Fitness cost of virulence differs between the AvrLm1 and AvrLm4 loci in Leptosphaeria maculans (phoma stem canker of oilseed rape)

Abstract

???The original publication is available at www.springerlink.com??? Copyright Springer [Full text of this article is not available in the UHRA]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

Evolution of virulence in fungal plant pathogens: exploiting fungal genomics to control plant disease

“…Zhan and McDonald (2013) observed that fitness cost of mutation of avirulence genes of fungi can affect the effectiveness of recycling the corresponding resistance gene in crops. Fitness costs are associated with mutation of AvrLm1 and AvrLm4 in L. maculans (Huang et al 2010). This is consistent with our observations of much higher frequencies of AvrLm1 in fungal populations in regions in Australia where cultivars with Rlm1 resistance have not been sown, compared to areas where these cultivars have been extensively sown.…”

Pathogen effectors and plant immunity determine specialization of the blast fungus to rice subspecies

“…On the one hand, positive and negative fitness costs of effectors were demonstrated in rare field studies involving the fungus Leptosphaeria maculans (Huang et al, 2006, 2010) or the bacterium Xanthomonas oryzae pv oryzae (Vera Cruz et al, 2000). Under controlled conditions, a reduced number of ‘avirulence’ activities had a significant negative impact on fitness as in the case of Phytophthora infestans infecting potato (Montarry et al, 2010).…”

Spatio‐temporal connectivity and host resistance influence evolutionary and epidemiological dynamics of the canola pathogen Leptosphaeria maculans

“…In addition, a number of studies have attempted to measure such costs in either the field or under controlled conditions (e.g., Chin & Wolfe, 1984; Huang et al., 2006, 2010; Barrett, Bell, Dwyer, & Bergelson, 2011; Zhan & McDonald, 2013). However, temporal changes in infectivity patterns in agricultural systems are not always consistent with theoretical expectations.…”