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I.A. Merwin and W. C. Stiles

Eight groundcover management systems (GMS) have been evaluated since 1986 in an apple orchard replant site. Tree-row GMS have included post-emergence herbicide (glyphosate) “killed sods,” pre-emergence herbicide (norflurazon + diuron) strips, a crownvetch “living mulch,” hay-straw mulch, monthly cultivation, a close-mowed sod, and an unmowed, chemically growth-regulated (maleic hydrazide + 2,4-D) sodgrass. Soil organ&matter content, surface aggregate structure, and water infiltration have improved under vegetative groundcovers relative to herbicide treatments. Extractable soil N, K, P and B have increased under straw mulch. Except for K, foliar nutrient content (dry wt basis) has not been closely coupled with soil nutrient content. Leaf K, P and B contents have increased, while leaf N, Mg and Zn, have decreased in trees in sodgrass relative to herbicide GMS.

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D.K. Isutsa, I.A. Merwin, and B.B. Brodie

Apple replant disease (ARD) is a serious problem in fruit production, and none of the major clonal rootstocks are resistant to ARD. We have screened Malus domestica clones and species accessions from the USDA Malus Germplasm Repository at Geneva, N.Y., including M. angustifolia-2375.03 (MA), M. coronaria-2966.01 (MC), M. fusca-3031.01 (MF), M. ioensis-3059.01 (MI), M. sieversii-3530.01 (MS), and M. kirghisorum-3578.01 (MK), for resistance to ARD and root-lesion nematodes (RLN, Pratylenchus spp.), in a composite soil collected from 11 New York orchards with known ARD. Plant dry mass and height, root necrosis, and nematode populations in different apple species and clones were compared after 60 days growth in steam-pasteurized (PS), RLN-inoculated (IS), and naturally infested field (FS) soils with 1200 RLN per 100 cm3. More severe stunting, reduced plant dry mass, and root necrosis occurred in FS seedlings compared with those in PS, but M. angustifolia seedlings were substantially more resistant or tolerant to RLN and ARD than the other species tested. Plant dry mass ranked MK>MS>MA>MI>MF>MC, and these differences were significant at the 5% level. RLN root populations were negatively correlated with plant dry mass, and accounted for about 10% of its variation, with nematode populations in roots ranking MC>MF>MK>MI>MS>MA. Useful resistance to ARD and parasitic nematodes apparently exists within Malus germplasm collections, and can be identified by testing more genotypes, developing rapid resistance screening methods, and comparing RLN host preferences among Malus genotypes and various orchard cover crops.

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G. Psarras, I. Merwin, A. Lakso, and R. Zobel

We are evaluating techniques for measuring intact apple rootstock (Malus domestica cv. M.9 and MM.111) responses to low, medium, and high soil-water potential, and low, medium, and high concentrations of N, K, and Ca, in sterile sand culture. Root respiration and functional surface area were estimated with an IRGA chamber and electric capacitance meter, respectively. Root length and surface area were determined by digital image analysis of extracted root systems. Low N supply reduced root respiration, while low K levels increased respiration relative to well-nourished controls. Calcium effects were inconsistent among the rootstocks. Total root length and respiration rates of MM.111 were higher than M.9, but M.9 had higher root:shoot ratios. Root capacitance was correlated with total root length (P < 0.001); and M.9 root systems had greater capacitance than MM.111. In a related field experiment, root growth and respiration of 4-year-old `Mutsu' apple trees on M.9 rootstock were measured in soil under low and moderate drought stress established by rain exclusion shelters, using capacitance and IRGA meters, and a minirhizotron video camera inserted into Plexiglas tubes transecting the rhizosphere. Root growth rates peaked in July (coinciding with maximal shoot growth), then declined gradually during late summer; but variability among trees was greater than among water stress treatments. Root/soil respiration maxima of 4.5 μmol CO2/m2 per s occurred in mid June, late July (when new root counts peaked), and the end of August (when root turnover was maximal).

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I. Kadzere*, C.B. Watkins, I. Merwin, F. Akinifessi, and J.D. Saka

Postharvest biology of Uapaca kirkiana, a native tree fruit to the miombo woodlands of some parts of Southern Africa, is little understood. Experiments have been carried out to determine the influence of pre-ripening storage treatments on subsequent fruit ripening characteristics. Mature but unripe fruit, collected from Dedza District in Malawi, were either held under ambient conditions, incubated in clay pots for 3 d or at 4 °C for 11 d. Fruit were removed from clay pots and cold storage, held under ambient conditions, and quality assessed daily. Color changed from green-yellow and/or brown-yellow in the unripe fruit to brown in ripe fruit. Low initial fruit compression was associated with hard and unripe fruit at harvest. Compared with both ambient and cold storage, incubating the fruits in clay pots resulted in advanced fruit softening as reflected by the high compression levels even on the day of removal from the clay pots. By day six after removal, compression had increased to a mean of 81 mm in the clay pot fruits while maximum levels were 56 and 38 mm for ambient and cold storage, respectively. Storing fruit at cold temperature delayed softening and deterioration compared with ambient and clay pot storage treatments. There was a general decrease in the total soluble solids content of the fruit during ripening, and was not influenced by the pre-ripening storage treatments. Decay increased during ripening for all the three treatments. Deterioration of the pulp in fruit, indicated by the development of a brown color and/or disintegration of the pulp, was observed with increasing time from removal. These results will be discussed in relation to the potential for improving storage of U. kirkiana.

