Production of European pears (Pyrus communis L.) in the eastern United States is limited by a number of physiological and pathological problems. In an attempt to expand sustainable pear production in that region, a series of long-term field trials of Asian pear [Pyrus pyrifolia (Burm. F) Nak. {syn. P. serotine L.}] were established at two sites in Maryland. To compare precocity, productivity and survival, nine Asian pear cultivars and three European cultivars were planted in 2010 at the Wye Research and Education Center. Asian pears were precocious and productive and many trees flowered and fruited in the second leaf. After the fourth leaf, survival of ‘Isi’iwasi’, ‘Shinsui’, ‘Kosui’ and ‘Olympic’ was good. Many ‘Hosui’ and ‘Ya Li’ (Asian pear) trees as well as ‘Bartlett’ and ‘Golden Russett’ (European pear) trees had died at that point, following bloom infections of fire blight (Erwinia amylovora). Eighteen pear cultivars in two established plantings were evaluated for their field-tolerance to fire blight following a severe hailstorm at Keedysville. The cultivars ‘Shin Li’, ‘Daisu Li’, ‘Shinsui’ and ‘Olympic’ fared as well as ‘Magness’, a fire blight-tolerant European pear that served as a benchmark in that evaluation. On the other hand, ‘Hosui’, ‘Choju’, ‘Kosui’, ‘Seigyoku’, ‘Ya Li’ and ‘Ts’e Li’ were severely damaged. Using fruit from the replicated trial at Wye, consumer tastings were also conducted. In these tastings, ‘Yoinashi’, ‘Atago’, ‘Shinko’ and ‘Olympic’ were well-received by consumers. After tasting Asian pears, most people reported that they would be interested in purchasing the fruit and asked for the names of local producers, even those less familiar with the crop. Based on our long-term research results, there appears to be a good potential for locally-produced Asian pear fruit. With the correct cultivar selection for fire blight management, local growers should be able to produce this alternative crop sustainably and market their fruit profitably.

Nine Asian pear cultivars ('Atago', 'Hosui', 'Isiiwase', 'Kosui', 'Olympic', 'Shinko', 'Shinsui', 'Ya Li' and 'Yoinashi') were evaluated for quality (firmness, titratable acidity, and soluble solids) and susceptibility to the blue mold pathogen Penicillium expansum. Fruit were grown at the University of Maryland Extension Wye Research and Education Center in Queenstown, Maryland and transported to the USDA-ARS research facility in Beltsville, Maryland. Data from pears harvested in 2012 and 2013 were combined and mean values were calculated. Force required to puncture the epidermis varied from 11.3 ('Kosui') to 28.8 N ('Olympic'). Soluble solids ranged from 10.9 ('Atago') to 15.9 degrees Brix ('Shinsui'), and titratable acidity from 0.09 ('Kosui') to 0.18% malic acid equivalents ('Hosui'). All cultivars were susceptible to blue mold decay; mean lesion diameters ranged from 28.9 ('Isiiwase') to 39.1 mm ('Yoinashi') after 7 days storage at 25 degrees C. Variation in fruit quality and susceptibility to blue mold decay was observed among the nine cultivars. This information will help both small scale niche growers and commercial pear producers decide whether to immediately market or store fruit of specific Asian pear cultivars depending on their quality parameters and susceptibility to blue mold.

A one-hectare apple and Asian pear orchard was established in 2003 to compare the growth and productivity of trees under organic and conventional management systems. Trees planted in this plot were selected from three broad categories; conventional apple cultivars, disease-resistant apple cultivars and Asian pears. One plot in each of five blocks was managed using current conventional methods. The other plot was managed using approved organic inputs and certified by the Maryland Department of Agriculture (MDA). Trees survived and grew under both production programs but tree vigor and fruit yields were greater in the conventional plantings. We encountered four difficulties in managing the organic plots; 1) slow growth of young trees, 2) difficulty in controlling weed competition, 3) direct pests affecting the fruit and 4) reduced yields. A strong cultivar-by-treatment interaction on yield was measured in two apple cultivars and one Asian pear cultivar. 'Enterprise' trees were very productive under the conventional program but significantly less productive in the organic blocks. An economic analysis was conducted to compare the two management programs. This economic evaluation focused on farming practices and inputs that differed; pest control, nutrient applications, field labor operations and tree support. Organic production took more time than conventional production due to the labor required for weed control and the additional pesticide applications. A great difference in the relative system profitability was caused by the differences in yields from organic plots. Lower organic fruit yields appeared to be a greater barrier to profitability than the higher expenses required for chemicals or labor in the organic plots.

