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Thomas M. Gradziel and Dechun Wang

Colonization and sporulation of aflatoxigenic Aspergillus flavus Link on intact and injured seed was evaluated for a selection of almond [Prunus dulcis (Mill.) D.A. Webb] cultivars. Barriers to fungal development were identified at the intact seedcoat and at the seed cotyledon tissue. The seedcoat barrier was expressed as a delay in fungal colonization for up to 3 days following the inoculation of intact seed. Seedcoat resistance was uniformly high for all cultivars tested. Cotyledon resistance, which was expressed as a lower rate of disease development was identified only in the cultivars Ne Plus Ultra, Ruby, and Carrion.

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Nan Wang and Barbara M. Reed

Roots of greenhouse-grown mint plants and in-vitro-grown shoot cultures were inoculated with Verticillium dahliae Kleb. conidial suspensions to study wilt symptom development and detection and elimination of the fungus. There were significant differences in the symptom expression between control and infected shoot cultures at all conidia concentrations for the four mints tested. Disease-symptom ratings were proportional to the V. dahliae inoculum density. Infected shoot cultures were stunted when inoculated with ≥ 103 conidia/mL. Verticillium dahliae was re-isolated from infected shoot cultures at all levels of inoculum, but not from any control cultures. Verticillium infections were easily detected by plating mint stems on potato dextrose agar. Shoot tips (0.5 to 15 mm) from infected in-vitro- and greenhouse-grown plants were isolated and screened for fungus. The most effective shoot length for fungus elimination was 3-5 mm. Shoot tips isolated from in vitro spearmint cultivars infected at 102 and 103 conidia/mL were 100% Verticillium free, but only 42% of `Black Mitcham' and 54% of `Todd's Mitcham' peppermints were free of the disease. Shoot tips from infected greenhouse plants produced Verticillium-free cultures from 79% of `Black Mitcham' and 90% of `Todd's Mitcham' plants. These results indicate the utility of testing for Verticillium and the safety of micropropagated mint shoots for certified planting stock programs.

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M. Wang and I.L. Goldman

The importance of folic acid in the human diet has been recognized in recent years by major increases in government recommended allowances. Red beet (Beta vulgaris L.) is an important vegetable source of folic acid, however little is known about the extent of variation for native folic acid content in red beet germplasm. A total of 18 red beet entries, including 11 hybrids (F1) and seven open-pollinated cultivars (OP), were evaluated for free folic acid content (FFAC) in replicated field experiments during 1993 and 1994. Significant differences among entries were detected in all studies. FFAC ranged from 3.3 to 15.2 μg·g-1 on a dry mass basis. A significant entry × year interaction was detected. Changes in rank of entries between years were minimal among F1 hybrids, while the changes in rank among OP cultivars were large. These data demonstrate significant variability among cultivated red beet germplasm sources for FFAC. Entries with high FFAC may be useful for increasing levels of this vitamin in red beet.

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T.M. Gradziel and Dechun Wang

Rate of brown rot lesion development following inoculation with Monilinia fructicola (Wint.) honey varied within clingstone peach (Prunus persica (L.) Batsch) germplasm evaluated in 1990 and 1991. High levels of resistance were identified in selections derived from the Brazilian clingstone peach cultivar Bolinha. Resistance appeared to be limited to the epidermal tissue. No relation was detected between brown rot resistance and concentration of phenolic compounds or polyphenol oxidase activity in the susceptible California germplasm. An inverse relation was observed between disease severity and rating for phenolic-related discoloration when `Bolinha' derived selections were analyzed. A moderate positive correlation was observed for all germplasm tested between genotype means for phenolic content and enzymatic browning. Any causal relationship, if it exists, between phenolic content and brown rot resistance is obscured by an array of physical and chemical changes in the maturing fruit.

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Yin-Tung Wang and Thomas M. Blessington

Rooted cuttings of Euphorbia pulcherrima Willd. ex Klotzsch cv. Gutbier V-14 Glory were planted in 2-liter containers with growth media having 0% to 75% composted cotton burrs (CCB) in combination with sphagnum peat and/or composted pine bark. Leachates from media with 50% or more CCB had higher initial electrical conductance (EC) (3.7 to 4.0 dS·m-l) than that from media with 25% or no CCB (2.8 to 3.0 dS·m-l) 2 weeks after planting. The differences in leachate EC declined after an additional 9 weeks. Media containing CCB produced slightly shorter and narrower plants with 10% smaller inflorescences and less dry weight than plants grown in a medium consisting of equal volumes of peatmoss and bark. Number of branches and bracts, days to bloom, and plant grade after 30 days under 15 μmol·s-l· m-2 photosynthetic photon flux were unaffected by media.

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Z. Wang, M.C. Acock, and B. Acock

Flower development in opium poppy (Papaver somniferum L. `album DC') is enhanced by long photoperiods (PP ≥ 16-hours). Predicting time to flower in field-grown opium poppy requires knowledge of which developmental stages are sensitive to PP and how the rate of flower development is changed by changes in PP. The objective of this work was to determine when poppy plants first demonstrated developmental changes in response to PP and how long PP continued to influence the time to first flower under consistent temperature conditions. Plants were grown in artificially lit growth chambers with either a 16- (inductive) or a 9-hour PP (noninductive). Plants were transferred at 1 to 3-day intervals from a 16- to a 9-hour PP and vice versa. All chambers were maintained at a 12-hour thermoperiod of 25/20°C. Poppy plants demonstrated developmental changes in response to PP four days after emergence and required a minimum of four inductive cycles before the plant flowered. Additional inductive cycles, up to of a maximum of nine, hastened flowering. After 13 inductive cycles, flowering time was no longer influenced by PP. These results indicate four phases between emergence and first flower: 1) a photoperiod-insensitive juvenile phase (JP); 2) a photoperiod-sensitive inductive phase (PSP); 3) a photoperiod-sensitive post-inductive phase (PSPP); and 4) a photoperiod-insensitive post-inductive phase (PIPP). The minimum durations (days) of these phases under the conditions of our experiment were JP = 4, PSP = 4, PSPP = 9, and PIPP = 14.

