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One of the highest levels of common bacterial blight (CBB) resistance identified in Phaseolus vulgaris is found in XAN-159, which was developed for leaf resistance to CBB through six generations of pedigree selection of progenies derived from the interspecific cross [(`Pinto UI 114' × PI 319441) × P. acutifolius PI 319443] × `Masterpiece'. A RAPD genetic linkage map was previously constructed in a recombinant inbred population derived from the common bean cross PC-50 × XAN-159 for identification of genomic regions associated with bacterial disease resistance in XAN-159. To confirm that chromosomal regions associated with CBB resistance in XAN-159 were introgressed from tepary bean, we investigated the parentage of each genomic interval in XAN-159 by studying the genomic constitutions of the four different parents involved in the pedigree. The results indicate that all genomic regions associated with CBB resistance contain intervals derived exclusively from tepary bean. The uniqueness of marker polymorphisms associated with resistance to CBB in XAN-159 will allow the application of marker assisted selection for these resistance genes in most populations of common bean.
). He had a keen interest in generating wide crosses between distant relatives in hopes of shuffling genomes and artificially selecting extreme or disruptive phenotypes ( Burbank et al. 1914 ), and as such produced hundreds of thousands of seedlings for
The peanut root-knot nematode (Meloidogyne arenaria race 1) is potentially a major pest of pepper cultivars belonging to the species Capsicum chinense. Greenhouse tests were conducted to: 1) compare the level of resistance to the peanut root-knot nematode exhibited by the recently released C. chinense germplasm line PA-353 to that exhibited by the C. annuum cv. Carolina Cayenne; 2) to determine the inheritance of the resistance in the C. chinense germplasm line PA-353; and 3) to determine the genetic relationship between the resistance exhibited by the C. chinense germplasm line PA-353 and that exhibited by the C. annuum cv. Carolina Cayenne. The level of resistance exhibited by the C. chinense germplasm line PA-353 was equal to the high level of resistance of the C. annuum cv. Carolina Cayenne. Evaluation of parental, F1, F2, and backcross populations of the cross between the resistant C. chinense germplasm line PA-353 and the susceptible C. chinense accession PA-350 indicated that the resistance in C. chinense is conditioned by a single dominant gene. The F2 population of the interspecific cross between the resistant C. chinense germplasm line PA-353 and the resistant C. annuum cv. Carolina Cayenne did not segregate for resistance, indicating that the dominant resistance gene in C. chinense is likely allelic to or closely linked to a gene conditioning resistance in C. annuum. The availability of a simply inherited source of outstanding resistance makes breeding for peanut root-knot nematode resistance a viable objective in C. chinense breeding programs.
Foliar diseases are a major constraint to cultivated tepary bean (Phaseolus acutifolius A. Gray var. latifolius Freeman) production in some environments. The reactions of 12 cultivated teparies to eight individual races (41, 47, 49, 51, 53, 58, 67, and 73) of the bean rust fungus Uromyces appendiculatus (Pers.) Unger var. appendiculatus maintained at Beltsville, Md., were examined under greenhouse conditions. These diverse races, used together, overcome all of the major rust-resistance genes present within the 19 host differential cultivars of common bean (Phaseolus vulgaris L.). Seven lines (GN-605-s, GN-610-s, PI 321638-s, PI 502217-s, Neb-T-6-s, Neb-T-8a-s, and Neb-T-15-s) exhibited similarly high levels of resistance (immunity or necrotic spots without sporulation) to all eight races. Inheritance of resistance was examined across five susceptible × resistant (S × R) and three resistant × resistant (R × R) populations. The rust reactions in the F1, F2, and F3 generations derived from S × R crosses revealed that the immune or necrotic resistance response was conditioned by a single locus exhibiting incomplete dominance. The rust resistance of four lines tested for allelism in R × R crosses was found to be derived from the same gene. This apparent lack of variability for rust resistance suggests that a single introgression event may realize the full potential for cultivated tepary bean to contribute rust resistance to common bean through interspecific hybridization. In addition, the limited variability for resistance to the highly variable rust pathogen in cultivated tepary bean supports the occurrence of a “bottleneck effect” during domestication of this species, as observed in germplasm diversity studies.
Open-pollinated southern highbush (V. corymbosum L. hybrids) and F1 (southern highbush × V. simulatum Small) hybrid blueberry seedlings were compared for fertility in a high-density nursery in Gainesville, Fla. Most of the pollen sources in the field were tetraploid southern highbush seedlings. Berries were collected from 100 southern highbush seedlings and from 100 seedlings from southern highbush × V. simulatum crosses. The seeds were extracted and dried on a laboratory bench for several days before weighing. No significant differences were found in seed mass/berry between the two types of seedlings. Although the F1 interspecific hybrids averaged slightly lower in seed mass per berry, this was due to the smaller size of their well-developed seeds, not to poor seed development. The estimated number of well-developed seeds per berry was 35.4 and 39.1 for southern highbush blueberries and their F1 hybrids with V. simulatum, respectively. These results indicate that reduced fertility should not be a problem in using V. simulatum to breed southern highbush blueberries.
