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

Abstract Leaf scald disease (LSD), caused by Xanthomonas albilineans , and ratoon stunting disease (RSD), caused by Leifsonia xyli subsp. xyli , 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 a 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 tested for LSD by 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. The data showed DBI robustness since each antibody could identify negative samples from diseased positive samples; DBI permitted detection of both diseases in the same sample but also single ones. Ten-month cane is the appropriate age for testing LSD by DBI. As for genotype resistance to LSD, cultivar RB966928 was the most susceptible and cv. RB867515, the most resistant.