Phenotypic and genetic variability of fungal isolates associated with the Septoria leaf spot disease of lettuce (Lactuca sativa) in Brazil

• Published in: Journal of plant diseases and protection (2006) Vol. 129; no. 1; pp. 53 - 62
• Main Authors: Cabral, C. S., Fonseca, M. E. N., Boiteux, L. S., Barboza, E. A., Veloso, J. S., Lourenço, V., Reis, A.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.02.2022
• Subjects: Biomedical and Life Sciences; Life Sciences; Original Article; Plant Pathology; Plant Physiology; Plant Sciences; Phylogenetic analysis; Septoria leaf spot; Lettuce; Diversity
• ISSN: 1861-3829; 1861-3837
• DOI: 10.1007/s41348-021-00537-9

Septoria leaf spot is a severe disease of lettuce in tropical and subtropical regions, inducing yield/quality losses and increasing production costs. Globally, Septoria lactucae has been reported as the major pathogen associated with this disease. However, a complex of Septoria species has been also reported in association with lettuce crop around the world. Extensive surveys of Septoria species associated with this disease have not been conducted in the Neotropics. Therefore, the objective of the present study was to undergo a phenotypic and genetic characterization of a collection of 32 Brazilian Septoria isolates causing lettuce leaf spot. Morphometrical characterization of conidia and pycnidia was conducted with ten isolates obtained from three lettuce-producing regions in Brazil. In addition, partial sequences of four gene regions ( β -tubulin, RPB2, actin, and calmodulin) were used in phylogenetic analyses of all 32 Septoria isolates. All tested isolates were pathogenic to two lettuce cultivars and morphometrically similar to each other. These isolates grouped together into a single monophyletic clade composed exclusively by genuine S. lactucae isolates. Therefore, S. lactucae was found to be the sole species associated with the Septoria leaf spot of lettuce in Brazil. The number of polymorphic sites ( n  = 27), mutations ( n  = 190), the level of nucleotide diversity (0.00262), and the average number of nucleotide differences (2.961) were relatively low. Notwithstanding, this genetic variability allowed the identification of 17 haplotypes amongst the 32 Brazilian isolates. This information will help to guide resistance breeding programs and establish more effective management strategies of this disease.