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  • Author or Editor: R. M. Davis x
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Abstract

The term “vein tract” is better than “suture” to denote the longitudinal indentations or unnetted strips which sometimes characterize the outward appearance of fruits of Cucumis melo L., reticulatus Naud. The term “suture” has a botanical ring in comparison to “grooves” or “stripes,” and I confess to having used it as much as anybody. Unfortunately, “suture” is here applied incorrectly; thus it is misleading to one who may be considering physiological explanations for unexplained variations in this surface feature.

Open Access
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Abstract

Six-month-old nonmycorrhizal or mycorrhizal [Glomus fasciculatum (Thaxter) Gerd. and Trappe] sour orange (Citrus aurantium L.) seedlings grown in a sandy soil amended with 0, 50, or 100 μg P/g soil were completely girdled 5 mm below the basal leaves. Eight weeks later, root exudates and extracts were analyzed and one-half of the nonmycorrhizal plants were inoculated with G. fasciculatum. Amounts of soluble sugars were greater in exudates from girdled nonmycorrhizal plants than in exudates from nongirdled or mycorrhizal plants. Girdling consistently reduced the amount of sugars in root extracts in all plants. Amounts of amino acids in exudates or extracts were not consistently affected by any treatment. Intensity of mycorrhizal infection was similar in girdled and nongirdled plants grown in sand without supplemental phosphorus, but mycorrhizal development was insignificant in plants inoculated after girdling and grown in sand amended with 50 or 100 μg P/g soil. Root infection was apparently dependent both on levels of photosynthates supplied to the roots and on the amount of nutrients in root exudates.

Open Access

The susceptibility of 46 carrot cultivars to infection by Alternaria radicina Meier, Drechsler, and Eddy, causal agent of black rot disease, was evaluated in field trials with a toothpick inoculation method. Toothpicks infested with A. radicina were inserted into the shoulders of 10- to 12-week-old carrots (Daucus carota L.) and lesion areas were measured 9 to 10 weeks later. There were significant differences in lesion size among cultivars. Relatively resistant cultivars included `Panther' and `Caro-pak', and susceptible cultivars included `Royal Chantenay' and `Nogales'. Nine of the cultivars were inoculated with A. radicina-infested toothpicks and maintained in cold-storage for 10 weeks. Lesion development was greater in cold-storage than in the field, but the relative ranking of cultivars in terms of resistance to A. radicina was similar.

Free access

Abstract

Fruit of ‘Ruby Red’ grapefruit (Citrus paradisi Macf.) were treated postharvest with sodium-o-phenylphenate (SOPP), benomyl, imazalil, and etaconazole and stored under ambient conditions or were treated with SOPP, imazalil, and etaconazole and stored at 12°C. Imazalil and etaconazole were as effective as benomyl under ambient conditions and were more effective than SOPP under refrigerated conditions; 85% of the stem-end-rot was caused by Phomopsis citri (Fawc).

Open Access

Abstract

Concentrations of soluble solids (SSC) in fruits of Cucumis melo L., cv. PMR 45, were positively correlated with 2 physical measures of soil samples from producing fields: a) the degree of cracking which occurred during dehydration, and b) the rapidity with which water or a CaSC>4 solution percolated the soils. Very low SSC was associated with sandy, non-cracking soils, which in addition permitted only low rates of percolation. Low SSC also was found to be associated with soils having subsurface hardpans or dense subsoil strata, and also with the distance to lower bounds of plant containers and experimentally placed barriers which obstructed downward root growth. SSC, under adverse conditions, varied further as a function of fruit numbers per plant.

Open Access

Abstract

Growth responses of ‘sour orange’ (Citrus aurantium L.), ‘Swingle citrumelo’ [C. paradisi Macf. x Poncirus trifoliata (L.) Raf.], ‘Cleopatra mandarin’ (C. reticulata Blanco), ‘Volkamer lemon’ (C. volkameriana Pasq.), and ‘Troyer citrange’ [C. sinensis (L.) Osbeck x P. trifoliata], infected by the mycorrhizal fungi Glomus etunicatum Becker and Gerd., G. microcarpum (Tul. and Tul.) Tul. and Tul., or 2 isolates of G. fasciculatum (Thaxter) Gerd. and Trappe, were compared. Overall, G. fasciculatum 92 caused the greatest growth responses and G. microcarpum the least. ‘Cleopatra mandarin’, the slowest growing cultivar, was the most mycorrhizal dependent cultivar while ‘sour orange’ and ‘Volkamer lemon’, which exhibited the greatest growth, were the least dependent. The greatest growth responses were usually associated with high concentration of phosphorus in leaf tissue, but phosphorus concentrations were not always related to mycorrhizal dependency. Rarely did mycorrhizal species affect different cultivars in dissimilar ways.

