Exogenous Application of Polycationic Nanobactericide on Tomato Plants Reduces the Liberibacter Solanacearum Infection.

Liberibacter solanacearum (Lso) is associated with diseases in tomato crops and transmitted by the tomato psyllid A polymeric water-dispersible nanobactericide (PNB) was evaluated against Lso as a different alternative. PNB is a well-defined polycationic diblock copolymer designed to permeate into the vascular system of plants. Its assessment under greenhouse conditions was carried out with tomato plants previously infected with Lso. Using a concentration as low as 1.0 mg L, a small but significant reduction in the bacterial load was observed by real-time qPCR. Thus, to achieve an ecologically friendly dosage and set an optimum treatment protocol, we performed experiments to determine the effective concentration of PNB to reduce 65% of the initial bacterial load. In a first bioassay, a 40- or 70-fold increase was used to reach that objective. At this concentration level, other bioassays were explored to determine the effect as a function of time. Surprisingly, a real reduction in the symptoms was observed after three weeks, and there was a significant decrease in the bacterial load level (98%) compared to the untreated control plants. During this period, flowering and formation of tomato fruits were observed in plants treated with PNB.