Modeling the Spread of Alfalfa Stem Nematodes: Insights into their Dynamics and Control

Alfalfa is a major cash crop in the western United States, where fields that are infested with the alfalfa stem nematode (Ditylenchus dipsaci) can be found. With no nematicides available to control alfalfa stem nematode spread, growers can use nematode resistant varieties of alfalfa to manage nematode populations in a field. A deterministic, discrete-time, host-parasite model is presented that describes the spread of alfalfa stem nematodes on resistant hosts that was fit to experimental data obtained in Weber County, Utah. Numerical results obtained from simulations with the model are used to compare how varying levels of resistance can affect harvest yield. Resistant varieties can also affect the invasion speeds of epidemics in crops. A continuous time, spatial model is presented that describes how these resistant varieties affect invasion speeds in general crop systems. Speeds of traveling wave fronts are determined for simple epidemics in crops that contain a mixture of resistant and non-resistant hosts. For the model, it was found that the wave speeds will slow down as highly nematode resistant varieties of alfalfa are used. The speed of invasion for the alfalfa stem nematode can be determined by using a mathematical relationship that is know as the contact distribution. We present a spatial model for the spread of alfalfa stem nematodes that uses a Gaussian distribution as the contact distribution of the alfalfa stem nematodes, which was determined by experimental data. Using this contact distribution we are able to approximate the speed of nematode invasive fronts in absence of advection, i.e. without nematode trans-port through flood irrigation. The contact distribution is then used to calculate front speeds when resistant varieties of alfalfa are introduced. We found that, unsurprisingly, invasive speeds are relatively low and cannot support the rapid dispersal of the disease among fields as seen in practice. However, this result leads to conjecture that changing current irrigation practices, from flood to sprinkle irrigation, could effectively contribute to control the spread of alfalfa stem nematodes. Resistant varieties of alfalfa can be used to effectively control the spread of the alfalfa stem nematode. In this work we have shown that using resistant varieties of alfalfa can increase yield up to 83%, they can slow down invasion speeds of nematodes, and switching from flood to sprinkler irrigation could effectively contribute to the control of the alfalfa stem nematode

Seed degeneration in potato : the need for an integrated seed health strategy to mitigate the problem in developing countries

Seed potato degeneration, the reduction in yield or quality caused by an accumulation of pathogens and pests in planting material due to successive cycles of vegetative propagation, has been a long-standing production challenge for potato growers around the world. In developed countries this problem has been overcome by general access to and frequent use of seed, produced by specialized growers, that has been certified to have pathogen and pest incidence below established thresholds, often referred to as certified seed. The success of certified seed in developed countries has concentrated the research and development agenda on the establishment of similar systems in developing countries. Despite these efforts, certified seed has had little penetration into the informal seed systems currently in place in most developing countries. Small-scale farmers in these countries continue to plant seed tubers acquired through the informal seed system, i.e. produced on-farm or acquired from neighbours or local markets. Informal seed tubers frequently have poor health status, leading to significant reductions in yield and/or market value. This review emphasizes the need to refocus management efforts in developing countries on improving the health status of seed tubers in the informal system by integrating disease resistance and on-farm management tools with strategic seed replacement. This 'integrated seed health strategy' can also prolong the good health status of plants derived from certified seed, which would otherwise be diminished due to potential rapid infection from neighbouring fields. Knowledge gaps, development challenges and impacts of this integrated seed health strategy are discussed.PostprintPeer reviewe

Diversity and Management of Phytophthora in Southeast Asia

Crop Production/Industries,

A critical review of plant protection tools for reducing pesticide use on grapevine and new perspectives for the implementation of IPM in viticulture

Several pests and diseases have grapevine as their favourite host and the vineyard as preferred environment, so an intensive pesticide schedule is usually required to meet qualitative and quantitative production standards. The need to prevent the negative impact of synthetic chemical pesticides on human health and the environment and the consumer expectations in term of chemical residues in food stimulated the research of innovative tools and methods for sustainable pest management. The research project PURE (www.pure-ipm.eu) was a Europe-wide framework, which demonstrated that several solutions are now available for the growers and evaluated several new alternatives that are under development or almost ready for being applied in practice. Although the use of resistant/tolerant varieties is not yet feasible in several traditional grape growing areas, at least part of the synthetic chemical pesticides can be substituted with biocontrol agents to control pests and pathogens and/or pheromone mating disruption, or the number of treatments can be reduced by the use of decision support systems, which identify the optimal timing for the applications. This review presents the state of the art and the perspectives in the field of grapevine protection tools and strategies

