Monitoring virulence of Bremia lactucae as a breeding tool against lettuce downy mildew from south and southwest Brazili
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Monitoring virulence of Bremia lactucae as a breeding tool against lettuce downy mildew from south and southwest Brazilian regions C. A. Franco & M. V. Marin & E. H. C. Silva & R. S. Soares & W. S. Candido & L. N. Souza & C. H. Caprio & R. L. Vidal & R. C. Panizzi & L. T. Braz
Accepted: 10 November 2020 # Koninklijke Nederlandse Planteziektenkundige Vereniging 2020
Abstract Lettuce downy mildew caused by Bremia lactucae is one of the main diseases in high humidity and low temperature conditions. The identification of virulence factors appearing in the pathogen population could help improve breeding programs against this disease. This study aimed to monitor and evaluate virulence dynamic changes in B. lactucae virulence among two Brazilian regions to recommend resistance genes for breeding programs. Isolates from São Paulo, Rio Grande do Sul, and Paraná states were assessed using the sextet code EU-C composed by 16 Lactuca spp. genotypes, between 2015 and 2016. To understand the population dynamics, the frequencies of virulence phenotypes and factors and the virulence complexity per isolate (Ci), phenotype (Cp), and Gleason (Ig), indexes were calculated. C. A. Franco and M. V. Marin contributed equally to this work. C. A. Franco (*) : E. H. C. Silva : R. S. Soares : W. S. Candido : L. N. Souza : C. H. Caprio : R. L. Vidal : L. T. Braz (*) Department of Crop Production, School of Agricultural and Veterinarian Sciences, UNESP- São Paulo State University (Unesp), Jaboticabal, SP 14884-900, Brazil e-mail: [email protected] e-mail: [email protected] M. V. Marin (*) Gulf Coast Research and Education Center, University of Florida, Wimauma, FL 33598, USA e-mail: [email protected] R. C. Panizzi Department of Plant Pathology, School of Agricultural and Veterinarian, UNESP- São Paulo State University (Unesp), Jaboticabal, SP 14884-900, Brazil
B. lactucae virulence from Paraná, Rio Grande do Sul and São Paulo were similar and shared nine out of the 15 evaluated virulence factors. In total, 90 isolates were analyzed, and 27 virulence phenotypes were found. The most frequent sextet codes were 31–00-00, 31–00-02, 31–0100, and 31–01-02. The genes or resistance factors present in ‘Argelès’ (Dm38), ‘Balesta’, and ‘Bartoli’ could be used as sources of resistance by Brazilian lettuce breeders. Keywords Bremia lactucae . Lactuca sativa . Race determination . Lettuce breeding . Resistance genes . Race-specific resistance
Introduction Lettuce (Lactuca sativa L.) is the most popular leaf vegetable worldwide. Lettuce downy mildew caused by Bremia lactucae Regel is one of the most significant diseases of this crop. Due to pathogen infection, chlorosis and necrotic spots appear on the leaves, leading to depreciation of the final product. Under conducive weather conditions, which are low temperatures (12– 20 °C) and high humidity (90–100%), up to 80% loss can be expected (Töfoli et al. 2014; Fall et al. 2015). The high variability of B. lactucae allows the pathogen to adapt quickly to different management strategies, which is a li
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