Open Access

Abstract

Nonmycorrhizal or mycorrhizal (Glomus fasciculatum, G. etunicatum, or Gigaspora heterogama) sour orange (Citrus aurantium L.) seedlings were fertilized with 3 phosphorus levels applied in the irrigation water. At 0 mg P/L fertility, dry weight and cytokinin production of mycorrhizal plants were more than twice those of the nonmycorrhizal plants. Concentrations of P in leaves of mycorrhizal plants also were greater than the concentrations of P in the nonmycorrhizal plants. At 50 mg P/L fertility, concentrations of P in leaves were similar whether or not plants were mycorrhizal. Dry weight and cytokinin production of the mycorrhizal plants, however, were still twice those of the nonmycorrhizal plants. At 100 mg P/L fertility, dry weight and cytokinin production did not differ between nonmycorrhizal plants and plants infected with 2 of 3 mycorrhizal fungi. In G. heterogama-infected plants, cytokinin production was greater than that of nonmycorrhizal plants despite similar dry weights and P concentrations in the leaves. Enhancement of cytokinin production seemed to be associated with mycorrhizal infection rather than with increased P uptake.

Open Access

Mustard (Brassica spp.) cover crop residue has been reported to have significant `biofumigant' action when incorporated into soil, potentially providing disease suppression and yield improvement for the succeeding crop. The effects of growing over-winter mustard cover crops preceding processing tomato (Lycopersicon escultentum Mill.) production were investigated in six field trials in the Sacramento Valley of California from 2002–04. A selection of mustard cover crops were compared to a legume cover crop mix, a fallow-bed treatment (the current grower practice in the region), and in two of the six trials, fumigation treatments using metam sodium. Mustard cover crops removed 115 to 350 kg·ha–1 N from the soil profile, reducing NO3-N leaching potential. Soil populations of Verticillium dahliae Kleb. and Fusarium spp. were unaffected by the cover crops, and there was no evidence of soilborne disease suppression on subsequent tomato crops. Mustard cover crops increased tomato yield in one field, and reduced yield in two fields. In one of two fields, metam sodium fumigation significantly increased tomato yield. We conclude that, while environmental benefits may be achieved, mustard cover cropping offers no immediate agronomic benefit for processing tomato production.

Free access

Mustard cover crop residue has been reported to have a “biofumigant” action when incorporated into the soil, potentially providing significant disease suppression and yield improvement for the succeeding crop. Such activity could be particularly useful in processing tomato rotations, where consecutive cropping invariably results in yield decline. Agronomic and environmental effects of growing over-winter mustard cover crops preceding tomato production were investigated in three field trials between 2002 and 2004. Two mustard cover crops [`Pacific Gold', a brown mustard (Brassica juncea), and `Caliente', a blend of brown and white mustard (Sinapis alba)] were compared to a legume cover crop mix, a fallow bed treatment (the standard grower practice in this region), and, in two of the three trials, a fumigation treatment using metam sodium. No suppression of soil populations of Verticillium dahliae or Fusarium spp. was observed with the mustard cover crops, nor was there any visual evidence of disease suppression on subsequent tomato crops. In these fields, the mustard either had no effect, or reduced tomato yield, when compared to the fallow treatment. At one of two sites, metam sodium fumigation significantly increased tomato yield. The presence of a cover crop, whether mustard or legume, reduced winter runoff by an average of 50% over two years of trials. No benefit of mustard cover cropping beyond this reduction in winter runoff was observed.

Free access

The toxic bait, Adios, was tested with the use of a trap crop in a field experiment at the Univ. of Nebraska during Summer 1998. The insecticide contains the secondary plant metabolites known as cucurbitacins that are highly attractive to the striped and spotted cucumber beetles, Acalymma vittatum and Diabrotica undecimuncata howardi, respectively. These beetles serve as the vector of the bacterial pathogen, Erwinia tracheiphila, which causes severe wilting and eventual death of susceptible cucurbits. The objective of the study was to determine whether treatments of Adios, when applied to a flowering trap crop of resistant squash plants, would lure the cucumber beetles away from the susceptible cucumber plants and reduce bacterial wilt. The study compared the effectiveness of a sprayed trap crop, the direct application of Adios to the cucumber plants and no treatment in a randomized complete-block design. A greater number of beetles were attracted to the sprayed and untreated cucumbers compared to the cucumbers surrounded by the treated trap plants. However, significant numbers of dead beetles were found near the sprayed cucumber plants. Untreated plants showed more feeding damage, diminished fruit quality, and an earlier observation date of wilt symptoms as compared to the other treatments. The treated trap plants and the direct application of Adios were effective in delaying infection in cucumbers compared to the untreated plants in the experimental plots. This treatment may be useful to home gardeners.

Free access