Hexyl gallate for the control of citrus canker caused by Xanthomonas citri subsp citri

Abstract

Brazil is the biggest producer of sweet oranges and the main exporter of concentrated orange juice in the world. Among the diseases that affect citriculture, Asiatic citrus canker, caused by the bacterial pathogen Xanthomonas citri, represents one of the most significant threats. The current Brazilian legislation regulating the control of citrus canker no longer requires the eradication of affected trees in states where the incidence of the disease is high. Instead, control involves disease control measures, including periodic preventative spraying of copper compounds. The long‐term use of copper for plant disease control has raised concerns about environmental accumulation and toxicity, as well as the selective pressure it exerts leading to the emergence of copper‐resistant X. citri strains. Here, we evaluated hexyl gallate (G6) as an alternative to copper compounds for citrus plant protection. G6 was able to protect citrus nursery trees against X. citri infection. Thirty days after inoculation, the trees treated with G6 developed 0.5 lesions/cm2 leaf area compared with the 2.84 lesions/cm2 observed in the untreated control trees. Also, G6 did not interfere with germination and root development of tomato, lettuce, and arugula, which is consistent with our previous data showing that G6 is safe for tissue culture cell lines. Membrane permeability tests showed that the primary target of G6 is the bacterial outer membrane. Finally, we could not isolate spontaneous X. citri mutants resistant to G6 nor induce resistance to G6 after long‐term exposures to increasing concentrations of the compound, which suggests that G6 may have multiple cellular targets. This study demonstrated that G6 is a promising candidate for the development and use in citrus canker management.

Isolation and agricultural potential of penicillic acid against citrus canker

“…Penicillic acid had a protective effect on leaves similar to the effect observed by Cavalca et al (2020) with the application of hexyl gallate (600 µg ml −1 ) for citrus canker treatment where the mean of lesions observed for the compound was of 0.5 lesions/cm². Maxwell et al (2019) also reported a ternary zinc chelate solution (TSOL) at 800 µg ml −1 with similar results to copper chemicals in a 3‐year study conducted in greenhouse and field conditions.…”

“…Penicillic acid had a mean of 0.437 lesions/cm² (SE ± 0.087), when applied at 25 µg ml −1 , while the positive control, with application equivalent to 700 µg ml −1 of metallic copper, showed values of 0.270 lesions/cm² (SE ± 0.080) and in the negative control the mean was 1.772 lesions/cm² (SE ± 0.294). Penicillic acid had a protective effect on leaves similar to the effect observed by Cavalca et al (2020) with the application of hexyl gallate (600 µg ml −1 ) for citrus canker treatment where the mean of lesions observed for the compound was of 0.5 lesions/cm². Maxwell et al (2019) also reported a ternary zinc chelate solution (TSOL) at 800 µg ml −1 with similar results to copper chemicals in a 3year study conducted in greenhouse and field conditions.…”

Benzenetriol-Derived Compounds against Citrus Canker

“…Panels C and G in Figure 2 correspond to the negative control cells with intact membrane and panels D and H to positive control cells with permeabilized membrane. Membrane disruption has also been highlighted as the main mode of action of phenolic molecules with antimicrobial activity by several other studies [ 17 , 18 , 19 , 20 , 21 ], including anti- X. citri compounds previously reported by our group [ 3 , 4 , 22 , 23 ].…”

Hexanoic acid: a new potential substitute for copper‐based agrochemicals against citrus canker

“…At the end of the experiments, leaves were detached and digitalized at 600 dpi. The software ImageJ was used to evaluate bacterial infection and infection severity, which were expressed as the number of citrus canker lesions formed per square centimetre of leaf (lesions per cm 2 ) as described by Cavalca et al (2020). The data obtained were submitted to nonparametrical statistical analysis of Kruskal-Wallis (Dunn), with three degrees of freedom using the software BioEstat 4.…”