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Gregory M. Peck, Ian A. Merwin, Christopher B. Watkins, Kathryn W. Chapman, and Olga I. Padilla-Zakour

Maturity and quality of fruit harvested from an orchard of disease-resistant ‘Liberty’ apple (Malus ×domestica Borkh.) trees was investigated during and after the transition from conventional to integrated (IFP) and organic fruit production (OFP) systems. Over 4 years, internal ethylene concentration, starch pattern index, flesh firmness, soluble solids concentration (SSC), titratable acidity (TA), and percent of surface blush of fruit at harvest were not consistently different between fruit from IFP and OFP systems. Total phenolic content and antioxidant capacity of the fruit were also similar between treatments. IFP-grown fruit contained more potassium during the first 2 years and more calcium in all years than OFP-grown fruit. After fruit were stored in air at 0.5 °C for 9 weeks in 2007, OFP-grown apples were firmer and had higher SSC, TA, and SSC:TA ratios. In double-blind triangle taste tests, consumer panelists were able to discriminate between the fruit from each treatment, but in double-blind hedonic and intensity tests, panelists did not consistently rate one treatment more highly than the other. Overall, consumer panelists favorably rated internal quality of fruit grown under both IFP and OFP systems. In 2006, when weather and disease caused a high percentage of OFP-grown fruit to have cosmetic defects, the panelists rated the appearance of OFP-grown apples as less acceptable than the cleaner-looking IFP-grown apples. Our study of ‘Liberty’ apple fruit maturity and quality during a 4-year transition period from conventional to IFP and OFP systems showed that differences were small if present, whereas internal fruit quality was rarely different between systems.

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I.A. Merwin, D.A. Rosenberger, C.A. Engle, D.L. Rist, and M. Fargione

Natural (hay, wood chips, recycled paper pulp) and synthetic (polypropylene film and polyester fabric) mulches were compared with mechanical tillage and residual herbicides as orchard groundcover management systems (GMSS). In two New York orchards-the Clarke farm and Hudson Valley Lab (HVL—GMSS were applied from 1990 to 1993 in 1.8-m-wide strips under newly planted apple (Malus domestica; `Liberty', `Empire', `Freedom', and advanced numbered selections from the disease-resistant apple breeding program at Geneva, N.Y.) trees. GMS impacts on soil fertility, tree nutrition and growth, yields, crop value, and vole (Microtus spp.) populations were evaluated. After 3 years at the Clarke orchard, extractable NO3, Mn, Fe, B, and Zn concentrations were greater in soil with herbicides than synthetic mulches; soil K and P concentrations were greater with herbicides and wood chips than synthetic mulches. At the HVL orchard, topsoil NO3, K, and Mg concentrations were greater with hay mulch than herbicides or other mulches; Mg, Fe, and B concentrations were lower in soil with wood chips than other GMSs. Soil organic matter content was not affected by GMS. Apple leaf N, K, Cu, and Zn concentrations were greater with herbicides, hay mulch, and polypropylene mulch than cultivation or recycled paper mulch at the HVL orchard during hot, dry Summer 1991. Despite transient differences among GMSS during the initial years, after 4 years of treatments there were no consistent GMS trends in cumulative tree growth or gross yields. The higher establishment and maintenance costs of several mulches were offset by their prolonged efficacy over successive years; crop market values from 1992 to 1994 were considerably greater for trees with polypropylene film, polyester fabric, and hay mulches than herbicides, cultivation, or other mulches. Voles caused more serious damage to trees in synthetic and hay mulches, despite the use of mesh trunk guards and rodenticide bait.

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S.S. Miller, R.W. McNew, B.H. Barritt, L. Berkett, S.K. Brown, J.A. Cline, J.M. Clements, W.P. Cowgill, R.M. Crassweller, M.E. Garcia, D.W. Greene, G.M. Greene, C.R. Hampson, I. Merwin, D.D. Miller, R.E. Moran, C.R. Rom, T.R. Roper, J.R. Schupp, and E. Stover

Cultivar and planting site are two factors that often receive minimal attention, but can have a significant impact on the quality of apple (Malus ×domestica) produced. A regional project, NE-183 The Multidisciplinary Evaluation of New Apple Cultivars, was initiated in 1995 to systematically evaluate 20 newer apple cultivars on Malling.9 (M.9) rootstock across 19 sites in North America. This paper describes the effect of cultivar and site on fruit quality and sensory attributes at a number of the planting sites for the 1998 through 2000 growing seasons. Fruit quality attributes measured included fruit weight, length: diameter ratio, soluble solids concentration (SSC), titratable acidity (TA), flesh firmness, red overcolor, and russet. Fruit sensory characteristics rated included crispness, sweetness, and juiciness, based on a unipolar intensity scale (where 1 = least and 5 = most), and acidity, flavor, attractiveness, and desirability based on a bipolar hedonic scale (where 1 = dislike and 5 = like extremely). All fruit quality and sensory variables measured were affected by cultivar. The two-way interaction of cultivar and planting site was significant for all response variables except SSC, TA, russet, crispness, and sweetness ratings. The SSC: TA ratio was strongly correlated with sweetness and acidity sensory rating, but was weakly correlated with flavor rating. The results demonstrate that no one cultivar is ideally suited for all planting sites and no planting site is ideal for maximizing the quality of all apple cultivars.