Temperature response, fungicide sensitivity, and aggressiveness of Colletotrichum isolates associated with cowpea anthracnose on legume hosts

ABSTRACT Anthracnose is a major constraint to cowpea production in Brazil and has historically been associated mainly with Colletotrichum truncatum . Recent studies, however, have also identified C. musicola and C. plurivorum on cowpea and other legumes, suggesting potential variability among species and isolates in thermal adaptation, fungicide response, and aggressiveness. We evaluated four Colletotrichum isolates: one C. musicola isolate from cowpea, one C. truncatum isolate from cowpea, and two C. plurivorum isolates, one from cowpea and one from lablab bean. Mycelial growth, sporulation, and conidial germination were assessed at 15, 20, 25, 27, 29, 32, and 35 °C. In vitro sensitivity to difenoconazole and thiophanate-methyl was evaluated at 0.5, 1.0, 1.5, and 2.0 μg a.i. mL -1 , and pathogenicity and aggressiveness were assessed on two cultivars each of cowpea, common bean, lima bean, and soybean. All isolates exhibited mycelial growth, sporulation, and conidial germination across the temperature range tested, but response patterns differed among isolates and developmental traits. Mycelial growth optima were near 25 °C for the C. musicola and C. plurivorum isolates and slightly lower for the C. truncatum isolate. The C. musicola isolate showed particularly high sporulation at 35 °C, whereas conidial germination maxima differed among isolates. Difenoconazole inhibited mycelial growth and conidial germination more than thiophanate-methyl, although neither fungicide completely inhibited the isolates at the highest concentration tested. All isolates were pathogenic to the four legume species evaluated, with disease severity varying among isolate–cultivar combinations. Common bean and soybean cultivars were generally more susceptible, whereas lima bean cv. Branquinha showed consistently lower disease severity. Overall, these findings indicate isolate-level variability among Colletotrichum isolates associated with cowpea anthracnose and suggest that thermal response, alternative legume host susceptibility, and reduced in vitro fungicide sensitivity should be considered when developing integrated management strategies for anthracnose in legume-based production systems.