Adaptabilidade comparativa de espécies do complexo Fusarium fujikuroi associadas com a podridão da coroa da banana

Abstract

Banana (Musa spp.) production is highly economically important in Brazil, but diseases cause many postharvest losses, especially crown rot. This disease is caused by several fungi, including species of the Fusarium fujikuroi complex (FFSC), with F. annulatum, F. musae and F. sacchari being the most prevalent. Studies on fitness components are important to understand how isolates respond to disturbance or physiological stress. Still, no studies of this nature involving Fusarium species associated with crown rot. Therefore, the objective of this dissertation was to compare the adaptability of nine isolates of F. annulatum, F. musae and F. sacchari, three of each species, in relation to: (a) mycelial growth rate, sporulation and spore germination at 25 °C; (b) optimum temperatures and water potentials for mycelial growth, sporulation and spore germination; (c) sensitivity to different fungicides; and (d) pathogenicity and aggressiveness of the isolates in banana, mango and papaya fruits. Isolates of the same species showed significant differences (P≤0.05) in the analyzed variables. With incubation at 25 °C, mycelial growth ranged from 4.1 to 6.7 mm/day, sporulation from 1.9 x106 to 44.7 x 106 spores/mL, and spore germination from 67.4 to 100%. The optimum temperatures for mycelial growth ranged from 26.6 to 30.1 °C, for sporulation from 25.5 to 34.9 °C, and for spore germination from 27.1 to 31.5 °C. The optimum water potentials for mycelial growth ranged from -0.16 to -1.24 MPa, for sporulation between 0.01 and -1.88 MPa, and for spore germination between -0.05 and -1.80 MPa. Only thiophanate-methyl did not show inhibitory activity on the mycelial growth of any isolates, while only this fungicide and azoxystrobin inhibited the sporulation of all isolates. Only azoxystrobin and pyraclostrobin inhibited spore germination of all isolates, while tebuconazole and thiophanate-methyl did not show any inhibitory effect on spore germination of the isolates. All isolates were pathogenic to banana and mango, with different levels of aggressiveness. No isolate was pathogenic to papaya. Using the data set and UPGMA analysis, the isolates were separated into six similarity groups. These differences in fitness should be considered when developing efficient strategies for managing banana crown rot. Keywords: Musa spp., fungal physiology, temperature, water potential, fungicides, aggressiveness, physiological stress.