Seedlings of six tomato (Lycopersicon esculentum Mill.) cultivars were evaluated for differences in ice-nucleation activity. Freezing temperatures of tissues were not significantly affected by cultivar. Greenhouse-grown seedlings, 0.3- to 34-g fresh weight, of ‘Beefsteak’, ‘Pixie’, ‘Supersteak’, ‘Red Cherry’, ‘Big Boy’, and ‘Supersonic’, with and without natural infestations of ice-nucleation active (INA) bacteria, had an overall mean freezing temperature of −5.9°C. Plants without detectable INA bacteria exhibited mean freezing temperatures ranging from −6.1° to −6.9°, while seedlings with INA bacteria froze from −4.7° to −5.7°. Plant mass and presence of INA bacteria significantly affected plant freezing temperatures. Innate differences in frost avoidance capability among the tomato cultivars examined were not apparent.
Experiments were conducted from 1989 to 1991 to compare the effectiveness of various cultural techniques in reducing solar injury (SI) and increasing yield of bell pepper (Capsicum annuum var. annuum `California Wonder') in southern Oklahoma. Treatments included black plastic mulch, white plastic mulch, straw mulch, living rye, spunbonded polypropylene used as a plant canopy shade, and bare soil. Marketable yields from plots shaded with spunbonded polypropylene rowcovers were equal to or greater than those from other treatments each year. Two out of 3 years, plots with a black plastic soil mulch had marketable yields lower than those from other treatments. SI was reduced by rowcover shade.
Frostgard did not effectively promote the supercooling of flowering `Arking' strawberry (Fragaria ×ananassa Duch.) plants in the presence or absence of ice-nucleation-active bacteria when applied as a spray in laboratory experiments. Frostgard effectively promoted supercooling and reduced the ice propagation rate of aqueous solutions. Detached leaves infiltrated with Frostgard exhibited a negative linear relationship between freezing temperature and Frostgard concentrations from 0% to 20% (by volume). Leaves infiltrated with 20% Frostgard supercooled 1.7C lower than those infiltrated with distilled water. Ice propagation barriers in strawberry plants were observed. Individual leaves froze independently, and a thermal ice propagation barrier sometimes was observed at the crown.
Electrolyte leakage (EL) and ethane:ethylene ratio (EER) responses of pepper (Capsicumannuum L. Early Calwonder) leaf disks to temperature stresses were in close agreement. Midpoints of sigmoidal response curves following freezing stress were -4.6 and -4.4C for EL and EER, and 49.0 and 48.8C following high temperature stress. Evolution of ethane and EL were measured from disks infiltrated with a saturation series of 18-carbon fatty acids ranging from 0 to 3 double bonds. Only linolenic acid (18:3 n-3) stimulated ethane production and EL. In a second fatty acid experiment with 18- and 20-carbon acids with a double bond 3 (n-3) or 6 (n-6) carbons from the nonpolar end of the molecule, n-3 fatty acids stimulated more ethane than n-6 acids with the same number of carbons. Trienoic 18-carbon fatty acids stimulated more ethane than trienoic 20-carbon acids. Both 18-carbon acids yielded significantly greater EL than controls. Propyl gallate, a free radical scavenger, reduced ethane production without decreasing EL or K+ leakage.
The linear propagation of ice in peach [Prunus persica (L.) Batsch] shoots was measured during and after bloom. The mean rate of ice propagation was 9.3 ± 2.3 mm·s-1 at — 3C, with no significant differences observed among ‘Redskin’, ‘Reliance’, and ‘Redhaven’ cultivars. No barriers to the spread of ice were observed. Flowers froze within 30 sec from the time the advancing ice front passed their location on the stem. No ice-nucleation active bacteria were detected on the shoots or flowers.
Bell pepper (Capsicum anuum L.) leaves inoculated with Race 1 of Xanthomonas campestris pv. vesicatoria (XCV) produced more ethylene and methanol than water-infiltrated controls in studies with leaves attached or detached during inoculation and dissipation of water-soaking. `Early Calwonder 20R'. a pepper genotype resistant to Race 1 of XCV, evolved more ethylene and methanol than `Early Calwonder 10R' (susceptible) following syringe inoculation of detached leaves with ≈ 7 × 107 cells/ml. A light intensity of ≈ 500 μmol· m-2·s-1 during dissipation of water-soaking of attached leaves triggered more ethylene and methanol than covering inoculated leaves with aluminum foil. Volatile hydrocarbon production from leaves infiltrated with distilled water was not significantly affected by light intensity during dissipation of water-soaking. The lipid peroxidation products, ethane and pentane, were not detected by headspace sampling following bacterial inoculation.
One strategy to reduce postharvest losses of fruits to pathogens is to introduce organisms with biological control capabilities. Our objective was to determine the effectiveness of two yeast isolates in inhibiting lesion development caused by Botrytis cinerea (Bc) on freshly harvested apples differing in maturity. `Golden Delicious' apples were harvested on 29 Aug., 23 Sept., and 10 Oct. 1995. Apples receiving the seven treatments [control, wound, Cryptococcus humicola (Ch), Sporobolomyces roseus (Sr), Bc, Ch + Bc, Sr + Bc] were placed in plastic boxes with damp paper towels. Each day for 7 days, ethylene production and lesion diameter at the wound were recorded. Ethylene production was not affected by treatment, and increased with later harvest date. Lesion diameter on apples treated with Bc was smaller on the first harvest than on the second and third harvests. Sr provided partial control on the second and third harvests, and Ch completely inhibited lesion development except for day 7 of the third harvest.