Identification of Armillaria field isolates using isozymes and mycelial growth characteristics

This research was conducted to develop procedures based on mycelial growth characteristics and patterns of esterase (EST) and polyphenol oxidase (PPO) production by diffuse mycelia for identification of Armillaria field isolates from Quercus-Carya-Pinus forests in the Ozark Mountains (central USA). The 285 isolates collected were first identified by standard diploid-haploid pairing tests as A. gallica, A. mellea, or A. tabescens. A strong PPO band was diagnostic for A. gallica. All A. mellea isolates tested and 91% of the A. tabescens isolates tested were distinguished based on production of EST bands in three standardized R f ranges. A procedure based on mycelial growth and morphology on tannic acid medium (TA) at 24 degrees C and on malt extract medium (ME) at 33 degrees C correctly identified 98% of A. gallica isolates and all A. mellea and A. tabescens isolates. On TA, A. gallica grew slowest. On ME, A. mellea grew slowest: mycelial morphology differed among species; A. gallica typically stained the agar and produced an appressed/submerged growth pattern with concentric bands of decreasing hyphal density, A. mellea typically did not stain the agar and produced round mycelia with smooth margins and abundant aerial hyphae, A. tabescens typically stained the agar and grew appressed/submerged with very irregular margins and patchy hyphal density. These are the first published systems evaluating the potential for identifying Armillaria field isolates based on their mycelial growth characteristics and EST and PPO complements.