New Pythium Taxa Causing Root Rot on Mediterranean Quercus Species in South‐west Spain and Portugal

Abstract

Pythium spiculum, a recently described new taxon, has been frequently isolated from declining Quercus rotundifolia and Q. suber roots and rhizosphere since 2003 in southern Iberia. In soils of declining Quercus forests this species was found as frequently as Phytophthora cinnamomi which, until now, was the only oomycete described as a Quercus root rot pathogen in the region. Inoculation tests conducted on young Q. rotundifolia plants showed that Py. spiculum is an aggressive root pathogen, although producing severities of symptoms significantly lower than those of P. cinnamomi. This new pathogen could play a role as decline factor in southern Iberia. Another new species, Py. sterilum, was also found to be pathogenic to Quercus roots but there are presently only few records of this organism isolated from rhizosphere of declining oaks in central Spain. More than an active decline factor, this species should be considered as a potential risk for Quercus forests.

Diversity, host, and habitat specificity of oomycete communities in declining reed stands (Phragmites australis) of a large freshwater lake

“…A number of studies in previously unexplored natural ecosystems have also revealed several undescribed Pythium species (e.g. Nechwatal & Osswald 2003;Paul 2003;Romero et al 2007), as well as oomycetes from the Saprolegniaceae (e.g. Dick 1971).…”

Calcium fertilizers induce soil suppressiveness to Phytophthora cinnamomi root rot of Quercus ilex

“…Briefly, this was obtained by mixing together the same quantity of mycelium from both isolates, to obtain a single suspension of chlamydospores. The inoculum suspension was adjusted to 650 chlamydospores per g of soil (Romero et al 2007). Ten days after soil infestation, each fertilizer was separately added to the soil at 15 mM of Ca 2+ .…”

Lupinus luteus, a new host of Phytophthora cinnamomi in Spanish oak-rangeland ecosystems

“…Three open forests were chosen from those previously studied, with known presence of P. cinnamomi infecting oak roots (Romero et al 2007). The fourth site was a recently forested rangeland (10 years-old trees) free of oak root disease.…”

“…Trays were incubated in a growth chamber (12 h light per day, 18-24°C), with watering as needed. Twenty five days after inoculation, root symptoms were assessed for each plant on a 0-4 scale, according to the percentage of root necrosis recorded (0=0% necrotic tissue, 1=1-33%, 2=34-66%, 3=67-99%, 4=dead plant) (Romero et al, 2007). ANOVA was performed for emergence and root symptom values, considering the cultivar, the presence of P. cinnamomi in the soil, and their interaction as factors.…”

“…Lupin roots were carefully washed under running water. Necrotic roots were cut into segments 3-4 mm long with a sterile scalpel, and plated in Petri dishes containing 20 ml of NARPH medium (NystatinAmpicillin-Rifamicin-PentachloronitrobenzeneHymexazol-Cornmeal agar, selective for the genus Phytophthora) (Romero et al 2007). For each plant, one or two dishes (depending on availability of roots), each containing six root segments, were prepared and incubated at 22°C in the dark for 4 days.…”