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- Author or Editor: Wanda W. Collins x
The response of 501 open-pollinated seedlings of 9 parental clones of sweet potato [Ipomoea batatas (L.) Lam.] to the severe russet crack strain of sweet potato feathery mottle virus (SRC-FMV) was evaluated under greenhouse conditions. Sixty-four percent of the seedlings showed foliar, root, or foliar/root symptoms, indicating that SRC-FMV can be sap-transmitted to seedlings. Fifty-nine percent showed foliar symptoms only. Seedlings from the parental clone with the highest percentage of symptom expression (88%) in the greenhouse were used to study the effect of selected environmental factors on foliar symptom expression. The predominant symptom was veinbanding. The percentage of plants showing symptoms varied from 0% to 46% and was influenced significantly by the interaction of light intensity × daylength × temperature.
Flooding is a serious problem in sweet potato production in Atlantic and Gulf Coast states. Studies have been attempted using irrigation to simulate flooding (1, 3). Results have been inconsistent and flood damage was often difficult to induce. However, during 5 days in 1984, Hurricane Diana resulted in 267.5 mm of rainfall on sweet potato cultivar plots at the Horticultural Crops Research Station in Clinton, N.C. The plots were planted in a Norfolk sandy loam soil. When plots were harvested 2 weeks later, flood damage was readily apparent. Typical symptoms of flooding injury included visible soft, rotted areas, growth of saprophytic fungi on the surface and a noticeable odor of fermentation. Roots were separated into three groups (total marketable, culls, and flood-damaged roots) and weighed. Samples were also taken of apparently sound roots for intercellular space and dry matter evaluations (four roots each) and for determining amount of sub-sequent rotting during curing and storing (12–13 kg). Intercellular space and percent dry matter were determined according to Kushman and Pope (2).
Streptomyces soil rot or pox, caused by the actinomycete Streptomyces ipomoea, is a destructive root disease of sweetpotato. Evaluation for resistance to S. ipomoea in naturally infested fields, requires much space and results may vary from year to year. In this study a greenhouse method for evaluating the response of sweetpotato clones to infection with S. ipomoea was developed. The greenhouse method used fibrous roots, developed on terminal vine cuttings. Experiments showed no time by clone interaction, indicating that this method gave consistent results when repeated. A study to determine corrrelation between field resistance of clones and resistance as found by the greenhouse method was done. Thirty-nine clones were screened for resistance using the greenhouse method and were also planted in a field naturally infested with S. ipomoea. Severity of disease on fibrous roots (greenhouse method) and on storage roots (field method) was evaluated visually using a scale of 0 to 5 (0: no symptoms. 5: severe symptoms). Although correlations between data from the greenhouse and field methods were low lo moderate (r=0.17 to 0.49). extremely susceptible or resistant clones were identified as such by both methods. These results suggest that it is possible to select clones with high resistance to S. ipomoea using the greenhouse method, which provides a better controlled environment, and requires less space than field evaluations.
Crimson clover Trifolium incarnatum L.) was used as a N source for sweet potato [Ipomoea batatas (L.) Lam.]. Treatments were designed to compare estimated N delivery by clover incorporation amounts of N delivered by inorganic fertilizer. Plants were sampled every 14 days and sectioned into four parts: shoots, stem tips, fibrous and storage roots. Dry matter content was significantly influenced by time. Total plant dry matter was lowest in the highest inorganic N treatment. Nitrogen concentration (DWB) decreased over time and was highest in the highest inorganic N treatment. Similar vine weights were noted in N and clover treatments while number of storage roots per plant was unaffected by treatment as was weight per storage root, which increased linearly over time. No significant difference existed between the high and low N application treatment or late clover incorporation treatment in any grade of storage roots except culls, which were 90% lower in clover treatments than in N fertilizer treatments.
Genetic control of seven enzymes in Ipomoea trifida (H.B.K.) G. Don. (diploid, tetraploid, and hexaploid populations) and I. batatas (L.) Lam. was studied by starch gel electrophoresis. Inter- and intraspecific polymorphisms were detected for all enzymes in the populations analyzed, except catalase (CAT, EC 188.8.131.52). Phosphoglucomutase (PGM; EC 184.108.40.206), phosphoglucose isomerase (PGI; EC 220.127.116.11), glutamate oxaloacetate transaminase (GOT; EC 18.104.22.168), menadione reductase (MNR; EC 22.214.171.124), shikimate dehydrogenase (SAD; EC 126.96.36.199), and malate dehydrogenase (MDH; EC 188.8.131.52) collectively were encoded by a minimum of 13 genetic loci resulting in 24 allozymes. Results from the diploid I. trifida were used to infer the genetic basis of these enzymes in the polyploid species. All polyploid populations shared almost the same number of allozymes with diploid I. trifida. PGM and PGI showed evidence of duplicated genes in the polyploid series. A unique allele for MNR was detected only in polyploid series.
Randomly amplified polymorphic DNA (RAPD) analysis was performed on 18 accessions belonging to four different species of the genus Ipomoea, including sweetpotato and three related species. Twenty-two out of 30 primers tested revealed polymorphisms among these four species. Eight primers were selected on the basis of the number and repeatability of polymorphism produced. With these, a total of 98 different DNA bands were obtained and 85% of them were polymorphic. Based on the presence/absence of the bands, a genetic similarity among accessions and among species was calculated. Unweighted pair-group method with arithmetical averages (UPGMA) based on the similarity coefficients clearly discriminated these four species. Ipomoea trifida and sweetpotato share more genetic similarity. Ipomoea triloba and I. leucantha fall into another cluster. This study demonstrated that RAPD techniques can be a very useful tool for genotype/accession identification and studying the genetic relationship among genotypes/accessions of sweetpotato and among species of Ipomoea.
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.
Eight clones of sweetpotato [Ipomaea batatas (L.) Lam.] at five N levels in 1992 and five clones at three N levels in 1993 were evaluated for genotypic variation in N use efficiency [NUE (yield/unit N fertilizer applied)], uptake efficiency (N accumulated/unit N fertilizer applied), and utilization efficiency (yield/N accumulated). There were significant genotypic differences for all NUE components and the variables used for calculation. When total marketable yield was used in calculating NUE, utilization efficiency was always more important than uptake efficiency in accounting for NUE variation. Regression equations developed from 1992 NUE components and selected non-N variables used to calculate them ranked the 1993 NUE components correctly when averaged over all clones. Uptake efficiency could be predicted by biomass; utilization efficiency by total marketable yield.