Application of Hydrothermal Time Models to Predict Sclerotial Germination of Athelia rolfsii

Abstract

Athelia rolfsii, causal agent of ‘southern blight’ disease, is a soil-borne fungal pathogen with a wide host range of more than 500 species. This study's objectives were to: (i) quantify the effects of two environmental factors, temperature, and soil moisture, on germination of A. rolfsii inoculum (sclerotia), which is a critical event for the onset of disease epidemics; and (ii) predict the timing of sclerotial germination by applying population-based threshold-type hydrothermal time (HTT) models. We conducted in vitro germination experiments with three isolates of A. rolfsii isolated from peanuts that were tested at five temperatures (T), ranging from 17 to 40°C, four matric potentials (Ψm) between -0.12 MPa and -1.57 MPa, and two soil types (fine sand and loamy fine sand) using a factorial design. When Ψm was maintained between -0.12 and -0.53 MPa, T from 22 to 34°C were found to be conducive for sclerotial germination (>50%). The HTT models were fitted for a range of T (22 to 34°C) and Ψm (-0.12 to -1.57 MPa) that accounted for greater than 84% variation in the timing of sclerotial germination. The estimated base T ranged between 0 and 4.5°C and the estimated base Ψm between -2.96 and -1.52 MPa. The results suggest that the HTT modelling approach is a suitable means of predicting the timing of A. rolfsii sclerotia germination. This HTT methodology can potentially be tested to fine-tune fungicide application timing and in-season A. rolfsii management strategies.