SENSIBILIDADE DE ISOLADOS DE Macrophomina phaseolina À fluxapiroxade+piraclostrobina

Abstract

The plant pathogen Macrophomina phaseolina is the causal agent of charcoal rot in several crops such as soybeans, beans, corn, and cotton. It causes significant losses in production, being considered by many as an emerging plant pathogen that its sensitivity to molecules is influenced by chemical groups directed to other plant pathogen. The objective of this work was to evaluate the growth physiology and sensitivity of M. phaseolina isolates from soybean. The experiment consisted of eight isolates represented by IF 195, IF 202, IF 249, IF 203, IF 191, IF 201 (outgroup Colletotrichum truncatum, Passo Fundo, RS), IF 254 and IF 273, from secundary’s soybeans located in Silvânia (GO) ) and Vianópolis, were submitted to five dosages (0; 0.1; 1; 10 and 100 ppm or g mL-1) of the fungicide fluxapyroxad [167 g L-1] + pyraclostrobin [333 g L-1] (Orkestra®). The aliquots were added to the potato-dextrose-agar (PDA) medium at 50 oC. Each dosage presented three repetitions, totaling 120 experimental units. The colony diameter (mm) was evaluated daily during the seven-day period, allowing calculation of the mycelial growth rate (TCM, mm day-1), calculation of the area under the mycelial growth progress curve (AACPCM), and finally, using the drc package of the R Studio program, the EC50 (g mL-1) was calculated via regression. Isolates 195, 203, 254 and 273 had a lower EC50 compared to isolates 202, 249, 191 and 201. There was no significant difference between isolates from 3-7 DAI, AACPCM and TCM, only between dosages for the variables answers. The isolates IF 201 [26.40 g mL-1], IF 191 [24.57 g mL-1] and IF 202 [16.74 g mL-1] showed the highest lethal dosages capable of inhibiting growth mycelial at 50 %, and these isolates from the sample were considered more insensitive to the fluxapyroxad + pyraclostrobin mixture. Considering that C. truncatum is a pathogen of the aerial part, it has more contact with molecules than M. phaseolina, a pathogen of the collar and soil, with less comparative selection of isolates for resistance to fluxapyroxad+pyraclostrobin.