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and other hybrids. The objective of this report is to summarize the interspecific crosses in the genus Penstemon at the UNL WCREC over 10 years, 1996–2005, and compare those results to other reports in the literature. The majority of species used in
intraspecific crossing combinations within L. chalcedonica and L. × haageana ; 2) 102 interspecific crossing combinations within Lychnis spp.; and 3) 47 intergeneric crossing combinations between Lychnis spp. and Silene spp. Five crosses including
the number of inflorescences/number of fruit and this was used to determine self-incompatibility. Self-pollinations were conducted in 2006 and 2007 ( Table 1 ) and intra- and interspecific crosses were conducted in 2006 to 2008 ( Table 2 ). Because
Cucurbita ecuadorensis is a valuable source of multiple virus resistance. It is resistant to zucchini yellow mosaic virus (ZYMV), papaya ringspot virus (PRSV), watermelon mosaic virus, tobacco ringspot virus, squash mosaic virus, and cucumber mosaic virus (CMV). Its virus resistance can be transferred to squash and pumpkin, but sterility barriers must be overcome. The cross Cucurbita maxima× C. ecuadorensis can readily be made, and there is no need for embryo culture. Pollen fertility of the hybrid is somewhat reduced, but sufficient for producing F2 seed. Segregation for sterility occurs in the F2, but selection can be made for fertile plants that are homozygous for virus resistance. Cucurbita ecuadorensis is much more distantly related to C. pepo than to C. maxima, and there are more formidable barriers in this interspecific cross. The cross is very difficult to make with some C. pepo cultivars, but other cultivars are more compatible. Viable seed were not produced, but hybrid plants were obtained by embryo culture. Although both parents were monoecious, the hybrid was gynoecious. Male flower formation was induced by treating the hybrid with Ag or GA, but they were male-sterile. F2 seed was not obtained, but backcross seed was easily produced by using the interspecific hybrid as the maternal parent in crosses with C. pepo. The most refractory barrier was achieving homozygosity for ZYMV resistance. Disturbed segregation occurred in succeeding generations and the progeny of most resistant plants segregated and were not uniform for resistance. This and other barriers to interspecific gene exchange were overcome and a summer squash variety homozygous for resistance to ZYMV, PRSV, and CMV is being released this year.
Three classes of crosses using four genotypes of V. riparia (wild Riverbank grape) as maternal parents were evaluated for evidence of reproductive expression of genetic incongruity. The classes were: I V. riparia x V. vinifera cultivars (European domesticated grape); II V. riparia x French Hybrids (complex interspecific hybrids); III V. riparia x V. riparia. Percent fruit set and seeds per berry were recorded for two years. If incongruity is a factor in interspecific grape crosses, then the values for these traits would be expected to be lower in classes I and II than in class III. Analysis of variance indicated significant differences for some half-sib families. Fruit and seed set were lower in classes I and II than in class III, suggesting that incongruity is operative in wide grape crosses. In the process of creating French hybrids, genomes of several species came together over generations of hybridization. In concert with selection for fertility, repeated interspecific genomic exposure would be expected to have ameliorated the effects of initial incongruity between American species and V. vinifera, increasing their value as genetic bridges in breeding programs.
To generate a linkage map for further genetic analysis of the traits involved in cold hardiness of potato, we are constructing a RAPD-based linkage map using a two-generation interspecific pedigree of Solanum commersonii and S. cardiophyllum, a hardy and non-hardy species, respectively. We initially screened 220 primers of 10-base arbitrary sequences and selected 86 to amplify a total of 577 polymorphic bands: 301 S. commersonii-specific and 276 S. cardiophyllum-specific bands. Segregation of a total of 247 markers was scored on a population of 44 F1 individuals. From these 247 markers, we have identified 117 markers, which segregate 1:1 in the F1 progeny following a test cross configuration. A RAPD linkage map for S. commersonii will be presented.
Linkage relationships among eight isozyme genes (Acp-3, Est-1, Est-5, Prx-1, Prx-2, Prx-3, Me, and Adh) and two morphological markers (Inh and Twh) were investigated in one F2 and two BC1 families of interspecific crosses between the American chestnut (Castanea dentata Borkh.) and the Chinese chestnut (C. mollissima Blume). Inh was consistently linked with Prx-1 and Est-5 in all families. In addition, four other gene pairs, Acp-3–Inh, Acp-3–Prx-1, Me–Inh, and Twh–Inh, were linked in one of the three families investigated. The two isozyme genes and two morphological marker genes were tentatively integrated into one linkage group with the gene order Twh–Inh–Prx-1–Est-5.
Linkage relations among eight isozyme genes, Acp-3, Est-1, Est-5, Prx-1, Prx-2, Prx-3, Me and Adh, and two morphological markers, Inh, and Twh, were investigated in one F2 and two BC1 families of interspecific crosses between the American chestnut (Castanea dentata) and the Chinese chestnut (C. mollissima). Inh was found to be consistently linked with Prx-1 and Est-5 in all families. The order of these three genes was determined to be-Ihn--Prx1--Est5. In addition, four other gene pairs, Acp3--Inh, Acp3--Prx1, Me--Inh and Twh--Inh were found to be linked in one of the three families investigated. The four isozyme genes and two morphological marker genes were tentatively integrated into one linkage group with the following gene order Acp3--Me--Twh--Inh--Prx1-Est5. This study demonstrated that isozyme genes can be integrated with morphological marker genes into a single linkage map without the need for additional crosses.
Effective genetic resistance to common bacterial blight [Xanthomonas campestris pv. phaseoli (Smith) Dye] is not present in common bean (Phaseolus vulgaris L.) cultivars grown in Ontario. Foliar symptoms and seed yield of white pea bean breeding lines from a P. vulgaris/P. acutifolius interspecific cross in the presence and absence of common blight were evaluated. In inoculated plots, seven of the 20 breeding lines did not differ significantly in severity of foliar symptoms from the most resistant controls, XAN 159 and XAN 161. The most susceptible lines tended to have the highest yield when grown under disease-free conditions (r = 0.61 and 0.49 at two locations). However, the susceptible lines showed an average yield loss of 25% when disease-free and inoculated plots were compared, while resistant lines had little or no yield loss. The most severely infected lines tended to have the greatest loss in yield (r = 0.72 and 0.53 at two locations). A resistant breeding line from this study is available as OAC 88-1.
The transfer of multigenic traits into tomato has been slow due to interspecific barriers (hybrid breakdown) found in the F2 of the Lycopersicon esculentum × L. pennellii cross (esc × pen), including blocks in normal reproductive development and nonfecundity. In a typical (esc × pen) F2 population, failure to flower and premeiotic blocks in pollen development occurred in 2% and 11% of the population, respectively. The remaining plants showed a mean of 37% stainable pollen. Twenty three percent of the F2 plants set seed, with an average of 4.5 seeds/fruit. An average of 33% of the stainable pollen from the 7 F2 plants with the highest stainable pollen measurements germinated in vitro, but only 4 of these 7 plants set seed. Thus, percent stainable pollen is not an adequate predictor of fecundity, and the non-fecundity in the F2Le plants must involve barriers occurring after pollen germination.
A method was developed which greatly reduces or eliminates each of the F2 barriers. The method and its efficacy on each of the aspects of hybrid breakdown will be discussed.