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  • Author or Editor: L. Proebsting x
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Abstract

An accurate frost alert system is the first step in planning for frost protection. Forecasting methods are being updated by statistical studies from historical records at the fruit frost forecast stations. It is planned to put information in a computer at Yakima, Washington, which will permit retrieval of data for all past days with meteorological characteristics similar to the day of the forecast (7). Florida uses a regression-based model to relate forecast temp of 300 stations to actual forecasts for 15 key stations. Forecasts are updated at 10 pm based on new weather data and reports from growers on current conditions including extrapolations made with inexpensive net radiometer measurements (14, 23).

Open Access

Abstract

As pomologists, our primary responsibility is to fruit trees growing in the frequently hostile environments which we insist on calling “fruit sites.” For most of the country the most consistently and effectively hostile element in a fruit tree’s environment is low temperature.

Open Access

Abstract

There is need for rapid determination of cold resistance of plants in the field. Exotherm analysis was adapted to such needs for dormant fruit buds of peach (Prunus persica (L.) Batsch). Buds were excised with 1-2 mm of vascular tissue attached and then held near the thermocouple junction with an A1 foil wrap. Exotherms could be recorded from most of 25-30 buds per junction. Resolution was improved by slow rates of temperature decrease in the critical range (near l°/hour). At high rates of temperature decrease (8 to 15°/hour) buds were killed at higher temperatures. The distribution of bud mortality with temperature was very close to the standard skewed curve for buds evaluated by the tissue browning method.

Open Access

Differential thermal analysis (DTA) was used to measure deep supercooling in flower buds of Prunus dulcis Mill., P. armeniaca L., P. davidiana (Carr.) Franch, P. persica (L.) Batsch, three sweet cherry (P. avium L.) selections, and `Bing' cherries (P. avium L.) during Winter 1990-91 and 1991-92. Low temperatures in Dec. 1990 killed many flower buds. After the freeze, dead flower primordia continued to produce low-temperature exotherms (LTEs) at temperatures near those of living primordia for >2 weeks. In Feb. 1992, cherry buds that had been killed by cooling to -33C again produced LTEs when refrozen the next day. As buds swelled, the median LTE (LTE50) of dead buds increased relative to that of living buds, and the number of dead buds that produced LTEs decreased. LTE artifacts from dead flower priimordia must be recognized when DTA is used to estimate LTE50 of field-collected samples.

Free access

Abstract

Low temperature injury to flower buds of peach [Prunus persica (L.) Batsch.] and sweet cherry [Prunus avium L.] and to one-year-old shoots of peach and apricot (Prunus armeniaca L.) during fall and winter was more severe on trees treated with paclobutrazol (PP 333) than on those not treated. Paclobutrazol had no measurable effect on cold resistance of apricot buds or cherry shoots. The average date of 1st bloom was advanced by one to 2 days in all 3 species by paclobutrazol.

Open Access

In Dec. 1990, sweet cherry (Prunus avium L.) selections varied in floral bud kill from 9% to 92% following exposure to severe cold. In the following winter, the hardiness of two hardy and two tender selections was analyzed by differential thermal analysis (DTA) to screen selections for hardiness. In a mild winter, when buds remained at their minimum hardiness level, the hardy selections consistently were > 2C hardier than the tender selections. About one-half of that hardiness difference was associated with differences in tissue water content, the other half with unknown factors. Buds of the tender selections began to develop earlier and bloomed earlier than the hardy selections. DTA analysis of floral bud populations separated selections that clearly differed in floral bud hardiness.

Free access

Abstract

As ‘Bing’ cherries (Prunus avium L.) matured, the quality characteristics changed rapidly but not consistently from year to year over 9 years. Color increased rapidly and at similar rates in all years. Soluble solids increased rapidly during years when the crop was light, but slowly when the crop was heavy. When crops were light, the fruit was full sized before color reached fresh market standards and there was no further growth as the fruit continued to mature. With heavy crops the fruit increased in size until they began to shrivel. Early in maturation the fruits were very firm, but they softened rapidly during the early fresh market stage, then more slowly.

