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C. D. Stanley and G. A. Clark

The use of the recently developed fully-enclosed seepage subirrigation system for fresh market tomato production has demonstrated an improved ability to maintain a water table at a desired level (when compared to conventional ditch-conveyed seepage subirrigation) by means of more precisely controlled application and a greater uniformity throughout the field. This is achieved through use of microirrigation tubing rather than open ditches to convey water to raise the water table to desired levels. When manually controlled, the system has shown to save 30-40% in irrigation amounts primarily due to almost total elimination of surface runoff. An automated control system was designed and evaluated with respect to practicality, durability, and performance of various designs of level-sensing switches. The advantages and limitations of the designs in relation to water table control for tomato production will be presented.

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C.D. Stanley and G.A. Clark

The effect of water table level and fertilizer rates on bell pepper production grown with the fully enclosed subirrigation (FES) system was studied over three fall growing seasons (1992–94). The FES system uses buried microirrigation tubing in the field to convey water for maintaining a water table level and has shown to achieve application savings of 30% to 40% compared to the conventional subirrigation method that maintains a high water table using lateral field ditches. Controlled water table levels of 45, 60, and 75 cm below soil surface and fertilizer rates of 1194, 1716, and 2239 kg·ha–1 (18–0–21 expressed as N–P–K) were used as treatments replicated in time over 3 growing seasons. The 45-cm water table level and 2239 kg·ha–1 fertilizer rate are considered the conventional commercial practices. Results showed that comparable seasonal production levels were achieved among fertilizer rates and water table levels with no significant interactions between treatments. These data indicate that using a lower target water table level allows lower rates of fertilizer to be used because the susceptibility of the fertilizer to leaching caused by excessive rainfall is lessened due to increased soil water storage capacity.

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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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J.E. Barrett, J.C. Bradley, C.A. Bartuska, T.A. Nell, and D.C. Clark

More than 60 new poinsettia cultivars have been introduced in the past 3 years, and many of these have nontraditional bract color or plant form. About 75% of all poinsettias sold are red and `Freedom' represents more than 50% of the red poinsettia market in the United States In Fall 1999, 212 individuals were surveyed and asked to indicate their favorite 10 cultivars out of the 89 in a cultivar trial. The top choices were `Plum Pudding', `Winter Rose Dark Red', `Cranberry Punch', and `Monet Twilight', which were selected by 48%; 38%; 32%, and 31% of the participants, respectively. These cultivars are all nontraditional in appearance. The top red cultivars were `Freedom', `Orion', and `Red Velvet', which were selected by 27%, 26%, and 23%, respectively. The participants were then asked to rate on a 1 to 10 (most favorable) scale 15 plants that represented different poinsettia forms and colors. Five of these plants were cultivars with different shades of red that the industry easily separates. However, the participants' ratings of these were not significantly different, which indicates the shade of red in bract color may be more important to the industry than it is to the public. These results also indicate that there are strong differences in individual preferences for poinsettias. Each of the 15 plants received both high and low ratings. Also, of the participants that included `Freedom Red' in their top 10 selection, only 13% of those selected `Plum Pudding', which has purple bracts, and only 11% selected `Winter Rose Dark Red', which has a nontraditional plant form.

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C. Gupton, J. Clark, D. Creech, A. Powell, and S. Rooks

Rabbiteye (Vaccinium ashei Reade) and southern highbush (mostly V. corymbosum L.) type blueberry selections were evaluated in regional trials at five locations. Entry × location interactions (E × L) were significant for all traits in the rabbiteye type and all except plant productivity, plant volume, Julian date of 50% ripe fruit, and berry weight at harvest 3 in the southern highbush type. Despite the significant interactions, selection FL80-11 and `Gulfcoast' were the earliest flowering rabbiteye and southern highbush entry, respectively, at each location. Significant E × L for plant volume and yield suggests that adaptation to the local environment is important in the selection of potential cultivars. Fruit quality traits appear less affected by environment than fruit production traits for the entries tested.

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J.W. Prevatt, G.A. Clark, and C.D. Stanley

Three vegetable irrigation systems, semi-closed subirrigation (seepage), fully enclosed subirrigation (seepage), and drip irrigation, were evaluated for use on sandy soils with naturally high water tables to determine comparative irrigation costs for tomato production. Investment, fixed (ownership), and variable (operating) costs were estimated for each irrigation system. The investment costs of the drip irrigation system were significantly greater than those for the semi-closed and fully enclosed irrigation systems. The variable costs, however, for the semi-closed system were considerably less than those for the fully enclosed and drip irrigation systems. The semi-closed irrigation system, therefore, was determined to be the least-cost tomato irrigation system under present fuel cost and nonlimiting water supply conditions.

