Effects of hydrogen fluoride on susceptibility of soybeans to Rhizoctonia solani and Phytophthora megasperma f. sp. glycinea

Ten 14-day-old soybean plants, cv. ‘Williams 82’ were exposed continuously to hydrogen fluoride (HF) at 2 μg F m⁻³ in a controlled-environment chamber. After 1 week, the plants were transplanted into a potting mix infested with Rhizoctonia solani (Rs) or Phytophthora megasperma f. sp. glycinea (Pmg), and again exposed to HF for 1 week. Immediately after transplanting, plants inoculated with Pmg and uninoculated plants were flooded for 48 h, whereas plants with Rs and uninoculated checks were not flooded. One week after inoculation, hypocotyl lesions induced by Rs and Pmg were significantly larger on plants exposed to HF. Total root length infected was increased by exposure to HF, but this effect was not significant. Dry weights of individual plant parts were not affected by HF, but shoot:root ratios were higher after exposure to fluoride in experiments with Pmg. Fluoride concentrations in the leaf blades were positively correlated with root lesion length of plants inoculated with Pmg but not in those of plants inoculated with Rs.