Eight highbush blueberry (V. corymbosum L.) triploids (2n = 3x = 36) were crossed with diploids (2n = 2x = 24), tetraploids (2n = 4x = 48), and hexaploids (2n = 6x = 72). No plants were recovered from 4021 3x × 2x crosses. One triploid was relatively fertile in 3x × 4x and 3x × 6x crosses, which is most likely attributable to 2n gamete production in the triploid. The lack of fertility of triploids, which do not produce 2n gametes, in crosses with diploids and tetraploids suggests that the production of gametes with numerically balanced (n = 12 or 24) chromosome numbers is extremely low. In addition, the inability to recover progeny from 3x × 2x crosses also suggests that aneuploid gametophytes and/or zygotes, including trisomics, are inviable in blueberry. Pollen stainability was also highly reduced in triploids. Frequency distributions of anaphase I pole chromosomal constitutions of three triploids were significantly different from one another. Two of the three distributions were shifted toward the basic chromosome number of 12, with one triploid having 25% poles with 12 chromosomes. However, the sterility of 3x × 2x and 2x × 3x crosses indicates that lagging chromosomes during meiotic anaphases are probably not excluded from gametes, resulting in unbalanced gametes in blueberry. Triploids can be used as a bridge to facilitate gene transfer from the diploid and tetraploid levels to the hexaploid level in blueberry.
N. Vorsa and James R. Ballington
Yiping Zhang, Vince K. Lackney, James P. Prince, Jim P. Blauth, and Molly M. Kyle
Pepper (Capsicum spp.) has the same basic chromosome number as tomato and other solanaceous plant species (2n = 2x = 24). By using the probes mostly from a tomato map, we have generated three molecular maps of pepper from interspecific F2 crosses of C. frutescens BG 2814-6, C. chinense PI 159234 and C. annuum `NuMex RNaky' with restriction fragment length polymorphisms, isozymes, random amplified polymorphic DNAs, and morphological traits. The best developed map is from C. annuum × C. chinense F2 cross, which currently has 366 markers covered 1081 cM in 18 linkage groups. Three linkage groups were assigned to three chromosomes based on primary trisomics. Several disease resistance genes including monogenic resistance to potyviruses and quantitative trait loci for resistance to tobacco mosaic virus and cucumber mosaic virus have been mapped. The distribution of allele frequency and marker segregation ratios have been analyzed. Chi-square analyses of all clones showed more skewing of segregation ratios in C. annuum × C. chinense population than the other two populations. The skewing occurs throughout the genome and tends towards heterozygote and one of the parents. The order of markers among three pepper maps will be compared and the comparisons of synteny between pepper and tomato maps will be described. A composite of three pepper maps will be presented using JoinMap software.
Jason D. Lattier and Ryan N. Contreras
Chromosome atlas of flowering plants. Macmillan, New York, NY Diao, W.-P. Bao, S.-Y. Jiang, B. Cui, L. Chen, J.-F. 2009 Primary trisomics obtained from autotriploid by diploid reciprocal crosses in cucumber Sex. Plant Reprod. 22 45 51 Farco, G.E. Dematteis, M