Commercial N fertilizer formulations, ammonium nitrate, calcium nitrate, sodium nitrate, potassium nitrates (15-0-14 and 13-0-44) applied at 84 and 168 kg N/ha in 3 or 5 split applications did not affect total marketable yield of dry onion. Application frequencies causing an increase in total amount of N applied during the spring months (Feb.-Apr.) increased marketable yield by 5 MT/ha. Bulb decay was the highest when ammonium nitrate was applied, whereas the least number of decayed bulbs resulted from sodium nitrate applications. Plants grown with potassium nitrate (13-0-44) were most susceptible to cold injury. Ammonium nitrate and sodium nitrate applications produced the highest percentage of onions that bolted. The lowest percentage of plants showing bolting incidence resulted from calcium nitrate applications. Bolting of onions was closely associated with rapid growth and increased onion size. However, cold injury and bulb decay were not influenced by these growth factors.
William S. Conway, Rowel B. Tobias, Stephane Roy, Alley E. Watada, Stephane Roy, William P. Wergin, and Carl E. Sams
Decay caused by Botrytis cinerea is significantly reduced by increasing the calcium concentration of apple fruit tissue. Electron microscope studies have revealed that cracks in the epicuticular wax may be an important pathway by which calcium penetrates into the fruit and increases the calcium concentration. In fruit inoculated with B. cinerea, the decay induced compositional changes in the cell walls of high-calcium fruit were smaller than those observed in the low calcium treatment. The effect of calcium in reducing decay is associated with maintaining cell wall structure by delaying chemical changes in cell wall composition. B. cinerea produced five polygalacturonase isozymes in vitro but only one in vivo. Among the cations studied-m was the most potent inhibitor of polygalacturonase activity in in vitro studies. Its mode of inhibition appears to involve the alteration of substrate availability for hydrolysis, rather than any direct effect on the active sites of the enzyme.
Clusters of four varieties of table grapes were packed in TKV lugs and fumigated with 4, 6, or 8 Deccodione Smoke Tables (DST) for a period of 30 minutes in a fumigation chamber. After fumigation, inoculum of Botrytis cineraria was placed among the berries in the clusters in predetermined locations. Fruit was stored at 0C and high relative humidity for up to 16 weeks. Fruit was examined at 4, 8, 12, and 16 weeks of storage. Decay control index, freshness of stems, and bleaching of pigments around the capstem was recorded at each evaluation time. Size of aerosol particles was determined. Satisfactory control of decay was obtained with 8 DSTs. Lower doses failed to give satisfactory decay control. Bleaching of capstems typically seen with sulfur dioxide fumigation was not noticed with DST fumigation.
John R. Stommel, Robert W. Goth, and Kathleen G. Haynes
Bacterial soft rot of bell pepper (Capsicum annuum L.), caused by Erwinia spp., is a destructive postharvest market disease of this crop. Control is presently limited to chemical treatments. Methods of inoculating pepper fruit were evaluated to develop a reliable technique for soft rot resistance screening. Erwinia carotovora subsp. atroseptica (Eca) was isolated from partially decayed field grown pepper fruit at Beltsville, MD. Fruit were inoculated with suspensions of Eca via: (a) abrasion with Carborundum, (b) hypodermic puncture, or (c) non-wounded tissue. Inoculated fruit were held under high humidity at 21-23C for two to three days prior to scoring. Degree of soft rot decay was determined via fruit weight loss from two replicates of the experiment over the course of the growing season. Significant differences were not evident among varieties or experiment dates for weight loss due to tissue decay. Hypodermic puncture inoculation was superior to other methods for inducing fruit rot.
Luis Luchsinger, Alvaro Villalobos, and Antonio Lizana
Postharvest response to high CO2 controlled atmosphere (CA) was studied in the blueberry (Vaccinium corymbosum L.) cultivar Elliot. Fruit was stored at 0 °C, 90% relative humidity and 15%, 18%, and 21% of CO2 and 5% of O2 and in air (0.03% CO2 and 21% O2). Evaluations were performed after 30 and 60 days of storage and an aditional period of 3 and 6 days at 10 °C (ripening period). Parameters meassured were: color (lightness, hue, and chroma), firmness, soluble solids (SS), titrable acidity (TA), SS/TA ratio, pH, weight loss, decay, physiological disorders, and appearance. The CA caused a positive effect, preserving the quality of the fruit in storage, by decreasing the respiratory rate and decay incidence. The 15% CO2 controlled atmosphere presented the best firmness and lowest decay. Acceptable conditions of quality were kept for 60 days of storage.
