Reduction of brown leaf spot and changes in the chlorophyll a content induced by fungicides in cassava plants
2020
Julião, Evair Cintra | Santana, Marthony Dornelas | Freitas-Lopes, Rejane do Livramento | Vieira, Alberto dos Passos | de Carvalho, Josabete Salgueiro Bezerra | Lopes, Ueder Pedro
Brown leaf spot (BLS), caused by the fungus Clarohilum henningsii, is one of the most common leaf diseases in cassava, leading to losses in root yield due to the extensive defoliation of the plants. Despite this, BLS has been neglected and little is known about the disease. This study aimed to evaluate the ability of systemic fungicides (cyproconazole, thiophanate-methyl, pyraclostrobin, tebuconazole, azoxystrobin, and flutriafol) to inhibit the in vitro growth of C. henningsii isolates and to control BLS in cassava plants. In addition, we verified the effect of the fungicides on the plant physiology by measuring the chlorophyll a content. The results showed that the isolates were sensitive to all fungicides, as demonstrated by the low EC₅₀ (effective concentration of fungicide able to inhibit mycelial growth by 50%) values, which ranged from 0.06 to 0.43 μg.mL⁻¹. In addition, all fungicides were able to reduce the severity of BLS in cassava plants, but with different effectiveness. In general, flutriafol had the highest efficiency in reducing the disease severity under greenhouse and field conditions. Cassava plants treated with pyraclostrobin, azoxystrobin, and flutriafol had the highest increase of chlorophyll a content, which has not been reported in this crop. Based on our results, flutriafol is the most promising fungicide to control BLS in cassava, since it had the highest effectiveness in reducing the disease and provided the highest increase in the chlorophyll a content of the plants.
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