Caracterização e manejo da mancha branca (Phaeoramularia manihotis (F. Stevens & Solheim) MB Ellis) na cultura Mandioca (Manihot esculenta Crantz)

Abstract

The white spot (Phaeoramularia manihotis) causes significant loss of cassava, when associated with other leaf spots. This pathogen can present morpho-physiological variability depending on environmental conditions. The measures to control the disease are very scarce and limited. The lack of registered products is making the use of alternative methods an increasingly viable option. The objective of this study was to characterize the morpho-physiologically P. manihotis and evaluate the efficiency of natural products for disease control. In the evaluation of mycelial growth means of PDA, LCA, CA, ADA, V8 and FDM culture were used. To assess sporulation media V8, PDA and CA the conditions of continuous darkness, continuous light and alternating light (12 hours), incubating isolated for 25 days. The determination of dry weight was performed by growing mycelial discs in liquid culture media (PD, CC and V8), followed by filtering and drying the mycelial mass at 60 ° C for 48 hours. Disks containing mycelia were transferred to Petri dishes with PDA medium containing natural products (cassava, spearmint oil, extracts of garlic, melon and São Caetano Ecolife ®) , Trichoderma sp. and mancozeb. Was used as control plates containing PDA medium with inoculum of the pathogen disk and evaluated the percentage of the pathogen mycelial growth after 7 days of incubation. In greenhouse-sprayed if cassava leaves CV rosinha with the same natural products tested "in vitro". And after two days was inoculated with a PDA disc containing the mycelium of the fungus. 16 days after it was determined the severity of the disease. The culture media showed significant differences in relation to the growth of this fungus, and the V8 which means greater mycelial growth. The culture media were not able to produce spores of P. manihotis. V8 medium was which favors a greater amount of mycelium of P. manihotis. The cultural characteristics of the isolate of P. manihotis varied according to the substrate used, but in general the colonies showed that mycelium ranged from flaky, cotonoso and drain; with regular to irregular edges; radial growth of branches without ramifications and uniform; whitish translucent coloration, and no mycelial growth in the culture medium or production of conidia. All treatments except the melon Sao Caetano, were able to inhibit the mycelial growth of the fungus, and Ecolife ®, mancozeb and peppermint promoted an inhibition of 100%. Trichoderma sp. was the only witness to differ, being able to inhibit lesion formation in cassava leaves, but no significant difference of the melon Sao Caetano, mancozeb, cassava juice, mint-pepper and garlic extract. Ecolife ® was toxic to cassava leaves.