Thidiazuron andColletotrichum coccodesEffects on Ethylene Production by Velvetleaf (Abutilon theophrasti) and Prickly Sida (Sida spinosa)

Abstract

The effects of the plant growth regulator thidiazuron and the plant pathogenColletotrichum coccodeson ethylene synthesis by velvetleaf and prickly sida were investigated. Untreated velvetleaf seedlings produced 1.5 and 2.3 pmol ethylene/mg fresh weight 24 and 48 h after treatment. Treatment with thidiazuron at 200 g ai/ha orC. coccodesat 1 × 109spores/m2increased ethylene production by 4.9 and 3.5 pmol/mg, respectively, in 24 h; and by 10.6 and 15.8 pmol/mg, respectively, in 48 h. Combination treatments caused synergistic increases in ethylene production by velvetleaf seedlings of 17.7 and 49.6 pmol/mg in 24 and 48 h, respectively. Thidiazuron at 10 μM, combined with an extract ofC. coccodesmycelia, increased ethylene synthesis by more than 4-fold in vacuum-infiltrated excised velvetleaf petioles within 48 h. Thidiazuron at 50 g/ha, combined with an extract ofC. coccodesmycelium, increased ethylene synthesis 16-fold in prickly sida seedlings in 24 h. Aminocyclopropane carboxylic acid (ACC), a precursor of ethylene, stimulated ethylene production by velvetleaf petioles more than 8-fold when supplied at 0.75 mM; thidiazuron and the pathogen effects were not discernible in its presence. Aminoethoxyvinyl-glycine (AVG), an inhibitor of ACC synthase, inhibited overall ethylene production by velvetleaf seedlings more than 40% when supplied at 0.58 to 0.67 mM, without obscuring the stimulatory effects of thidiazuron and the pathogen. These results indicate that the growth regulator and the plant pathogen or an extract of the pathogen act in concert to increase ethylene synthesis in velvetleaf. Stimulation probably occurs before the synthesis of ACC in the ethylene biosynthetic pathway.