Evaluation of Arthrobacter sp. for biological control of the pitch canker fungus (Fusarium moniliforme var. subglutinans) on slash pines

Abstract

Slash pines (Pinus elliottii var. elliottii) were wounded, treated with Arthrobacter sp., and then inoculated 24 h later with Fusarium moniliforme var. subglutinans, the causal organism of pine pitch canker. Among three Arthrobacter isolates tested, A6 and A16 significantly decreased the numbers of conidia of the pitch canker fungus collected from surfaces of inoculated wounds (average 17 657/mL and 28 398/mL, respectively) compared with inoculated wounds treated with isolate A50 (84 562/mL) or a control (average 156 857/mL). Another study evaluated the effects of different intervals between wound treatment with Arthrobacter and inoculation with F. moniliforme var. subglutinans. Pitch cankers developed on trees inoculated 1 day after wounding but not on trees inoculated 7, 14, or 21 days after wounding. Arthrobacter isolate A6 significantly reduced conidial production (average 2250/mL) compared with the control treatment (average 960 250/mL) on inoculated 1-day-old wounds. In both studies, 5 months after treatment, arthrobacters were recovered from treated wounds at 450 colony-forming units/mL (initial inoculum density 108 colony-forming units/mL). Thirteen months after treatment, the numbers of F. moniliforme var. subglutinans and arthrobacters were greatly reduced or were absent from washes and wood samples on wound surfaces. Treatment with Arthrobacter did not significantly reduce the size of cankers developing from inoculated wounds. Arthrobacters alone actually slowed wound closure by the tree.