Effects of plant extracts of Bothriochloa pertusa and Urochloa mosambicensis on seed germination and seedling growth of Stylosanthes hamata cv. Verano and Stylosanthes scabra cv. Seca

Abstract

Effects of osmotic stress and of aqueous plant extracts from 4 pasture species on seed germination and seedling growth of the tropical legumes S. hamata (L.) Taub cv. Verano and S. scabra Vog. cv. Seca were investigated. Allelopathic effects of plant extracts from B. pertusa (L.) A. Camus were measured on S. scabra cv. Seca in terms of lower germination (35%) and shorter root length (35%). Extracts from Urochloa mosambicensis(Hack.) Dandy cv. Nixon had no adverse effect on Seca germination, but also reduced Seca root length. There was no evidence to support the hypothesis that B. pertusa had allelopathic effects on Verano germination or seedling growth. Extracts from Verano and Seca also reduced germination, seedling weight, and root length of Seca as well as root length of Verano.

Root length was more sensitive than seedling length for ascertaining allelopathic effects, as there was no osmotic potential effect on root length up to 300 mmol/kg, whereas seedling weight and shoot length declined linearly with increasing osmotic potential (r = -0·92 and -0·99, respectively).

Germination responses of Verano and Seca in solutions of both mannitol and polyethylene glycol-600 (PEG) were similar up to 300 mmol/kg, but at 600 mmol/kg Verano had a significantly higher germination in mannitol.

Since the osmotic potential of the plant extracts did not exceed 78 mmol/kg, the use of osmotically adjusted control treatments had little effect on the conclusions drawn from using a distilled water control treatment.