Although always among the top five vegetables in value, little genetic information has been published on the bulb onion. Genetic and molecular analyses are hampered by the plant's biennial nature, severe inbreeding depression, and huge genome. Research is underway to construct a low-density genetic map of onion based on RFLPs, AFLPs, and RAPDs. Among open-pollinated populations (OPPs), levels on DNA polymorphisms were in agreement with those of other outcrossing diploid species. However, we identified little putative-allelic diversity among the OPPs (1.9 polymorphic bands per polymorphic probe–enzyme combination) supporting a bottleneck during the domestication of onion. Our segregating family is from the cross of two diverse inbreds and will be used to map quantitative trait loci conditioning phenotypically correlated production (maturity, storability, and firmness), consumer-preference (pungency, flavor, and bulb shape), and health-enhancing (anti-platelet aggregation) attributes of onion. We are also attempting to tag chromosome regions controlling relatively simply inherited traits that are difficult or expensive to characterize classically.
Michael J. Havey
Michael J. Havey, Joseph J. King, James M. Bradeen, and Ockyung Bark
Five edible mountain vegetables (Saussurea sp., Aster tataricus, A. scaber, Synurus deltoides, Ligularia fischeri) were investigated on the basis of amplified DNA polymorphisms resulted from PCR–polymerase chain reaction analysis. The sampled plants consisted of 38 individuals in five taxa. Only 10 primers out of 62 [60 random (10-mer) primers, one 15-mer-M13 core sequence, and (GGAT)4 sequence] tested gave rise to polymorphisms in all of the tested plants, producing 176 DNA fragments amplified randomly and specifically. Intraspecific polymorphisms found in each taxa showed intra-variety constancy (31.1% to 40.9%) in the banding patterns of individual plants—Saussurea sp., 31.1%, 15 bands; Aster tataricus, 40.9%, 18 bands; A. scaber, 38.5%, 15 bands; Synurus deltoides, 34.7%, 17 bands; Ligularia fischeri, 38.9%; 22 bands, respectively. All five species were well-differentiated from each other at the 0.93 level of similarity index value. Genetic relationships among intraspecific and interspecific variations were closely related at the levels ranging from 0.62 to 0.99. Based on these results, our PCR analyses support the previous data derived from external morphology of the five edible mountain vegetables, but very low levels of intraspecific variations were detected in all of these taxa.
Leigh K. Hawkins, Fenny Dane, and Thomas L. Kubisiak
Morphological traits were examined in an F3 generation derived from a cross between C. lanatus var. lanatus [(Thunb.) Matsum. & Nakai] and C. lanatus var. citroides. At least three genes, C (yellow) vs. c (red), i (inhibitory to C) vs. I (non-inhibitory to C), and y (yellow) vs. yw (white), with epistatic and inhibitory actions were found to govern the inheritance of fruit flesh color. The high frequency of yellow-fleshed fruit and low frequencies of white and red fruits can be explained by the presence of a new allele (yw recessive to y) in the multiple allele series at the Y locus. The low frequency of tan colored seeds in segregating populations could be explained by at least three genes governing inheritance of seed-coat color. Single factor analysis of variance was conducted for each pairwise combination of random amplified polymorphic DNA (RAPD) locus and fruit or seed characteristics. Several RAPD loci were identified to be loosely linked to morphological characteristics.
Antonio Figueira, Jules Janick, Morris Levy, and Peter Goldsbrough
Genetic similarities among eight Theobroma and two Herrania species, including 29 genotypes of T. cacao, were estimated by rDNA polymorphism. A phenogram based on these genetic similarities significantly separated two clusters: one cluster included all Herrania and Theobroma species, except T. cacao, while the second contained 28 of 29 T. cacao genotypes. There was no clear distinction between Herrania and Theobroma species. Separation of 29 T. cacao genotypes, representing all races and various origins, had no congruency with the conventional classification into three horticultural races: Criollo, Forastero, and Trinitario. Genetic similarities in T. cacao, estimated with RAPD markers, indicated continuous variation among the generally similar but heterogeneous genotypes. The wild genotypes formed an outgroup distinct from the cultivated genotypes, a distinction supported by the rDNA data. The phenograms constructed from RAPD and rDNA data were not similar within the wild and cultivated cacao subsets.
