Chitosan embedded with ZnO nanoparticles and hydroxyapatite: synthesis, antiphytopathogenic activity and effect on tomato grown under high density

This study aimed to the synthesis of the new composite ZnOHap@Cs made with ZnO nanoparticles, hydroxyapatite and chitosan, and to examine its effect on tomato grown under normal conditions or under high density in the greenhouse. In addition, its antimicrobial activities were assessed in vitro against several fungal phytopathogens, and in planta against Pseudomonas syringae pv. tomato, the causal agent of bacterial speck disease of tomato. Results showed that ZnOHap@Cs was able to reduce radial growth of Fusarium oxysporum f.sp. melonis and Alternaria solani by more than 75 and 67%, respectively. Furthermore, the composite revealed to be effective in reducing disease severity of bacterial speck when used as a foliar spray. Our study showed that the variety of tomato, Campbell 33, was affected by shade generated when grown at high density, as evidenced by increased plant height, stem thinning, decreased root biomass, and reduced photosynthetic pigments and net photosynthesis. ZnOHap@Cs treatment enhanced root biomass, content of photosynthetic pigments, and net photosynthesis of tomato when grown under low density. However, most of these variables were maintained in pre-treated plants when they grow at high density. These results highlight that ZnOHap@Cs improves partly plant physiological properties to cope with the effect of shade, and it could be used as effective fungicides for sustainable health plant protection.