Fine root dynamics of oak saplings in response to Phytophthora cinnamomi infection under different temperatures and durations

Abstract

Summary The belowground effects of Phytophthora cinnamomi on 1‐year‐old saplings of two common oak species in mid‐Atlantic US forests, white (Quercus alba) and red oak (Q. rubra), were examined after incubation in pathogen‐infested soilless potting mix. Fine root lengths (0–1.5 mm in diameter) of both oak species were quantified after incubation at successive 30‐day intervals up to 300 days, for a total of 10 incubation periods. In addition, colony‐forming units (CFU) of P. cinnamomi were quantified after white oak saplings were incubated in infested soilless potting mix at different temperature/duration combinations that reflect soil conditions present in the mid‐Atlantic United States. Impact of P. cinnamomi on fine root lengths of red and white oak saplings varied considerably over time. Significant periods of fine root loss occurred primarily during spring, when bud break and leaf flush began for both oak species. Red oaks had 17% fine root loss on average, while white oaks appeared more resistant to P. cinnamomi infection with a 2% decrease in fine roots over the course of the experiment. Phytophthora cinnamomi CFU declined significantly with exposure to all incubation temperatures except 8°C. This was in contrast to in vitro experiments, where the optimum temperature for mycelial growth was determined to be 21°C and above. Significant fine root loss caused by P. cinnamomi depended on plant phenology and the oak species tested. Extreme soil temperatures have a significant adverse impact on temporal changes of P. cinnamomi population.

Canker and decline diseases caused by soil- and airborne Phytophthora species in forests and woodlands

“…Most significantly, both in the field and in pathogenicity tests P. cinnamomi -associated fine root losses were shown to be related to the propagule density of the pathogen. It was demonstrated that fine root losses are driving oak decline events in moist low-elevation stands where inoculum levels of the pathogen are higher and in areas like plant hardiness zones 6 and 7 where fine root regeneration is limited due to climatic constraints ( McConnell & Balci 2014a , b ).…”

Phytophthora cinnamomi

“…Blockage of the xylem through hyphal obstruction and deposition of material by the plant inhibits water movement from the roots to the shoots, resulting in water stress (Ruiz G omez et al, 2015). Necrosis of infected fine feeder roots exacerbates the problem and can lead to rapid plant death (McConnell and Balci, 2015;Oßwald et al, 2014).…”

Phytophthora cinnamomi exhibits phenotypic plasticity in response to cold temperatures

“…Sub-alpine regions were long considered free of P. cinnamomi because harsh environmental conditions were thought to limit its survival (Green 2016). Phytophthora cinnamomi becomes inactive in soil when the soil temperature drops below 10°C (Weste and Marks 1987), and no growth is shown on artificial media below 5°C (McConnell and Balci 2015). Podger et al (1990) modeled damage caused by P. cinnamomi in Tasmania and hypothesized that it is unlikely to cause disease in areas where annual mean temperature is less than 7.5°C.…”