RAPD-based genetic diversity study of fifty cassava (Manihot esculenta Crantz) genotypes

Fifty cassava clones were studied using RAPD technique. They included landraces from the Wenchi, Nkoranza, Dormaa Ahenkoro and Asonafo districts of the Brong Ahafo region of Ghana and three improved varieties. Genetic diversity of these genotypes was studied using four primers, OPK-01, OPR-02, OPR-09 and OPJ-14. A total of 41 different bands were detected. Levels of polymorphic fragments detected by the four primers ranged from 90% to 100%. By pooling bands from individual accessions together, mean number of fragments per accession per primer ranged from 5.50±1.04 for the Improved cultivars to 7.00±0.71 for populations of landraces from Dormaa. Mean frequencies of fragments not detected by the primers for the accessions were 0.524±0.12, 0.460±0.12, 0.561±0.12 and 0.523±0.12 for landraces from Wenchi, Nkoranza, Dormaa Ahenkro, Asonafo and the Improved varieties, respectively. The grand mean frequency of individuals showing fragments not present in populations was 0.522±0.10. Genetic diversity estimates ranged from 0.290 to 0.425 (mean 0.352±0.05) for primer OPK-01, 0.001 to 0.381 (mean 0.309±0.06) for primer OPR-02, 0.335 to 0.344 (mean 0.283±0.04) for primer OPR-09 and 0.152 to 0.352 (mean 0.261±0.07) for primer OPJ-14. Within the accessions mean gene diversity estimates were 0.316±0.03, 0.293±0.09, 0.331±0.02, 0.322±0.07 and 0.247±0.03 for accessions from Wenchi, Nkoranza, Dormaa Ahenkro, Asonafo districts and the Improved varieties, respectively. Interpopulational genetic divergence ranged from 0.069 to 0.203 (mean 0.119±0.04). Rate of nucleotide substitution among the landraces was 9.8 per cent per site per year, while that for the Improved varieties was 15 per cent. This revised version was published online in August 2006 with corrections to the Cover Date.     

Turnover and irrigation service fees

This paper reviews the implications of the new economic policies of turning over public irrigation systems to local water users and irrigation service fees that are in the process of being implemented by the Indonesian Government. These policies are designed to ensure that irrigation is economically sustainable over the next decades. The turnover program has already made considerable progress and, once government policies are clarified, has the potential to major impact on irrigation in the more mountainous provinces. It is expected by the year 2002 that 108 billion Rupiah will be raised from service fees. However, with respect to the collection of such fees, there is still bureaucratic uncertainty and local resistance that must be overcome before the policy can be successfully implemented throughout the country.     

Activation of proestrogens from hops (Humulus lupulus L.) by intestinal microbiota; conversion of isoxanthohumol into 8-prenylnaringenin

Hop, an essential ingredient in most beers, contains a number of prenylflavonoids, among which 8-prenylnaringenin (8-PN) would be the most potent phytoestrogen currently known. Although a number of health effects are attributed to these compounds, only a few reports are available about the bioavailability of prenylflavonoids and the transformation potency of the intestinal microbial community. To test these transformations, four fecal samples were incubated with xanthohumol, isoxanthohumol (IX), and 8-PN. Upon incubation with IX, present in strong ales up to 4 mg/L, 36% was converted into 8-PN in one fecal sample and the estrogenic properties of the sample drastically increased. In an experiment with 12 fecal cultures, this conversion was observed in one-third of the samples, indicating the importance of interindividual variability in the intestinal microbial community. Eubacterium limosum was identified to be capable of this conversion (O-demethylation) of IX into 8-PN, and after strain selection, a conversion efficiency of 90% was achieved. Finally, strain supplementation to a nonconverting fecal sample led to rapid and high 8-PN production at only 1% (v/v) addition. Up to now, the concentration of 8-PN in beer was considered too low to affect human health. However, these results show that the activity of the intestinal microbial community could more than 10-fold increase the exposure concentration. Because prenylflavonoids are present in many beers with IX being the major constituent, the results raise the question whether moderate beer consumption might contribute to increased in vivo levels of 8-PN and even influence human health.     

