Search Results

You are looking at 21 - 30 of 30 items for

  • Author or Editor: Fenny Dane x
Clear All Modify Search

Fusarium wilt, caused by the soilborne fungus Fusarium oxysporum f.sp. niveum (FON), is a serious disease of the watermelon (Citrullus lanatus). Three races of this pathogen (races 0, 1, and 2) have been identified based on differential pathogenicity assays. Most commercially available cultivars are resistant to races 0 and 1. Inheritance for resistance to these races is thought to be controlled by a single dominant gene. No cultivars are resistant to race 2 and resistance is thought to be a quantitative trait. F2 lines derived from a cross between the Fusarium-resistant Citrullus lanatus PI296341, and the Fusarium-susceptible watermelon cultivar `New Hampshire Midget' were used to generate a RAPD-based map of the Citrullus genome. F2:3 families were assayed in the greenhouse for resistance to races 1 and 2. Those families that were either highly resistant or highly susceptible were used in identifying markers linked to Fusarium wilt resistance. A preliminary map of the Citrullus genome based on random amplified polymorphic DNA (RAPD) markers has been expanded with the inclusion of simple sequence repeats (SSRs), amplified fragment length polymorphisms (AFLPs), and isozymes.

Free access

The genus Castanea (Fagaceae), which contains three sections and seven species, is widely distributed in the deciduous forests of the Northern Hemisphere. The phylogeny of Castanea was estimated using DNA sequence data from five different regions of the chloroplast genome. Sequencing results support the genus Castanea as a paraphyletic group with C. crenata, the Japanese chestnut, representing an early divergence in the genus. The three Chinese species form a strongly supported sister clade to the North American and European clade. A unique westward expansion of extant Castanea species is hypothesized with Castanea originating in eastern Asia, an initial diversification within Asia during the Eocene, followed by intercontinental dispersion and divergence between the Chinese and European/North American species during the Oligocene and a split between the European and North American species in the early Miocene. The differentiation within North America and China might have occurred in late Miocene or early Pliocence. The North America species are supported as a clade with C. pumila var. ozarkensis, the Ozark chinkapin, as the basal lineage, sister to the group comprising C. pumila var. pumila, the Allegheny chinkapin, and C. dentata, the American chestnut. Morphological evolution of one nut per bur in the genus may have occurred independently on two continents.

Free access

Little research is reported on container production of ornamental lotus (Nelumbo nucifera Gaertn.). In this study, fertilization has a critical impact on growth index of lotus `No.7', a numbered clone, in 29 liter (7.5 gallon) containers. Compared to the control treatment (zero fertilization), 1–3 tsp. (4g/tsp.) of 20-10-20 (Pro·Sol) applied every 20 days significantly increased plant height (1.3–1.6 times), fresh biomass (2.4–3.3 times), emerging leaf number (1.9–2.7 times), flower number (2.4–2.7 times), and propagule number (1.3–1.5 times). There was a quadratic response as growth parameters increased with increasing fertilizer rates. Growth indices increased linearly from 0–2 tsp. and then leveled as fertilizer rates reached 3 tsp. No difference was recorded in flower number and plant height for 1–3 tsp. fertilizer treatments. Absorption of nutrition increased with fertilization concentration, an absorption peak value appeared between 13 July and 2 Aug. For 1-3 tsp. treatments, nitrogen is nearly 100% absorbed by lotus every 20 days. However, there is some residue for P and K, especially in 3-tsp. treatment in the earlier and later growth season. Analysis of young leaf tissue indicated that macronutrients N, P, K, and dry mass increased, but Ca decreased with increasing fertilizer rates. In tuber tissue, K, Na, and dry mass increased, while Ca and Fe content decreased. The most efficient rate of fertilizer for 7.5 gallon container production of `No.7' lotus was 2 tsp. per 20 days. Although soluble fertilizer also stimulated proliferation of algae growth in the early growth stage of lotus, this problem dissipated as emerging leaves shaded the water surface.

