Efficacy of AAC00-1ΔhrcC as a seed treatment under greenhouse
conditions. To determine the efficacy of AAC00-1ΔhrcC as
a seed treatment under transplant house conditions, seed naturally
infested with AAC00-1 were treated and planted under greenhouse
conditions highly conducive to BFB development. Seed treatment
with AAC00-1ΔhrcC reduced BFB seedling transmission and epidemic
development relative to the negative control. For naturally
infested seed treated with PBS, mean BFB seedling transmission
percentage was 37 (±3)% (Fig. 6A). In contrast, seed treated with
AAC00-1ΔhrcC displayed 23 (±7)% BFB incidence by 21 dap
(Fig. 6A), which represents a 37.8% reduction relative to PBStreated
seed. BFB seedling transmission for seed treated with
AAC00-1ΔhrcC was significantly lower than for PBS-treated seed
(P = 0.02) according to the Student’s t test. BFB transmission for
AAC00-1ΔhrcC-treated seed was delayed by 5 days in the greenhouse
compared with 2 days in the growth chamber.
Efficacy of AAC00-1ΔhrcC as a blossom protectant against
seed infestation by A. citrulli. Watermelon fruit produced from
female blossoms protected with AAC00-1ΔhrcC or AAA 99-2 and
subsequently challenged with AAC00-1 did not develop BFB
symptoms at harvest maturity. Based on ANOVA, the effect of
experiment on seed infestation was not significant (P = 0.64);
hence, the data for the two experiments were pooled for analysis.
Blossom protection with biocontrol agents reduced seed infestation
by A. citrulli and this effect was statistically significant (P < 0.01).
Approximately 36% of seed produced from blossoms protected
with PBS developed BFB symptoms in the modified seedling
grow-out assay. In comparison, seedlots produced from blossoms
protected with AAA 99-2 and AAC00-1ΔhrcC had mean BFB
seedling transmission percentages of 4 and 8%, respectively (Fig.
7). Tukey-Kramer’s HSD analysis indicated that A. citrulli infestation
for seed from blossoms protected with AAC00-1ΔhrcC or
AAA 99-2 was significantly less than for those treated with PBS (P
< 0.01; Fig. 7). However, there was no significant difference between
the abilities of AAC00-1ΔhrcC and AAA 99-2 to limit seed
infestation by A. citrulli (P = 0.8). ANOVA of seed germination
percentage data indicated that the effect of experiment was statistically
significant (P = 0.002). Hence, the data for the two experiments
were analyzed separately. In experiment 1, mean germination
percentages were 91, 86, and 81% for seed from blossoms
protected with PBS, AAA 99-2, and AAC00-1ΔhrcC, respectively.