Fourteen Prunus rootstock cultivars and selections budded with either 'Redtop', 'Redhaven' or 'Cresthaven' peach were planted at 11 locations in North America in 2001 in a randomized block design with a tree spacing of 5 by 6 m and 8 replicates. This test planting was a NC-140 Cooperative Regional Rootstock Project (www.nc140.org). There were 14 rootstocks, which included three peach seedling rootstocks: 'Lovell', 'Bailey', and Guardian (R) 'BY520-9' [selection SC-17] and 11 clonal rootstocks. Clonal rootstocks included peach x almond hybrids 'BH-4' and 'SLAP' ('Cornerstone'); peach x plum hybrids 'K146-43' ('Controller 5'), 'K146-44', and 'P30-135' ('Controller 9'); interspecific plum hybrids 'Hiawatha', 'Jaspi' and 'Julior'; interspecific Prunus hybrids 'Cadaman (R)' and 'VVA-1' (Krymsk (R) 1); and Prunus pumila selection 'Pumiselect (R)'. The largest trees were from Georgia, Maryland, and South Carolina. 'BH-4', 'SLAP', SC-17, Lovell, and 'Cadaman (R)' were the most vigorous rootstocks. 'Jaspi', 'K146-43', 'K146-44' and 'VVA-1' were the least vigorous, having trunk circumferences 30-40% smaller than Lovell. No rootstock had a significantly higher survival rate than Lovell at all locations. 'Julior', 'Jaspi', and 'VVA-1' had significantly more root suckers. Cumulative fruit yields were highest on the peach seedling, peach x almond, and 'Cadaman (R)' rootstocks. Lowest cumulative yields were from trees on 'Jaspi', 'VVA-1', and 'K146-44' rootstocks. Fruit weight was significantly larger on 'BH-4', 'SLAP' and 'Bailey' rootstocks. 'Bailey' and 'Jaspi' had the highest and lowest cumulative yield efficiency, respectively.

Title of Thesis: Evaluation of Raspberry (Rubus sp.) Genotypes for Postharvest Quality and Resistance to Botrytis cinerea Julia Mae Harshman, Master of Science. 2012 Thesis Directed by: Christopher S. Walsh, Ph.D Department of Plant Science and Landscape Architecture Raspberries are a delicate, high value specialty crop with an extremely short shelf life. This is exacerbated by their susceptibility to postharvest decay caused by Botrytis cinerea. Of the commercially available species, red raspberry (Rubus idaeus L.) is the most widely grown. Yellow (R. idaeus L.), black (R. occidentalis L.) and purple raspberries (R. × neglectus Peck.) are mainly available from direct marketers. The storageability of 17 cultivars was examined weekly from June to September during two growing seasons. Storage life was assessed weekly, while firmness, color, respiration and ethylene evolution rates were measured in select harvests. Black and purple raspberries outperformed red and yellow cultivars in their ability to resist B. cinerea colonization. Black raspberries also had the lowest ethylene evolution rates and incidence of decay. This information will be useful to raspberry breeding programs by identifying physiological characteristics that are correlated with greater resistance to B. cinerea. EVALUATION OF RASPBERRY (RUBUS SP.) GENOTYPES FOR POSTHARVEST QUALITY AND RESISTANCE TO BOTRYTIS CINEREA

This project began in 1991 with a cross between 'McIntosh Wijcik' and 'Gala' apples in an effort to develop a new apple cultivar that was well-suited to the Mid-Atlantic's hot and humid growing season. The goal was to create a grower friendly cultivar that was dwarfing which would not require labor intensive methods of budding, pruning, and branch angle manipulation. A second cross made in 1999 between the 'CompactGalaMac' (CGMx) progeny of the 1991 cross and four commercial cultivars yielded progeny which had compact phenotype; field tolerance to diseases and pests; precocity and productivity; heat tolerance, fruit firmness and lack of preharvest drop typical of 'Gala'; fruit taste attributes from both 'Pink Lady' and 'Fuji'. These trees could potentially be grown on their own roots, avoiding the problems that accompany size-controlling rootstocks.

