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Open access

Noel F. Sommer, Jack R. Buchanan, and Robert J. Fortlage

Abstract

Pectolytic enzymes of fungal origin (mostly Rhizopus spp.) contaminating raw apricot fruits may not be completely inactivated during thermal processing (i.e., 100°C/18 minutes). The remaining enzymes may seriously macerate fruits over a 6-to-18 month period after canning. Inactivation of crude enzymes was near exponential over a 4-log-cycle reduction of activity after heating at 121°C for up to 20 minutes. Serious overcooking of fruit at elevated temperatures discouraged further studies of heat inactivation. Laboratory and cannery tests demonstrated that a dilute spray or dip of sodium hydroxide (i.e., 1n/1 minute) at ambient temperature offered an inexpensive, simple means of inactivating fungal enzymes contaminating apricot fruits. Crucial to success was accurate maintenance of solution concentration and contact times. For adequate penetration of solutions, the fruit skins over fungal lesions required breaking. Jet sprays broke the skin over the Rhizopus softrot lesions if they contacted all fruit surfaces.

Open access

D. W. Buchanan, J. F. Bartholic, and R. H. Biggs

Abstract

A delay in flowering of up to 14 days was obtained in the 1974-75 and 1975-76 seasons with ‘Sungold’ and ‘Sunrich’ nectarines and ‘Flordagold’ peach [Prunus persica (L.) Batsch] by intermittent sprinkling when tree temperatures exceeded 18°C. Flowering and foliation was also hastened in 1974-75 on trees shaded with 55% saran cloth. Sprinkling did result in heavy bud abscission on certain cultivars. Shading and sprinkling lowered cambial temperatures by 5 to 10° and delayed harvest from 5 to 7 days.

Open access

Jack R. Buchanan, Noel F. Sommer, and Robert J. Fortlage

Abstract

Aflatoxin production by Aspergillus flavus growing on potato-dextrose agar, cooked rice medium, and raw pistachio nuts, was suppressed in 2 ways. First, CO suppressed growth of the fungus if O2 was low. Second, CO suppressed aflatoxin production, evidently by interfering with aflatoxin metabolism, even if the atmosphere permitted nearly normal fungal growth. Fungal growth was equal or better in 2% O2 than in air (20.8% O2). Addition of 10% CO slowed growth materially only if O2 was low, but aflatoxin accumulation was suppressed by CO only slightly more in low O2 atmospheres. After growth for 32 days at 20°C in cooked rice medium or raw pistachios in an atmosphere containing 2% O2 + 10% CO, aflatoxin was <2% of the production in an atmosphere containing 2% O2 or air without CO.

Open access

D. W. Buchanan, R. H. Biggs, and J. F. Bartholic

Abstract

The cambium of both ‘Early Amber’ peach and ‘Sungold’ nectarine, Prunus persica L. Batsch gained cold hardiness from November through January even though day and night temperatures were above 15°C. Cultivars attained the greatest hardiness in January, surviving temperatures of -12°C. ‘Early Amber’ maintained its hardiness until just prior to bud break (February 8) and decreased thereafter. ‘Sungold’ remained somewhat resistant to cold until February 15 and gradually lost hardiness until March 8. Characteristically the low chilling cultivars reached an acclimation base higher than reported for cultivars adapted to higher latitudes.

Open access

D. W. Buchanan, R. H. Biggs, and J. F. Bartholic

Abstract

‘Early Amber’ peach and ‘Sungold’ nectarine (Prunus pérsica (L.) Batsch) growing in north central Florida acclimated sufficiently to cold to withstand −14° to −15°C although day temperatures were above 20° and night temperatures were above 7°. Rest and acclimation to cold in short chilling cultivars occur at higher temperatures than in long chilling ones. However, Florida cultivars also become acclimated to a lesser degree. Wood chips taken from the trunks of ‘Early Amber’ trees in January survived −10°C but were killed at −13°. Young trees were killed at −11° but survived −10° in January. Subsequent death of tissue occurs as a result of low temperature stress.

Open access

R. M. Carlson, J. R. Buchanan, T. E. Kapustka, and K. Uriu

Abstract

The correction of K deficiency in fruit trees frequently has not been obtained due to failure of surface applications of fertilizer K to penetrate into root zones. The effectiveness of gypsum, as a displacing agent, to move K downward was studied using soil columns. Postassium applied at the surface accumulated in a shallow zone of K-rich soil. Increasing amounts of gypsum resulted in displacing the K to both a greater depth and a broader zone in the soil.

Open access

J. A. Anderson, D. W. Buchanan, and R. E. Stall

Abstract

Strategies for reducing bacterially induced frost damage to tender plants were examined. Introduction of the competitive bacterium, Erwinia herbicola M232A (not active in ice nucleation) did not lower the temperature at which freeze injury of tomato shoots occurred. Streptomycin was effective in reducing freeze damage of tomato shoots only when mixed with the Pseudomonas syringae suspension prior to plant inoculation. Spectinomycin, another aminoglycoside, was effective in reducing frost damage to tomato plants due to P. syringae. Bacteria present intercellularly (within the plant) may play a significant role in bacterial ice nucleation.

Open access

J. A. Anderson, D. W. Buchanan, R. E. Stall, and C. B. Hall

Abstract

Pseudomonas syringae van Hall, an ice nucleation active (INA) bacterium, increased frost susceptibility of tomato (Lycopersicon esculentum Mill.) and soybean (Glycine max L.) when sprayed on leaves prior to low temperature stress. Tomato and soybean plants inoculated with INA bacteria were nucleated and frozen at −4° and −5°C respectively. Control plants that were free of INA bacteria supercooled and survived to −8°. A threshold INA bacterial concentration of about 4 × 105 cells/ml was necessary for ice nucleation. Ice nucleating active bacteria preconditioned at 2° showed a marked increase in efficiency of ice nucleation. Preconditioned INA bacteria had ice nucleation temperatures 5° higher than INA bacteria held at 21°.

Open access

D. W. Buchanan, R. H. Biggs, J. A. Blake, and W. B. Sherman

Abstract

Sprays of various concentrations of Fruitone, a commercial formulation containing 2-(3-chlorophenoxy)-propionamide and 2-(3-chlorophenoxy)-propionic acid (3CPA) or of 2-chloroethylphosphonic acid (Ethrel) were applied to ‘Early Amber’, a short cycle (70 days), low-chilling (300 hours < 45 F) peach grown in Florida. Adequate thinning of fruits was obtained from treatments during the 4-day interval that the endosperm was changing from the free nuclear to the completely cellular stage. The most satisfactory concn of 3CPA and Ethrel for fruit thinning were 300 and 30 ppm, respectively. All concn of 3CPA and Ethrel which caused fruit thinning also increased ethylene concn in the fruit.

Open access

J. R. Buchanan, N. F. Sommer, R. J. Fortlage, E. C. Maxie, F. G. Mitchell, and D. P.H. Hsieh

Abstract

Concentrations of patulin in blue mold lesions caused by Penicillium expansum Lk. ex Thom in pears and stone fruits were similar to those reported for apples. Of fruits tested, only the plum was a poor substrate for accumulation of the mycotoxin. The total patulin within disease lesions increased as the lesions enlarged. However, the concentration of patulin varied considerably, with the largest lesions usually yielding the lowest concentrations. Little or no patulin permeated healthy tissue surrounding the disease lesions unless fruits were overripe or had senescent breakdown.