Brassicaceae : Turnip yellows virus interactions

Abstract

Turnip yellows virus (TuYV) is the most common and important virus infecting oilseed rape (Brassica napus) in the UK. It causes reductions in growth and seed yield in oilseed rape. Between 2007 and 2010, the prevalence of TuYV in oilseed rape crops in Lincolnshire, Warwickshire and Yorkshire was determined; incidences of infection ranged from 0 and 100%. The highest levels of infection were detected in Lincolnshire and the lowest in Yorkshire. Highest incidences were recorded during 2009-10 and the lowest in 2008-9. Incidences of TuYV were closely related to the flight activities Myzus persicae vector. Most fields showed slightly aggregated pattern of infection during autumn but spring sampling revealed more random patterns. Phylogenetic analysis of both nucleotide and amino acid sequences of the P0 and P3 genes of TuYY revealed three and two genetic groups of TuYV respectively, infecting oilseed rape in Lincolnshire, Warwickshire and Yorkshire. The P0 gene was more variable than the P3 gene and both were under purifying selection. TuYV populations in the three regions were highly structured with limited gene flow between them. Analysis of molecular variance (AMOVA) indicated 96- 97% of the observed variation was due to the variation between isolates within fields. Three RT-PCR assays were developed to differentiate the three genotypes. They successfully detected and discriminated isolates of the two major genotypes from oilseed rape in Lincolnshire. Twenty seven accessions of a B. napus Diversity Fixed Foundation Set (DFFS) screened for resistance against TuYV infections varied in their susceptibility to the virus. An accession Yudal had partial resistance to some but not all the isolates of the two major genetic groups tested. TuYV caused yield losses of up to 44.7% in a glasshouse experiment. A major QTL for the partial TuYV resistance was detected on chromosome C4 (N14), explaining up to 50.5% of the observed resistance.EThOS - Electronic Theses Online ServiceGhanaUniversity of Cape CoastGBUnited Kingdo