Free access

The northern fringe of the Gulf of Mexico has an excellent climate for growing high-quality satsumas that are available in U.S. retail chain stores before most other citrus. In part because of high fruit quality, satsuma mandarin production grew into a major industry in Alabama, Louisiana, Mississippi, and the panhandle of Florida in the early 1900s. Freeze protection measures were not sufficient to prevent devastation of the industry by severe freezes. For the period encompassing the late 1900s, freeze risk was estimated using a mathematical approach that determined killing temperature based on air temperature. Freeze injury was determined to occur 1 out of every 4 years on average, although the freezes tended to come in clusters that have as yet not been correlated with long-term climate patterns. Within-tree microsprinkler irrigation, which was not available in the early 1900s, has been shown to reduce the severity of injury. Within-tree microsprinkler irrigation allows full production the year after the freeze, whereas unprotected trees must be grown from the base or replanted. The northerly geographical limit in the southeastern United States whereby satsumas can be successfully grown commercially is currently not known. Methods of protecting the entire tree, including overtree microsprinkler irrigation plus windbreaks and high tunnel houses, are being evaluated. More cold-tolerant satsuma cultivars have been selected, but they reduce freeze risk by at most 2 °C in this region compared with current commercial cultivars. Genetic modification is one possible mechanism for improving cold tolerance sufficiently to reduce freeze risk similar to that of the citrus industry in Florida.

Free access

Selected tomato (Lycopersicon esculentum Mill) genotypes were evaluated for their fruit-setting ability under high-temperature field conditions. A temperature-controlled greenhouse study was conducted to determine the percent fruit set from the total number of flowers and fruit produced per plant. Ratings for set obtained under high-temperature field conditions were significantly (P = 0.001) correlated with percent fruit set determined under similar greenhouse conditions. Most of the Asian Vegetable Research and Development Center (AVRDC) selections, Beaverlodge lines, `Nagcarlan', and `Red Cherry' could be considered heat-tolerant. Small-fruited, abundantly flowering genotypes were less affected by heat stress than larger-fruited cultivars. Prolonged periods of high temperature caused drastic reductions in pollen fertility in most genotypes, except `Red Cherry' and L. esculentum var. cerasiforme (PI 190256). Stigma browning and stigma exsertion commonly occurred on all lines, except AVRDC CL-5915-553 and PI 190256. Diallel analyses indicated that pollen fertility and fruit set under high field temperatures were primarily under additive gene control.

Free access

Commercial citrus species, some of the most important fruit crops worldwide, are sensitive to sub-freezing temperatures. Poncirus trifoliata, a species closely related to commercial citrus and tolerant to –30 °C, has been used in breeding programs or as a rootstock to impart greater freeze tolerance. Gene expression of P. trifoliata and C. unshiu (Satsuma mandarin) were investigated and compared under slow and fast cold-acclimation regimes. The mRNA differential display-polymerase chain reaction (DDRT-PCR) and cDNA-AFLP, coupled with quantitative relative RT-PCR or real-time PCR were used. Many unique gene fragments were isolated and found to be up- or down–regulated as a result of exposure to low temperature. The up-regulated fragments in Poncirus show high similarities to genes involved in osmotic regulation (betaine/proline transporter, water channel protein, and nitrate transporter), oxidative stress (aldoketo reductase, early light induced protein), and protein interaction (tetratricopeptide-repeat protein, F-box protein, and ribosomal protein L15). In C. unshiu the up-regulated genes show high similarities to genes involved in transcription (zinc finger and GTP-binding protein-related), signal transduction (14–3–3 protein and extension-like protein), protein synthesis and amino acid translocation (permease and ribosomal proteins), chromosome folding (chromosome condensation, structural maintenance of chromosomes-like protein), and carbohydrate metabolism (glycosyl transferase). Several genes involved in photosynthesis, defense and cell wall metabolism were down regulated. Characterization of cold responsive genes will be discussed.

Free access

Isozyme inheritance and variation in Actinidia was investigated using 23 enzyme systems. Ten isozyme loci from six enzyme systems, Acp-2, Est, Prx-1, Prx-2, Prx-4, Prx-5, Pgi-2, Pgm-2, and Tpi, were found to be inherited as single Mendelian genes in families of two interspecific crosses. Disomic inheritance detected at ten loci in progenies of a cross between the hexaploid A. deliciosa × diploid A. chinensis, provided convincing evidence that A. deliciosa is an allohexaploid. Allelic segregation for tetrasomic inheritance at ten isozyme loci was demonstrated in the progenies of a cross between the tetraploid A. chinesis × diploid A. eriantha, a result suggesting the autotetraploid origin of the tetraploid A. chinensis which apparently originated from its diploid ancestor A. chinensis. A high level of isozyme variation and heterozygosity were observed in the 22 cultivars and 56 plants of 28 Actinidia taxa. Allozyme phenotype can be used effectively for cultivar identification.

