Seed scarification and plant extracts enhanced germination, seed health and seedlings vigour of Tetrapleura tetraptera

Seed dormancy and seed-borne fungi are main biological constraints to the domestication of edible non-timber forest products such as Tetrapleura tetraptera fruits. This study aimed to evaluate the effect of thermal and mechanical scarification on seed dormancy and the efficacy of three plant aqueous extracts (Cymbopogon citratus, Callistemom viminalis, Tephrosia vogelii) against seed-borne diseases and seedlings vigour of T. tetraptera. Treatments consisted of soaking the seeds in water at 80˚C for 2 and 4 hours, scarification of seeds with abrasive paper at 1 mm and 2 mm depths. The antifungal activity of plant extracts was evaluated both in vitro (by the poising method on agar medium) and in vivo at 2.5, 5.0 and 7.5 mg/mL. Momtaz (Imidacloprid 250 g/kg + Thiram 200 g/kg) was used as a positive control. Dormancy was lifted by scarification at 2 mm depth; this treatment had the highest germination percentage (92.33%) and the lowest infection rate (20.67%). The more frequent seed-borne fungi isolated belong to Aspergillus sp. (18.43% - 21.78%). The pathogenicity test was positive with Alternaria alternata, A. fumigatus and Cercospora sp. T. vogelii extract totally inhibited the growth of the pathogenic fungi at all the concentrations tested. Seed infection obtained with T. vogelii (4.12%) extracts at 7.5 mg/mL was significantly similar to Momtaz (3.33%). The extract of C. viminalis had the highest vigour index (674.42) at 7.5 mg/mL. Mechanical scarification using abrasive paper and seed treatment with plant extracts of T. vogelii could be used in the domestication process of the species.