The Induced Resistance Response of Carrot Root Slices to Heat-killed Conidia and Cell-free Germination Fluid of Botrytis cinerea Pers. ex Pers. 1. The Possible Rôle of Cell Death

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Abstract
The ability of a cell-free secretion from germinating conidia (germination fluid) and heat-killed conidia of Botrytis cinerea Pers. ex Pers. to induce resistance in exposed carrot root tissues was unaffected during freezing to −25 °C and rapid thawing, and by heating to 50 °C for 10 min. Activity was lost by boiling for 10 min or at room temperature after 24 h. There was less cell death (Evans blue and neutral red staining) in the surface tissue of slices pretreated with heat-killed conidia and subsequently exposed to infection than in similar tissue of untreated, inoculated slices. Both inducing preparations alone caused maceration and cell death in one or two cell layers of the slice surface. Healthy tissue killed by freezing to −25°C for 2 h and rapid thawing, released a factor which, when similarly tested on slices, resulted in germ-tube inhibition and reduced visual symptoms following inoculation with live spores. The possibility that cell death triggered the release of a host elicitor which caused enhanced accumulation of phytoalexins and suberin deposition is discussed.