Ploidy level and fertility status are often the two biggest barriers a breeder must overcome when trying to incorporate novel characteristics among related taxa. This study was aimed at developing an efficient chromosome doubling method for Buddleja L., commonly known as butterfly bush, with the goal of equalizing the ploidy level and restoring the fertility of a diploid (2n=38) F1 interspecific hybrid that has a unique orange color but happens to be sterile. This method would ease the crossing of the hybrid to the tetraploid (2n=76) B. davidii Franch. cultivars commonly found in the industry. An antimitotic treatment of oryzalin was tested on 02-25-142 (B. madagascarensis Lam. × B. crispa Benth.) in vitro using nodal sections. A factorial of varying concentrations [3, 5, and 7 μM (micromolar)] by different exposure times (1, 2, and 3 day) plus controls was set up. Oryzalin appeared to be an efficient agent for chromosome doubling in Buddleja. Significant differences in the number of polyploids were not seen between chemical concentrations and exposure times. However, higher chemical concentrations and exposure times did have a significant effect on the number of nodes that survived tissue culture. Increased leaf size and color, stem thickness, shortened internode length, and upright growth habit were all good early phenotypic indicators of polyploidy induction as later confirmed by flow cytometry. Significant increases in pollen viability accompanied chromosome doubling as crosses between 02-25-142 × B. davidii cultivars produced viable seedlings.
Hydrangea popularity and use in the landscape has expanded rapidly in recent years with the addition of remontant varieties. Most cultivars in production belong to the species Hydrangea macrophylla but H. paniculata, H. arborescens, H. serrata, H. aspera, H. heteromalla, H. integrifolia, H. anomala, H. seemanii, and H. quercifolia are also commercially available. In addition to species diversity there is high intra-species variation, particularly in H. macrophylla, which includes mopheads, lacecaps, French, Japanese, dwarf, and variegated varieties. Relatively little is known about the genetic background or combinability of these plants. DNA sequence data, genome size, RAPD, AFLP, and ISSR markers have been used for taxonomic identification and to estimate diversity within the genus. All of these methods have limited usefulness in a large scale breeding program. We recently established microsatellite markers for Hydrangea and evaluated their utility for estimating species diversity and identifying cultivars within H. macrophylla and H. paniculata. We also verified an inter-specific cross between H. macrophylla and H. paniculata using these markers. Future research includes marker assisted breeding, particularly with respect to remontant flowering traits.
Alstroemeria, the Inca Lily or Lily-of-the-Incas, is becoming a popular garden plant in the United States. In past years, the primary interest in Alstroemeria has been for its cut flowers. However, recent cold-hardy introductions (USDA hardiness zone 5) have expanded the interest of this colorful plant as a garden perennial throughout the United States. Previously, garden interests were restricted to warmer zones in the southern United States where Alstroemeria could overwinter. This research describes a breeding procedure that has been used with the objective to develop a cold-hardy, white-flowered Alstroemeria. The interspecific hybrids were bred with the use of in ovulo embryo rescue. Reciprocal crosses were made between several white-flowered cultivars and the cold-hardy Chilean species Alstroemeriaaurea during Summer 2004. Ovaries were collected 10–23 days after hand pollination and their ovules were aseptically excised. Ovules were placed in vitro on 25% Murashige and Skoog (MS) medium under dark conditions until germination. Three weeks after germination, they were then placed on 100% MS medium, and subcultured every 3–4 weeks thereafter until they were large enough for rooting. After rooting and acclimation, plants were transferred to the greenhouse. Successful hybrids that were produced in 2004 were evaluated under greenhouse and field trials during 2005, and the number of plants with white-colored flowers was noted. Although certain morphological characteristics indicate if plants are coldhardy, the hybrids will be overwintered outside in Ithaca, N.Y. (USDA zone 5), during the next several years to determine winter hardiness.
Apomixis is asexual reproduction through seed. Apomixis in the genus Pennisetum is of the gametophytic (aposporous) type. Genes for apomixis have been transferred from a wild apomictic species (P. squamulatum) to pearl millet (P. glaucum) by conventional breeding to produce an obligately apomictic backcross 3 (BC3) plant (Dujardin and Hanna, 1989, J. Genet. Breed. 43:145). Molecular markers based on restriction fragment length polymorphisms and random amplified polymorphic DNAs were identified in BC3 that were shared only with the apomictic parent. Segregation of these informative markers in a BC4 population indicated that three linkage groups from P. squamulatum were present in BC3 and that minimal recombination between these alien chromosomes and those of the recurrent parent occurred. Transmission of only one of the linkage groups was required for transfer of apomixis. Recombination is essential for genetic mapping, thus we are beginning to map the informative molecular markers in an F, interspecific cross between pearl millet and P. squamulatum, a population that segregates for apomictic and sexual reproduction.
Genetic resistance to cucumber mosaic virus (CMV) in pepper (Capsicum spp.) is recessive, polygenic and, therefore, has been difficult to transfer in breeding programs. Although a few varieties have been released with some resistance, in our tests, these develop severe symptoms that are eventually indistinguishable from the susceptible reactions. Furthermore, accurate and consistent screens for the disease can be relatively difficult; therefore, we report on the detection molecular markers linked to two CMV resistance genes using distributional extreme analysis to identify the relevant quantitative trait loci (QTL). The 12 most resistant and 15 most susceptible individuals were selected from a segregating F2 population of 316 individuals that were derived from the interspecific cross (C. annuum `Jupiter' × C. frutescens BG2814-6). A total of 132 tomato genomic, cDNA, and pepper genomic clones were hybridized to filters with DNA extracted from the distributional extremes. These clones included framework markers representing all pepper linkage groups and also selected clones from regions of the genome identified in a preliminary analysis as possibly involved with CMV resistance. Several clones from the two regions of the genome previously identified appear to be nonrandomly cosegregating with the CMV resistance phenotype in this larger population. Further analysis will be done by adding more markers in the regions and refining the positions of the resistance QTL.