Efficacy of AAC00-1ΔhrcC as a biocontrol seed treatment for
BFB under growth chamber conditions. To evaluate the efficacy
of AAC00-1ΔhrcC as a biocontrol seed treatment, naturally infested
seed extracted from symptomatic watermelon fruit from a
BFB outbreak in Reidsville, GA in 2005 were used. Samples (four
replicates of 100 seeds) of this seedlot displayed 75% mean BFB
seedling transmission and 76% mean germination using a modified
seedling grow-out assay (40). Infested seed (n = 100) were incubated
in 20 ml of cell suspension containing AAC00-1ΔhrcC, AAA
99-2 at approximately 1 × 108 CFU/ml, or PBS as a negative
control. Watermelon seed were then subjected to continuous vacuum
infiltration for 20 min, which allowed the biocontrol agents to
be deposited under the testae. After inoculation, seed were air dried
at approximately 25°C for 24 h and then assayed for BFB seed-toseedling
transmission using a modified seedling grow-out assay.
Briefly, seed (n = 100) were planted in transparent plastic boxes on
two layers of blotter paper (Hoffman Manufacturing) saturated
with deionized water. Germination boxes were incubated in a
growth chamber (Percival) under conditions of 100% RH, 30°C,
and continuous fluorescent light for 12 days. Seed were monitored
daily and germination percentage (number of seed that produced
radicles and plumules divided by the total number of seed planted
× 100) and BFB seedling transmission (number of seedlings displaying
typical BFB symptoms divided by the number of seedlings
that germinated × 100) percentages were recorded daily. The experiment
was conducted twice and mean BFB seedling transmission
percentage data were plotted over time to generate AUDPC
data. AUDPC data were used to conduct ANOVA and to determine
the significance of the effect of AAC00-1ΔhrcC on BFB seedling
transmission using Tukey-Kramer’s HSD. Seed germination data
were used to determine the effect of AAC00-1ΔhrcC on seed
physiology. The ability of AAC00-1ΔhrcC and AAA 99-2 to limit
BFB seedling transmission was determined using the formula described
by Moss et al. (27).