LAUSR

In breeding for resistance, knowledge of the optimum conditions for both pathogen and disease development are essential. The aim of this study was to evaluate different conditions for mycelial growth, conidial production, and the severity of Fusarium spp. and Neoscytalidium hyalinum, which are the causal agents, respectively, of dry root rot (DRR) and black root rot (BRR) on cassava. Mycelia and conidia production were evaluated at five temperatures (10, 15, 25, 35 and 40 °C) and two culture media (PDA and SNA). The influence of temperature on the severity of the disease was also evaluated. For the DRR pathogen, the optimum temperature for mycelial growth was between 24 and 29 °C, while for sporulation it was 28 °C. For the BRR pathogen, the optimum range of temperature for mycelia growth and sporulation was between 30 and 36 °C. The PDA medium favoured mycelial growth and sporulation for both DRR and BRR pathogens. Highest BRR severity was observed at 32 to 36 °C and ranged from 25 to 32 °C for DRR. This is the first study to define optimal growth conditions for the DRR and BRR pathogens of cassava.