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  • Author or Editor: J.M. Davis x
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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

Abstract

Clonal multiplication of carnation (Dianthus caryophyllus L.) was accomplished in three stages: 1) shoot tip culture initiation stage, 2) shoot multiplication stage, and 3) rooting stage. The culture medium for the initiation stage was examined by comparing various inorganic salt mixtures, vitamin mixtures, carbohydrates, growth regulators, agars, pH’s, and additional supplements for their effect on growth and development of multiple shoots from shoot tips. When shoot tips (ca. 1 mm high) were grown on a modified Murashige and Skoog medium with 10 µM kinetin and 1 µM NAA, apical dominance was counteracted and morphologically normal shoots proliferated rapidly. Transferring these cultures after 4 wk to 100 ml flasks (one per flask) with 50 ml of same medium without agar and supplements, and with the kinetin concentration reduced to 2.5 µM, resulted in an average per original shoot tip of 28 shoots over 2 cm in height being produced in another 3 weeks. These shoots were rooted in BR-8 blocks or Jiffy-7 peat pellets under intermittent mist. Plantlets rooted in these supports were transferred easily to greenhouse conditions. Incorporation of carnation micropropagation into a pathogen-free propagative stock program should not be difficult, and might prove beneficial even if large scale use is limited by economic considerations.

Open Access

Abstract

Minnesota 266 is an early maturing, andromonecious, short-internode breeding line of muskmelon, Cucumis melo L., from the vegetable improvement program of the Departments of Horticultural Science and Landscape Architecture, and Plant Pathology. It has value for the home garden and, in addition, it should be useful as a germplasm source for selection as well as for the development of commercial hybrids and/or types for mechanical harvesting.

Open Access

Wild Anagallis monelli exhibits blue or orange flower colors in geographically isolated populations. A new red flower color was developed through breeding, and a three-gene model was proposed for the inheritance of flower color in this species. In this study, blue and orange wild diploid accessions were used as parents to develop six F2 populations (n = 19 to 64). Sexual compatibility between blue and orange wild individuals was low with only 29% of the hybridizations producing F1 individuals. Six of 14 cross combinations between F1 siblings produced fruits, and fruiting success ranged from 55% to 90%. The number of seeds per fruit averaged 14.1 and germination rates for the F2s were low (16.8% to 30.7%). In three of six F2 populations obtained, flower color segregation ratios for orange, blue, and red were not significantly different from the expected ratios under a previously proposed three-gene model. White flower color was obtained as a fourth color variant in two of the remaining F2 populations. For one of these populations, segregation ratios were not significantly different from expected ratios for an expanded four-gene model. White flowers did not contain anthocyanidins, suggesting that there was a mutation in the early stage of the anthocyanin pathway. Orange flower color was found to be primarily the result of pelargonidin, blue to malvidin, and red to delphinidin. These three pigments may be present simultaneously, and their ratios play a significant role in determining flower color. Other factors such as copigments, metal ions, or a different molecular conformation of the anthocyanin could also be involved in flower color determination.

Free access

Abstract

Minnesota 101 is a monoecious, short intemode breeding line of muskmelon, Cucumis melo L. Its primary use is envisaged as that of a breeding line useful as a parent in the production of F1 hybrid cultivars, and as germplasm in the long term improvement of muskmelon.

Open Access

Abstract

A controlled environment technique using freshly silked, excised ears artificially infested with 1st instar larvae was developed for evaluating sweet com (Zea mays L.) for resistance to 2nd-brood European com borer, Ostrinia nubilalis (Hiibner). At 14 days, infested ears of the moderately resistant dent inbred ‘B52’ held in plastic bags at 27°C (day) 21° (night), high humidity, and 16 hour photoperiod (8.6 klx) had fewer 4th and 5th instar larvae and possibly lower larval weight Use of this technique could improve the efficiency of screening via artificial infestation by reducing environmentally caused variability.

Open Access

Two crack-resistant and two crack-susceptible fresh-market tomato (Lycopersicon esculentum Mill.) cultivars were evaluated at varied soil moisture levels for physiological fruit defects and yield. Cultural practices recommended for staked-tomato production in North Carolina with raised beds, black polyethylene mulch, and drip irrigation were used. Soil moisture levels of less than −15.0, −30 to −40, and greater than −70 kPa were maintained and monitored using daily tensiometer readings. Soil moisture level had no effect on fruit cracking, blossom-end rot, zippers, or yield. However, there-were large differences among cultivars for fruit defects and total and marketable yields.

Full access

Abstract

Interplot interference, or the influence of one host genotype on another when grown in adjacent plots, can be a problem with the evaluation of partial resistance to airborne pathogens. Moreover, interplot interference may affect selection in the plant breeding nursery. To estimate the degree of interference in a typical sweet corn (Zea mays L.) breeding nursery, the partial resistance of 3 hybrids grown in several field plot treatments was examined. Treatments consisted of differing spatial arrangements of the 3 hybrids. In a 2-year study, mean rust level differed significantly for 5 field plot treatments. As the potential for leaf rust increased, the ability to distinguish between hybrid disease reaction diminished. In addition, the variability in disease reaction was reduced as rust potential increased for hybrid and field plot treatment, indicating that when high levels of leaf rust existed, disease gradients tended to flatten.

Open Access

Abstract

Evaluation of the progeny populations from crosses between a resistant sweet corn inbred (Zea mays L.) and 3 susceptible inbreds indicated that the variation for partial resistance to corn leaf rust (Puccinia sorghi Schw.) depended on the parents used. Heritability estimates were high with both additive and dominance gene effects important in character expression. Epistasis was shown to influence rust reaction in at least one cross. The ability to improve partial resistance in 2 sweet corn populations was demonstrated by 3 methods of selection.

Open Access

Abstract

The influence of common leaf rust (Puccinia sorghi Schw.) on 2 sweet corn (Zea mays L.) hybrids was compared in rusted and nonrusted plots for several maturity and ear quality characters. Differences were found for time of silking, ear length, ear diameter, and percentage of moisture between rusted and nonrusted plots. The percentage of Brix ranged from 4% to 25%, with the rusted plots always having reduced mean values. Correlations (P = 0.01) were found between ear diameter and percentage of moisture, percentage of Brix and percentage of moisture, and between ear length and ear diameter.

Open Access