Ploidy analysis in water yam, Dioscorea alata L. germplasm

Poor reproductive development in yams (Dioscorea spp.) has often been attributed to the polyploid nature of the crop. In this study, flow cytometry was used to determine the ploidy level of 53 accessions of Dioscorea alata, mostly from West African countries, Chad and Puerto Rico. Nuclei were isolated from young leaf material and stained with DAPI(4,6-diamidino-2-phenylindole). The nuclear genome size (2C) was measured as an indicator of the ploidy level. Dioscorea rotundata genotypes with known ploidy levels were used as standards. The results showed that the majority of plants were hexaploid (84.9%) with a smaller percentage of tetraploids (15.1%). A higher number of male plants were hexaploid than tetraploids. This is at variance with earlier findings, which reported that hexaploid male plants are rare. Higher ploidy levels were not directly related to sparse or erratic flowering as previously reported as profuse flowering occurred in some male hexaploid accessions. These findings have important implications for yam breeding in relation to yam genetic resources. This revised version was published online in August 2006 with corrections to the Cover Date.     

PCR Marker-based Analysis of Wild and Cultivated Yams (<Emphasis Type="Italic">Dioscorea</Emphasis> spp.) in Nigeria: Genetic Relationships and Implications for <Emphasis Type="Italic">ex situ</Emphasis> Conservation

Reliable characterization of the variation among wild and cultivated yams in Nigeria is essential for improved management and efficient utilization of yam genetic resources. RAPD and double stringency PCR (DS-PCR) analyses were used to investigate genetic relationships and the extent of redundancy among 30 accessions of two cultivated, and 35 accessions of four wild yam species collected from Nigeria. Twenty-five selected random decamer and two microsatellite primers were used individually and in combination to generate DNA profiles for each accession of the six Dioscorea species. The number of amplified fragments varied from 7 to 18 fragments per primer/primer combination. Different levels of intraspecific genetic diversity were found, with Dioscorea rotundata Poir. being the most variable. Based on identical profiles for the RAPD and DS-PCR primers, 12 duplication groups consisting of a total number of 37 accessions were observed in the present study. An UPGMA analysis grouped the majority of plants according to the species. Cultivated yams belonging to the D. cayenensis–rotundata species complex, which were classified into seven morphotypes/varietal groups, could be clearly separated into two major groups corresponding to D. rotundata Poir. and D. cayenensis Lam. D. cayenensis cultivars exhibited a low level of intraspecific variation and were genetically close to the wild species Dioscorea burkilliana J. Miège. D. rotundata cultivars classified into six varietal groups showed a high degree of DNA polymorphism and were separated into two major groups that appeared most closely related to Dioscorea praehensilis Benth. and Dioscorea liebrechtsiana de Wild. We propose, based on these results, that cultivars classified into D. cayenensis should be considered as a taxon separate from D. rotundata. The implications of intraspecific variability for the ex situ conservation of wild and cultivated yam germplasm in Nigeria are discussed.     

Ploidy levels of Dioscorea alata L. germplasm determined by flow cytometry

Dioscorea alata L. is a highly important crop, widely distributed in the humid and semi-humid tropics. Flow cytometry was used to determine the ploidy levels of 74 D. alata genotypes collected mainly from West African countries. Sixty three of the genotypes were found to be tetraploid, one was hexaploid and ten were octoploid. The high percentage of tetraploids together with the small percentage of hexaploid individuals and the absence of diploid individuals gives us some more clues on the possible origin of these species. No association between ploidy level and place of cultivation was found for the tested material. The obtained results represent important knowledge for enhancing the breeding methodologies and optimize germplasm management of this species. It also offers further insights to the phylogeny and evolution of Dioscorea species.     

