 24.6 to 9.8%. A major difference between the intensity of rainfall events, as well as the total amount of precipitation, in Norway compared to Milton-Freewater, most likely explains the improvement with ground covers and fungicides, possibly preventing up to 50% fruit cracking as a result of internal (soil-plant) water relations.

Two applications of 1% Biofilm B, at straw color and again 10 d later, resulted in a significant acceleration of fruit maturity in The Dalles, Milton-Freewater, and Sunny-slope. Although these fruit were slightly softer than the untreated control fruit, they were still suitable for marketing. In addition, the Biofilm-treated fruit at these sites had significantly higher stem pull-forces and were significantly sweeter than control fruit. Most importantly, fruit size was not affected. Consequently, it appears that in addition to a significant reduction in fruit cracking, Biofilm can be used to accelerate maturity without negatively reducing stem pull-force. In many instances, earlier harvested fruit would increase market value. Furthermore, this could help stagger the harvest period for a given cultivar where some blocks are left unsprayed, albeit at a higher risk of fruit cracking.

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ACKNOWLEDGEMENTS The authors express their grateful appreciation to the following people and

organizations: Shin-Etsu Chemical Company Ltd and Pacific BioControl Ltd for funding, Pam Manning and Katie Alaimo for technical assistance, Kevin Asai, Tim Dahle, Tim Kennedy, Vern Rodigheiro and Randal Montgomery for collaboration. Literature Cited Belmans, K. and Keulemans, J. 1996. A study of some fruit skin characteristics in relation

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cracking of sweet cherries and the distribution of surface stress of the fruit analyzed by a newly developed system. J. Jap. Soc. Hort. Sci. 59:509-517.

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Tables Table 1. Fruit quality parameters of ‘Bing’ sweet cherry at harvest from trees sprayed to

the point of run-off with 0 or 1% Biofilm B in Milton Freewater, Oregon, in 2008. Parameter Control 1% Biofilm s.e.d. Prob. CV% Firmness (g mm-1) 353 319 9.98 <0.001 9.4Total soluble solids (°Brix) 23.8 24.4 0.276 0.032 3.6Pullforce (g) 1,068 1,147 43.3 0.074 12.4

Table 2. Fruit quality parameters of ‘Royal Rainier’ sweet cherry at harvest from trees

sprayed to the point of run-off with 0 or 1% Biofilm B in The Dalles, Oregon, in 2008. Parameter Control 1% Biofilm s.e.d. Prob. CV% Firmness (g mm-1) 252 258 14.44 0.39 6.0Total soluble solids (°Brix) 17.4 18.5 0.477 0.032 5.9Pullforce (g) 1,197 1,308 71.5 0.004 6.1

Table 3. Fruit quality parameters of ‘Bing’ sweet cherry at harvest from trees sprayed

twice with 1% Biofilm B, compared to untreated control trees in Sunnyslope, Idaho, in 2008. (Color Scale: 1= low, 5= high).

Treatment Firmness (g mm-1)

Total soluble solids (°Brix)

Pullforce (g)

Colour (1-5)

Average fruit weight

(g) Control 555 a 19.5 b 711 b 4.0 a 8.2 a1% Biofilm 585 a 22.2 a 950 a 4.2 a 8.7 a

Table 4. Fruit quality parameters (%) of ‘Sweetheart’ sweet cherries at harvest in Loftus,

Norway, sprayed with 1% Biofilm B at straw colour and again 10 d later. This was in combination with or without a preharvest fungicide (fenhexamid) and plastic ground covers, compared to untreated control trees. (Colour scale 1 = low; 6 = high).

Parameter Control Biofilm

Biofilm+

fungicide

Biofilm+ Soil

cover

Biofilm+ fungicide+ soil cover s.e.d. Prob.

CV%

Fruit weight (g)

10.6 9.8 9.8 8.9 10.2 0.47 0.025 7.5

Firmness (g mm-1)

79.8 83.4 84.2 84 84.4 2.72 0.438 5.2

Colour (1-6)

5.4 5.4 5.5 5.9 5.8 0.24 0.15 6.8

Total soluble solids (°Brix)

18.6 20.5 20.4 21.4 21.3 0.59 <0.001 4.6

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Figurese

Fig. 1. Percentage of postharvest fruit cracking of ‘Bing’ sweet cherry fruit, coated on 29 May 2007 with either 5 or 10 g L-1 Biofilm A or 5 or 10 g L-1 Biofilm B, allowed to dry and subsequently immersed in distilled water for up to 48 hours.

Fig. 2. Percentage of cracked fruit at harvest on 7 September 2007 for ‘Bing’ trees

sprayed on 1 June 2007 in Hood River with different concentrations of Biofilm B.

488

Fig. 3. ‘Tieton’ cracked fruit (%) at harvest on 1 July 2007 from trees sprayed on 11 June

2007 in Milton-Freewater with either 0 g L-1 Biofilm, 10 g L-1 Biofilm A, 10 g L-1 Biofilm B or 20 g L-1 Biofilm B.

Fig. 4. Average cracked fruit (%) of ‘Sweetheart’ cherries at harvest in Loftus, Norway,

sprayed with 1% Biofilm B at straw colour and again 10 d later. This was in combination with or without a preharvest fungicide (fenhexamid) and plastic ground covers, compared to untreated control trees in 2008.