B.A. Edmunds and G.J. Holmes
Most sweetpotato packers use the fungicide Botran (dicloran) to reduce losses caused by Rhizopus soft rot. However, certain markets are no longer accepting Botran-treated sweetpotatoes and packers are searching for suitable alternatives. We evaluated 12 products applied as dip treatments for their ability to control Rhizopus soft rot. Sweetpotato roots (`Hernandez') were wounded and artificially inoculated with a Rhizopus spore suspension (106 spores/mL). Roots were dipped for 30 sec. in treatment solutions and stored at about 65 °F. After 10 days, roots were evaluated for incidence of decay. The inoculation method produced 100% decay in nontreated roots. Bio-Save 11LP and Pristine, a biopesticide (strain of Pseudomonas syringae) and reduced-risk chemistry respectively, both provided very high levels of decay control. Other products such as Biosave 10LP (a different strain of P. syringae), Scholar and Freshgard 25 were marginally effective, while copper ionization, bleach, and Storox were ineffective against Rhizopus soft rot.
C.L. Barden, G.M. Greene, L.A. Hull, and K.D. Hickey
Tufted apple bud moth (TABM) damage had little or no effect onthe soluble solids, starch, or firmness of stored apples. Decay increasedfrom 0% to 18% in `Golden Delicious' and from 2% to 6% in `Delicious' between control fruit and those with the most TABMdamage (> 10 mm aggregate diameter, significant linear relationships R 2 = 0.41 and 0.12, respectively). Weight loss increased 2- to 3-fold in apples in the highest damage category. These results show that the post-storage quality of apples with slight TABM damage (<5 mm aggregate diameter) does not decline more rapidly than undamaged fruit. The best controlled atmospheres for storing undamaged fruit were also the best for storing damaged fruit. Widely varying fungicide spray programs did not influence the quality or decay levels of apples following storage. However, even those fruit from blocks with few or no sprays had very little decay due either to low inoculum or unfavorable environmental conditions.
Charles F. Forney, Stephanie Bishop, Michele Elliot, and Vivian Agar
Extending the storage life of fresh cranberries (Vaccinium macrocarpon Ait.) requires an optimum storage environment to minimize decay and physiological breakdown (PB). To assess the effects of relative humidity (RH) and temperature on storage life, cranberry fruit from four bogs were stored over calcium nitrate, sodium chloride, or potassium nitrate salts, which maintained RH at 75%, 88%, and 98%, respectively. Containers at each RH were held at 0, 3, 5, 7, or 10 °C and fruit quality was evaluated monthly for 6 months. Both decay and PB increased with increasing RH in storage. After 6 months, 32%, 38%, and 54% of fruit were decayed and 28%, 31%, and 36% developed PB when stored in 75%, 88%, and 98% RH, respectively. The effects of RH continued to be apparent after fruit were removed from storage, graded, and held for 7 days at 20 °C. The decay of graded fruit after 4 months of storage in 75%, 88%, or 98% RH was 10%, 13%, and 31%, respectively, while PB was 12%, 12%, and 17%, respectively. Fresh weight loss decreased as RH increased averaging 1.9%, 1.4%, and 0.7% per month for storage in 75%, 88%, and 98% RH, respectively. Fruit firmness was not affected by RH. Storage temperature had little effect on decay. However, PB was greatest in fruit stored at 10 °C, encompassing 55% of fruit after 5 months of storage. When graded fruit were held an additional 7 days at 20 °C, decay and PB were greater in fruit previously stored at 0 or 3 °C than at 5, 7, or 10 °C. Fresh weight loss increased as storage temperature increased, averaging 0.8%, 1.0%, 1.3%, 1.7%, and 1.9% per month at 0, 3, 5, 7, and 10 °C, respectively. Fruit firmness decreased during storage, but was not affected by storage temperature. To maximize storage and shelf life, cranberry fruit should be stored in a RH of about 75% at 5 °C.
P. Perkins-Veazie and J.K. Collins
Okra stored at 3C in 12.7-pm high-density polyethylene (HDPE) bags developed less chilling injury than fruit stored in plastic boxes. Okra held in HDPE bags at 12.5C for 8 days had more decay and reduced overall appearance than fruit held in plastic boxes. `Emerald Green' okra lost more weight in storage than the other four cultivars regardless of temperature or storage duration, while `Blondy' had the most decay. `Annie Oakley' and `Clemson Spineless' had better shelf life than the other cultivars.
Abdel Hameed M. Wassel and Moawad Abdel Hameed
Different treatments were carried out inluding that achieved in the modern packing houses which are established for preparing citrus fruits for export. Decay of Washington navel oranges was reduced due to spraying benlate at 500 and 750 ppm as a preharvest treatment. Fruits coated with thin film of wax containing benlate were less susceptible to decay than any other treatment including that carried out in the packing houses. On the other hand no adverse effect could be noticed for this treatment on the chemical properties of the fruils. Thereby, the disinfectant process which is followed by rinsing could be eliminated, conseqently, raising the productive capacity of these packing houses.