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C.A. Weber, W.B. Sherman, and G.A. Moore

Segregating F2 peach populations in the Univ. of Florida breeding program were analyzed to determine linkage relationships among five qualitative traits: flower type, Sh/sh, flesh type, M/m; flesh color, Y/y; leaf gland type, E/e; and pubescence, G/g. Independent segregation was confirmed between flesh color and leaf gland type, between pubescence and flesh color, and between flower type and pubescence. Previously undocumented independent segregation was found between leaf gland type and flesh type and between pubescence and leaf gland type in our populations. The relationship between these latter characteristics should be investigated in other breeding populations. No correlation was found between fruit development period and flesh type. Also, no correlation was found between chilling requirement and flesh type.

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H.S. Costa, K.L. Robb, and C.A. Wilen

A field study was conducted to assess the effect of various commercially available polyethylene plastic greenhouse coverings on the persistence of viable spores of the microbial insecticide Beauveria bassiana. Selected coverings blocked the transmission of UV light with wavelengths of 360 nm and below or 380 nm and below. Two coverings also contained an infrared blocking component. A commercial formulation of B. bassiana was applied for 3 consecutive weeks to plants growing in the plastic covered hoop houses. The percentage of viable spores was calculated up to 13 days after the final application. The persistence of viable B. bassiana spores was significantly longer under the plastic that blocked a greater portion of the UV spectrum (<380 nm) than the plastics that only blocked UV wavelengths below 360 nm. One week after application, percentage of spore germination was at least twice as high under the <380 nm blocking plastic compared to <360 nm blocking plastics.

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C.A. Mach, J.W. Buxton, and R.S. Gates

The CWT irrigation system consists of a capillary mat placed on a level bench so one side extends over the edge of the bench into a trough containing a nutrient solution maintained at a controlled distance below the bench. The nutrient solution is drawn by capillarity up to and over the bench surface. As plants use the nutrient solution or as water evaporates from the media, it is replaced from the trough. The automatic system maintains a constant air/water ratio in the growing media. Geraniums were grown in a peat based media in 15-cm pots at 0, 2, and 4 cm CWT. In a separate study, the water potential was determined in two media. Water potential was determined at the bottom, middle, and top of the container at 0, 2 and 4 cm CWT every 2.5 hrs during the light period. Geraniums at 0 and 2 cm had the greatest leaf area and dry weight. The 0- and 2-cm treatments were >25% greater than plants at 4 cm CWT. The roots of plants at 0 cm CWT were concentrated at 2–4 cm above the bottom of the container, whereas roots at 2 cm CWT uniformily extended from the center to the bottom. Water potential was about the same in each media within each CWT treatment. The water potential from top to bottom decreased slightly about midafternoon on a sunny day when water demand was the greatest. Media at 0 CWT at the container bottom had 0 water potential; whereas the water potential at 2 and 4 CWT had a lower water potential.

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F.A. Buffone, D.R. LaBonte, and C.A. Clark

Chlorotic leaf distortion is a common disease of sweetpotato caused by Fusarium lateritium. This fungus is unique among Fusarium species in that it grows epiphytically on leaves and shoot tips of sweetpotato. Fusarium lateritium mycelia appear as white masses on leaves, and this fungus can cause chlorosis under periods of bright sunlight. When environmental conditions are not favorable for growth, this organism is not readily observed on sweetpotato. The objective of this research was to see if DNA of F. lateritium is amplified using PCR techniques during amplification of sweetpotato DNA. Our results show cTAB extracts of sweetpotato inoculated with F. lateritium have additional bands not present in a control free of F. lateritium. Furthermore, these bands correspond to banding patterns obtained from the F. lateritium isolate DNA when amplified alone. Researchers who use sweetpotato tissue in PCR-based research, e.g., phylogenetic research, should be aware of these amplified products. This situation is further compounded because numerous F. lateritium biotypes are present in the environment.

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D. Janik, E. Fava, C.A. Madramootoo, and K.A. Stewart

The yield of bell peppers (Capsicum annuum L. cv. King Arthur) was measured when grown in the field under eight mulching/irrigation/nitrogen fertilization systems, was studied at the Macdonald Campus of McGill Univ., using a randomized block design replicated three times. All treatments received a preplant fertilizer application of 60 kg N/ha with four of the treatments receiving additional fertigation during the season. Of the four treatments receiving fertigation, one silver reflective mulched plot and one black mulched plot received an additional 40 kg N/ha in 4 kg N/ha/week over a 10-week period beginning 12 June weekly up to and including 14 Aug. 1995. The remaining two fertigated treatments only received additional N, when leaf nitrogen, based upon leaf chlorophyll content, dropped below a 95% sufficiency index as measured by a Minolta SPAD 502 meter. Marketable yields of the fertigated plots range between 100%–126% higher than those of the control plot for the entire growing season. However, most notably was the early yields (first three harvests), which ranged from 146%–493% higher than that of the control plot, economically, significantly increasing the producers income. The experiment will be duplicated in Summer 1996 to confirm our findings.