Plant Microbial Interactions in Wheat: Fusarium Head Blight and Arbuscular Mycorrhizal Fungi

Plant microbial interactions consist of the many relationships between plants and microbes which involve studies that observe the biology and molecular genetics of pathological, symbiotic, and associative interactions. Worldwide studies involving these interactions are scarcely available in wheat (Triticum aestivum L.). In South Dakota (SD), wheat research is a major platform used to understand the nature and consequences of these interactions. Specifically, our research efforts here at South Dakota State University (SDSU) concentrate on two different, but valuable, interactions in wheat: the fungal pathogen that causes fusarium head blight (FHB) and the symbiotic interaction of arbuscular mycorrhizae fungi (AMF) with wheat. These interactions were selected to help provide a better understanding of plant microbial interactions in wheat. In our first project, we studied FHB, which is one of the most devastating plant diseases in the world. It is responsible for significant economic loss due to lower crop yield and quality, as well as human health concern due to mycotoxin accumulation in infected grains. To date, no sources of resistance conferring complete resistance to FHB have been identified in wheat. Using double haploid (DH) populations derived from selected four-way crosses combining several sources of resistance, we developed wheat lines that display resistance to FHB. Screening evaluations followed by selections were conducted using both DH spring and winter wheat populations to further evaluate the potential usage of this material to enhance adapted wheat germplasms. Selection for resistance quantitative trait loci (QTL’s) and the use of fungicide (Prosaro) are two different approaches, which when combined, may present a better way of minimizing disease damage. We conducted a field experiment to evaluate the effect of combining resistance QTL’s and fungicide application on FHB severity. In our second project we studied AMF, which forms a mutualistic symbiotic interaction with the majority of land plants. Like many plant microbial interactions, not much information is available on AMF and wheat. Consequently, we conducted a field study to examine the contribution of AMF to nutrient uptake and biomass yields of spring wheat genotypes. Our results demonstrate that there are differences in mycorrhizal responsiveness and nutrient efficiency with the presence of AMF on wheat. This could suggest that there is a genetic control of these genotypic differences. Overall, our findings assist ongoing efforts aimed to describe the causes and benefits of these plant microbial interactions. Our studies are potential baselines that can assist both development and production of wheat and other major crops

Effects of non-adapted quantitative trait loci (QTL) for Fusarium head blight resistance on European winter wheat and Fusarium isolates

