Eric J. Hanson

Efficacy of chlorine dioxide gas sachets for enhancing the microbiological quality and safety of blueberries.

In response to increasingly stringent microbial specifications being imposed by purchasers of frozen blueberries, chlorine dioxide (ClO2) gas generated by a dry chemical sachet was assessed for inactivation of Listeria monocytogenes, Salmonella spp., and Escherichia coli O157:H7 as well as five yeasts and molds known for blueberry spoilage. Fresh blueberry samples (100 g) were separately inoculated with cocktails of L. monocytogenes, Salmonella, E. coli O157:H7 (three strains each), or yeasts and molds (five strains each) to contain approximately 10(6) CFU/g and exposed to ClO2 (4 mg/liter, 0.16 mg/g) for 12 h in a sealed 20-liter container (99.9% relative humidity) at approximately 22 degrees C. After gassing, 25 g of blueberries was added to 225 ml of neutralizing buffer, pulsified for 1 min, and plated using standard procedures to quantify survivors. This treatment yielded reductions of 3.94, 3.62, 4.25, 3.10, and 3.17 log CFU/g for L. monocytogenes, Salmonella, E. coli O157:H7, yeasts, and molds, respectively. Thereafter, 30 lugs of uninoculated blueberries (approximately 9.1 kg per lug) were stacked on 1.2 by 1.2-m pallets (5 lugs per level x six levels), tarped, and exposed to ClO2 (18 mg/liter, 0.13 mg/g) for 12 h. After gassing, significant (P < 0.05) reductions of 2.33, 1.47, 0.52, 1.63, and 0.48 log CFU/g were seen for mesophilic aerobic bacteria, coliforms, E. coli, yeasts, and molds, respectively, compared with non-gassed controls. No significant differences (P > 0.05) in microbial inactivation were seen between lug levels and, with one exception (mesophilic aerobic bacteria), between the bottom and top surface of individual lugs. Based on these findings, ClO2 sachets may provide a simple, economical, and effective means of enhancing the microbial shelf life and safety of blueberries.

Calcium accumulation in delicious apple fruit

Abstract Seasonal patterns of fruit growth and calcium (Ca) accumulation in ‘Delicious’ apple fruit were observed over four years and four growing regions. Although temperature and precipitation varied greatly, fruit consistently accumulated Ca in a quadratic fashion, with maximum uptake occurring early in the season. Little Ca accumulated in fruit during the three weeks prior to harvest. Under some conditions, fruit appeared to lose Ca during this time. Loss of fruit Ca was not closely associated with precipitation. Calcium uptake was greatest during periods of high evaporative demand.

A First Assessment of the Cranberry Fruit Rot Complex in Michigan

Samples of ripe fruit were taken at harvest from all eight commercial cranberry farms in Michigan over a 3-year period to determine the distribution and incidence of fruit rot diseases and the fungal pathogens associated with rotted fruit. Totals of 23, 33, and 28 beds were sampled in 1999, 2000, and 2001, respectively. Fruit rot incidence varied widely among beds and farms and ranged from 5 to 97% (mean 33.4%) in 1999, 1 to 91% (mean 26.3%) in 2000, and 1 to 67% (mean 12.8%) in 2001. Differences in fruit rot incidence were observed among cultivars, but rankings differed among farms. In general, cultivars Ben Lear, Bergman, and Pilgrim tended to have lower and Beckwith and WSU61 higher fruit rot incidence than other cultivars grown in the same location. Colletotrichum acutatum, Pestalotia vaccinii, and Phyllosticta vaccinii were the fungi most frequently recovered from rotted fruit. Fusicoccum putrefaciens, Phomopsis vaccinii, Physalospora vaccinii, Allantophomopsis lycopodina, Coleophoma empetri, and Botrytis cinerea were isolated occasionally in 1999. The isolation frequency of Physalospora vaccinii, Phomopsis vaccinii, and C. empetri increased markedly in 2000. Glomerella cingulata was first detected in 2001. Fusicoccum putrefaciens was most common in the northern and Glomerella cingulata in the southern growing areas. A comparison of sound and rotted fruit from selected beds showed that Phyllosticta elongata predominated in sound fruit, whereas G. cingulata predominated in rotted fruit.

