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

Athelia rolfsii, causal agent of "southern blight" disease, is a soilborne 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, which were tested at five temperatures (T), ranging from 17 to 40°C, four matric potentials (Ψm) between -0.12 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 was found to be conducive to 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 84% or more of 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 modeling approach is a suitable means of predicting the timing of A. rolfsii sclerotial germination. This HTT methodology can potentially be tested to fine-tune fungicide application timing and in-season A. rolfsii management strategies. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Xylem biomechanics, water storage, and density within roots and shoots of an angiosperm tree species.

Xylem is a complex tissue that forms the bulk of tree bodies and has several functions, including to conduct water, store water and nutrients, and biomechanically support the plant body. We examined how xylem functional traits varied at different positions within 9-year-old Populus balsamifera subsp. trichocarpa. Whole trees were excavated, and xylem samples were collected at 1-m increments along the main root-to-shoot axis of six trees, from root tip to shoot tip. We examined biomechanical and water-storage traits of the xylem, including using a non-invasive imaging technique to examine water content within long, intact branches (high-resolution computed tomography; microCT). Xylem density, strength, and stiffness were greater in shoots than roots. Along the main root-to-shoot axis, xylem strength and stiffness were greatest at shoot tips, and the tissue became linearly weaker and less stiff down the plant and through the root. Roots had greater water storage with lower biomechanical support, and shoots had biomechanically stronger and stiffer xylem with lower water storage. These findings support trade-offs among xylem functions between roots and shoots. Understanding how xylem functions differ throughout tree bodies is important in understanding whole-tree functioning and how terrestrial plants endure numerous environmental challenges over decades of growth.