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Petra Wolters and Wanda W. Collins

Ipomoea trifida (2X = 30) is purported to be the wild Ipomoea species most closely related to the commercially grown Ipomoea batatas (sweetpotato, 6X = 90). The two species can be crossed with much difficulty, but seed occur rarely. Ipomoea trifida has been shown to possess some agronomically desirable traits that are missing in sweetpotato (e.g., sweetpotato-weevil resistance). Attempts to locate morphological markers in the diploid trifida that would serve as indicators of successful crosses with sweetpotato resulted in the identification of two traits controlled by single genes: nectary color and male sterility. Both traits require flowering to identify, and flowering is often difficult to induce in Ipomoea species. An analysis of I. trifida accessions using RAPD molecular markers was undertaken. Using a segregant population resulting from crossing a green nectary, fertile plant with a yellow nectary, male, sterile plant, RAPD analysis resulted in clear markers for both the nectary color trait and the male sterility trait. These traits now can be identified in the absence of flowering plants.

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Luz M. Reves and Wanda Collins

Eight populations including Ipomoea batatas and I. trifida species were assayed at six polymorphic enzyme loci. Differences in allele frequencies among populations allowed distinction of the two species and among levels of ploidy. Principal component and cluster analyses using isozyme and morphological data were performed. Results from isozyme characterization in general supported the results from morphological classification. Cluster analysis from isozyme assays indicated that the hexaploid species I. trifida is not a different species than I. batatas but may be a wild type. Significant deviations of genotypic frequencies from Hardy-Weinberg equilibrium in some of the loci were detected and were possibly due to effects of natural selection; this fact was reflected in the level of homozygosity observed among populations for the loci in disequilibrium.

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Douglas Maxwell and R. Daniel Lineberger

Bush morning glory (Ipomoea carnea ssp. fistulosa) and the ornamental sweetpotato cultivar Blackie (Ipomoea batatas) were used to demonstrate various grafting methods to students in an undergraduate horticulture class at Texas A&M Univ. Grafting the vining species onto the upright shrubby species produced an attractive ornamental plant and illustrated that graft union formation was independent of plant morphology. Graft “take” was high, ranging from 83% to 100%. Stock plants of both species are easily maintained in the greenhouse and can be rooted readily to “batch up” plants for laboratory sessions. Cuttings from both species can also be used in various rooting experiments, with cuttings of sweetpotato rooting in days rather than weeks, as with some species. The wide difference in morphology and coloration of these two plants also creates an easily distinguishable division between stock and scion.

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Ki-Cheol Son, Ray F. Severson and Stanley J. Kays

Methodology was developed for the rapid quantitative and qualitative screening of sweetpotato [Ipomoea batatas (L.) Lam.] germplasm for the concentration of the major sweetpotato weevil oviposition stimulant, boehmeryl acetate, and its alcohol, boehmerol. The major surface components were rapidly quantified, using a minimum of plant material. Boehmeryl acetate, present in methylene chloride root extracts, did not degrade when held under normal laboratory conditions for 45 days. Boehmeryl acetate and boehmerol were found only in the outer 1 to 1.2 mm of periderm and the distribution of the compounds appeared to be relatively uniform over the surface of the root.

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Chana Phromtong, Floyd M. Woods, James O. Garner Jr. and Juan L. Silva

Sixteen sweet potato (Ipomoea batatas L.) genotypes were chilled for 36 hours at 5C with 85% RH and a 12 hour photoperiod. Transpiration, leaf diffusive resistance and visual scores for plant quality were taken before chilling and 2 days after the chilling treatment. Differences between the before and after readings were used to indicate the extent of chilling injury or tolerance. Visual score gave a better separation of the genotype for tolerance, however, the difference in transpiration was the most critical of the two objective measurements.

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Warren Roberts and Vincent Russo

The sweetpotato [Ipomoea batatas (L.) Lam] cultivars Jewel, Shore Gold, and Cordner, and the breeding line W241 were either 1) not flooded, 2) flooded for 5 days during midseason, or 3) flooded for 5 days just before harvest. Flooding just before harvest did not affect marketable yield, but flooding at midseason reduced marketable yield by 36% in 1989 and by 53% in 1990 and reduced the No. 1 grade yield by 46% in 1989 and by 57% in 1990. Marketable yield of `Jewel' was higher than that of `Cordner' in 1989, and that of `Shore Gold' exceeded that of `Jewel' in 1990. There were no interactions between flooding treatments and cultivars.

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Ki-Cheol Son, Ray F. Severson and Stanley J. Kays

Levels of major root surface components for two sweetpotato [Ipomoea batatas (L.) Lam.] cultivars that differ in susceptibility to the sweetpotato weevil [Cylas formicarius elegantulus (Summers)] were determined. Analyses were made 30 days before harvest, at harvest, after curing, and after 2 months of storage during two seasons. Significant variation in the amounts of individual components, especially boehmeryl acetate, which is known to be an ovipositional stimulant for the weevil, was found before and after harvest, with season, and between cultivars. These results suggest that variation in field susceptibility of cultivars displaying moderate levels of resistance may be due in part to seasonal variation in the level of ovipositional stimulants.

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James M. Schalk, Philip D. Dukes, Alfred Jones and Robert L. Jarret

The reactions of eight sweetpotato [Ipomoea batatas (L.) Lam.] introductions were categorized for root damage by wireworms, Diabrotica sp., Systena sp. (WDS), sweetpotato flea beetle (SPFB), and grubs. Clones were compared with resistant (`Regal') and susceptible (`SC-1149-19') entries. The number of resistant clones for the WDS, SPFB, and grubs were three, four, and one, respectively, intermediate five, four, and one, and susceptible zero, zero, and six, respectively. This test demonstrated that significant levels of soil insect resistance exist in these sweetpotato introductions for use by plant breeders.

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Lavetta L. Newell and James O. Garner Jr.

In two experiments, 16 sweetpotato genotypes (Ipomoea batatas L.) were evaluated for drought tolerance using the detached-leaf water loss method. Dry weight loss was also determined. Difference in the rate of leaf water loss over a 48 hour period were found. `Vardaman' had the greatest amount of dry weight loss and the least amount of water loss. No relationship between dry weight loss and water loss was found.

When measuring chlorophyll fluorescence using two sweetpotato genotypes, `Vardaman' had a higher rate of photosynthetic transport activity.

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Melvin R. Hall

Immersion of sweetpotato [Ipomoea batatas (L.)] storage roots in low concentration (5 and 50 mg·liter-1) of gibberellic acid (GA) in solutions of benzyl adenine plus GA4+7 increased early but not total plant production from bedded roots of `Georgia Jet' and `Jewel'. Immersion in 0.5 and 1 mg·liter-1 solutions of GA3 increased early plant production from `Georgia Jet'. Neither weight nor visual appearance of the harvested plants nor root yield from transplants were influenced by gibberellin treatments of the bedded roots.