Analysis of Colletotrichum musae populations from Brazil reveals the presence of isolates with high competitive ability and reduced sensitivity to postharvest fungicides

Abstract

In this study, the sensitivity of 218 isolates of Colletotrichum musae to imazalil and thiabendazole was evaluated, as well the fitness and competitive ability of less sensitive isolates. There was a positive correlation between the sensitivity to the two fungicides, but the isolates were more sensitive to imazalil. The estimated effective concentration of the fungicide able to inhibit mycelial growth by 50% (EC50) was used to select four isolates with the lowest and the highest values for both fungicides, which were considered as sensitive (S) and less sensitive (LS), respectively. The level of sensitivity was maintained after 10 successive transfers on fungicide‐free medium. Both fungicides were effective in controlling the disease caused by S isolates of C. musae in detached banana fruit when recommended doses were used. However, only imazalil was able to control the disease caused by LS isolates. For both fungicides, analysis of fitness‐related variables (mycelial growth, sporulation, germination, and virulence) showed no difference between the groups of S and LS isolates, but a large variation was observed within the group. The LS isolates to thiabendazole that showed a mutation (F200Y) in the β‐tubulin gene did not have fitness penalties. Our results allow a better understanding of the sensitivity and fitness of isolates of C. musae from Brazil, and demonstrate the importance of periodic monitoring to determine the frequency of LS isolates in populations, aiming at more effective management of anthracnose in banana orchards in Brazil.

Fungicide resistance in populations of Colletotrichum musae from Brazil and evidence of fitness costs for QoI resistant isolates

“…Typically, chemical control relies on the usage of imazalil and thiabendazole fungicides, belonging to the demethylation inhibitor (DMI) and methyl benzimidazole carbamate (MBC) groups, respectively. It is worth noting that instances of isolates displaying reduced sensitivity to fungicides from both of these groups have been previously documented (Leite et al, 2020).…”

“…In the projected tness experiment, the S and R isolates for azoxystrobin, pyraclostrobin, and tri oxystrobin (Table 1) were employed in assays aimed at scrutinizing the subsequent variables: mycelial growth, conidial production and germination frequencies in vitro, and virulence. The methodology employed adhered to that proposed by Leite et al (2020), incorporating necessary modi cations. In order to ascertain mycelial growth rates, a 5-mm diameter plug was extracted from both S and R isolates (gathered from the periphery of 4-day-old cultures) and subsequently transferred to the central region of a Petri dish containing PDA devoid of fungicides.…”

“…The 50 isolates were acquired in 2012 and 2013 from banana orchards located in the Brazilian states of São Paulo, Minas Gerais, Espírito Santo, Bahia, Pernambuco, Pará, Paraná, Santa Catarina, Goiás, and Distrito Federal. These isolates had previously undergone analysis regarding their sensitivity to thiophanate-methyl (Vieira et al, 2017), imazalil, and thiabendazole (Leite et al, 2020). Three QoI fungicides, azoxystrobin (Priori, 250 g of a. i. L -1 , Syngenta Crop Protection), pyraclostrobin (Comet, 250 g of a. i. L -1 , BASF) and tri oxystrobin (Flint 500 WG, 500 g of a. i. kg -1 , Bayer) were used for sensitivity studies.…”

“…The occurrence of Brazilian populations of C. musae in banana with reduced sensitivity to postharvest fungicides has already been recorded for imazalil (imidazole, DMI), thiabendazole and thiophanate-methyl (benzimidazoles, MBC) (Leite et al, 2020;Vieira et al, 2017), but there is no information on the sensitivity of these populations to QoI fungicides.…”

Target and non‐target site mechanisms of fungicide resistance and their implications for the management of crop pathogens

“…For MBCs, plant pathogens, such as Botrytis cinerea , 195,196 Monilinia fructicola , 205 Monilinia laxa , 207 and Ustilaginoidea virens , 212 exhibit fitness costs linked to E198A/V/K, F200Y, L240F, and M233I mutations in the β‐tubulin gene (Table 3). No fitness costs associated with MBC resistance have been found in Botryosphaeria dothidea , 193 Botrytis cinerea , 21 Colletotrichum musae , 199,200 Monilinia fructicola , 179,206 Oculimacula sp., 208 Phomopsis obscurans , 142 and Pseudocercosporella fijienses 211 (Table 3).…”