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  • Author or Editor: C. M. Jones x
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Abstract

(2-Chloroethyl)phosphonic acid (ethephon) increased the proportions of perfect and completely pistillate flowers, especially on lower nodes of the main vine where normally only staminate flowers are formed, on several muskmelon (Cucumis melo L.) cultivars in growth chambers and in the field. Lower concn were needed for female conversion under short days than long days. Early-maturing cultivars appeared more responsive to ethephon than late cultivars. No daylength-ethephon combination was effective in changing sex expression of watermelon (Citrullus vulgaris Schrad).

Open Access

Abstract

Resistance to the spotted cucumber beetle, Diabrotica undecimpunctata howardi Barber, the western striped cucumber beetle, Acalymma vittata (Fabricius) and the banded cucumber beetle, Diabrotica balteata LeConte was studied in “near isogenic populations” of cucumbers for the Bi locus. These 3 insects reacted similarly to cucurbitacins in cucumbers but in vitro studies indicated differences in other cucurbits. Bacterial wilt desease was less severe in non-bitter than bitter cucumbers.

Open Access

Abstract

Nymphs of Aphis gossypii Glover (Western Biotype) reared on bitter plants of ‘Tablegreen 65’ and ‘Marketmore 70’ cucumber required less time to reach maturity and produced more generations in 184 days than those reared on non-bitter plants. The greatest number of nymphs per adult aphid was produced by aphids on 8-week-old non-bitter plants of ‘Tablegreen 65’. Non-bitter plants of both cultivars supported a significantly greater aphid population density after 30 days than bitter plants.

Tests of aphids in greenhouse cages indicated no significant differences in damage caused by melon aphids to bitter and non-bitter plants of ‘Tablegreen 65’ and ‘Marketmore 70’.

Open Access

Abstract

The southern root-knot nematode, Meloidogyne incognita Kofoid and White (Chitwood), damaged bitter (Bi-) and non-bitter (bibi) plants of cucumber (Cucumis sativus L. cvs. Tablegreen 65 and Marketmore 70) to the same extent in greenhouse tests as shown by their root-knot index and general plant vigor. However, a significantly greater number of root-knot nematode larvae developed in the non-bitter root tissue and nematodes were significantly more attracted to non-bitter than to bitter excised root pieces on both water agar and in sand. Purified extract discs from bitter cucumber in 2% water agar repelled root-knot nematodes.

Open Access

Abstract

Root injury of sweet potato (Ipomoea batatas (L.) Lam) was significantly increased when eggs of banded cucumber beetles (Diabrotica balteata (LeConte)) in a agar-water mixture were applied at preroot enlargement. This technique should prove useful in screening sweet-potato lines or cultivars for insect resistance.

Open Access

Abstract

Spotted and striped cucumber beetles (Diabrotica undecimpunctata howardi Barber and Acalymma vittata Fab., respectively) caused significantly more damage to bitter cucumber (Cucumis sativus L.) wilted by drought or infection by Erwinia tracheiphila E.F.S.-Holland than to bitter non-wilted or non-bitter wilted and non-wilted plants. Bitter wilted plants had significantly more cucurbitacin than did bitter non-wilted material.

Open Access

Abstract

Temperature, cultivar, locus of inoculation, and prior-inoculation (inoculation 24 hr earlier with 3 nonpathogenic fungi) affected the expression of fusarium wilt caused by Fusarium oxysporium f. niveum (E.F.Sm.) Snyder & Hansen, in watermelons. Prior inoculation with Helminthosporium carbonum Ulktrup was found to be more effective in cross protection than were Fusarium oxysporium f. lycopersici (Sacc.) Snyder & Hansen, or Verticillium alboatrum Reinke & Berth. Temperatures of 27°C resulted in more fusarium infection than at 20° and obscured the expression both of genetic resistance and resistance induced by the prior-inoculations. Induced resistance increased plant survival and plant growth for 3 cultivars in field trials, but possibly produced deleterious effects in a resistant cultivar.

Open Access

Abstract

The N form had a pronounced effect on the levels of free amino acids. When compared to NO3, NH4 brought about a several fold increase in free amino acids (dry basis) in the roots, while smaller increases were observed in mature, fully expanded leaves, in young growing leaves, and in tomato fruit. Plants fed a combination of the 2 N forms had intermediate levels. The pattern of response to NH4 indicated that aspartic and glutamic acids as well as their amides were predominantly snythesized in the roots when the N source was NH4. The site of synthesis shifted to the leaves when the N source was NO3. The amino acids arginine, serine, alanine, and γ-aminobutyric acid were predominantly synthesized in the leaves irrespective of N form. Topical application of Ca on fruit grown with NH4 resulted in amino acid levels in the fruit similar to those of NO3 fruit. Ammonium toxicity was found to be accompanied by large increases in the levels of GABA and serine in the leaves. It is suggested that ammonium toxicity is a manifestation of intracellular Ca deficiency.

Open Access

Abstract

Carbohydrate (CHO) accumulation in ‘Valencia’ orange leaves, sampled in February, was inversely related to the fruit load on the tree at the time of sampling but directly related to the amount of fruit produced from the flowering which followed the time of leaf sample. Late harvest reduced fruit production in the following year but did not significantly alter CHO accumulation.

Open Access

Petunia ×hybrida (Hook) Vilm. cv. Mitchell was transformed with an E. coli gene encoding mannitol-1-phosphate dehydrogenase (mtlD). Four plant lines that grew on kanamycin and contained the mtlD transgene were identified. Two of these lines contained high levels of mannitol [high-mannitol lines M3 and M8; mean mannitol = 3.39 μmol·g-1 dry weight (DW)] compared to nontransformed wild-type plants (0.86 μmol·g-1 DW), while two lines had mannitol levels similar to wild-type plants (low-mannitol lines M2 and M9; mean mannitol = 1.05 μmol·g-1 DW). Transgenic and control plants were subjected to chilling stress (3 ± 0.5 °C day/0 ± 0.5 °C night, 12-hour photoperiod and 75% relative humidity) to evaluate the role of mannitol in chilling tolerance. Based upon foliage symptoms and membrane leakage after a 3-week chilling treatment, the high-mannitol containing lines, M3 and M8, were more tolerant of chilling stress than the low-mannitol containing transgenic lines, M2 and M9, and wild-type. Under nonchilling conditions mannitol was the only carbohydrate that differed among transgenic lines, but all carbohydrates were present. When subjected to chilling stress, mannitol levels dropped by 75%, sucrose by 52%, and inositol by 54% in the low-mannitol lines (M2 and M9). In M3 and M8, the high-mannitol lines, mannitol levels decreased by 36%, sucrose by 25%, and inositol by 56%, respectively. Raffinose increased 2- to 3-fold in all lines following exposure to low-temperature chilling stress. In the higher mannitol lines only 0.04% to 0.06% of the total osmotic potential generated from all solutes could be attributed to mannitol, thus its action is more like that of an osmoprotectant rather than an osmoregulator. This study demonstrates that metabolic engineering of osmoprotectant synthesis pathways can be used to improve stress tolerance in horticultural crops.

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