Resistance-breaking Nasonovia ribisnigri By Gemma Hough Supervisor: Dr. Rosemary Collier
Aphids Approximately 4000 recorded species with a huge host plant range 250 species infest major agricultural crops reducing yield Successful pest due to: High reproductive rates Polymorphisms
Populations of parthenogenetic aphids can double in just 3 days such that a single aphid weighing 1mg can, in just 6 months, theoretically generate a population of total weight more than 100 times the global human population (assuming 6 billion people of a mean weight of 50kg). Karley, A. J et al (2004) The mid-season crash in populations: why and how does this occur? Ecological Entomology 29, 383-388
Nasonovia ribisnigri The currant-lettuce aphid is a major lettuce pest Heteroecious- a primary winter woody host and a secondary summer herbaceous host Holocyclic- asexual and sexual reproduction Possibly anholocyclic surviving on lettuce and other related hosts including Chicory, Speedwell and Hawkweed species
Control Feeding preference makes control difficult Currently: Insecticides Imidacloprid seed treatment New insecticide- Movento Resistant lettuce varieties Introduced in 1998 Introgressed a resistance gene (Nr) from the wild lettuce species L. virosa into commercial varieties of the cultivated lettuce L. sativa Nr gene
First reports of resistance-breaking (Rb) Reports first originated in 2007 Investigated by breeding companies: Rb Nasonovia developed on all lettuce varieties with the Nr gene Rb Nasonovia multiply 50% slower than the WT aphids on lettuce with no Nr gene. No significant differences between locations in France and Germany Now in the UK!
Percentage Survival (%) Preliminary Experiment Percentage survival of resistance-breaking and wild type N. ribisnigri on resistant and susceptible lettuce varieties 100 90 80 70 60 50 40 30 20 10 0 Rb N. ribisnigri + Susceptible Saladin Rb N. ribisnigri + Resistant Eluarde Rb N. ribisnigri + Resistant Rotary WT N.ribisnigri + Susceptible Saladin WT N. ribisnigri + Resistant Rotary WT N. ribisnigri + Resistant Eluarde Treatment (type of aphid and lettuce)
Average Development Time to adult (days) Average developmental time to adult of resistance-breaking and wild type N. ribisnigri on resistant and susceptible lettuce varieties 12 11 10 9 8 7 6 5 4 3 2 1 0 Susceptible Saladin Resistant Eluarde Resistant Rotary WT N.ribisnigri + Susceptible Saladin Treatments (type of aphid and lettuce)
Average fecundity for 5 days after reaching adulthood 10 9 8 7 6 5 4 3 2 1 0 Number of nymphs produced during the first 5 days after reaching adulthood for resistance-breaking and wild type N. ribisnigri on resistant and susceptible lettuce varieties Susceptible Saladin Resistant Eluarde Resistant Rotary Treatment (type of aphid and lettuce) WT N.ribisnigri + Susceptible Saladin
Proportion of adults becoming alate and apterous Proportion of resistance-breaking and wild type N. ribisnigri nymphs becoming alate or apterous on resistant and susceptible lettuce varieties 1 0.9 0.8 0.7 0.6 0.5 Alate Apterous 0.4 0.3 0.2 0.1 0 Susceptible Saladin Resistant Eluarde Resistant Rotary WT N.ribisnigri + Susceptible Saladin Treatment (type of aphid and lettuce)
What s next Developmental rates Different sources of resistant lettuce varieties Geographically different resistance-breaking Nasonovia Alternative host plant preference experiment Microsatellites
Developmental rates Determine how temperature impacts developmental rates of both Rb and WT Nasonovia. Repeat preliminary experiment at 5, 10, 15, 17.5, 20 and 25 C. Record developmental time to adult, total achieved fecundity and mortality.
Different sources of resistant lettuce varieties Determine whether different Nr gene introgression backgrounds have a different effectiveness in controlling WT and Rb Nasonovia. List resistant lettuce varieties from different breeding companies Initially looking at Butterhead varieties. Compare survival and development between the varieties
Alternative host plant preference Determine which alternative host plants Rb and WT Nasonovia will colonise at optimum temperatures. Identified 14 species of alternative hosts Determine preference Determine whether these alternative hosts are capable of overwintering
Microsatellites Create genetic profiles of each aphid culture to determine whether they are different clones Microsatellites- repeating sequences of 1-6 base pairs of DNA and the number of repeat units at any given locus can vary so it is possible to identify different genotypes within a population. PCR Primers- designed by the Scottish Crop Research Institute for use on Myzus persicae (peach-potato aphid)
Geographically different resistancebreaking Nasonovia Collect resistance-breaking Nasonovia from different geographic locations across Europe. Carry out survival and developmental comparisons. Use microsatellites to create genetic profiles of each culture to determine whether there are different clones and whether there is a geographic pattern.
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