Fitness cost of virulence differs between the <Emphasis Type="Italic">AvrLm1</Emphasis> and <Emphasis Type="Italic">AvrLm4</Emphasis> loci in <Emphasis Type="Italic">Leptosphaeria maculans</Emphasis> (phoma stem canker of oilseed rape) |
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| Authors: | Yong-Ju Huang Marie-Hélène Balesdent Zi-Qin Li Neal Evans Thierry Rouxel Bruce D L Fitt |
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| Institution: | (1) Rothamsted Research, Harpenden, Herts, AL5 2JQ, UK;(2) INRA-UMR1290, BIOGER-CPP, Versailles Cedex, 78026, France;(3) Present address: Plant Protection Institute, Inner Mongolia Academy of Agricultural Sciences, Huhhot, 010031, China |
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| Abstract: | To investigate whether the reported fitness cost of virulence at the AvrLm4 locus in Leptosphaeria maculans is common to other loci, near-isogenic (NI) isolates differing at AvrLm1 locus were produced in vitro. Fitness of virulent (avrLm1) or avirulent (AvrLm1) isolates on Brassica napus without the corresponding R (resistance) gene Rlm1 was investigated in controlled environment (CE) and field experiments. Results indicate that there is a measurable fitness
cost for avrLm1 compared to AvrLm1 isolates in terms of number of lesions, size of lesions, distance grown through leaf tissue towards the petiole in CE experiments
and systemic growth from leaf lesions to stems in field experiments. There were differences in fitness cost between the AvrLm1 and AvrLm4 loci. There was a cultivar effect on fitness cost of virulence at the AvrLm1 locus but not at the AvrLm4 locus. In CE experiments, the optimal temperature for leaf infection was greater for AvrLm4 isolates than for AvrLm1 isolates. Field experiment results suggest that on the same host AvrLm4 isolates are more fit than AvrLm1 isolates in warmer seasons. The fitness cost at the AvrLm4 locus was generally greater than at the AvrLm1 locus, suggesting that the corresponding R gene Rlm4 may be more suitable than Rlm1 for redeployment in commercial cultivars after an interval of a few years. |
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