EFFECT OF AMYGDALIN ON GROWTH OF NEMAGUARD PEACH SEEDLINGS

This study addresses the possible role of amygdalin, a cyanoglucoside, on the replant disease of Prunus crops. The allelopathic effects of amygdalin on Nemaguard (P. persica x P. davidiana) seedlings were assessed by growing seedlings in containers with different soil treatments reflecting increasing levels of amygdalin. Treatments were as follows: healthy soil (control), healthy soil plus amygdalin at 0, 500, 1000 and 2000 mg L^-1; bitter almond seed extract; roots extract of adult Nemaguard trees, a combination of the last two treatments and a “replant disease”soil taken from an old peach orchard possessing an amygdalin content of 258.6 mg L^-1 (14.7 mg L^-1 of cyanide). The putative autoallelopathy was assessed by effects on plant height, trunk diameter, total dry matter and root length. The residual content of cyanides in the soil was determined at the end of the assay. There was a substantial growth inhibition with amygdalin treatments on all growth variables measured, with the level of inhibition increasing with the concentration of the soil-associated amygdalin. A curvilinear relationship between amygdalin concentration (x) and levels of cyanide (y) in the soil (described by the equation: y = -8•10^-07 x2 + 0.0031x + 0.0546; R² = 0.96) was established. Cyanide concentration was about four-fold greater in “replant disease” soil than in control soils. Results provide evidence for the involvement of an amygdalin-associated autoalleopathic factor in the replant disease of Prunus crops.