Fusarium head blight (FHB), caused by Fusarium graminearum and F. culmorum, is a devastating disease responsible for tremendous damage in wheat fields and contamination of grain with mycotoxins deoxynivalenol (DON) and nivalenol (NIV), rendering the harvest unsafe for human and animal consumption. The variability of Fusarium populations is high and changes in aggressiveness, chemotypes or species within and among Fusarium populations are known. Stable FHB resistance combined with high yield is one main target in wheat breeding programs. Mapping studies detected several quantitative trait loci (QTL) for FHB resistance in non-adapted sources, such as Sumai3 from China. The two most important and commonly used major QTL are located on chromosome 3BS (Fhb1) und 5A (Qfhs.ifa-5A). However, negative side effects of non-adapted resistance sources introgressed in elite winter wheat material are feared in Europe. Furthermore, the stability of the QTL effect against changing Fusarium populations is unknown. The objectives of this research were to analyze whether (1) the QTL Fhb1 and Qfhs.ifa-5A introgressed from a non-adapted resistance source into two winter wheat varieties have possible side effects on agronomic and quality performance, (2) 3-ADON and 15-ADON chemotypes are significantly different in their aggressiveness and DON production, (3) competition among Fusarium isolates in mixtures exists, and if so, how the resistant host will influence this competition. In conclusion, both resistance QTL are effective and stable in elite spring and winter wheat backgrounds. For improvement of FHB resistance both QTL are valuable, but Qfhs.ifa-5A would suffice for European breeding programs. Due to chemotype shifts, 3-ADON isolates could pose a greater risk to food safety than 15-ADON but breeding and use of highly resistant lines can reduce the risks associated with DON in wheat. Accordingly, resistant spring wheat lines were less affected by the tested Fusarium isolates and mixtures and, therefore, confirmed a high stability of these QTL. Directed selection of highly aggressive isolates due to the resistance QTL seems to be unlikely in the short term.In Europa verursachen Ährenfusariosen hohe Ertrags- und Qualitätsverluste. Die Hauptpathogene im Weizen sind Fusarium graminearum und F. culmorum. Diese kontaminieren das Erntegut mit den von ihnen produzierten Mykotoxinen Deoxynivalenol (DON) und Nivalenol (NIV). Die genetische Variabilität der Pilze ist groß, so dass immer wieder Veränderungen in ihrer Aggressivität auftreten. Es gibt sowohl Verschiebungen zwischen Arten und zwischen Chemotypen als auch innerhalb von Populationen. Ein großes Ziel der Pflanzenzüchtung ist es daher ertragreichen Sorten mit stabiler Resistenz zu etablieren. Bisher konnten in verschiedenen Kartierungspopulationen quantitative vererbte Genorte (quantitative trait loci, QTL) für die Fusarium-Resistenz gefunden werden. Eine Resistenzquelle ist die chinesische Weizensorte Sumai3, welche zwei weit verbreitete major QTL auf den Chromosomen 3BS (Fhb1) und 5A (Qfhs.ifa-5A) trägt. Bei einer Einkreuzung dieser QTL in Elitematerial werden jedoch negative Nebeneffekte aufgrund der nicht adaptierten Quelle befürchtet. Des Weiteren ist die Stabilität dieser QTL gegenüber sich verändernden Fusarium-Populationen nicht bekannt. Die Ziele dieser Studie waren (1) die Analyse möglicher Nebeneffekte der zwei QTL Fhb1 und Qfhs.ifa-5A auf agronomische Eigenschaften und Qualitätsparameter, da die QTL aus nicht adaptierten Resistenzquellen in zwei Elite-Winterweizensorten eingekreuzt wurden, (2) die Messung der Aggressivität und der DON-Produktion von 3-acetyldeoxynivalenol (3-ADON) im Vergleich zu 15-ADON Chemotypen, und (3) die Modellierung des Wettbewerbs zwischen Fusarium-Isolaten in Mischungen in Abhängigkeit von unterschiedlich resistenten Wirtsgenotypen. Beide Resistenz-QTL waren im Elite-Sommer- und Winterweizenhintergrund effektiv und stabil. Zur Verbesserung der Fusarium-Resistenz sind beide QTL sinnvoll einsetzbar. Die Ergebnisse zeigten, dass der Einsatz von Qfhs.ifa-5A in europäischen Zuchtprogrammen vorteilhaftesten wäre. Durch die Veränderung innerhalb der Chemotypenzusammensetzung von Fusarium-Populationen könnten 3-ADON-Isolate ein höheres Risiko für die Nahrungsmittelsicherheit bedeuten als 15-ADON-Isolate. Die Züchtung und der Anbau von hochresistenten Sorten kann dieses Risiko, das mit erhöhten DON-Werten im Erntegut verbunden wäre, verringern. Die resistenten Sommerweizenlinien waren weniger mit den getesteten Fusarium-Isolaten und -Mischungen infiziert als die anfälligen, was die Stabilität der QTL bestätigt. Eine gerichtete Selektion von hoch aggressiven Isolaten durch den Anbau von Sorten mit Resistenz-QTL ist zumindest kurzfristig unwahrscheinlich

Cereal crop diversity: Implications for production and products

This proceeding comprises papers based on oral and poster presentations at the COST860 - SUSVAR workshop on cereal crop diversity held in La Besse, France, 13-14 June 2006. The main aims of the SUSVAR network are to ensure stable and acceptable yields of good quality for low-input, especially organic, cereal production in Europe. This will be achieved by developing ways to increase and make use of crop diversity, by establishing methods for selecting varieties, lines and populations taking into account genotype-environment interactions and by establishing common methodology for variety testing where appropriate. The present workshop focused on ways to increase and make use of crop diversity from the production to the product. As crop diversity often is argued to be an advantage for the grower but a problem for the end user of high quality grain products, the six introductory oral presentations (Topic 0) gave introduction to farmer’s conception of diversity and examples of practical applications of variety mixtures for baking and distilling quality. The remaining part of the workshop was open for poster contributions reflecting the ongoing research within the SUSVAR network on crop diversity. The posters were grouped into four topics: Growing variety mixtures (Topic I), Evolutionary processes in diverse crops (Topic II), Genetic diversity (Topic III) and Variety and species mixtures, diseases and soil (Topic IV). The posters were introduced by a moderator and their contribution is included as an introduction to each topic