بررسی کارایی عصاره‌های گیاهی در کنترل بیماری لکه‌برگی گیاهان زینتی

Alternaria alternata, the most common pathogenic fungus in plants, causes various symptoms such as leaf spots and blight, damping-off, stem, fruit, and tuber rot in agricultural, vegetable, horticultural, and ornamental plants. Early blight, the most well-known disease caused by this fungus, has been reported in over 380 plant species. To control this disease, plants are sprayed with fungicides. Given the limitations of using fungicides in residential and office spaces to control diseases in flowers and ornamental plants, non-chemical methods such as using plant extracts are employed. To investigate the efficacy of plant extracts in disease control, extracts from savory (Satureja hortensis), rosemary (Rosmarinus officinalis), peppermint (Mentha piperita) and Shirazi thyme (Zataria multiflora) plants, extracted using 70% methanol solvent, were mixed with potato dextrose agar (PDA) culture medium along with the fungicides mancozeb (Dithane M-45), iprodione + carbendazim (Rovral TS), and tebuconazole (Folicur). The inhibition of mycelial growth of A. alternata was measured under laboratory conditions. In other words, the extract or fungicide was first added to the culture medium, and then a fungal colony disk was inoculated onto it, and the growth rate of the fungus was measured for three days. All extracts were tested at doses of 1, 10, 100, 500, 1000, 10000, 25000, 50000, 750000, 80000, 85000, 90000, 95000, and 100000 parts per million (ppm) with 4 replications. Fungicides were also tested at their registered doses. To ensure the results, the experiment was repeated. The results obtained from comparing the average mycelial growth and the percentage of inhibition of fungal growth of Alternaria showed that the highest mycelial growth was observed in the treatment containing peppermint extract (4.49 mm/day) and the lowest mycelial growth was observed in the treatment containing rosemary (3.97 mm/day). Treatments containing rosemary and thyme extracts (3.97 and 4.15 mm/day) were in one statistical group, and the treatment containing savory extract (4.19 mm/day) was between these two groups. The overall conclusion is that fungicides were able to inhibit mycelial growth of the fungus by almost 90 to 100%, and the percentage of inhibition of mycelial growth by plant extracts was between 53 and 60%. Rosemary extract also caused the greatest inhibition of mycelial growth of the Alternaria fungus. Based on this result, it is suggested that further studies be conducted to formulate the best extracts.