Sprout development and processing quality changes in potato tubers stored under ethylene: 1. Effects of ethylene concentration

Ethylene effectively inhibits sprouting of potatoes (Solanum tuberosum L.) during storage, but it often darkens fry color. The objective of the work described here was to determine if altering the concentration of ethylene applied would reduce the darkening while retaining adequate sprout inhibition. Trials were conducted over three consecutive years (1991–1992, 1992–1993, and 1993–1994). Tubers of cv Russet Burbank (ca 150–300 g) were stored at 9 C for 25 wk in closed chambers in a refrigerated room under continuous exposure to 0.4, 4, 40, or 400 µL L^?1 ethylene gas delivered with the ventilation airstream (ca 0.5 air exchanges per h, for 6 h each day). Untreated control and chlorpropham-treated (CIPC) check tubers were stored under the same conditions but without ethylene supplementation. Sprout number, length, and biomass, fry color, loss of tuber mass, disease, and dry matter content were evaluated at 5-wk intervals. Dose-dependent effects (400>40>4>0.4 µL L^?1) of ethylene on sprout growth and fry color were observed. The 400, 40, and 4 µL L^?1 ethylene treatments inhibited sprout growth as effectively as CIPC, whereas in 0.4 µL L^?1 ethylene sprouting was midway between CIPC and the untreated control. Sprout mass and maximum sprout length in all ethylene treatments were significantly lower (P<0.05) than in the untreated control. Compared with the initial value (57.3 Agtron reflectance units [ARu]), after 5 wk of storage fry color was up to 5 ARu darker in the ethylene treatments, but recovered steadily at the subsequent evaluation dates. At 25 wk of storage the fry color of tubers from the 40 and 4 µL L^?1 ethylene treatments were, however, still darker than tubers stored with CIPC. Inhibition of sprout growth was slightly more effective in the 400 and 40 µL L^?1 ethylene treatments than in 4 µL L^?1, although there were no significant differences (P<0.01) in fry color between these treatments. In comparison with the other ethylene treatments, fry color in 0.4 µL L^?1 ethylene was lighter, but inhibition of sprout growth was significantly (P<0.05) poorer. There were no differences in tuber disease incidence or dry matter content between the treatments. At 25 wk, the untreated tubers had ca 50% greater loss of tuber mass than any other treatment, attributable to their heavy sprouting. Loss of tuber mass in the ethylene treatments was not significantly different (P<0.001) from that in the CIPC treatment.     

Ploidy level studies on the <Emphasis Type="Italic">Dioscorea cayenensis</Emphasis>/<Emphasis Type="Italic">Dioscorea rotundata</Emphasis> complex core set

The Guinea yams, Dioscorea cayenensis Lam. and D. rotundata Poir. (D. cayenensis–D. rotundata complex), represent a highly important crop, widely distributed in the humid and semi-humid tropics. The ploidy levels of 170 accessions of the core set of Guinea yams from West African countries was determined using flow cytometry with propidium iodide staining. One hundred and eight of the genotypes were found to be tetraploid, 47 were hexaploid and five were octoploid. One mixoploid individual containing tetraploid and hexaploid nuclei was also detected. A deeper analysis considering each separate taxon revealed that while for D. rotundata the majority of individuals were tetraploid, for D. cayenensis this ploidy level was not detected in any of the accessions. Also, no association between ploidy level and place of cultivation was found for the evaluated germplasm. The obtained data is highly valuable for breeding programs of Guinea yam, especially for the optimization of future hybridization experiments directed to the genetic improvement of this economically important crop.     

Assessment of Heavy Metal Pollution in the Sediments of the River Pra and Its Tributaries

