RESUMO
Acibenzolar-S-methyl (ASM) is a plant activator that triggers systemic acquired resistance that is labeled for use in Brazil for managing tomato bacterial spot. The aim of this study was to define the optimum relationship between interval and number of applications of ASM for the most efficacious control of bacterial spot on processing tomato. Four intervals between applications (4, 7, 10, and 14 days) and four application frequencies (4, 6, 8, and 10 applications) were evaluated in five trials performed between 2010 and 2011 in Brasília, Distrito Federal, and in Morrinhos, in the state of Goiás. Copper hydroxide (CH) was applied after ASM applications to complete 13 applications per growing season. Two check treatments were added: standard CH weekly applications and untreated. The following variables were evaluated: severity of bacterial spot, yield, percentage of ripe and rotten fruit, soluble solids content, and the benefit/cost ratio. Disease severity varied between treatments in three trials and yield varied in two trials. A greater number of applications resulted in a reduction of bacterial spot, and the ideal interval between applications was between 8 to 10 days. However, there was a reduction in yield with 10 ASM applications. The temporal effect of ASM applications on bacterial spot severity was evaluated under greenhouse conditions. Reduction in disease severity was observed up to 6 days following ASM application. Additionally, the weekly treatment of seven applications of ASM followed by six applications of CH was compared with a standard program of CH under commercial production conditions in Itaberaí, Goiás, where bacterial spot occurred naturally. The program with ASM and CH resulted in significantly less foliar disease severity than the standard program, which did not result in yield gains. In addition, no differences were detected between the two programs for soluble solids content, industrial yield, plant height, and percentage of ripe and rotten fruit.
RESUMO
BACKGROUND: South American leaf blight (SALB) of rubber has been the main constraint to production in its neotropical centre of origin since commercial plantations were first established. The fungal causal agent was identified and described more than a century ago but its precise placement within the Ascomycota still remains uncertain. Indeed, such is the ambiguity surrounding the pathogen that each of the spore morphs would, according to their present classification, be placed in different ascomycete families: the Microcyclus sexual morph in the Planistromellaceae and the two purported asexual morphs--Fusicladium and Aposphaeria--in the Venturiaceae and Lophiostomataceae, respectively. Given the historical importance of the fungus and the ever-menacing threat that it poses to rubber production in the Palaeotropics--and, thus to the rubber industry and to the global economy--its phylogeny, as well as its biology, should be resolved as a matter of urgency. METHODS AND RESULTS: Here, six genomic regions (LSU rRNA, mtSSU, MCM7, EF-1α, Act and ITS) were used for reconstructing the molecular phylogeny of the SALB fungus based on material collected throughout Brazil. The analyses support the classification of the fungus in the family Mycosphaerellaceae s. str. (Capnodiales, Dothideomycetes) and place it firmly within the clade Pseudocercospora s. str., now accepted as one of the distinct genera within Mycosphaerellaceae. The new combination Pseudocercospora ulei is proposed and the life cycle of the fungus is confirmed, based on both experimental and phylogenetic evidence, with the Aposphaeria morph shown to have a spermatial rather than an infective-dispersal function. CONCLUSIONS: Because the phylogeny of the SALB fungus has now been clarified, new insights of its epidemiology and genomics can be gained following comparison with closely-related, better-researched crop pathogens.
