Variations in mycelial growth and virulence below 26 °C among five Colletotrichum strains from strawberry

Anthracnose caused by Colletotrichum spp. is a serious threat to many crops, and C. siamense has become increasingly prevalent worldwide. However, the mycelial growth and virulence of many of these species, especially below 26 °C, has largely remained unknown. Here, mycelial growth of five representative Colletotrichum strains (three C. siamense [Cs], one C. fructicola [Cf] and one C. gloeosporioides s.s. [Cg]) from diseased strawberry was measured at 10, 14, 18, 22 and 26 °C. Their virulence on Fragaria vesca and highly susceptible F. × ananassa cv. Benihoppe was tested at 14 °C and 22 °C. The strains did not differ much in mycelial growth between 10 and 26 °C, although growth of the Cs and Cg strains was somewhat faster than that of Cf. However, the strains varied greatly in their virulence on the two hosts. Strain Cs GQHZJ19, which grew fastest at 22 °C, was also the most virulent on both hosts at 14 °C and 22 °C. But growth rate of Cs was only positively correlated with virulence on susceptible cv. Benihoppe after 3 days at 22 °C. Based on the virulence analysis of the five Colletotrichum strains on hosts that vary in susceptibility at distinct temperatures, host genotype might play a decisive role in disease severity at an early stage, while temperature might influence the host–Colletotrichum spp. interaction at a later stage. More Colletotrichum strains (especially C. siamense) need to be tested to determine the mycelial growth and virulence in a wider temperature range and thus we can effectively manage disease.