D.Q. Fang and M.L. Roose
`Chandler' pummelo [Citrus maxima (Burm.) Merrill] was found to be citrus tristeza virus (CTV)–resistant. The inheritance of this resistance in 84 progeny of two crosses derived from `Chandler' pummelo and trifoliate orange [Poncirus trifoliata (L.) Raf.] was controlled by a single dominant gene designated Ctv2. Progeny analysis of four molecular markers closely linked to the Ctv gene, which confers resistance to CTV in trifoliate orange, demonstrated that Ctv2 was an independently assorting gene from Ctv.
Jennifer A. Kimball, M. Carolina Zuleta, Matthew C. Martin, Kevin E. Kenworthy, Ambika Chandra, and Susana R. Milla-Lewis
approaches to assess variability in clonal plants have been reported, but indistinguishable morphology has been difficult to characterize. Molecular markers have the ability to detect genetic variation and provide a reliable method to ensure the integrity of
Mohammad Sadat Hosseini Grouh, Kourosh Vahdati, Mahmoud Lotfi, Darab Hassani, and Nejat Pirvali Biranvand
was the best for apple ( Zhang and Lespinasse, 1991 ). Molecular marker analysis showed that all the diploid plants recovered were zygotic and no spontaneous double haploid plants were obtained in this work, whereas in melon ( Lotfi et al., 2003
Mirko Siragusa, Fabio De Pasquale, Loredana Abbate, and Nicasio Tusa
A collection of 18 accessions of sour orange (Citrus aurantium L.) coming from Sicily and other countries was investigated by two polymerase chain reaction (PCR)-based DNA marker technologies. Ten inter-simple sequence repeat (ISSR) primers and fifteen randomly amplified polymorphic DNA (RAPD) primers were used to identify and to evaluate the genetic variability and relationship of accessions. A total of 111 ISSR and 145 RAPD amplified fragments were used to estimate the Dice's coefficient of similarity for cluster analysis using a unweighted pair-group method using an arithmetic averaging (UPGMA) algorithm. The genetic relationships identified using ISSR and RAPD markers were highly concordant, such that the correlation between ISSR and RAPD genetic distance (GD) estimates was r = 0.93. The ISSR and RAPD analysis of 18 sour orange accessions found a high grade of genetic diversity in foreign accessions, while a low variability was detected in local accessions. Sicilian accessions could be grouped in two distinct clusters, including indistinctly plants from three origin regions. Some markers could be linked to the different growing areas. The ISSR and RAPD molecular reference system seems to be suitable for a fine identification of tightly related plants and the obtained results can form the basis for future setting up of Citrus rootstock genetic improvement projects.
Kanta Kobira, Khalid Ibrahim, Elizabeth Jefferey, and John Juvik
Considerable epidemiological evidence exists on the association between consumption of antioxidant-rich vegetables and incidence of chronic diseases, including cancer and cardiovascular disease. Broccoli (Brassica oleracea L. sp. italica) florets are relatively abundant sources of antioxidants, and potentially amenable to genetic manipulation to enhance this vegetable's health-promoting properties. This investigation focuses on the identification of chromosomal segments in the nuclear genome of broccoli associated with antioxidant carotenoid and tocopherol variability. A broccoli F2:3 population consisting of 163 families derived from a cross between two parents (VI-158 and BNC) and previously mapped with 62 polymorphic SSR and SRAP marker loci was evaluated for carotenoid and tocopherol concentration in floret tissue over two growing seasons. Significant differences were observed among F2:3 family means for concentrations of lutein (10-fold difference between the lowest and highest family), beta-carotene 17-fold), alpha-tocopherol (8-fold) and gamma-tocopherol (6-fold). On a concentration basis, beta-carotene, lutein, alpha-tocopherol, and gamma-tocopherol were the most abundant antioxidant forms in broccoli. Heritability estimates of primary phytochemicals ranged from 0.35 to 0.38, 0.40, and 0.44 for beta-carotene, alpha-tocopherol, gamma-tocopherol, and lutein, respectively. Composite interval mapping (CIM) identified two quantitative trait loci (QTL) associated with carotenoid variability on two linkage groups and five QTL associated with tocopherol variability on four linkage groups. The QTL identified in this study have potential for use in marker-assisted crop improvement programs to develop elite germplasm designed to promote health among the consuming public.