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Z. Wang, M.C. Acock, and B. Acock

Flower development in opium poppy (Papaver somniferum L.) has been divided into four phases from emergence to anthesis, which mark changes in its sensitivity to photoperiod: a photoperiod-insensitive juvenile phase (JP), a photoperiod-sensitive inductive phase (PSP), a photoperiod-sensitive post-inductive phase (PSPP), and a photoperiod-insensitive post-inductive phase (PIPP). To predict flowering time under field conditions, it is essential to know how these phases are affected by temperature. Plants were grown in artificially lit growth chambers and received three temperature treatments: 15/10, 20/15, and 25/20°C in a 12-hr thermoperiod. Plants were transferred within each temperature regime from a non-inductive 9-hr to an inductive 16-h photoperiod or vice versa at 1- to 4-day intervals to determine the durations of the four phases. Temperature did not affect the durations of the first two phases (i.e., JP lasted 3 to 4 days and PSP required 4 to 5 days). The most significant effect of temperature was on the duration of PSPP, which lasted 28, 20, and 17 days at 15/10, 20/15, and 25/20°C, respectively. The temperature effect on PIPP was small (maximum difference of 3 days for treatments) and the data too variable to indicate a significant trend. Our results indicate that PSPP is the only phase that clearly exhibits sensitivity to temperature.

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J. Jiao, X. Wang, and M.J. Tsujita

Uniconazole was applied as a drench or spray to six hybrid lily (Liliurn sp.) cultivars. Spray application was generally more effective than drench in reducing shoot elongation rate in the first few weeks, and then the efficacy decreased and was less effective than the drench at later stages of plant development. At flowering, a uniconazole drench at 0.1 mg/pot was ineffective for height reduction in `Bravo', `Juliana', and `Sunray' lilies. At higher rates, uniconazole drench was similar to spray in reducing shoot growth in `Bravo' and 306-1 but less effective than spray in `Juliana', `Star Gazer', and `Sunray' lilies. Uniconazole spray reduced plant height at flowering in all the lilies compared to control plants. Days to flower was not affected in `Bravo', `Juliana', and `Sunray' but was increased in `Star Gazer', 306-1, and 306-2 by uniconazole spray treatments. Flowering duration was decreased only in 306-1 by uniconazole spray at 0.2 mg/pot. Chemical name used: (E)-1-(4-chlorophenyl) -4,4 -dimethyl-2-(l,2,4 -triazol-1-yl)-1-penten-3 -ol (uniconazole).

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Yin-Tung Wang and Thomas M. Blessington

Uniconazole and paclobutrazol were tested for their effects on greenhouse production of four foliage species. Soil drenches of uniconazole retarded shoot and petiole elongation of Brassaia actinophylla Endl. Paclobutrazol reduced shoot elongation, but required higher doses than uniconazole and did not reduce petiole growth. Foliar sprays with either retardant at 12.5 mg·liter-1 resulted in short stems on lateral shoots of Codiaeum variegatum (L.) Blume `Karen' after pinching, but soil drenches at low rates were less effective. Soil drenches of uniconazole or paclobutrazol were equally effective in reducing stem growth of Syngonium podophyllum Schott `White Butterfly' and increasing leaf width, but had no effect on the rate of leaf production or blade length. Both retardants induced short petioles in this species. Severe growth reduction occured on Plectranthus australis R. Br. even at the lowest rates of uniconazole and paclobutrazol (0.025 and 0.20 mg/pot, respectively) as soil drenches. Production of lateral shoots was inhibited for P. australis by both retardants. Chemical names used: (E)-1-(p-chlorophenyl)-4,4-dimethy1-2-(1,2,4-triazol-1-yl)-1-penten-3-ol (uniconazole); (2RS,3RS)-1-(4-chlorophenyl)-2-(1,1-dimethylethyl)-(H-1,2,4-triazol-l-Yl-)Dentan-3-ol (paclobutrazol).

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S. Y. Wang, H. J. Jiao, and M. Faust

An increase in ascorbic acid, reduced form of glutathione (GSH), total glutathione, total non-protein thiol (NPSH) and non-glutathione thiol (RSH) occurred as a result of induction by thidiazuron during bud break, whereas dehydroascorbic acid and oxidized glutathione (GSSG) decreased during the same period. Thidiazuron also enhanced the ratio of GSH/GSSG, and activities of catalase, superoxide dismutase (SOD), ascorbate free radical reductase (AFR), ascorbate peroxidase (POD), dehydroascorbate reductase (DHAR), ascorbate oxidase (AAO), and glutathione reductase (GR). The ascorbic acid content and the activities of catalase, SOD, AFR, POD, AAO, and DHAR peaked when buds were in the side green or green tip stage just prior to the start of rapid expansion, and declined thereafter. The GSH, NPSH, RSH, ratio of GSH/GSSG, and activity of GR increased steadily during bud development.