Estimating the delay between host infection and disease (incubation period) and assessing its significance to the epidemiology of plant diseases.

Knowledge of the incubation period of infectious diseases (time between host infection and expression of disease symptoms) is crucial to our epidemiological understanding and the design of appropriate prevention and control policies. Plant diseases cause substantial damage to agricultural and arboricultural systems, but there is still very little information about how the incubation period varies within host populations. In this paper, we focus on the incubation period of soilborne plant pathogens, which are difficult to detect as they spread and infect the hosts underground and above-ground symptoms occur considerably later. We conducted experiments on Rhizoctonia solani in sugar beet, as an example patho-system, and used modelling approaches to estimate the incubation period distribution and demonstrate the impact of differing estimations on our epidemiological understanding of plant diseases. We present measurements of the incubation period obtained in field conditions, fit alternative probability models to the data, and show that the incubation period distribution changes with host age. By simulating spatially-explicit epidemiological models with different incubation-period distributions, we study the conditions for a significant time lag between epidemics of cryptic infection and the associated epidemics of symptomatic disease. We examine the sensitivity of this lag to differing distributional assumptions about the incubation period (i.e. exponential versus Gamma). We demonstrate that accurate information about the incubation period distribution of a pathosystem can be critical in assessing the true scale of pathogen invasion behind early disease symptoms in the field; likewise, it can be central to model-based prediction of epidemic risk and evaluation of disease management strategies. Our results highlight that reliance on observation of disease symptoms can cause significant delay in detection of soil-borne pathogen epidemics and mislead practitioners and epidemiologists about the timing, extent, and viability of disease control measures for limiting economic loss.ML thanks the Institut Technique français de la Betterave industrielle (ITB) for funding this project. CAG and JANF were funded by the UK’s Biotechnology and Biological Sciences Research Council (BBSRC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

First Report of Root-Knot Nematode Meloidogyne enterolobii on Tomato and Cucumber in Switzerland

Severe stunting and extensive root galling were observed on tomato rootstock (Solanum lycopersicum L. cv. Maxifort) resistant to Meloidogyne incognita (Kofoid & White, 1919) Chitwood, 1949, M. javanica (Treub, 1885), and M. arenaria (Neal, 1889) Chitwood, 1949 and cucumber (Cucumis sativus L. cv. Loustik) from two commercial greenhouses in the cantons Aargau and Lucerne in northern Switzerland. Examination of the roots of infected plants revealed the presence of root-knot nematodes in large numbers. Juveniles, males, and females were isolated, and the species was determined on the basis of morphological characteristics, including the female perineal pattern. Identification was confirmed by female esterase (Est) and malate dehydrogenase (MdH) electrophoresis (20 each for Est and MdH). All methods of identification were consistent with M. enterolobii Yang & Eisenback, 1983 (4). For further confirmation, type material of M. enterolobii (from the original host Enterolobium contortisiliquum (Vell.) Morong) from China (4) was used. Furthermore, comparison of the sequence data from 12 individuals of each of the two Swiss populations and the type material of a 310-bp fragment of cytochrome oxidase I (COI), a 723-bp fragment covering the internal transcribed spacer (ITS) region 1, 5.8s, ITS2, and part of the 26s, the mtDNA 63-bp repeat region, and a 780-bp fragment of the intergenic spacer region (1¿3) showed 100% homology and confirmed the identification as M. enterolobii. The species M. enterolobii is of great importance because it is able to reproduce on resistant tobacco, pepper, watermelon, and tomato (4). To our knowledge, this is the first report of M. enterolobii in Switzerland

Preandpostharvest management of aflatoxin in maize: an African perspective

Pre- and postharvest contamination of aflatoxin in maize is a major health deterrent for people in Africa where maize production has increased dramatically. This chapter highlights management options for pre- and postharvest toxin contamination in maize. Sound crop management practices are an effective way of avoiding, or at least diminishing, infection by Aspergillus flavus and subsequent aflatoxin production. Pre- and postharvest practices that reduced aflatoxin contamination include: the use of resistant cultivars, harvesting at maturity, rapid drying on platforms to avoid contact with soil, appropriate shelling methods to reduce grain damage, sorting, use of clean and aerated storage structures, controlling insect damage, and avoiding long storage periods. These contamination reducing management practices are being tested in collaboration with farmers. Work continues on food basket surveys, the bio-ecology of aflatoxin production, developing biological control through a competitive exclusion strategy, reducing the impact of postharvest management practices on human blood toxin levels, and breeding to reduce the impact of mycotoxins on trade

Comparison of two short DNA barcoding loci (COI and COII) and two longer ribosomal DNA genes (SSU & LSU rRNA) for specimen identification among quarantine root-knot nematodes (Meloidogyne spp.) and their close relatives

Root-knot nematodes (Meloidogyne spp.) are important pests of numerous crops worldwide. Some members of this genus have a quarantine status, and accurate species identification is required to prevent further spreading. DNA barcoding is a method for organism identification in non-complex DNA backgrounds based on informative motifs in short DNA stretches (˜600 bp). As part of the EU 7th Framework project QBOL, 15 Meloidogyne species were chosen to compare the resolutions offered by two typical DNA barcoding loci, COI and COII, with the distinguishing signals produced by two ribosomal DNA genes (small and large subunit rDNA; SSU¿˜¿1,700 and LSU¿˜¿3,400 bp). None of the four markers distinguished between the tropical species Meloidogyne incognita, M. javanica and M. arenaria. Taking P ID (Liberal) values =0.93 as a measure for species delimitation, the four mtDNA and rDNA markers performed well for the tropical Meloidogyne species complex, M. enterolobii, M. hapla, and M. maritima. Within cluster III A (Holterman et al. Phytopathology, 99, 227–235, 2009), SSU rDNA did not offer resolution at species level. Both mtDNA loci COI and COII did, whereas for LSU rDNA a longer fragment (=700 bp) is required. The high level of mitochondrial heteroplasmy recently reported for M. chitwoodi (Humphreys-Pereira and Elling Nematology, 15, 315–327, 2013) was not found in the populations under investigation, suggesting this could be a regional phenomenon. For identification of RKNs, we suggest the combined use of SSU rDNA with one of three other markers presented here