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Mario I. Buteler, Don LaBonte, and Raul Macchiavelli

The breeding of new sweetpotato varieties is a highly inefficient process, confounded by incompatibility, poor fertility, open-pollination, and its hexaploid nature. Upwards of 12 to 20 lines are currently combined in open-pollinated nurseries based on good horticultural characteristics. Most progeny after several years of selection can be traced back to just three or four maternal lines. A method that would identify the paternal parent of superior progeny would enable breeders the ability to combine parents that exhibit superior combining ability in more-efficient, smaller nurseries. The objective of this work is to explore by means of computer simulation the application of genealogy reconstruction techniques on hexaploid individuals with PCR-based data. The progeny obtained on each female parent is fractionally assigned to each male with non zero exclusion probability proportional to its paternity likelihood. Computer simulations show that at least five different alleles per loci are needed to reach a reasonable discriminatory level. Also, the number of loci scored should not be less than 20. An increment in the number of alleles or loci increases the discriminatory power; but, the number of alleles produces a far more important effect than the number of loci.

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Mario I. Buteler, Don R. LaBonte, and James H. Oard

RAPD and the single dose polymorphic band (SDPB) are powerful tools for genome map construction of higher polyploids, such as hexaploid sweetpotato. Duplication in the genome of higher polyploids results in fewer polymorphisms per primer screened than one would expect in diploids. The Stoffel fragment (Sf) is suggested as an alternative to the most commonly used Taq DNA polymerase to maximize the number of polymorphisms. Genomic DNA from two sweetpotato varieties, `Excel' and `Beauregard', and F1 progeny was isolated using a modified CTAB procedure. The DNA was assayed with twelve primers from Operon Technologies groups A and F. Each enzyme was tested with and without a ramp temperature treatment between the annealing and the extension temperatures. Results are based on three separate amplifications and electrophoretic runs. Band reproducibility was better using Sf than Taq; unfortunately, resolution was lower making bands difficult to score. 8.4% more scorable bands and 20.3% more storable polymorphisms were obtained with Taq. The ramp treatment did not alter results using Sf, but did improve the reproducibility of Taq and ease scoring. The number of bands and their location were the same.

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Mario I. Buteler, Don R. LaBonte, and Robert L. Jarret

Microsatellites or simple sequence repeats (SSRs) were used to characterize 20 sweetpotato genotypes and to assign paternity for offspring from crosses among them. The PCR amplifications were performed with each of the sweetpotato genotypes and primers flanking a SSR loci previously characterized with the varieties Beauregard and Excel and 20 offspring from a cross among them. The PCR reaction products were separated in nondenaturing 12% acrylamide gels run at 25 V·cm–1 for 5 hours, and DNA fragments were visualized with silver staining. Gels were scanned on a flat bed scanner and analyzed using the Pro-RFLP software package. Three primer pairs were sufficient to produce an allelic profile capable of differentiating the 20 genotypes from each other. More than seven alleles/loci were found using each of the three primer pairs assayed. Occasionally primers produced allelic products clearly localized in two or three regions of the gel. These multiple loci segregated independently in a diploid fashion. This evidence suggests that there is not total homology among the three sweetpotato genomes.

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Bong-kyoo Kim, Don R. La Bonte, Christopher A. Clark, and Mario I. Buteler

Narrow-sense heritabilities for reaction to chlorotic leaf distortion (CLD), incited by Fusarium lateritium Nees: Fr., were estimated in sweetpotato [Ipomoea batatas (L.) Lam] by variance component analysis and parent–offspring regression. Visually rated severity reactions to CLD varied greatly among the 20 parents used to generate half-sib progeny from open-pollinated nurseries in 1990 and 1991. Progeny from each nursery were evaluated along with parents in a completely randomized design in two consecutive years. Narrow-sense heritability (h 2) estimates based on variance components were moderate on an entry mean basis at 0.61 in 1990, 0.38 in 1991, and 0.33 for the two years combined. Slightly higher, but still moderate, estimates were obtained on an individual plant basis. Narrow-sense heritability estimates using parent–offspring regression were 0.35 in 1990, 0.33 in 1991, and 0.33 for the two years combined. Predicted next-generation response was highest using a half-sib family recurrent selection among three schemes compared at a 10% selection intensity. Our data indicate –0.63 improvement in the half-sib family CLD severity rating in one breeding cycle.