An investigative study was conducted to determine the heavy metal pollution in the sediment in the Pra Basin of Ghana from 27 sampling points during the dry and wet seasons using the geo-accumulation index (Igeo), enrichment factor (EF), and pollution load index (PLI). Sediments were acid digested and analyzed for the following selected metals: arsenic (As), lead (Pb), cadmium (Cd), zinc (Zn), manganese (Mn), total chromium (Cr), nickel (Ni), and iron (Fe) using the dual atomizer and hydride generator atomic absorption spectrophotometer (model ASC-7000 No A309654, Shimadzu, Japan). The metal concentrations (mg kg^?1) in the sediments were as follows: As (0.175)?<?Cd (3.206)?<?Ni (79.927)?<?Zn (118.323)?<?Cr (216.708)?<?Mn (234.742)?<?Pb (335.381)?<?Fe (1354.513) in the dry season and As (0.002)?<?Cd (7.279)?<?Ni (72.663)?<?Zn (35.622)?<?Pb (135.863)?<?Cr (167.604)?<?Mn (183.904)?<?Fe (1138.551) for the wet season. The EF which is an indication of whether metal concentrations are due to anthropogenic activities shows enrichment at all site for the metals Cr, Pb, and Cd in the wet seasons. However, only 4 out of the 27 sites showed Ni enrichment in the wet season. Contrary to the wet season, only Pb and Cr recorded enrichment at all sites during the dry season. Fifteen out of the 27 sites recorded Cd enrichment and 24 out of the 27 sites recorded Ni enriched during the dry season. None of the sites were enriched with Fe, As, Zn, and Mn in either the dry or wet seasons. For both dry and wet seasons, the pollution load index for all the sites except one was at the background levels which is a sign of non-deterioration of the sites studied. In the wet season, the calculated Igeo reveals that the study area is not contaminated with respect to As, Zn, Fe, and Mn; uncontaminated to moderately contaminated with Cd; moderately contaminated with Cr; uncontaminated to moderately to heavily contaminated with Ni; and moderately to heavily contaminated with Pb. The dry season Igeo results reveal non-contamination of the study area with respect to As, Fe, and Mn; uncontaminated to moderately contaminated with Zn; moderately contaminated with Cr; uncontaminated to heavily contaminated with Cd; uncontaminated to extremely contaminated with Ni; and moderately to extremely contaminated with Pb. The high levels of Cd, Pb, and Cr in all the sites are due to unregulated illegal mining activities occurring in and around the study area. It is hoped that this study will prompt the basin management board to improve their management strategies in controlling unregulated illegal mining in the basin sediments.     

Responses of white yam (Dioscorea rotundata) cultivars to inoculation with three viruses

The responses of 24 white yam ( Dioscorea rotundata ) cultivars to mechanical and vector transmission with each of three viruses infecting yams were assessed through enzyme-linked immunosorbent assay (ELISA) and symptom development. The viruses were Dioscorea alata virus (DAV), genus Potyvirus ; Dioscorea alata bacilliform virus (DaBV), genus Badnavirus ; and Cucumber mosaic virus (CMV), genus Cucumovirus . Only TDr 95-128, a landrace cultivar from Nigeria, developed symptoms of infection with CMV and DaBV following mechanical and vector transmission, respectively. PAS-ELISA showed that nine genotypes remained uninfected by DAV and 11 were uninfected by CMV or DaBV. Genotypes TDr 747 and TDr 1640 both showed resistance to all three viruses.     

A comprehensive study of Easter lily poisoning in cats.

This study was conducted with 3 objectives in mind: first, to identify the toxic fraction (aqueous or organic) in leaves and flowers; second, to identify diagnostic marker(s) of toxicosis in cats; and, third, to evaluate the morphologic effects of intoxication. The study was conducted in 2 phases. Phase 1 was to identify which extract, organic or aqueous, was nephrotoxic and also to determine the appropriate dose for use in the phase 2 studies. Results indicated that only the aqueous extracts of leaves and flowers were nephrotoxic and pancreotoxic. To identify the proximate toxic compound, cats in the phase 2 study were orally exposed to subfractions of the aqueous flower extract, 1 subfraction per cat. Results confirmed vomiting, depression, polyuria, polydipsia, azotemia, glucosuria, proteinuria, and isosthenuria as toxic effects of the Easter lily plant. Another significant finding in serum was elevated creatinine kinase. Significant histologic kidney changes included acute necrosis of proximal convoluted tubules and degeneration of pancreatic acinar cells. Renal ultrastructural changes included swollen mitochondria, megamitochondria, edema, and lipidosis. Subfraction IIa3 of the aqueous floral extract contained most of the toxic compound(s). These studies reproduced the clinical disease, identified the most toxic fraction of the Easter lily, and helped characterize the clinical pathology, histopathology, and ultrastructural pathology associated with the disease.