Ascophyllum extract application causes reduction of disease levels in field tomatoes grown in a tropical environment

• Foliar application of Ascophyllum extract (ANE) in tomato caused suppression of disease incidence and enhanced fruit yield.
• The dosage of application of ANE and integrated use of fungicides were optimized.
• The mechanism of ANE on disease reduction was mostly due to induction of systemic resistance.

The effect of Ascophyllum nodosum (brown seaweed) extract (ANE) application on diseases of field tomatoes was studied in the field and greenhouse under tropical conditions in Trinidad, West-Indies. Different methods of applications of ANE (foliar spray/+ root-drench, spray alternated with fungicides) and ANE concentrations (0.2% and 0.5%) were evaluated. Application of ANE resulted in significant reduction of disease incidence by foliar pathogens including Alternaria solani and Xanthomonas campestris pv vesicatoria, particularly when ANE spray at 0.5% concentration was alternated with fungicides. Foliar application with 0.5% ANE reduced diseases caused by A. solani and X. campestris pv vesicatoria by up to 63% and 44%, respectively. Similar effects on the control of above pathogens were observed in controlled greenhouse inoculation experiments. The fruit yield increased up to 42% due to ANE application. ANE-treated plants had significantly higher levels of activity of defense enzymes (PPO, PAL, PO, chitinase, glucanase), and accumulated higher levels of phenols compared to controls. Investigation of transcript levels of defense pathway marker genes demonstrated the upregulation of JA/Ethylene pathway than SA pathway. The reduction of disease incidence in ANE treated plants may be attributed to induction of disease resistance and enhanced plant growth effect and earlier recovery from infection damage. Our experiments demonstrated positive effects of ANE on tomato disease control and plant productivity.