Selection of pathometric variables to assess resistance and infectivity in the passion fruit woodiness pathosystem

Abstract

The objective of this work was to compare the efficiency of four pathometric variables, i.e., grading scale, infection intensity index, global leaf disease index, and global incidence and severity index, in evaluations of the passion fruit/Cowpea aphid-borne mosaic virus (CABMV) pathosystem. In ‘yellow’ passion fruit plants, mechanically inoculated with CABMV isolates, the degree of association between leaf symptoms and the total fruit yield was determined, as well as the relative infectivity between viral isolates. Only infection intensity index and the global incidence and severity index presented significant regressions with yield (p = 0.007 and 0.006, respectively). These two pathometric variables could also distinguish groups of viral isolates inducing different severity levels (0.001 and 0.002, respectively). The results indicate that infection intensity index and global incidence and severity index are equally efficient in early identification of passion fruit populations with a higher resistance/susceptibility level to CABMV, and can be helpful in identifying more severe CABMV isolates, both useful aids in breeding programs.