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  • Author or Editor: Bernard Bible x
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Abstract

Five cultivars of tomato (Lycopersicon esculentum Mill.) grown in the season of 1973 and 3 cultivars of pepper (Capsicum annuum L.) grown in 1974 were classified into left-handed and right-handed plants respectively according to the clockwise and counterclockwise spiraling arrangement of their alternate leaves around and up the main stem. In 4 of 5 tomato and 2 of 3 pepper cultivars, total yield, in terms of both fruit weight and number of fruit was higher in right-handed than in left-handed plants. The results suggest that the regulation of foliar spirality can perhaps be used to advantage for increasing productivity of certain crop plants with alternate phyllotaxy.

Open Access

One factor in the development of poinsettia (Euphorbia pulcherrima Willd. ex Klotzch) bract necrosis is plant nutrition. Twenty poinsettia cultivars were grown as 15-cm single-pinched plants in Metro mix 510 with standard commercial practices for irrigating, fertilizing, and pest control. Seventy days after initial anthesis, plants were harvested and the number of necrotic and healthy bracts recorded. Mineral nutrients in bract margins were determined. The only nutrient that had a significant relationship to incidence of bract necrosis across the 20 cultivars was bract B content (R 2=49.5%, P< 0.001). This suggests that cultivars with lower bract B content are more susceptible to bract necrosis. Using `Supjibi' plants grown in the Metro mix 510, we applied topical sprays of B (0, 4, or 8 mm) weekly during bract development or once at initial anthesis (8 mm). Also a weekly drench treatment of B (10 mm) was applied initially at bract color change and continued for 2 more weeks. By 42 days after initial anthesis, all B treatments averaged together reduced incidence of bract necrosis from 33.1% for controls to 10% for plant receiving B treatment. The B drench treatment resulted in leaf scorching and there was some leaf tipburn with the 4 and 8 mm B weekly sprays. The single spray (8 mm B) treatment at initial anthesis caused no injury. Although B sprays are not a replacement for Ca sprays as a control for bract necrosis, the results suggest a role for B in the etiology of bract necrosis.

Free access

Poinsettia (Euphorbia pulcherrima Willd. ex Klotzch) bracts are susceptible to postharvest disorders like the pathogen Botrytis cinerea and the abiotic disorder bract necrosis that degrade plant appearance. `Freedom Red' and `Supjibi' poinsettias were grown hydroponically with Ca concentrations of 0.5 or 4 mm. Forty days after initial anthesis, plants were harvested and their bracts subdivided into true-bracts and transitional-bracts for determination of incidence of botrytis lesions and bract necrosis. Mineral nutrients in bract margins were determined only for true-bracts. Margin Ca concentrations were relatively high in true bracts only for `Supjibi' plants exposed to 4 mm Ca solutions. Botrytis incidence was increased for transitional-bracts but not true-bracts for both cultivars by plant exposure to low (0.5 mm) Ca solutions compared to control (4 mm Ca) plants. The smaller the poinsettia roots relative to shoots, the higher the incidence of botrytis for `Freedom Red' transitional-bracts and `Supjibi' true-bracts. Botrytis incidence was higher on transitional-bracts (13%) than on true-bracts (3.5%) for both cultivars exposed to low Ca, whereas the incidence of bract necrosis on `Supjibi' was the same on true-bracts and transitional-bracts in either Ca solution. Bract necrosis was not evident on `Freedom Red' plants in either the 0.5 or 4-mmmm Ca solutions, however for `Supjibi' exposure to low Ca solutions increased incidence of bract necrosis from 5.5% for controls to 19.3%. The effect of Ca stress applied to poinsettia roots was genotype dependant for bract necrosis but not for botrytis.

