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C.L. Chu

Our study found that storage temperature, storage atmosphere and growing region interactively affect the probability of internal browning disorder in `McIntosh' apples (Malus domestica Borkh.). Higher incidence of internal browning occurred in apples stored for 6 months at 1 °C (34 °F) in controlled atmosphere (CA) with 2.5% O2 + 1.5% CO2 or in CA with 1.0% O2 + 0.5% CO2 than apples stored at 1 °C in air or stored at 3 °C (37 °F) in air or CA conditions. The magnitude of the incidence of internal browning varied among apples harvested from different growing regions. Apples from London, Ontario, Canada were less tolerant to these two storage conditions and therefore greater number of fruit developed internal browning than apples from other regions. In addition, apples from the London growing region and stored at 1 °C in CA with 1.0% O2 + 0.5% CO2 had greater probability of internal browning than apples stored at 1 °C in CA with 2.5% O2 + 1.5% CO2. However, there was no difference between these two CA storage conditions in causing internal browning among apples harvested from other three growing regions. Few apples showed internal browning when they were stored at 3 °C, no matter of what storage atmosphere was used. Therefore, internal browning disorder can be avoided or significantly reduced by storing apples at 3 instead of 1 °C, in these two CA conditions. Internal browning disorder will not be a risk if apples are stored in air at 1 or 3 °C.

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C.L. Chu

`Bartlett' pears were harvested from four commercial orchards at their optimum harvest date and 3 or 7 days later (depending on grower orchard). Samples were held for 3 or 7 days before stored in cold storage and two controlled-atmosphere conditions: 1) cold storage at 1C; 2) regular CA storage (2.5% O2 + 1.0% CO2 at –1C); 3) low-oxygen CA (1.0% O2 + 0.2% CO2 at –1C). After 2 months of cold and CA storage, pears showed that postharvest prestorage holding temperature, affected the rate of change in weight loss, firmness, ground color, and senescent breakdown. After 4 months of CA storage, `Bartlett' pears maintained their quality at about 53–58 N of firmness. Firmness loss, peel ground color change, and senescent breakdown of `Bartlett' pears were affected by the holding temperature and the length of the holding period between harvest and storage. In conclusion, pear quality was reduced depending on the holding temperature and holding period between harvest and storage. CA storage maintained better pear quality than cold storage. Fast oxygen pulldown in order to establish CA condition sooner was essential to maintain better pear quality.

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C.Y. Chu and S.L. Knight

An efficient micropropagation system is being investigated to produce low cost and high quality miniature rose plants. Dormant literal buds of miniature roses were cultured on media containing MS, 30 g·l-1 sucrose, 8 g·l-1, and 25 combinations of NAA and BA. Initial explant growth was achieved on a medium containing NAA at 0.001-0.01 ppm and BA at 0.1 ppm. The highest multiplication rate was achieved when explants were subcultured on a medium containing MS, NAA at 0.01 ppm, BA at 2 ppm, and sucrose at 30 g·l-1. Growth was enhanced after culturing when dormant buds had more parental stem tissue. In addition, explants from the lowest two nodes with the shortest internode length exhibited the poorest growth. The higher the photosynthetic photon flux (PPF) (5 to 40 μmol·s-1m-2), the more quickly explants grew and aged. The most optimal PPF for initial growth was 20 μmol·s-1m-2. Subculture microcuttings of one cm or more in length grew vigorously one month after cuttings were dipped in 1000 ppm IBA and placed on a mist bench. Our results indicate that micropropagation of miniature roses has high potential for use in commercial industry.