During the past three years we conducted a series of studies on peach storageability. Longitudinal studies using incubators set at 0, 2.5, 5, 7.5 and 10°C showed that less juice was extractable after storage at temperatures below 7.5°C. Fruits held at 7.5C° or greater were capable of fully softening in storage, while fruit held at 5°C softened less. Studies demonstrated that storage at 2.5°C or less suppressed ethylene production dramatically. Shipping-mature 'Redhaven' fruits were successfully held for up to six weeks in storage at 0°C. After holding for seven days at room temperature, fruit still softened and became juicy. Ethylene evolution also increased dramatically at room temperature. Six weeks of storage at 0°C did not appear to damage the fruit's ability to evolve ethylene. Short-term studies of the effect of temperature on ethylene were conducted at temperatures from 0 to 20°C. After equilibration, ethylene evolution was measured. Preliminary plots of ethylene production appeared to be log-linear and did not show an inflection point at chilling temperatures. High Q(10) values were measured for ethylene production in peach and nectarine. This temperature response may contribute to the development of storage disorders. Our working hypothesis was that flesh mealiness resulted from 'chilling injury.' While it was an attractive hypothesis, it was difficult to prove. Commercial observations of mealiness in late-harvested fruit would also argue against chilling injury. In hindsight, storage recommendations of 0°C rather than 5°C also seem illogical if mealiness is a symptom of chilling injury. We postulated that peach and nectarine disorders that occur in storage at 5°C are caused by the production of low levels of ethylene that induce some, but not all, ripening-related genes. Mealiness and the lack of juiciness may occur in response to senescent breakdown, rather than chilling injury.

The objectives of this study were to develop an objective and non-destructive harvest maturity index based on ground color for peaches [Prunus persica (L.) Batsch] and nectarines (P. persica var. Nectarina), and to evaluate statistical models to predict the maturity stage measured as ethylene evolution rate (EER). After fruit set, peach cv. Redhaven et Elegant Lady, and nectarine cv. July et August Red fruit were tagged in order to follow maturation and ripening on the tree. Before, during and after commercial harvest, 48 fruit of similar diameter and tree position were harvested every 2-4 days. EER (at 20 degrees C), fresh weight, ground and cover color (L*, a*, b*, C* and Hue value) were measured on all 48 fruit. Firmness at several fruit points, TSS, pH, TA and TSS/TA ratio were measured only on 24 fruit, and the rest were held for up to 7 days at 20 degrees C as a ripening period to measure all the parameters mentioned above. Pearson correlation coefficients were determined between variables to explore possible relations with the log of the EER (maturity index). The Stepwise procedure was used for model building. The log of the EER was used as the dependent variable. To test the validity of criteria used in the model and significance of coefficients of independent variables the Regression Procedure of SAS was performed. The models used to predict EER produced varying results depending on the cultivar, but the best fit was found with a quadratic model for ground color a* value (harvest index) with an R-2 = 0.69, and fruit firmness (R-2 = 0.71). It was also found that fruit softening varies according to the point of measurement in the fruit.

Peaches are among those temperate zone fruits susceptible to chilling injury. Woolliness is a factor of considerable commercial importance wherever peaches and nectarines are grown. Woolliness or mealiness was found to be the major problem affecting cold-stored peach fruit. A better understanding of this physiological disorder would be available today if researchers had taken certain basic precautions when working with peaches and nectarines. Both the effect of harvest maturity and storage temperature on the development of woolliness will be reviewed.

A factorial planting of three scion varieties ('Gala,' 'Fuji,' and 'Braeburn') on each of four rootstocks (Mark, M.26, M.7a, and MM.111) was established at two locations in Maryland in 1990. In 1993, trees were scored for trunk circumference (TC), extension growth, leaf color, burrknots (BK) and root mass proliferations (RMP) both above and below ground, and presence of pests on the shanks. Mark was the only rootstock with RMP; 75% of the trees examined had these tissue proliferations. The % of TC composed of RMP below ground was 2-3X higher in Mark grafted with 'Fuji' than was observed with other scion varieties. Across root: stocks, % TC composed of BK below ground was significantly affected by location. In each rootstock, regressions between growth parameters and % of TC with BK or RMP were almost all negative and many had significant correlations. In Mark, % of TC with RMP below ground (but not above) was significantly correlated with reduced TC at 25 cm. The occurrence of RMP was much greater below ground than above. Orchard surveys of trees on Mark were also conducted at several commercial sites in MD and NY. The percentage of trees showing RMP ranged from 0 to 90%. There was a significant reduction in TC at 25 cm with increasing levels of RMP. The percentage of trees with RMP and mean % of TC with RMP significantly correlated with percentage of trees having visible woolly apple aphids or their distinctive galls.