Open Access
Authors: and

Flower buds of 20 Prunus species representing 4 subgenera were collected during winter and spring of 1989-90. Buds were preconditioned at +3° or 7°C to test their minimum hardiness level (MHL) or the rate of hardiness increase. DTA revealed that most of the prunus species have flower primordia that supercool. The subgenus Padus have racemose inflorescences and do not deep supercool during dormancy. P. besseyi, P. nigra and P. americana had small exotherms between -22° and -27°C while P. davidiana and P. subhirtella had larger exotherms at higher temperatures. Exposure of flower buds to -7°C shifted LTES to lower temperatures and/or reduced the size of LTE, which became undetectable for many species including P. nigra and P. americana. P. davidiana and P. subhirtella increased hardiness by 6°/day at -7° while dormant. Deacclimation coincided with an increase in LTE50 and the development of xylem vessel elements in the bud axis, calyx and filaments as indicated by dye movenent. P. davidiana was the least hardy species and required only 700 chill units to satisfy the chilling requirement, while P. nigra and P. americana had LTE average of -26°C at MHL and required over 1000 chill unit accumulation.

Free access

Flower buds of 20 Prunus species showed quite different strategies to cope with low temperatures. Buds of most species deep supercooled. The two hardiest species, both from the subgenus Padus (P. padus L. and P. virginiana L.), did not supercool and survived -33C with no bud kill. Prunus serotina J.F. Ehrh., also in Padus, did supercool. Prunus nigra Ait., P. americana Marsh, P. fruticosa Pall., and P. besseyi L.H. Bailey had a low minimum hardiness level (MHL), small buds, and a low water content. Exotherms were no longer detectable from the buds of these species after 2 days at -7C and some buds survived -33C. Prunus triloba Lindl. and P. japonica Thunb. were similar to that group, but no buds survived -33C. Prunus davidiana (Carriere) Franch., P. avium L., and P. domestica L. had a relatively high MHL but hardened rapidly when the buds were frozen. Prunus persica (L.) Batsch., P. subhirtella Miq., P. dulcis (Mill) D. A. Webb, and P. emarginata (Dougl. ex Hook) Walp. deep supercooled, had large flower buds and a high MHL, and were killed in the Dec. 1990 freeze. Prunus salicina Lindl., P. hortulana L.H. Bailey, P. armeniaca L., and P. tomentosa Thunb. were in an intermediate group with a moderately low MHL and a moderate rate of hardiness increase while frozen. Prunus dulcis and P. davidiana had a low chilling requirement and bloomed early, whereas P. virginiana, P. fruticosa, P. nigra, and P. domestica had high chilling requirements and bloomed late.

Free access

Flower buds of Prunus serotina Ehrh. produced high temperature exotherms (HTEs) and low temperature exotherms (LTEs). Supercooling in P. serotina occurred during full dormancy in December and early January but disappeared thereafter, whereas no supercooling was observed in P. padus L. or P. virginiana L. Both intact and detached lnflorescences of P. serotina supercooled and froze as a unit and not as individual florets. Exotherms in dehydrated parts occurred at lower temperatures than in hydrated parts. Dormant buds of P. serotina lost the detectable exotherms when kept at -7C for 2 days, while buds stored at 3C exhibited LTEs between -20 and -26C. Dormant Morescences of P. serotina were filled with elongated procambium and pith cells. In contrast, P. padus and P. virginiana had differentiated xylem vessel elements (XVE) the entire length of the inflorescence and did not supercool. Bud scales and bud axis of P. serotina were the flower parts where water apparently migrated during storage at 3 and -7C. This was not observed for P. padus and P. virginiana flower buds. The rate of water migration from the inflorescences to bud scales and axis probably plays a role in the freezing behavior of P. serotina.

Free access