Free access

Incidences of poinsettia (Euphorbia pulcherrima Willd. ex Klotzch) bract disorders like the pathogen Botrytis cinerea and the abiotic disorder bract necrosis are related to nutrient stress. `Supjibi' poinsettias were grown hydroponically with four Ca-B combinations of 0 or 4 mm Ca added with either 5 or 120 μmol B added. Forty-one days after initial anthesis, plants were harvested and their bracts subdivided into true-bracts and transitional-bracts for determination of incidence of botrytis lesions and bract necrosis. Mineral nutrients in bract margins were determined for leaves, transitional-bracts and true-bracts. Leaf margins had the highest concentrations of Ca and B. Margins of transitional-bracts had substantially lower concentrations and margins of true-bracts the least. The low Ca (0 mm) or low B (5 μmol) treatments greatly reduced the concentrations of these elements, respectively, in all three tissue types. The low Ca-low B treatment increased the incidence of bract necrosis on true-bracts from 1.9% on controls (4 mm Ca, 120 μmol B) to 27%. Low Ca treatment increased bract necrosis on transitional-bracts from 1.6% on controls to 24.3%. Bract necrosis incidence was the same on true-bracts and transitional-bracts, whereas the incidence of botrytis was higher on transitional-bracts than on true-bracts. Botrytis incidence was increased for true-bracts and transitional-bracts by plant exposure to low Ca solutions compared to plants in 4 mm Ca. Low Ca reduced growth in roots, but not shoots. Ca and B stress to roots increased the incidence of bract necrosis on true-bracts, while only Ca stress increased incidence of botrytis.

Free access

Bract necrosis (BN) in poinsettia is thought to be caused by a localized calcium deficiency in the margins of bracts. Both calcium and silicate sprays can suppress the post-anthesis development of BN if applied repeatedly during bract development. However, studies conducted in 1993 and 1994, with BN-susceptible scions (`Supjibi') grafted onto either `Supjibi' rootstock or the BN-resistant `Annette Hegg Dark Red' (AHDR) rootstock, failed to support the calcium hypothesis. In these studies, higher calcium concentrations were found in the margins of `Supjibi' bracts on `Supjibi' rootstock, then in `Supjibi' bracts on `AHDR' rootstock, even thought the incidence of BN was highest on plants with `Supjibi' rootstock. These studies suggested that non-nutritional factors (possibly hormonal factors) may play a role in BN. In 1995, `Supjibi' plants were produced in the greenhouse, and at initial anthesis, were sprayed once with either deionized (DI) water, benzyladenine (BA) (100 ppm), or daminozide (2000 ppm). At initial anthesis, plants in all treatment groups showed a low level of BN (0.75% of bracts with symptoms). Four weeks after initial anthesis, 18.5% of bracts on DI water sprayed plants and 38.7% of bracts on daminozide treated plants had developed BN; but BA treated plants developed BN on only 1% of bracts. At final harvest (38 days after treatments were applied), BN was evident on 3.4% of BA-treated bracts, 28.7% of DI-treated bracts, and 46.3% of daminozide-sprayed bracts.

Free access

Bract necrosis (BN) first appears at anthesis, and symptoms become more numerous and severe with time. Previously, we reported that 3.6 mm sodium silicate (Na2SiO3) sprays, applied during bract development, were as effective as 10 mm CaCl2 sprays at suppressing BN on `Supjibi' and `Angelika White', but only for several weeks after initial anthesis. While applying Na2SiO3 during bract development dramatically suppressed BN (7.2% of bracts with BN 46 days after anthesis vs. 33.4% for untreated plants), applying Na2SiO3 after anthesis is ineffective (35.7% BN). In 1995, suppression of BN was evaluated on `Supjibi' plants sprayed with similar concentrations (2 or 4 mm) of Na2SiO3 and CaCl2; treatments were compared to unsprayed poinsettias, or plants sprayed with either deionized (DI) water, 4 mm SrCl2, 4 mm NaCl, 4 mm MgCl2, or a solution of Na2SiO3 plus CaCl2 (1 or 2 mm each). At harvest (38 days after initial anthesis), 40.6% of the bracts on unsprayed plants and 35.8% of the bracts on DI water sprayed plants had BN. In contrasts, only 5.3% of the bracts on the 4 mm CaCl2 treated plants and 5.9% of the bracts on 4 mm Na2SiO3 treated plants had BN. Plants sprayed with 4 mm SrCl2 or the combination of 2 mm Na2SiO3 plus 2 mm CaCl2 developed BN on 7.8% and 9.2% of bracts, respectively. NaCl and MgCl2 sprays (4 mm) were not as effective (29.6 and 26.4% BN) as Ca, Si, or Sr sprays at suppressing BN over the duration of this study.

