Dot blot immunoassay for diagnostic test of leaf scald disease and ranking of sugarcane genotypes

Leaf scald disease (LSD), caused by Xanthomonas albilineans (X.a.), and ratoon stunting disease (RSD), caused by Leisfonia xyli subsp. xyli (Lxx), are two major diseases of sugarcane in Brazil. Lab-diagnostic tests and resistant cultivars are the effective strategies to control both diseases. The dot blot immunoassay (DBI) is the diagnostic technology for both, which stresses the need to accurately identify each disease. The adequate sugarcane for DBI to provide trustful results also needs clarification. Moreover, DBI has the potential for ranking sugarcane genotypes based on difference of bacterial population the technology provides. Therefore, this work aimed to examine the usefulness of DBI to distinguish LSD from RSD, the adequate cane age of sampling and to establish protocol for ranking sugarcane genotype to LSD. For the first objective, sugarcane fields with distinct phytosanitary status were submitted to DBI; for plant age, contaminated saps from 8-, 9-, and 10-month-old canes were submitted to DBI; for genotype ranking, the spread and pathogen population density were examined across cultivars. Assays were carried out under completely randomized block design with ten replications per treatment; each replication with one plant per vase; the experiment was repeated. Our data showed DBI robustness since each antibody could identify samples disease-free from diseased samples; among the diseased, it separeted samples with both diseases from single ones, either LSD or RSD. The 10-month was the appropriate age for DBI. As for genotype rection to LSD, RB966928 was the most susceptible and RB867515, the most resistant.