Development of a protocol and a diagrammatic scale for quantification of bacterial leaf streak disease on young plants of maize

Abstract

Bacterial leaf streak (BLS), caused Xanthomonas vasi cola pv. vasculorum (Xvv), has become a major concern for maize pmduction, mainly in the United States and South America. Therefore, this study aimed to establish a pmtocol for Xvv inoculation in young maize plants under controlled conditions and to develop and validate a diagrammatic scale for evaluation of maize hybrids in regani to BLS resistance. The study was carried out in three steps: the establishment of a protocol for inoculation of Xvv in young maize plants under contmlled conditions; the development and validation of a diagrammatic scale for BLS severity evaluation; and the screening for BLS resistance of 45 hybrids using the proposed pmtocol for bacterial inoculation and the diagrammatic scale developed in this study. Besides repmducing a more natural Xvv infection, the bacterial suspension spraying without injury inoculation method induced higher disease incidence and severity, as well as reproducibility of results under the experimental conditions established in this study. The proposed diagrammatic scale allowed evaluating BLS severity with up to 97.49% of the leaf area affected by the disease. Further, the use of the diagrammatic scale resulted in an increase of accuracy from 0.909 up to 0.992. The reaction of 45 maize hybrids to BLS allowed establishing six major groups of susceptibility to the disease. The most resistant maize hybrids to BLS fomed a group of 13 hybrids, with disease severity below 5%.