The effect of geographical location on phoma stem canker on oilseed rape in the UK

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Effects of Leptosphaeria maculans race structure and fitness cost of virulence on management of phoma stem canker of oilseed rape

Fitness of virulent (avrLm1 and avrLm4) or avirulent (AvrLm1 and AvrLm4) isolates of Leptosphaeria maculans on Brassica napus without the corresponding resistance genes Rlm1 and Rlm4 was investigated in controlled environment (CE) and field experiments. Results indicate that there is a measurable fitness cost for virulent isolates compared to avirulent isolates in terms of number of lesions, size of lesions, distance grown through leaf tissue towards the petiole in CE experiments and in terms of systemic growth from leaf lesions to stems in field experiments. There were differences between the AvrLm1 and AvrLm4 loci in fitness cost. The optimal temperature for leaf infection was higher for AvrLm4 isolates than for AvrLm1 isolates. There was a cultivar effect on fitness cost of virulence at the AvrLm1 locus but not at the AvrLm4 locus. Results from field experiments suggest that on the same host without the corresponding Rlm1 and Rlm4 genes, AvrLm4 isolates were more fit than AvrLm1 isolates in warmer growing seasons. The fitness cost of virulence at the AvrLm1 locus was generally smaller than that at the AvrLm4 locus, suggesting that the corresponding resistance gene Rlm4 is more durable than Rlm1. Frequencies of avirulent AvrLm1 and AvrLm6 alleles in airborne inoculum for 2006/07, 2007/08 and 2008/09 growing seasons in the UK were investigated using quantitative PCR. There were differences in frequencies of AvrLm1 and AvrLm6 alleles in the three seasons. The detection of changes in frequencies of avirulent alleles provides essential information to guide deployment of cultivars with corresponding resistance genes to minimise the risk of breakdown of novel resistanceNon peer reviewe

Development of phoma stem canker (Leptosphaeria maculans) and light leaf spot (Pyrenopeziza brassicae) on current and historical oilseed rape cultivars in 2003/04, 2004/05 and 2005/06 UK growing seasons

Non peer reviewe

Regional variation in UK populations of Leptosphaeria maculans and L. biglobosa (phoma stem canker) on oilseed rape

Non peer reviewe

Geographic variation in severity of phoma stem canker and Leptosphaeria maculans/L. biglobosa populations on UK winter oilseed rape (Brassica napus)

“The original publication is available at www.springerlink.com” Copyright SpringerPhoma stem canker, caused by Leptosphaeria maculans and L. biglobosa, is the most important disease of oilseed rape in Europe. Differences between L. maculans and L. biglobosa in their life-cycles enable the two species to co-exist on oilseed rape crops over a cropping season. This review considers the factors affecting geographic variation in the severity of phoma stem canker epidemics and in the structure of the population of the pathogens in the UK, where the most severe epidemics occur in the south of England and cankers do not develop in Scotland. It is concluded that this variation is directly related to differences in climate, since weather-based models show that stem canker severity increases with increasing winter/spring temperature and temperatures are greater in the south of the UK. It may also be related to differences in pathogen populations, since surveys showed that the proportion of the more damaging L. maculans in stem cankers was greatest in southern England, with most L. biglobosa in northern England. Regional variation in agronomic practices such as cultivar choice and fungicide use may also indirectly influence phoma stem canker severity. Differences in cultivar choice result in differences in L. maculans race structure, which may influence the severity of epidemics. Differences in fungicide use may also influence pathogen populations, since L. maculans and L. biglobosa differ in their sensitivities to different azole fungicides. These factors are discussed in relation to strategies for sustainable production of oilseed rape by adaptation to threats posed by climate change.Peer reviewe