Acute effects of high-nitrate/low-sulfate acidic fogs with a pH of 2.5 and 3.0 were investigated on 3.5to 4-week-old Phaseolus lunatus L. in a series of replicated trials. After 24 hours, CO2 assimilation rates of primary leaves were reduced by at least one-third by 3-hour fogs with a pH value of 2.5 as compared to control plants treated with a fog of pH 6.3. A 3-hour fog at pH 3.0 reduced C0 2 assimilation a minimum of 20%. Stomatal resistance increased in primary leaves of plants exposed to an acidic fog of pH 2.5 by > 37% compared to plants subjected to pH 6.3 fogs. StomataI resistances in leaves exposed to pH 3.0 fogs increased at least 27%. However, internal CO2 concentrations were not significantly different between controland acidfogged plants at any pH. Standardizing plants for similar CO2 assimilation rates allowed statistical separation of photosynthetically important variables as compared to unstandardized experimental designs with higher interplant variability. Methacrylate plastic sections of foliar lesions resulting from exposure to pH 2.0 fogs revealed that damage usually progressed vertically from the upper to lower epidermis. Xylem was less susceptible to damage than other tissues.
John T. Trumble and Gregory P. Walker
The biochemistry of flowers is very complex, depending not only on the specific anthocyanin present but also on vacuolar pH, presence of metal ions, type of co-pigment present, and the molar ratio of co-pigment to anthocyanin. Because of the wide array of different flower colors, Petunia hybrida is an excellent model system to study the genetic interaction of all of these factors. The segregation of the different flower colors in an F2 population from a red × violet outcross could be explained through the combined inheritance of anthocyanin pigmentation and pH. The inheritance of anthocyanin pigmentation was controlled by two independent genes (hf and Mf) that followed simple Mendelian genetics. The inheritance of pH was more complex, being controlled by two independent co-dominant genes (Ph1 and Ph2). Linkage of the various pH and anthocyanin genes prevented the expression of all of the potential gene combinations.
Robert C. Musselman, Jerry L. Sterrett, and Victor Voth
Field plots of strawberry (Fragaria × ananassa Duch cv. Chandler) were exposed to two 1-hr nighttime simulated fog episodes per week at specific acidities from pH 1.6 to 3.2, or no fog. Small, distinct, irregularly shaped, rust-colored lesions developed on foliage and fruit after a single 1-hr exposure to acidic fog at low pH. Fog episodes at pH 1.6 resulted in death of the plants after 8 weeks. Strawberries tolerated short-term exposure to acidic fog at pH 2.0 or higher, with little or no negative effect on growth, yield, or fruit soluble solids. However, calyx injury from acidic fog reduced marketability at pH levels up to 2.8. ‘Douglas’, ‘Chandler’, ‘Selva’, ‘Parker’, and ‘Soque!’ differed in magnitude of response to acidic fog in greenhouse exposures.
Robert Saftner, Judith Abbott, and Arvind Bhagwat
A calcium ascorbate processing formulation is commercially used to prevent browning on fresh-cut apple slices but has little to no antimicrobial activity. Intact apples were surface-sanitized with chlorine water at 20 °C or water at 60 °C, processed into fresh-cut slices, and the slices dipped in a calcium ascorbate formulation or a solution of isoascorbic acid, calcium, and N-acetylcysteine at pH 2.0. The commercial and experimental dip treatments similarly maintained cut surface color, Kramer firmness, and aromatic volatile concentrations during 3 weeks of storage at 5 °C in air. Freshly prepared experimental dip treatment reduced the native bacterial population of the apple slices prepared from sanitized apples better than the calcium ascorbate treatment. With repeated use, the experimental dip solution became adulterated with apple tissue and juice and rapidly lost its antibacterial activity. Concomitantly the pH of the dip solution increased to 2.6 or higher. The lost antibacterial activity could be restored in highly contaminated experimental dip solutions by back titrating to pH 2.0. The experimental dip treatment also reduced the overall yeast and mold population, but specifically enhanced growth of Penicilliumexpansum on slices prepared from chlorine-sanitized apples. A hot water pretreatment of intact apples at 60 °C for 3 min prior to fresh-cut processing essentially eliminated P. expansum contamination on the slices. The results indicate that the experimental dip treatment is a promising alternative to calcium ascorbate treatment for analytical and microbial quality retention of fresh-cut apple slices during storage, especially when the apple slices are processed from hot water-treated apples.
