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 isola tes from Quercus-Carya-Pinus forests in the Ozark Mountains (central USA). The 285 isolates collected were first identified by standard diploid-haploi d pairing tests as A. gallica, A. mellea, or A. tabescens. A strong PPO ban d was diagnostic for A. gallica. All A. mellea isolates tested and 91% of t he A. tabescens isolates tested were distinguished based on production of E ST bands in three standardized Rf ranges. A procedure based on mycelial gro wth and morphology on tannic acid medium (TA) at 24 degrees C and on malt e xtract medium (ME) at 33 degrees C correctly identified 98% of A. gallica i solates 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/s ubmerged 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 patch y hyphal density. These are the first published systems evaluating the pote ntial for identifying Armillaria field isolates based on their mycelial gro wth characteristics and EST and PPO complements.