FILAMENTOUS FUNGI ASSOCIATED TO CASSAVA ROOT ROT DISEASE (CRRD) IN MISIONES PROVINCE (ARGENTINA)

MADRASSI L.M.; ALVARENGA A.E.; MÓNACO C.; ZAPATA P.D.

Congreso; Congreso Conjunto SAIB-SAMIGE 2020; 2020

Cassava roots are considered an important alimentary source and they are also used to produce a wide range of sub-products. They are cultivated in tropical and subtropical regions worldwide. In Argentina, main production is located in NEA provinces, especially in Misiones. Mayor yield lost are often related to root phytosanitary problems; they become rot, whether dry or soft, and lose their commercial value. These symptoms are known cassava root rot disease (CRRD) and their causal agent/s have not being recognize/ed yet in Argentina, even though it is generally believed that it is caused by soil edaphic fungi that becomes pathogenic. Causal agent´s recognition is a primary step toward disease control, because, otherwise, no specific products can be applied to counter them. In this work, we aimed to isolate filamentous fungi from cassava root rot samples taken from two crops (Wanda and Loreto districts) whose presented characteristic CRRD symptoms. Samples were kept under refrigerated conditions until arrival to laboratory. Once there, visible soil particles were removed using tap water. Roots were surface sterilized by submerging them in 70% alcohol solution for 5 minutes and then in 10% NaClO solution for 5 minutes. Whenever possible, root tissues (periderm, cortex, pith, xylem bundles) were carefully separated using sterilized bistoury. Periderm, cortex and xylem bundles were cut in 5x5mm pieces. Pith was cut in 5x5x5mm pieces. Remaining pieces´ surface particles were removed by putting them in tubes containing 10mm distilled water and centrifuging at 5000rpm for 5min, and then putting them in an identical tube in order to repeat this step up to 5-6 times. After centrifugation, samples were cultivated in Petri dishes containing 20ml of potato dextrose (3.9% PDA), malt extract (12,7% MEA) or malachite green (2.5% MGA) agar with antibiotics, for one week at 28ºC ±2 in darkness. 62 fungal strains were consecutively reisolated until pure colonies were obtained. Morphological characterization was made by determining color, texture, growth rate, pigments, etc. and microscopically by visualizing hypha and reproductive structures. Genus level identification was archived by using specialized morphological keys. Several fungal genera were found, mainly Fusarium spp., Geotrichum spp., Rhizopus spp., etc. and also sterile mycelia colonies. These results indicate the preponderance of common soil filamentous fungi that might cause CRRD in cassava crops in Misiones. These fungal genera might also affect crops as Yerba mate (Ilex paraguariensis) or Tea plant (Camellia sinensis). This is the first report of filamentous fungi isolated from cassava´s rot roots in Argentina. Further analysis might include strains´ molecular identification and virulence capability determination in order to determine whether these fungi are pathogenic or not.