INHIBITION OF GERMINATION AND GROWTH OF THIELAVIOPSIS-BASICOLA BY ALUMINUM

Soils suppressive to Thielaviopsis basicola typically have low pH values and high levels of exchangeable aluminum (Al). A series of experiments was conducted to determine the sensitivity of T. basicola to Al. All experiments were conducted in Al-amended carrot agar medium buffered at pH 5.0, except for experiments to determine effects of pH. Isolates of T. basicola from suppressive and conducive soils responded similarly to Al in most tests, but where differences were observed, the isolate from a suppressive soil was less sensitive to Al than was the conducive-soil isolate. Germination of endoconidia and chlamydospores of T. basicola decreased significantly when exposed to 0.55 or 1.1 meq of Al (1 meq = 9 ppm of Al) compared with Al-free controls. Effects of Al on germination were greatest at pH values <5.6 and at low nutrient levels. Radial growth of T. basicola was suppressed on agar amended with 1.1 meg of Al but not on that with 0.55 or 0.27 meq of Al, Development of colonies from chlamydospores was inhibited in agar medium amended with 0.55 or 1.1 meq of Al but not in that with 0.27 meq; colonies also took longer to develop in the presence of Al, Al(NO3)(3) was slightly more inhibitory to germination of endoconidia than were other sources of Al. Radial growth was similar on medium amended with different sources of Al.