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D.W. Miano, D. R. LaBonte, and C. A. Clark

Sweetpotato is an important staple food crop in Sub-Saharan Africa, with production being concentrated in East Africa, particularly around Lake Victoria. Productivity of the crop is greatly constrained by viral diseases. Four main viruses have consistently been detected from various surveys done in the region viz. sweet potato feathery mottle virus (SPFMV), sweet potato chlorotic stunt virus (SPCSV), sweet potato mild mottle virus (SPMMV), and sweet potato chlorotic fleck virus (SPCFV). Sweet potato caulimo-like virus (SPCaLV), sweet potato latent virus (SPLV), and cucumber mosaic virus (CMV) have also been detected though only in isolated cases. The most severe symptoms have been caused by co-infection with SPCSV and SPFMV, resulting in the synergistic Sweet potato virus disease (SPVD). Yield reductions due to virus infections have been estimated to be >90% in very severe cases. Virus detection has mainly been limited to the use of serological methods. Some plants have been observed with symptoms resembling those caused by viruses, but do not react with available antisera, indicating that the plants could be infected with viruses that have not been described, or not tested in the region. Use of other detection techniques such as PCR may result in identification of more viruses in the region. This report gives a summary of our research efforts towards detection of other viruses present in the region, and identification of resistant germplasm.

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D.W. Miano, D. R. LaBonte, and C. A. Clark

Sweet potato virus disease (SPVD) is a major constraint to sweetpotato production in East Africa. The disease is a result of co-infection with sweet potato feathery mottle virus (SPFMV) and sweet potato chlorotic stunt virus (SPCSV). Some local sweetpotato genotypes have been reported to recover from, or have localized distribution of SPVD, suggesting that the disease is not fully systemic. This has led to the suggestion that uninfected cuttings may be obtained from previously infected plants. Experiments were set to determine the possibility of obtaining cuttings long enough for propagation that are free from virus infection. This would form a basis for recommending to the local small-holder farmers of a way to reduce losses due to the disease. Field grown sweetpotato vines were cut into three pieces (15, 15 to 30, and >30 cm from the apex) and tested for SPCSV and SPFMV. Nine genotypes were selected from a group of 21 local clones and used for this study. The two viruses were equally present in all the three sections of infected vines, indicating that it is not easy to obtain a virus free cutting for field propagation from an infected vine.

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C.E. Wieland, J.E. Barrett, C.A. Bartuska, D.G. Clark, and T.A. Nell

Salvia (Salvia splendens F.), vinca (Catharanthus roseus L.), and pansy (Viola × wittrockiana Gams.) were examined to determine efficacy of growth retardants for inhibiting stem elongation of seedlings in the plug stage and after transplanting to 10-cm pots. Studies on salvia showed plugs sprayed with single applications of ancymidol at 10 or 20 ppm, paclobutrazol at 30 or 60 ppm, or daminozide/chlormequat tank mix at 2500/1500 ppm inhibited plug elongation by 17% to 22%. Pansy plugs were sprayed either once or twice with ancymidol at 5, 10, or 15 ppm. Number of applications was statistically significant with two applications reducing elongation by an average of 35%, whereas a single application resulted in a 23% average reduction. Ancymidol concentration was significant in reducing stem elongation with increasing rates in pansy; however, the concentration and application time interaction was not significant. In both pansy and salvia, plant size at flowering was similar to controls after transplanting. Vinca plugs were sprayed with ancymidol at 5, 10, or 15 ppm either the 3rd week, 4th week, or both weeks after sowing. As ancymidol concentrations increased, plug height decreased, and the concentration effect was greater week 3 than at week 4. Two applications of ancymidol was most effective in retarding stem elongation (36%) followed by one spray the 3rd week (29%) and one spray during week 4 (20%).

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C.D. Kokkinos, C.A. Clark, C.E. McGregor, and D.R. LaBonte

Sweet potato virus disease (SPVD) is the most devastating disease of sweetpotato [Ipomoea batatas (L.) Lam.] globally. It is caused by the co-infection of plants with a potyvirus, sweet potato feathery mottle virus (SPFMV), and a crinivirus, sweet potato chlorotic stunt virus (SPCSV). In this study we report the use of cDNA microarrays, containing 2765 features from sweetpotato leaf and storage root libraries, in an effort to assess the effect of this disease and its individual viral components on the gene expression profile of I. batatas cv. Beauregard. Expression analysis revealed that the number of differentially expressed genes (P < 0.05) in plants infected with SPFMV alone and SPCSV alone compared to virus-tested (VT) plants was only 3 and 14, respectively. However, these findings are in contrast with SPVD-affected plants where more than 200 genes were found to be differentially expressed. SPVD-responsive genes are involved in a variety of cellular processes including several that were identified as pathogenesis- or stress-induced.