Molecular characterization of taro (Colocasia esculenta) using RAPD markers

Forty-four taro (Colocasia esculenta), two tanier (Xanthosoma species) and one Colocasia gigantea accessions were evaluated for genetic diversity using random amplified polymorphic DNA (RAPD) primers. Seventy-three of 112 primers amplified PCR DNA products used to fingerprint the accessions. Thirty-two primers were considered highly informative because they amplified more than 5 bands or amplified one or more polymorphic bands that distinguished between accessions. RAPDs showed high genetic diversity in taro accessions from Indonesia, were capable in distinguishing between Hawaiian accessions, and could separate triploid from diploid accessions. UPGMA cluster analysis of genetic similarity estimates (Jaccard's coefficient), separated the accessions into 3 main groups with C. esculenta divided into 5 subgroups. These primers will be useful for future genetic analysis and provide taro breeders with a genetic basis for selection of parents for crop improvement. Polymorphic markers identified in the DNA fingerprinting study will be useful to screen a segregating population which is being generated in our laboratory aimed at developing a taro genetic linkage map. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Select Surfactants on Activities of Soil Enzymes Involved in Nutrient Cycling

Experiments were conducted to investigate the impact of commonly used herbicides and surfactants on the activity of acid phosphatase, β-glucosidase, arylsulfatase, β-glucosaminidase, and dehydrogenase, using two soils (silt loam and silty clay loam) from Mid-Missouri, USA. The surfactants used in this study were alkylphenol ethoxylate + alcohol ethoxylate (ACTIVATOR 90), polyethoxylate (Agri-Dex®) and a blend of ammonium sulfate, drift reduction/deposition polymers, and an antifoam agent (THRUST®). The herbicides were glyphosate, atrazine, and bentazon. Surfactants and herbicides were applied to soils at the label rate, either alone or combined. In general, enzyme activity was enhanced more in silt loam soil than in silty clay loam soil. Acid phosphatase displayed the greatest amount of enzymatic activity within soils; dehydrogenase displayed the most inhibition, whilst β-glucosidase and β-glucosaminidase fluctuated based on treatment. ACTIVATOR 90 appeared to have the most inhibitory effect on enzymatic activity within soils compared to the control.     

Dispersal of potato cyst nematodes measured using historical and spatial statistical analyses

Rates and modes of dispersal of potato cyst nematodes (PCNs) were investigated. Analysis of records from eight countries suggested that PCNs spread a mean distance of 5.3 km/year radially from the site of first detection, and spread 212 km over ≈40 years before detection. Data from four countries with more detailed histories of invasion were analyzed further, using distance from first detection, distance from previous detection, distance from nearest detection, straight line distance, and road distance. Linear distance from first detection was significantly related to the time since the first detection. Estimated rate of spread was 5.7 km/year, and did not differ statistically between countries. Time between the first detection and estimated introduction date varied between 0 and 20 years, and differed among countries. Road distances from nearest and first detection were statistically significantly related to time, and gave slightly higher estimates for rate of spread of 6.0 and 7.9 km/year, respectively. These results indicate that the original site of introduction of PCNs may act as a source for subsequent spread and that this may occur at a relatively constant rate over time regardless of whether this distance is measured by road or by a straight line. The implications of this constant radial rate of dispersal for biosecurity and pest management are discussed, along with the effects of control strategies.     

Evaluation of organic,synthetic and physical insecticides for the control of horse chestnut leaf miner (Cameraria ohridella)

Two separate trials during 2007 and 2008 were conducted using containerized white flowering horse chestnut trees (Aesculus hippocastanum L.) to assess the efficacy of a range of insecticides applied at three different times during a growing season against the insect pest, horse chestnut leaf miner (Cameraria ohridella Deschka and Dimic; HCLM). Insecticides were timed to coincide with the emergence of the adult moth, the target organism. A conventional synthetic insecticide (deltamethrin) used within the UK for HCLM control was included for comparison. A marked impact of insecticide type and frequency of application on HCLM severity was recorded. The effectiveness of each insecticide on mean number of HCLM mines per leaf and percent HCLM larvae/pupae mortality increased when applied at increasing frequencies, i.e. three sprays provided a higher degree of control than two sprays while two sprays provided a higher degree of control than one spray. Limited efficacy as HCLM protectant compounds was demonstrated when the insecticides pyrethrum and soap were applied, irrespective of number of applications. The synthetic insecticide deltamethrin and insect growth regulator diflubenzuron provided the greatest degree of HCLM control. In some instances two foliar sprays provided 100% HCLM control. Efficacy of remaining insecticides based on reduction of HCLM mines per leaf after three sprays averaged across both the 2007 and 2008 trials was in the order silicon dioxide > alginate/polysaccharide combination > organic plant extract > spray oil. Results show commercially registered insecticides exist that provide growing season control of HCLM provided two sprays are applied.