温室滴灌黄瓜产量和水分利用效率对水分胁迫的响应

为确定滴灌条件下温室黄瓜的适宜灌水方案,该文基于20 cm标准蒸发皿的累计水面蒸发量设计不同灌水处理,研究了滴灌条件下不同灌水处理(充分灌水T1,轻度水分亏缺T2,中度水分亏缺T3)对不同种植季节温室黄瓜生理特性、耗水量(Evapotranspiration,ET_c)、产量及水分利用效率(Water Use Efficiency,WUE)的影响,且于2017年8—12月(秋冬季)和2018年3—7月(春夏季)分别对不同灌水处理下土壤水分状况、作物生理指标、耗水量、产量和WUE等指标进行了系统的田间试验观测及分析。研究结果表明,随着灌水量的减小,温室黄瓜产量和WUE均呈降低趋势,不同程度的水分亏缺对黄瓜不同生育期ET_c有一定的抑制作用,在黄瓜生长任一阶段发生水分亏缺均会降低黄瓜植株的茎流速率、光合速率及气孔导度,进而可能影响黄瓜干物质的运转与积累,其中在作物生长中期,温室黄瓜茎流速率及产量对水分亏缺响应最为显著。黄瓜平均单果质量、果茎、果长和单株坐果数均随灌水量的降低而减小,黄瓜果实畸形比例随不同生长阶段水分亏缺的增大而增大。不同种植季节温室黄瓜T1处理的产量分别高出T2和T3处理的22.0%和51.2%(春夏季)、54.2%和73.9%(秋冬季);温室黄瓜T1处理的ET_c分别高出T2和T3处理的17.4%和34.9%(春夏季)、24.0%和48.0%(秋冬季);T1处理的WUE分别高出T2和T3处理的5.5%和25%(春夏季)、39.7%和50.0%(秋冬季)。综合研究结果,黄瓜发育期适宜灌溉水量为累计水面蒸发量的0.8倍,生长中、后期为累计水面蒸发量的1.2倍。研究结果对实现农业水分高效利用及促进设施作物优质、高产具有重要参考价值。     

Scale-dependent effects of terrestrial habitat on genetic variation in the great crested newt (Triturus cristatus)

Landscape Ecology - Terrestrial landscapes surrounding aquatic habitat influence the persistence of amphibian spatially structured populations (SSPs) via their crucial role in providing estivation...     

Historical and recent tomato black ring virus and beet ringspot virus isolate genomes reveal interspecies recombination and plant health regulation inconsistencies

Tomato black ring virus (TBRV) and beet ringspot virus (BRSV) are closely related but distinct members of subgroup B of the genus Nepovirus. Both viruses have broad host ranges and are transmitted by seed, pollen, and ectoparasitic nematodes. Although 13 TBRV and 3 BRSV genome sequences were already available, no attempt has been made to link sequence data from these recent sequences with those of historical isolates studied in the pre-sequencing era. High-throughput sequencing was used to generate eight new TBRV and BRSV genome sequences from three historical >60-year-old and two >30-year-old isolates, and three more recent isolates. These eight isolates were from the Czech Republic, Germany, and the UK. We compared these with all genomes sequenced previously. Intraspecies recombination (three of four TBRV and two of four BRSV isolates) was frequent amongst the eight new genomes. Interspecies recombination was also present within the RNA1 of TBRV isolates BRSV-3393 SG GB and BRSV-9888 ST GB. No satellite RNAs were associated with the eight new genomes. Two commercial enzyme-linked immunosorbent assay (ELISA) kits used to detect TBRV during routine testing differed in that one detected only TBRV and the other only BRSV, so they are likely to provide incorrect but potentially complementary virus occurrence information. We suggest both ELISA kits, or appropriate molecular tests, be used by biosecurity authorities to avoid this problem. This study illustrates the value of sequencing historical isolates preserved from the pre-sequencing era.