Evaluation of the Concept of Horizontal and Vertical Resistance by the Cotton-xanthomonas Malvacearum Host-pathogen System

Abstract

The objectives of this study were to determine the relative levels of horizontal and vertical resistance to selected races of Xanthomonas malvacearum in selected cotton differentials, to quan-tify and compare rates of reproduction and survival in the cotton differentials of X. malvacearum and several other phytopathogenic bacteria which do not attack cotton, and to determine the relationship between blight severity in the field and pathogen development in vivo. Seven cotton differentials with various levels of bacterial blight resistance were each inoculated with eight or nine races of X. malvacearum. P.. disease severity index was obtained for each combination and rankings were made. ln vivo studies of homologous and heterologous populations were made. Growth trends in bacterial populations were determined using the most probable number dilution technique.