and distribution of the pathogens in the
tomato phyllosphere.
Management of bacterial spot and speck
is a challenge in commercial production
fields due to limited efficacy of current disease
management strategies. Causal bacteria
readily acquire resistance to streptomycin
and fixed copper bactericides (9,30,42), and
host resistance has not proven durable (21).
There are currently two known races of X.
axonopodis pv. vesicatoria (T1 and T3)
and one race of X. vesicatoria (T2) (21).
Tomato host resistance to T1 (35) is not
effective against T3 strains that have recently
emerged as a predominant population
in Florida (21), nor against T2 strains
commonly found in the Midwest (28). Host
resistance to all three races has been identified
(36) in L. esculentum PI 114490, but
this resistance has not been incorporated
into commercial cultivars. In a similar
manner, virulent strains of P. syringae pv.
tomato lacking the avirulence gene avrPto
were documented in natural populations
(26) even prior to deployment of the Pto
resistance gene (33).