Selective phytotoxic activity of withanolides from Iochroma australe to crop and weed species.

Abstract

Phytotoxic effects of Iochroma australe extract and 4,7,20-oxowithanolides were examined in Petri dish bioassays at 10, 100, and 1000 ppm. The extract and the major constituent (17S,20R,22R)-4β,7β,20α-trihydroxy-1oxowitha-2,5,24-trienolide (2) reduced growth of the radicle of the weeds Sorghum halepense (Monoct.) and Chenopodium album (Dicot.). Neither the extract nor withanolides had significant effect on germination or radicle length of the commercial crop species Lactuca sativa. From our experimental data we conclude that the withanolides tested here are natural products with selective herbicidal activity against weed species.