Free access

Abstract

Little evidence is available concerning possible allelopathic effects of the thiocyanate ion (SCN-), a known toxin commonly found in plants of the Brassicaceae (crucifers). Seeds and seedlings of 39 species of crop plants were exposed to ionic thiocyanate (0.5 mM SCN- supplied as KSCN) to determine their relative sensitivity. Percent germination was unaffected by SCN- for all the species tested. Thiocyanate ion inhibited the total seedling (shoot and root) extension of 46% of the species tested, with 38% of the species showing inhibition of shoot and 49% showing inhibition of root extension. This demonstrates that SCN- has the capacity to harm a range of species. However, the toxicity was selective in that 44% of the test species were unaffected by exposure to SCN-. Wide differences in seed weight among species, in incubation time, and also systematics were major sources of variation for species sensitivity to SCN-.

Open Access

Silica sprays (Na2SiO3 or SiO2·nH2O) markedly reduced the incidence and severity of bract necrosis (BN) of Euphorbia pulcherrima Willd. cv. Supjibi Red compared to plants not sprayed with silica. BN has been associated with low Ca concentrations or high K: Ca ratios in tissues of bract margins. Silica had no effect on Ca or K concentrations in bract margin tissues, and BN was not associated with the macro- or micronutrient composition of bract margin tissues. Sixteen days after initial anthesis, nontreated and deionized-water-sprayed poinsettias developed a higher incidence of BN than did plants sprayed with Na2SiO3 or CaCl2. However, sprays of 3.56, 5.34, and 7.12 mm Na2SiO3 were as effective as 9.98 mm CaCl2 sprays in protecting against BN of `Supjibi Red' and `Angelika White' bracts for up to 30 days after initial anthesis. `Supjibi Red' developed a higher incidence of bract necrosis than did `Angelika White', but both cultivars showed a similar response to the treatments and similar symptoms of necrosis. In both cultivars, initial symptoms appeared as small necrotic lesions on bracts at the looped ends of lateral veins that displayed a closed-vein pattern after the plants reached initial anthesis.

Free access

Watercress (Nasturtium officinale R.Br.) plants were grown in growth chambers at 15 °C or 25 °C and either 8- or 12-h photoperiod (PP). The photosynthetic photon flux (PPF) was 265 μmol·m-2s-1 in all chambers, but beginning 1 week before harvest, half of the plants in each chamber were subjected to a higher PPF (435 μmol·m-2·s-1). At harvest, watercress leaves and stems were analyzed for phenethyl isothiocyanate (PEITC) concentration. Without supplemental PPF, watercress grown at 25 °C and 12-h PP produced higher PEITC concentration in leaves and stems than plants grown at 15 °C and 12-h PP, or plants grown at 8-h PP and either temperature. With one week of supplemental PPF before harvest, plants grown at 15 or 25 °C and the 8-h PP produced PEITC concentrations as high as plants exposed to 12-h PP and similar temperatures. However, a week of supplemental PPF did not alter PEITC concentrations in plants grown at the 12-h PP, regardless of temperature. At 25 °C, plants grown under the low PPF and the 12-h PP produced 62% greater dry mass than plants exposed to a week of high PPF and the 8-h PP, but did not differ in PEITC content. Thus, the effect of one week of high PPF on PEITC concentration depended on photoperiod.

Free access

Forty-two poinsettia cultivars were grown as a 15-cm single-plant pinched crop at 21/16.5°C (day/night) temperatures during Fall 1995 with standard commercial practices for irrigating, fertilizing, and pest control. On 7 Dec., 156 consumers rated the cultivars for their overall appeal. On 11 Dec., color coordinate (CIELAB) readings for bracts and leaves were taken with a Minolta 200b colorimeter. The colorimeter was set to illuminate C and has a 8-mm aperture. Bracts and leaves were placed on a white tile background for colorimetric readings. In 1996, a similar evaluation was conducted with 55 poinsettia cultivars. Using the L-value of leaves as a criterion, cultivars were separated into medium green-leafed and dark green-leafed groupings. For bracts among the red types, hue angle values were used to separate cultivars into cool red types (hue angle ≈20–22°) and warm red types (hue angle ≈24–25°). Based on the 1995 study, cultivars within the cool red bracts and dark green foliage group—those that were darker, duller red (lower L and chroma)—were less attractive (lower consumer ratings) than lighter, more-vivid red cultivars. For cultivars within the cool red bracts and medium green foliage group, consumers preferred the darker duller red cultivars. Perhaps dark foliage gives a more pleasing contrast with the more vivid cool reds than does the medium green foliage. In general, consumers rated red cultivars hire than non-red cultivars.

Free access