Differences in ethylene evolution rate among 'Biscoe,' 'Belle of Georgia,' 'Loring.' and 'Redskin peach (Prunus persica L.) and Fantasia' nectarine (Prunus persica L., v nuciperscia) fruits were investigated. The effect of cultivar on ethylene evolution rate was highly significant. The mean ethylene evolution rate in 'Belle of Georgia' peach fruits was higher than in any other cultivar. The lowest mean ethylene evolution rate was observed in 'Loring' peach fruits. Ethylene evolution rates were compared with ripening associated changes in accumulation of soluble mesocarp proteins. The soluble protein fraction extracted from fruits at three time points during ripening were resolved by denaturing polyacrylamide gel electrophoresis. Protein band density was determined by scanning laser microdensitometry. Cultivar and ethylene evolution rate were related to protein density and significant gel protein band by cultivar interactions were observed. Analysis of band variance tested the effect of cultivar on protein accumulation during maturation. Sixteen bands showed significant differences and five bands showed no significant differences among cultivars. For 'Belle of Georgia' fruits, the ethylene evolution rate was related to increased accumulation of two proteins with estimated molecular masses of 39.0 and 56.5 kDa. No increased accumulation of 39.0 or 56.5 kDa protein was observed in the three remaining Prunus cultivars with suppressed ethylene evolution rates, or in ripening 'Loring' fruits treated with (2-chloroethyl)phosphonic acid (ethephon).

Although high soil temperatures can occur in apple orchards throughout the world, there is little information on their effect. This investigation was conducted to determine the influence of various durations of root exposure to 34 degrees C on the growth and physiology of the apple plant. Roots of Royal Gala and McIntosh cultivars were exposed to 34 degrees C for 0, 8, 16, and 24 hours/day for seven weeks. Royal Gala grown at the 24 hours/day treatment exhibited significant decreases in leaf, shoot, and root growth; chlorophyll concentration of the older leaves; transpiration; discrimination against C-13 in leaves; and an increase in leaf temperature. In McIntosh, root growth and chlorophyll concentration of leaves were not affected. For both cultivars compared to the control treatment, the continuous high temperature treatment resulted in lower levels of P, Mg, and Mn in leaves. Royal Gala at this treatment showed significantly higher values of foliar N and K and lower values of Ca, Fe, and Zn. For McIntosh the levels of Cu and B decreased significantly in this treatment as compared to the control treatment. We conclude that 34 degrees C in the root-zone does not stress these cultivars unless it persists throughout the day/night cycle.

Although high soil temperatures can occur in apple orchards throughout the world, there is little information on their effect. This investigation was conducted to determine the influence of various durations of root exposure to 34 °C on the growth and physiology of the apple plant. Roots of Royal Gala and McIntosh cultivars were exposed to 34 °C for 0, 8, 16, and 24 hours/day for seven weeks. Royal Gala grown at the 24 hours/day treatment exhibited significant decreases in leaf, shoot, and root growth; chlorophyll concentration of the older leaves; transpiration; discrimination against13C in leaves; and an increase in leaf temperature. In McIntosh, root growth and chlorophyll concentration of leaves were not affected. For both cultivars compared to the control treatment, the continuous high temperature treatment resulted in lower levels of P, Mg, and Mn in leaves. Royal Gala at this treatment showed significantly higher values of foliar N and K and lower values of Ca, Fe, and Zn. For McIntosh the levels of Cu and B decreased significantly in this treatment as compared to the control treatment. We conclude that 34 °C in the root-zone does not stress these cultivars unless it persists throughout the day/night cycle.

World apple production has increased markedly in the past decade. All major production areas of the southern hemisphere except Australia have increased their apple production. A dramatic increase in apple plantings has occurred in New Zealand. 'Granny Smith', 'Cox's Orange Pippin', 'Delicious' and 'Golden Delicious', are the leading cultivars in that country. 'Gala', 'Fuji', 'Braeburn' and spur 'Delicious' trees were heavily planted during the 1980's, while processing cultivars such as 'Sturmer Pippin' were declining in New Zealand.

In the past three years we have studied the effects of oxygen on the maturation and ripening of `Gala' apples. Fruit-respiration, the onset of the climacteric rise in ethylene evolution and the rate of increase in ethylene production were measured. The effects of oxygen on softening and titrable acidity were also assessed. The delay in the onset of the climacteric rise in ethylene evolution shows enzymatic-type kinetics, with saturation levels of about 8-10% oxygen. Treatment with pure oxygen was highly detrimental; it induced visual symptoms of low-oxygen damage and high levels of ethanol. The slope of the rise in ethylene evolution is also a function of oxygen concentration, with an apparent Km for oxygen lower than that which delays the climacteric onset. The effect of oxygen on respiration is dependent on the physiological state of the fruit. In preclimacteric fruits, levels of oxygen between 2 and 8% eventually decrease respiration. Calculations of internal oxygen levels indicate that the diminution of respiration results from decreased metabolic activity in response to hypoxia.