Effect of low soil pH on aluminum availability and on mortality of cherry seedlings

Levels of Al in leaf samples from 250 cherry orchards and the relationship between soil pH and Al levels in soil, roots and stems, and growth of 16-year-old sweet cherry (Prunus avium) trees and 1-year-old mazzard cherry seedlings were investigated. Leaf samples from commercial orchards contained 21 to 500 μg of Al per g of dry weight. Soil pH in the sweet cherry orchard was as much as 3 pH units below the recommended range (6.5 to 7.0) for optimal growth, with the concentration of available Al increasing from approximately 0.1 to 2.4 meq per 100 g with decreasing pH below pH 5.5. Levels of Al in the root system were proportional to its availability in the soil. Levels of Mg and Ca in roots decreased while Mn and Zn increased significantly (P ≤ 0.05) with increasing Al concentrations. Changes in the concentrations of P, K, Fe, Cu, and B were not significant. Soil pH (3.9, 4.7, and 7.0) and Al levels (0 to 27 meq of Al per 100 g) observed in the field were simulated by applying aluminum chloride to potted seedlings in three greenhouse experiments. Seedlings receiving calcium chloride served as controls (experiment 4). All seedlings planted in soil below pH 4.7 died within 4 weeks, with or without Al or Cl treatment, and seedling mortality increased as Al treatment increased. Root (P ≤ 0.05) and plant growth in general decreased with decreasing pH. Increasing Al treatment had little effect on root growth at pH 3.9 and pH 4.7 (at which little growth took place). At pH 7.0, however, root growth was reduced (P ≤ 0.05) compared with the controls. The level of Al applied to the soil and the concentration of Al in stems of cherry seedlings was highly correlated (P ≤ 0.001). The concentrations of macro elements in the stem (P ≤ 0.05 to 0.001) and Mn and Zn increased (P ≤ 0.001) with increasing Al concentrations. The interaction effect between the level of Al applied to the soil and soil pH on seedling mortality was highly significant (P ≤ 0.001). While there was a significant interaction between soil pH and the level of Cl applied to the soil, the level of available Ca did not increase over treatments that received Al. Overall, the data suggest that low soil pH could result in seedling death in part by increasing the absorption of Al into plants to toxic levels.

Root Colonization by Ericoid Mycorrhizae and Dark Septate Endophytes in Organic and Conventional Blueberry Fields in Michigan

Ericoid mycorrhizae are interfaces for nutrient exchange between specialized fungi and roots of blueberries and other ericaceous plants. Dark septate endophytes also associate with roots of the Ericaceae and many other plant families, but the nature of the interaction is not well understood. We measured ericoid mycorrhizae and dark septate endophyte colonization in organic and conventional blueberry fields matched by soil series and, if possible, cultivar and field age. The percentage of hair root cells with ericoid mycorrhizae was generally higher in organic than conventional fields, while dark septate endophyte colonization was higher in sand than muck soils. Across both muck and sandy soil types, ericoid mycorrhizal colonization was negatively correlated with field age, and dark septate endophyte colonization was negatively correlated with soil carbon, total soil nitrogen, and soil ammonium levels. When only sandy soils were included in the analysis, ericoid mycorrhizal colonization was positively correlated with soil pH and hair-root diameter, and negatively correlated with field age, soil ammonium levels, and total soil nitrogen. On sandy soils, dark septate endophyte colonization was not correlated with any measured variable. The functions of ericoid mycorrhizae and dark septate endophytes in commercial blueberry fields require further investigation.

Effect of soil calcium applications on blueberry yield and quality

SUMMARY The response of mature highbush blueberries (Vaccinium corymbosum L. cv ‘Jersey’) to soil applied Ca was studied for five years. The study site was a mature field in southwest Michigan with a relatively low soil pH (4.2) and Ca content (85 ppm). The treatments were: (1) non-treated control; (2) 1,100 kg/ha calcitic limestone; and (3) 550 kg/ha gypsum (calcium sulfate). Lime and gypsum were spread in a 5 ft wide band under the plants in May of 1996,1997,1999, and 2000. Lime, and to a lesser extent gypsum, increased soil pH and Ca levels, but had inconsistent affects on Ca levels in leaves and fruit. No treatment affected berry yield or size (1999-2001), firmness (1996-2001) or fruit rot incidence (2001).

