Promising Integrated Management Strategy of Garlic Rust (Puccinia porri G. Wint.) with Improved Productivity Using Benzothiadiazole (BTH), Essential Oils and Fungicides

The essential oils (EOs) of lemongrass, clove, neem, and thyme, as well as the fungicides Dithane M-45®, Kocide-2000®, Sumi-8®, and Topas®, resulted in a significant reduction to the in vitro uredial germination percentage of Puccinia porri, the causal pathogen of garlic rust. The tested fungicides, in general, had a higher germination inhibitory effect than the essential oils as it ranged between 14.2-34.9% for the fungicides but ranged between 17.1-19.8% for the essential oils. Sumi-8® fungicide was the most efficient one in this concern followed by Topas® then clove oil. Meanwhile, Dithane M-45® was the lowest efficient one followed by Kocide-2000® then neem oil. Under greenhouse conditions, an integrated management plan consisted of soaking garlic seed cloves in 50 mM of Bion® (Benzothiziazole; BTH), a synthetic analogue of salicylic acid as plant resistance inducer, for two hours just before planting then spraying the grown plants with each of the tested essential oils, fungicides individually or their binary combinations, three days post challenge inoculation with the urediospores of Puccinia porri was applied. All treatments significantly reduced the severity of rust disease with a significant increase in the produced bulb yield compared with the control. Garlic plants grown from cloves soaked in BTH were highly protected against the pathogen and had improved productivity estimated as bulb weight (g) plant^-1 compared to control plants soaked in distilled water, either sprayed with tested EOs and fungicides or not. The combinations between the sprayed fungicides and EOs were of higher efficacy in lowering the severity of the disease and increasing the bulb weight (g) plant^-1 compared to spraying any of them individually. The estimated alkaloids, flavonoids, and phenolic compounds in the bulbs of garlic plants sprayed with the tested EOs and fungicides recorded considerable increments compared with both control treatments.