Acetic acid (AA) as a vapor at low concentrations was effective in preventing fruit decay by postharvest fungi. Fumigation with 2.7 or 5.4 mg AA/liter in air at 2 and 20C reduced germination of Botrytis cinerea Pers. and Penicillium expansum Link conidia to zero after they had been dried on 0.5-cm square pieces of dialysis tubing. Decay of `Golden Delicious', `Red Delicious', and `Spartan' apples (Malus domestica Borkh.) inoculated with 20 μl drops of conidia of B. cinerea (1.0 × 105 conidia/ml) or P. expansum (1.0 × 106 conidia/ml) was prevented by fumigating with 2.0 and 2.7 mg AA/liter, respectively. Tomatoes (Lycopersicon esculentum Mill.), grapes (Vitis vinifera L.), and kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et R. Ferguson var. deliciosa] inoculated with B. cinerea or navel oranges (Citrus sinensis L.) inoculated with P. italicum Wehmer did not decay when fumigated with 2.0 mg AA/liter at 5C. AA fumigation at low temperatures (1 and 5C) with 2.0 or 4.0 mg AA/liter prevented decay of `Spartan' and `Red Delicious' apples and `Anjou' pears (Pyrus communis L.) inoculated with B. cinerea and P. expansum, respectively. `Spartan' apples immersed in a suspension of P. expansum conidia (1.4 × 105 conidia/ml) and fumigated with 2.7 mg AA/liter at 5C had an average of 0.7 lesions per fruit compared to 6.1 for nontreated fruit. Increasing the relative humidity from 17% to 98% increased the effectiveness of AA fumigation at 5 and 20C. At the concentrations used in our trials, AA had no apparent phytotoxic effects on the fruit. The potential for commercial fumigation with AA to control postharvest decay of fruit and vegetables appears promising.
P.L. Sholberg and A.P. Gaunce
A.L. Moyls, P.L. Sholberg, and A.P. Gaunce
A fumigation technique using brief exposure of fruit to a low concentration of acetic acid vapor was combined with modified-atmosphere packaging to reduce storage rots and increase shelf life of grapes (Vitis vinifera L.) and strawberries (Fragaria ×ananassa Duch.) by two or three times normal values. Both commodities were inoculated with spores of Botrytis cinerea Pers. before fumigation with acetic acid, packaging, and storage at lowered O2 levels. Fumigation with acetic acid at 8.0 mg·L–1 followed by modified-atmosphere packaging for 74 days at 0 °C reduced the percentage of rotted grapes from 94% to 2%. Strawberries fumigated with acetic acid at 5.4 mg·L–1 were free of decay compared to 89% rotted for the control fruit stored for 14 days at 5 °C.
Thomas S.C. Li, K.E. Bedford, and P.L. Sholberg
Traditionally, American ginseng (Panax quinquefolium L.) seeds are stratified for 18 to 22 months, before seeding, in a sandbox buried outdoors in late August or early September. Uncontrolled fluctuating temperature and moisture levels and the presence of pathogenic organisms in the seed box can cause seeds to sprout prematurely, rot, dry out and die. A study was initiated to shorten the lengthy stratification period, and to increase seed viability and percentage of germination by stratifying seeds indoors under a controlled environment. Seeds were subjected to various periods of warm [15 or 20 °C (59 or 68 °F)] and cold [2 °C (35.6 °F)] temperature stratification regimes in growth chambers. Embryo growth and viability, and seed moisture content were tested periodically during stratification. The best warm regime for embryo development, seed viability and germination after subsequent cold treatment was 15 °C (59 °F). The first “split” seeds, indicating incipient germination, were observed after 3 months of warm [15 °C (59 °F)] and 4 months of cold [2 °C (35.6 °F)] treatment, when average embryo length reached 6 mm (0.24 inch). Greenhouse germination of stratified seeds was as high as 80%. The results from this study indicate that good germination is possible when ginseng seeds are stratified indoors under a controlled environment and seeds can be made to germinate at any time of the year.
J.E. Cossentine, P.L. Sholberg, L.B.J. Jensen, K.E. Bedford, and T.C. Shephard
Wooden fruit bins are a source of diapausing codling moth and postharvest pathogenic fungi. The redistribution of codling moths within bins is a problem where codling moth populations are being controlled by areawide codling moth sterile release programs, mating disruption programs, or both. Laboratory and fumigation chamber trials were carried out to determine the impact of relatively low levels of carbon dioxide on late-instar codling moth (Cydia pomonella L.) and two postharvest fruit pathogens, Penicillium expansum Link ex Thom and Botrytis cinerea Pers. ex Fr. Fumigation of diapausing codling moth with 40% CO2 in laboratory trials resulted in over 60% mortality after only 6 days of exposure and mortality increased with time of exposure. Significant mortality (68%) of diapausing codling moth larvae occurred after 14 days of exposure in the laboratory to 13% CO2 and a mean of 88% mortality was recorded after fumigation for 20 days. A significant number of P. expansum (46%) spores failed to germinate after laboratory exposure to 13% CO2 for 12 and 18 days respectively. Close to 100% of the P. expansum spores failed to germinate by day 20. When diapausing codling moth larvae and spores from both plant pathogens were placed in wooden fruit bins and fumigated for 21 days at 13% CO2, 75% of the diapausing codling moths died and 80% of the P. expansum spores failed to germinate. No effect on B. cinerea was observed.