Use of a detached leaf screening method for segregating Colorado potato beetle (Leptinotarsa decemlineata Say) resistant Solanum hybrid lines

A diploid segregating population for resistance to Colorado potato beetle (CPB) was developed by crossing the resistant Mexican species Solanum pinnatisectum (S. pnt., 2n = 2x = 24) with the susceptible S. cardiophyllum (S. cph., 2n = 2x = 24). A resistant hybrid plant from this cross was selected and backcrossed as a female to S. cph in order to generate a backcross family. A beetle feeding preference test bioassay was developed to examine segregation for CPB resistance in 345 backcross progeny. A screening method that optimized the length of the feeding period allowed the quantification of CPB resistance in the backcross progeny. Percent resistance of the test lines over the susceptible control was determined using the formula R = 100 × [C/(C + L)]

A first-generation map of the turkey genome

A primary linkage map of the domestic turkey (Meleagris gallopavo) was developed by segregation analysis of genetic markers within a backcross family. This reference family includes 84 offspring from one F1 sire mated to two dams. Genomic DNA was digested using one of five restriction enzymes, and restriction fragment length polymorphisms were detected on Southern blots using probes prepared from 135 random clones isolated from a whole-embryo cDNA library. DNA sequence was subsequently determined for 114 of these cDNA clones. Sequence comparisons were done using BLAST searches of the GenBank database, and redundant sequences were eliminated. High similarity was found between 23% of the turkey sequences and mRNA sequences reported for the chicken. The current map, based on expressed genes, includes 138 loci, encompassing 113 loci arranged into 22 linkage groups and an additional 25 loci that remain unlinked. The average distance between linked markers is 6 cM and the longest linkage group (17 loci) measures 131 cM. The total map distance contained within linkage groups is 651 cM. The present map provides an important framework for future genome mapping in the turkey.Key words: genetic map, Meleagris gallopavo, expressed sequence tag, RFLP.

Genetics of Floral Longevity in Petunia

Petunia hybrida Vilm. is one of the major bedding plants grown worldwide, and, like most bedding plants, is grown primarily for its seasonal floral display. While increased floral and reflowering capacity have been the focus of breeding programs for many ornamental species, floral longevity has received little direct attention. Increased floral longevity would enhance the value of any crop grown for floral effect. In this study, four parental genotypes (two with short flower life, two with long flower life) were crossed in a partial diallel mating design to create six F1 families. The F1 individuals were then selfed and backcrossed to the appropriate parents to create F2 and backcross families. Data from parental and F1 genotypes were analyzed to determine general and specific combining ability for floral longevity in petunia. Results indicated the presence of significant additive gene effects and nonsignificant nonadditive gene effects for floral longevity in this germplasm. However, aberrant F2 and backcross family means were observed in all families. For each family, F2 and backcross means were lower than expected given normal Mendelian segregation. Further experiments will be necessary to elucidate the causes for the deviate F2 and backcross family means before specific recommendations for selecting for increased floral longevity in petunia can be made.

Inheritance of Random Amplified Polymorphic DNA (RAPD) Markers in Theobroma cacao L.

RAPD markers have been used successfully in genetic analysis of several crop plants. This method poses difficulties with a highly heterozygous species such as Theobroma cacao because of the dominant phenotypic expression of bands. A backcross family derived from ctultivars Catongo and Pound 12 was analyzed to determine the efficacy of RAPD markers in analyzing cacao populations. A preliminary screen of the parents and the F1 plant used as the backcross parent was conducted with 180 RAPD primers; of these, 26% were polymorphic and reproducible and produced 104 storable loci. Genomic DNA from 54 individuals of the backcross population was then amplified with these primers; 68.3 % of the loci segregated as expected in a Mendelian fashion. Separation of RAPD fragments on acrylamide revealed an additional polymorphic locus from one primer that was indistinguishable on agarose. The results demonstrated that RAPD markers can be used to study the cacao genome.

680 PB 192 INRERITANCE OF KAPD PATTERNS IN THEOBROMA CACAO

While Random Amplified Polymorphic DNA (KAPD) has been used successfully in genetic analysis of several crop plants, the method poses difficulties with a heterozyaous species such as Theobroma cacao due to the dominant phenotypic expression of bands. A backcross family of the cultivars `Catoneo' and `Pound 12' was analyzed to determine the efficacy of this technique in analyzing cacao populations. A primary screen of the parents and F1 was conducted with 180 KAPD primers; of these, 39.5% either-did not amplify or did so poorly or irreproducibly, while 60.5% amplified well. Phenotypes produced by 42 primers represented possible test crosses, which can be used in linkage mapping. Genomic DNA from 50 individuals of the backcross population were then amplified with these 42 primers, which in most cases resulted in 1:1 segregation of bands. Preliminary experiments show that the Stoffel fragment of Taq DNA polymerase may provide additional markers. These results indicate that it should be possible to use RAPD bands as molecular markers to study the cacao genome.