Randy G. Gardner and Dilip R. Panthee
) source PI 126445 and NC EBR-2, which has moderate foliage resistance and a high level of stem lesion resistance to early blight derived from Campbell 1943 ( Gardner, 1988 ). The Ph-2 gene for late blight resistance was derived from Richter's wild tomato
Dilip R. Panthee and Randy G. Gardner
‘Mountain Bebe’ is the F 1 hybrid of NC 7 Grape × NC 8 Grape. It is resistant to late blight ( Ph-2 and Ph-3 genes), tomato spotted wilt virus ( Sw-5 gene), and fusarium wilt races 2 and 3 ( I-2 and I-3 genes). The hybrid has a compact
Dilip R. Panthee and Randy G. Gardner
blight ( Ph-2 gene) ( Phytophthora infestans Montagne, Bary), and Tomato spotted wilt virus (TSWV) ( Sw-5 gene). It has a compact indeterminate plant with short internodes conferred by the brachytic ( br ) gene and has dark red fruit with high total
Andrea E. Fiebig, J.T.A. Proctor, D.P. Murr, and R.D. Reeleder
Field experiments over 2 years were used to determine the effect of ethephon on: plant growth, weight of berries, proportion of red, green and immature berries, and root weight (economic yield) of 3-year-old north american ginseng plants (Panax quinquefolius L.). Ethephon sprays applied during bloom that thoroughly wetted the foliage and inflorescences immediately induced crop canopy descent (epinasty) exposing inflorescences and subsequently reducing plant height. Within a week the desired inflorescence and peduncle browning and flower drop took place. In each of four experiments ethephon, over the range 500 to 4000 mg·L-1, reduced berry weight and percent red berries, and increased the percent immature berries linearly. However, the responses to ethephon were variable. The highest concentration of 4000 mg·L-1 ethephon caused similar results in both years to the traditional practice of hand removal of inflorescences, but foliar reddening and some defoliation were observed. Buffering ethephon sprays at pH 2.6, 4.0, 5.0, and 6.0 gave similar results. The surfactant Tween 20 did not increase the effectiveness of the sprays. Generally, multiple applications of ethephon at lower concentrations were no more effective than comparable single higher concentration sprays. Carry-over effect of ethephon in the second year included crop stunting, an increase in root weight, and berry weights and berry color proportions similar to those plants on which hand removal was carried out in the first year. Chemical names used: 2-chloroethyl phosphonic acid (ethephon).
Moritz Knoche, Hiroto Tamura, and Martin J. Bukovac
The stability of the organosilicone surfactant Silwet L-77 (L-77) was investigated in growth regulator solutions representative of those frequently used as foliar sprays in horticultural research and production. Surfactant stability was followed by measurement of surface tension at selected time intervals after addition of the surfactant. Time-course studies revealed that surface tension of Ethrel (2.08 ml·liter) and Pro-Gibb (3.13 ml·liter) solutions made up with deionized water with 0.01% L-77 increased immediately after preparation. A lag phase of constant surface tension was observed at a higher (0.1'%) L-77 concentration. The rate of increase in surface tension was higher for the more acidic Ethrel solution (pH 2.5) than for the Pro-Gibb solution (pH 3.8). The water source used for preparation of the spray solution significantly affected surfactant stability. Surface tension of Ethrel solutions (2.08 ml·liter 0.1% L-77) prepared with well water remained constant over 4 hours, whereas surface tension increased when rain or deionized water was used. Surface tension increased in Pro-Gibb spray solutions prepared with deionized water at concentrations typical for low- (1/10 x), but not high- (1x), volume spray applications or when solutions were prepared with well water. In all experiments, pH of the spray solution was the only factor that affected L-77 stability. Chemical names used: (2-chloroethyl) phosphoric acid (Ethrel); gibberellin A (Pro-Gibb); polyalkyleneoxide modified polydimethylsiloxane copolymers (Silwet L-77).
Paul M. Chen, Diane M. Varga, and Clark F. Seavert
We have established that `d'Anjou' pears (Pyrus communis) are properly ripened for fresh-cut use when flesh firmness (FF) is between 5 lb (2.3 kg) and 7 lb (3.2 kg). In this study, the fruit was ripened in air enriched with 100 ppm (mL·L-1) ethylene at 68 °F (20.0 °C). Afterward, we investigated three slicing methods, each employing a fruit sectionizer for dividing individual pears into eight wedges. The easiest and most convenient cutting procedure involved pouring an antibrowning agent onto the incision, but without allowing the fruit to directly contact the air. We evaluated various combinations of L-ascorbic acid (vitamin C) and potassium chloride (KCl) for their ability to prevent any discoloration while also not affecting taste or injuring the cut surface. The most suitable antibrowning solution contained 10% L-ascorbic acid and 2% KCl (pH 2.3). A dipping time of 30 s was sufficient for maintaining the wedges with little discoloration over a 14-d period, at either 30 or 35 °F (-1.1 or 1.7 °C). Here, we also present a prototype design for a 1.6-pt (0.76-L) transparent plastic container with eight compartments for holding wedges sliced with a commercially available sectionizer.