Effects of powder and aqueous extracts of Euphorbia hirta on Phelipanche ramosa germination and haustorium initiation

Abstract

Abstract

Phelipanche ramosa, a devastating root parasitic weed, is a copious seed producer. The seeds are characterized by prolonged viability and special germination requirements. Following a conditioning phase seeds germinate in response to exogenous stimulants. Subsequent to germination the radicle elongates and in response to a second host-derived stimulant a haustorium is initiated and attachment to the host root occurs. The parasite inflicts most of its damage to the host prior to emergence. Therefore, manipulation of seed germination and pre-attachment stages are mandatory for successful management. A series of laboratory experiments was undertaken to investigate the effects of aqueous extracts and powder from Euphorbia hirta on germination, radicle elongation, and haustorium initiation in P. ramosa. P. ramosa seeds conditioned in water and subsequently treated with diluted E. hirta extract (10-25% v/v) displayed considerable germination (47-62%). Increasing extract concentration to 50% or more reduced germination in response to the synthetic germination stimulants GR24 and Nijmegen-1 in a concentration dependent manner. P. ramosa germlings treated with diluted Euphorbia extract (10-75% v/v) displayed haustorium initiation comparable to the synthetic haustorium initiation DMBQ at 20 µM. Euphorbia extract applied during conditioning reduced haustorium initiation in a concentration dependent manner. E. hirta extract or air-dried powder, applied to soil, induced considerable P. ramosa germination. The results indicate that there is a potential of E. hirta as a source of compounds that can be used as templates for synthesis of more active compounds to manipulate pre-attachment stages in P. ramosa.