A leaf spot of Tectona grandis caused by Xanthomonas fuscans in Brazil

Abstract

Tectona grandis (teak) is a major timber crop in the North Brazilian region. Necrotic leaf lesions often surrounded by chlorotic halos were observed in teak plants (100 days after germination) in a clonal mini-garden displaying ~15% incidence (of 400,000 plants), in Mato Grosso State (May, 2016). Five bacterial isolates (with yellow-pigmented, mucoid, domed colonies) were obtained by isolation of 15 distinct plants in NA medium (28 °C/72 h) and named Xanteca1 to 5. All isolates were inoculated in four teak clones (TG01 to TG04; 90 days after germination) via cuts (0.5 cm) with scissors at the end of the leaf blades followed by immersion into bacterial suspensions (108 CFU ml−1). The symptoms appeared 11 days after inoculation and similar colonies were re-isolated from symptomatic leaves. Two representative isolates (Xanteca3 and Xanteca4) were selected for identification. Genus identification was performed using 16S rRNA region (primers 27F/1492R) (MF033093 to MF033097) in EzBioCloud (Yoon et al. 2017), and recognized as a member of the Xanthomonas genus. Further identification of the bacteria was performed by sequencing gyrB partial sequence (emigyr-B1F/emigyrB4R) with 864 base pairs (bp) and rpoD (emirpo11F/ emirpo13R), also partial, with 873 bp. Phylogenetic analysis of both genes were executed with Bayesian inference, model GTR + G + I, selected with Akaike Information Criterion (AIC). For use as references, type strains sequences of several species were downloaded from GenBank (Parkinson et al. 2009). gyrB (MF034328 to MF034332) and rpoD (MH673499 to MH673501) phylogenetic analysis, both clustered XanTeca sequences with X. fuscans and X. fuscans subsp. aurantifolii (isolates ICMP10027, ICMP10030, ICMP8432, NCPPB381) with a value of “1” of posterior probability. Four X. fuscans isolates from teak (CCRMXF01, CCRMXF02, CCRMXF03, CCRMXF04) were deposited in the public culture collection “Rosa Mariano” of the Plant Bacteriology Lab (UFRPE, Recife-PE, Brazil). To our knowledge, this is the first worldwide report of X. fuscans infecting teak.