Effect of nitrogen fertilizers on leaf and soil nitrogen levels in highbush blueberries.

Abstract Leaf N and soil nitrate and ammonium levels were monitored in 1986 and 1987 following N fertilization of 8–9 year old highbush blueberries. Urea was applied at 76 kg N/ha in a single application at bud break or in two applications (split) at bud break and petal fall. Controlled release fertilizers (CRF), of two different residual effects (Osmocote 3 mo., Osmocote 8 mo.) were applied at 38 kg N/ha or 76 kg N/ha at bud break. Compared to controls, N applications increased soil ammonium and nitrate levels early in the season and leaf N levels throughout the season. Urea provided a greater increase in leaf N and soil ammonium levels than CRF. Split urea applications increase leaf levels slightly over single urea treatments. Fertilizers increased soil ammonium and nitrate levels below the root zone, indicating that some leaching losses occurred.

Regulated deficit irrigation effects on physiological parameters, yield, fruit quality and antioxidants of Vaccinium corymbosum plants cv. Brigitta

Highbush blueberries require sufficient water throughout the growing season, especially during fruit development. Regulated deficit irrigation (RDI) has been used in many fruit crops to save water and potentially increase fruit quality without reducing yield. Our aim was to determine the effects of RDI on yield, plant–water relations, and fruit quality at harvest. Three irrigation treatments based on actual evapotranspiration (ETa) were applied: 50, 75 and 100% (control) to six-year-old ‘Brigitta’ highbush blueberries in Colbún, Maule Region, Chile, for seasons 2013–2014 and 2014–2015 and to 26-year-old ‘Brigitta’ plants in South Haven, Michigan, USA, during the 2014 season. Severe water deficit treatment (50% ETa) decreased photosynthetic rate, vegetative growth (second season in Colbún and South Haven’s trial), and fruit quality (berry size, titratable acidity, soluble solids, weight), and increased oxidative stress during both seasons in Colbún. The 50% ETa treatment also had the highest yield reduction during Colbún’s second season. In contrast, mild water stress (75% ETa) resulted in similar fruit yields and quality (firmness, fruit size, titratable acidity, soluble solids and berry weight) but with higher water productivity than the 100% ETa treatment, while it achieved intermediate values for antioxidant capacity compared to the 50% ETa treatment.

Status Update on Organic Blueberries in Michigan

The Great Lakes Region is an important region of blueberry production in the U.S., producing 30% of the annual U.S. production. In Michigan, blueberry acreage increased from 17,724 acres on 590 farms in 2002 to 21,758 acres on 840 farms in 2007. However, despite considerable market potential for organic blueberries, less than 1% of total Michigan blueberry acreage is organically certified. There is high interest and demand for organic blueberries from the Great Lakes Region, and the Michigan State University Blueberry Team has been working on organic production methods over the past 4 years. The establishment of the Michigan State University Organic Blueberry Research and Extension Planting on the Michigan State University campus has been one of the major accomplishments of the Michigan State Uuniversity research team. The objective of this project has been to study practices associated with soil health, nutrition, disease, and insect and weed control. Additional organic blueberry projects in Michigan have focused on studying the interaction of blueberry mulches and compost on nutrient release, and on-station and on-farm testing of OMRI-approved pesticides.

Fertilizer use efficiency: Integrating soil tests and tissue analysis to manage the nutrition of highbush blueberries

Abstract A total of 539 leaf and soil samples collected from commercial blueberry (Vaccinium corymbosum L.) plantings throughout Michigan between 1975 and 1985 were analyzed for P, K, Ca and Mg. Significant but weak correlations were found between soil and leaf nutrient levels for P (r=0.084), K (0.239), Ca (0.088) and Mg (0.132). Soil levels of K, Ca and Mg were more closely correlated with leaf nutrient levels in young plants (< 7 years old) than in older plants, suggesting that soil tests may be most useful in monitoring the nutrient status of young plants.