Propagation method and germination condition of an arid and semi-arid species: Withania frutescens (L.)

Abstract

Withania frutescens (L.) is a species of the solanaceae family found in arid and semi-arid zones, and has a place in traditional phytotherapy. This plant is subject to over-exploitation by the indigenous population, which is reducing its distribution in their natural environment. Our aim is to find a method for in-situ and ex-situ conservation of this species. Seeds and cuttings were selected from different individuals of the same species. Viability tests were carried out (buoyancy test, tetrazolium test) to determine the seeds with the best germination rate. The selected seeds were subjected to chemical and mechanical tests (chemical scarification with sulphuric acid, hydrogen peroxide, potassium nitrate (KNO₃) and hot water). The second method of propagation is by cuttings with hormonal intervention to solve the problem of rooting the cuttings. The fruits of W. frutescens are berries 7 to 10 mm in diameter with a water content of around 12.48%. The length, width and average thickness of the seeds are 3 to 5 mm, 2 to 3 mm and 1 to 1.5 mm respectively. The control (water) showed no germination, compared to the hydrogen peroxide (H₂O₂) and hot water treatments with 16.34% and 12.69%, respectively. W. frutescens seeds show a common triphasic pattern of water uptake over the 72 hours of evaluation. Phase I is characterised by relatively rapid water uptake. During phase II, the seeds remain on average without any significant increase in weight. Phase III for the average population is around 50 hours. Monitoring of the growth parameters for 12 weeks shows that the W. frutescens cuttings showed growth from the second week and the parameters changed until the last week. The number of leaves (Nfe) was about 4.89±2.53 in the third week and about 22.88±8.71 in the last week (12 weeks). The number of flowers (NFL) was about 4.64±1.68 during the last week and the number of nodes (ND) about 5.60±1.78. However, when the growth of the cuttings was monitored, the rate of appearance of root callus in the cuttings was around 2.51±0.74% for cuttings not treated with AIB. However, treatment of the cuttings with AIB showed a root callus rate of 23.45±5.09% as a peak at a concentration of 312.50 µg/mL AIB. On the other hand, the high concentration (5 mg/mL) and the low concentration (78.10 µg/mL) showed a rate of about 0.0±0 and 8.91±1.42%, respectively. W. frutescens is an endangered species and requires in-situ and ex-situ conservation.