Free access

Lotus (Nelumbo) is a highly valued plant with a long history for vegetable, ornamental, and medicinal use. Little information is available on the effects of planting time on performance of lotus, especially when grown in containers. The objectives of this study were to find a suitable planting time and to determine best management practices that are of importance for container lotus production. Effects of planting time and disbudding on plant growth indices in southeast Alabama were evaluated in a container production system for the ornamental lotus, N. nucifera ‘Embolene’. Results indicated that plant growth indices were little influenced by different planting dates in March, but were much influenced by planting dates with a difference over a month between February and May. Plants potted and placed outdoors in March and April performed best, and lotus planted in the greenhouse in February and planted outdoors in February and May performed worst. Flower number was not largely influenced by the planting time, but flowering characteristics, especially the flowering peaks, were different among treatments. Planting lotus outdoors between March and May produced the largest return. Influence of planting time on plant growth indices of lotus appeared to be explained by effects of growth-season climate conditions after planting. Disbudding had no impact on plant height but significantly increased underground fresh weight and the number of propagules. Therefore, disbudding should be considered a best management practice to maximize the yield of rhizomes or propagules. Positive linear, quadratic, or cubic relationships were detected among emerging leaf number, underground fresh biomass, and propagule number. Based on the regression models, the yield of lotus rhizomes or propagules can be predicted by the number of emerging leaves. This research provided a guide for nurseries, researchers, and collectors to select the best time to plant lotus outdoors.

Free access

Genetic relationships among 970 cucumber (Cucumis sativus L.) plant introductions (PIs) in the U.S. National Plant Germplasm System (NPGS) were assessed by observing variation at 15 isozyme loci. Allozyme frequency data for these PIs were compared to allozyme variation in heirloom and modern (H&M) cultivars released from 1846-1985 (H&M cultivars; 178 accessions), and experimental commercial (EC) germplasm (EC germplasm; 82 accessions) in use after 1985. Multivariate analysis defined four distinct groups of accessions (Groups A-D), where Group A consisted of PIs received by the NPGS before 1992, Group B contained PIs from India and China obtained by NPGS after 1992, Group C consisted of EC germplasm, and Group D contained H&M cultivars. Morphological, abiotic stress (water and heat stress tolerance) and disease resistance evaluation data from the Germplasm Resources Information Network (GRIN) for the PIs examined were used in conjunction with estimates of population variation and genetic distance estimates to construct test arrays and a core collection for cucumber. Disease resistance data included the evaluation of angular leafspot [Pseudomonas lachrymans (E.F. Smith) Holland], anthracnose [Colletotrichum lagenarium (Ross.) Ellis & Halst], downy mildew [Pseudoperonospora cubensis (Berk. & Curt) Rostow], rhizoctonia fruit rot (Rhizoctonia solani Kuhn), and target leafspot [Corynespora cassiicola (Berk. & Curt) Wei] pathogenicity. The test arrays for resistance-tolerance to angular leafspot, anthracnose, downy mildew, rhizoctonia fruit rot, target leafspot, and water and heat stress consisted of 17, 16, 17, 16, 17, 16, and 16 accessions, respectively. The core collection consisted of accessions in these test arrays (115) and additional 32 accessions that helped circumscribe the genetic diversity of the NPGS collection. The core collection of 147 accessions (115 + 32) represents ≈11% of the total collection's size (1352). Given estimates of genetic diversity and theoretical retention of diversity after sampling, this core collection could increase curatorial effectiveness and the efficiency of end-users as they attempt to identify potentially useful germplasm.

Free access

Isozyme, randomly amplified polymorphic DNA (RAPD), and simple sequence repeats (SSR) markers were used to generate a linkage map in an F2 and F3 watermelon [Citrullus lanatus (Thumb.) Matsum. & Nakai] population derived from a cross between the fusarium wilt (Fusarium oxysporum f. sp. niveum) susceptible `New Hampshire Midget' and resistant PI 296341-FR. A 112.9 cM RAPD-based map consisting of 26 markers spanning two linkage groups was generated with F2 data. With F3 data, a 139 cM RAPD-based map consisting of 13 markers covering five linkage groups was constructed. Isozyme and SSR markers were unlinked. About 40% to 48% of the RAPD markers were significantly skewed from expected Mendelian segregation ratios in both generations. Bulked segregant analysis and single-factor analysis of variance were employed to identify RAPD markers linked to fusarium wilt caused by races 1 and 2 of F. oxysporum f. sp. niveum. Current linkage estimates between the resistance trait and the marker loci were too large for effective use in a marker-assisted selection program.

Free access