The potential mechanism of susceptibility of apple (Malus ×domestica Borkh.) fruit to sooty blotch due to carbohydrate leachates was examined. Fruit received applications of 0.5% apple juice to the fruit cuticle in order to mimic leachates. Nine cultivars of apple were selected from a variety block of potentially disease resistant breeding stock. Intact fruit on selected limbs received 0.5% apple juice applications on eight evenly spaced occasions during development. Trees received a minimal fungicide program only. Leachate samples from the fruit cuticles were collected monthly by immersion of whole, detached fruit in dH2O for 60 min. At harvest, fruit were evaluated for skin roughness, fruit rots, sooty blotch, sooty mold, flyspeck, and insect injury. Despite drought conditions, sooty blotch and sooty mold showed strong increases in disease intensity ratings, while flyspeck and skin texture damage showed moderate increases in intensity due to the dilute juice applications. Fruit rots and insect damage were unaffected by the juice applications.
Robert D. Belding
Robert D. Belding and Eric Young
Fruit from six cultivars of mature apple trees were evaluated for cuticular wax characteristics. Incidence of flyspeck, sooty blotch and russet was compared to the wax component of the cuticle. Three cultivars of Golden Delicious: Sundale Spur, Pure Gold, and Lys Golden; and three cultivars of Red Delicious: Starkspur Supreme, Oregon I, and Starkrimson, were examined.
Incidence of flyspeck on Golden Delicious apples was negatively correlated to cuticular wax per unit area. Sooty blotch appearance was greater on Golden Delicious fruit as compared to Red Delicious. Incidence of sooty blotch was positively correlated to cuticular wax weight per unit area among the cultivars of Red Delicious. Russeting was negatively correlated to wax weight per unit area for the Red Delicious cultivars. Wax compositional analysis will also be discussed.
Robert D. Belding and Gail R.W. Lokaj
`Biscoe' and `Encore' peach [Prunus persica (L.) Batsch] trees were treated in two years with AVG at 7, 14, or 21 days before first harvest (DBFH) or as a nontreated control (NTC). Fruit were harvested every 2 to 3 days based on observed initial yielding of fruit flesh and ground color. Fruit were further evaluated for maturity and quality based on the production of ethylene, ground color, diameter, flesh firmness, soluble sugars, and woolliness. Evaluations occurred 1 day after harvest and after 14 and 28 days in cold storage. AVG applications delayed early harvests of `Biscoe', but `Encore' harvests were not affected. Across all preharvest treatment timings, AVG reduced ethylene production by 64%. Ethylene production and fruit softening were most inhibited for fruit treated with AVG 7 DBFH. In this study, fruit treated with AVG demonstrated a significant negative correlation between fruit ethylene production and firmness. Average flesh firmness of fruit from AVG treatments were 11.8 Newtons greater than NTC fruit. Fruit treated 21 or 14 DBFH exhibited greener ground color than NTC fruit or fruit treated 7 DBFH. The NTC fruit had the highest ground color values, fruit treated 7 DBFH were intermediate, and fruit treated 21 or 14 DBFH had the lowest values for ground color. AVG has potential use as a management tool for controlling the timing of harvest and for allowing fruit to ripen more slowly and to hang longer on the tree, thus improving fruit size. In addition, AVG assists in maintaining the postharvest flesh firmness required to withstand handling during marketing. Chemical name used: aminoethoxyvinylglycine (AVG).
Robert D. Belding, Sylvia M. Blankenship, Eric Young, and Ross B. Leidy
Variation in amount and composition of epicuticular wax among several apple (Malus ×domestica Borkh.) cultivars was characterized by gas chromatography, thin-layer chromatography, and gas chromatography-mass spectroscopy. Across cultivars, wax mass ranged from 366 to 1038 μg·cm-2. Wax mass decreased during the 30 days before harvest. Ursolic acid accounted for 32% to 70% of the hydrocarbons that make up the epicuticular wax. Alkanes, predominantly 29-carbon nonacosane, comprised 16.6% to 49%. Primary alcohols of the hydrocarbons ranged from 0% to 14.6% of the epicuticular wax. Secondary alcohols of the hydrocarbons were the most cultivar specific, making up 20.4% of the epicuticular wax in `Delicious' and only 1.9% `Golden Delicious' strains. Aldehydes and ketones of the hydrocarbons represented a small amount of total wax, ranging from 0% and 6.0%. Percentage of primary alcohol in the epicuticular wax increased as fruit developed. Other components showed no distinct trends with fruit development. Examination of the ultrastructure of cuticular wax using scanning electron microscopy revealed structural differences among cultivars.
Robert D. Belding, Bradley A. Majek, Gail R.W. Lokaj, Jeffrey Hammerstedt, and Albert O. Ayeni
Peach (Prunus persica) trees were established and grown from 1996 to 1999 at the Rutgers Agricultural Research and Extension Center, Bridgeton, N.J., to compare performance under four methods of orchard floor preparation: flat no-till, flat cultivated, mound unmulched, and mound mulched orchard floors. The experimental site was flat and the soil was a well-drained Aura gravelly sandy loam (61% sand, 31% silt, 8% clay) with a pH of 6.5, cation exchange capacity 5.7, and organic matter content of 2.0%. Soil moisture holding and gas exchange capacity determine the efficacy of mounding in peach orchards. Under these conditions, the method of orchard floor preparation had no effect on peach tree trunk cross sectional area (TCSA), fruit number per tree, fruit size, and yield. Thus, without irrigation, there was no advantage to the early performance of peach trees associated with orchard floor mounding on Aura gravelly sandy loam when situated on a flat terrain.