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R.J. Henny, R.T. Poole, and C.A. Conover

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M. Wilcox, C.A. Sanchez, and T.M. Blackmer

Several studies in the midwestem United States have shown that chlorophyll meter readings (Minolta SPAD 502) are useful in determining the N status of corn (Zea Mays L.), and show promise as a tool for the efficient N management of corn. Studies were conducted to evaluate the potential of the `chlorophyll meter for evaluating N deficiencies in lettuce (Lactuca sativa L.). Data for chlorophyll meter readings, midrib nitrate-N, lettuce growth rate, and marketable lettuce yield were collected in five N fertility experiments in 1993 and 1994. Chlorophyll meter readings not only varied among lettuce types (butter, cos, leaf, crisphead), but also among cultivars of the crisphead type. Chlorophyll meter readings were generally poorly correlated to midrib nitrate-N levels and marketable lettuce yield. Lettuce leaves have more color variation than corn leaves, and perhaps this variation in relation to the small sensor size on the SPAD 502 confounded readings. The observation that subtle N deficiencies in lettuce are usually manifested in growth rate reduction rather than abrupt color changes may also limit the usefulness of the chlorophyll meter for lettuce.

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F.S. Davies, M.W. Fidelibus, and C.A. Campbell

An experiment was conducted to determine if gibberellic acid (GA; ProGibb, Abbott Labs) can be mixed with Aliette or Agri-Mek and oil to reduce application costs, without reducing GA efficacy, and if Silwet and Kinetic adjuvants enhance GA efficacy. Five tank mixes were tested along with a nonsprayed control. The tank mixes included: 1) GA, 2) GA + Silwet, 3) GA + Kinetic, 4) GA + Silwet + Aliette, and 5) GA + Silwet + Agri-Mek + oil. All compounds were applied at recommended concentrations. In September, ≈24 L of each tank mix was applied with a hand sprayer to mature `Hamlin' orange trees [Citrus sinensis (L.) Osb.] on sour orange (Citrus aurantium L.) rootstock. Peel puncture resistance (PPR), peel color, and juice yield (percent juice weight) were evaluated monthly between Dec. 1997 and Mar. 1998. On most sampling dates the fruit of treated trees had higher PPR and were less yellow in color than fruit from control trees. However, in Jan., fruit treated with GA + Silwet and GA + Kinetic had greater PPR than other treatments. In Feb., fruit treated with GA + Silwet + Agri-Mek + oil had the lowest PPR. The effect of the different tank mixes on juice yield was usually similar to the effect of the tank mixes on PPR and peel color. On 8 Jan. 1998, fruit from trees treated with GA alone yielded significantly more juice than fruit from control trees. On 24 Feb. 1998, fruit from trees treated with GA alone yielded more juice than fruit from the other treatments. Thus, GA efficacy is generally not reduced by these tank mixes, nor improved by adjuvants.

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F.S. Davies, M.W. Fidelibusa, and C.A. Campbell

Gibberellic acid (GA) applied in late summer or fall delays subsequent loss of peel puncture resistance (PPR) and development of yellow peel color in many citrus cultivars. Our objective was to determine the optimal time to apply GA for increasing juice yield of `Hamlin' sweet orange [Citrus sinensis (L.) Osb.]. Mature trees on sour orange (Citrus aurantium L.) rootstock were sprayed with ≈24 L of a solution of GA (45 g a.i./ha) and organo-silicone surfactant (Silwet, 0.05%). Trees were sprayed on 26 Aug., 9 Sept., 2 Oct. (colorbreak), or 13 Oct. 1997, or nonsprayed (control). Peel puncture resistance, peel color, and juice yield were evaluated monthly between Dec. 1997 and Mar. 1998. Fruit from trees sprayed with GA had peels with higher PPR and less yellow color than fruit of control trees for most of the harvest season. The effect of GA on PPR and peel color lasted about 5 months. Juice yield was usually numerically greater for GA-treated fruit than for nontreated fruit. Fruit treated with GA at color break had significantly greater juice yield when harvested in late February than fruit from control trees. Thus, GA applied at color break appears to be the most effective time for enhancing peel quality and juice yield of `Hamlin' oranges.