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W.T. Liu, C.L. Chu, and T. Zhou

Fumigation with 1 mg·L-1 of thymol vapor retarded mycelial growth of Monilinia fructicola (G. Wint.) Honey. Mean colony diameter was reduced from 49 mm in the control to 13 mm when the conidia were cultured on potato dextrose agar. Fumigation of apricots (Prunus armeniaca L.) with 2 mg·L-1 of thymol vapor reduced the germination of M. fructicola conidia to 2% compared with 98% on untreated fruit. Microscopic observations showed that the spores fumigated with thymol were shrunken and had collapsed protoplasts. In in vivo experiments, surface-sterilized apricots and plums (Prunus salicina L.) were inoculated with conidia of M. fructicola by applying 20 μL of a spore suspension to wounds on the fruit, and then were fumigated with thymol or acetic acid. The incidence of brown rot was reduced to 3% and 32% when `Manch' apricots were fumigated with thymol or acetic acid at 5 mg·L-1, respectively, compared with 64% incidence in untreated fruit. Fumigation of `Violette' plums with thymol or acetic acid at 8 mg·L-1 reduced brown rot from 88% in the control to 24% and 25%, respectively. Fumigation of `Veeblue' plums with thymol at 4 mg·L-1 reduced brown rot from 56% in the control to 14%. Fumigation of apricots with thymol resulted in firmer fruit and higher surface browning, but total soluble solids and titratable acidity were not affected. Fumigation of plum with thymol resulted in higher total soluble solids, but firmness and titratable acidity were not affected. Thymol fumigation caused phytotoxicity on apricots but not on plums.

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D.C. Elfving, E.C. Lougheed, C.L. Chu, and R.A. Cline

Foliar daminozide (DZ) applications to `McIntosh' apple trees (Malus domestics Borkh.) increased fruit color, reduced preharvest drop, resulted in greater firmness at harvest and after air storage, delayed starch hydrolysis, and reduced fruit ethylene production at harvest and after storage. Foliar paclobutrazol (PBZ) reduced preharvest drop and flesh firmness loss if applied within 5 weeks after full bloom (WAFB). Later applications had no effect. PBZ did not influence the progress of starch hydrolysis or ethylene production at harvest but reduced poststorage ethylene production in one season. Stem-cavity browning and brown core were increased by PBZ applied at 5 and 9 WAFB in 1987. In 1988, fruit soluble solids content (SSC) was reduced by a double application of PBZ and by uniconazole (UCZ). UCZ had little effect on `McIntosh' fruit other than the reduction in SSC. PBZ applications were less consistent in their effects than DZ. Chemical names used: butanedioic acid mono(2,2-dimethylhydrazide) (daminozide); ß-[(4-chlorophenyl) methyl]-α- -(l,l-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol); ß-[(4-chlorophenyl)methylene]-α-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (uniconazole).

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Wayne Brown, Theo J. Blom, George C.L. Chu, Wei Tang Liu, and Lisa Skog

The sensitivity of easter lilies (Lilium longiflorum) to either ethylene or methane (products of incomplete burning in gas-fired unit heaters) was tested during rooting [3 weeks at 18 °C (65 °F)], vernalization [6 weeks at 6 °C (43 °F)] and subsequent greenhouse forcing (15 weeks at 18 °C). Starting at planting, easter lilies were exposed for one of seven consecutive 3-week periods (short-term), or for 0, 3, 6, 9, 12, 15, 18, or 21 weeks starting at planting (long-term) to either ethylene or methane at an average concentration of 2.4 and 2.5 μL·L-1(ppm), respectively. Short- or long-term exposure to ethylene during rooting and vernalization had no effect on the number of buds, leaves, or plant height but increased the number of days to flower. Short-term exposure within 6 weeks after vernalization reduced the number of buds by 1 bud/plant compared to the control (no ethylene exposure). However, extensive bud abortion occurred when plants were exposed to ethylene during the flower development phase. Long-term exposure to ethylene from planting until after the flower initiation period resulted in only two to three buds being initiated, while continued long-term exposure until flowering caused all flower buds to abort. Short-term exposure to methane at any time had no effect on leaf yellowing, bud number, bud abortion, or height and had only a marginal effect on production time. Long-term exposure to methane from planting until the end of vernalization increased both the number of buds, leaves and height without affecting forcing time, leaf yellowing or bud abortion.