Resistance of cotton to Xcm is generally
associated with the rapid induction of a HE (17, 21).
The HR is macroscopically observed as confluent
lesions when cotyledons or leaves are infiltrated with
high titers of bacterial suspension (about lo7 colony
forming units or more per ml). This reaction becomes
visible in cotton leaves within 8-12 hours postinoculation
(h.p.i.) (Fig 1A). However, the phenotype
of HR on Cotton differs according to race of Xcm and
the complementary resistance genes in the host
examined (13, 21). These phenotypes are distinguished
by the timing of the onset of cell collapse, the intensity
of discoloration, and the degree of confluence.