Xanthomonas spp. associadas à mancha bacteriana do tomateiro em Minas Gerais e seu controle por suspensão inativada do patógeno

Abstract

Tomato bacterial spot, caused by species of Xanthomonas genus: X. euvesicatoria pv. euvesicatoria (Xee), X. hortorum pv. gardneri (Xhg), X. euvesicatoria pv. perforans (Xep) and X. vesicatoria (Xv), is one of the main bacterial diseases of the crop, as it significantly reduces production. Biochemical and molecular methods allow characterization, distinction between species, and assessment of the degree of genetic variation within populations. Chemical control of the disease is not eficiente, and alternative control measures should be assessed. The objectives of the work were (i) to characterize morphology, biochemical and molecularly 29 isolates obtained from tomato plants with bacterial spot symptoms collected in Espírito Santo and Minas Gerais; (ii) to evaluate the control of tomato bacterial spot using inactivated bacterial suspension, in preventive and curative applications. Species identification was performed by PCR, using specific primers. The genetic diversity was evaluated by rep-PCR using similarity dendrogram. Inactivated suspensions of X. hortorum pv. gardneri were used in preventive and curative application to control tomato bacterial spot. Inactivated of bacterial suspensions (IBS) were obtained by: exposure to ultraviolet light radiation (IBS-UV); autoclave sterilization (IBS-E); aging in culture medium (IBS-MC); and aging of the suspension on the laboratory bench (IBS-S). In the first assay, plants were preventively sprayed with the IBSs, copper hydroxide, acibenzolar-S-methyl (ASM) and water (control), and two days later were inoculated with the pathogenic bacterial suspension (108 and 109 CFU mL-1). In the curative application, the plants were inoculated with the pathogenic bacterial suspension and two days later, sprayed with the products. In the second assay, the plants were preventively sprayed with IBS-UV (108 CFU mL-1) and IBS-E (108 and 109 CFU mL-1), copper hydroxide, ASM and water. After two days, were inoculated with the bacterial suspension (107 and 108 CFU mL-1). Disease severity was assessed and the Area Under the Disease Progress Curve (AUDPC) was calculated. All isolates showed biochemical characteristics of Xanthomonas and 12 unidentified isolates did not show typical colony morphology. Only 17 isolates were identified at species level, one as Xee, 14 as Xep and two as Xhg. Rep-PCR analyses revealed high genetic diversity among the isolates, the groups formed did not show a direct relationship with the species, colony morphology, biochemical characterization, or geographic location. In the first and second assay, in preventive application, IBS-UV, IBS-E and ASM significantly reduced disease severity. In the first assay, in the curative application there was no significant difference between the products. IBS-UV and IBS-E effectively controlled tomato bacterial spot in the preventive application, reducing the disease severity.