Seed Germination of Tropical Trees under Polyethene Glycol-induced Osmotic Stress for Early Screening of Drought Tolerance

Abstract

Drought-induced water stress is a major environmental constraint affecting seed germination and early seedling establishment in forest ecosystems. The present study evaluated the effects of polyethylene glycol (PEG-6000)-induced osmotic stress on seed germination of seven tropical tree species—Hardwikia binnata, Butea monosperma, Acacia catechu, Acacia nilotica, Holoptelea integrifolia, Diospyros melanoxylon, and Pithecellobium dulce. Seeds were germinated under three water stress treatments: control (0 MPa), PEG-200 (0.5 MPa) and PEG-300 (1.0 MPa), corresponding to increasing osmotic stress levels. The experiment was conducted using a factorial completely randomized design with four replications, and germination was recorded at 24 h, 3 days, and 7 days. Under control conditions, Hardwikia binnata exhibited the highest germination (90%), followed by Butea monosperma (60.24%), Diospyros melanoxylon (60.24%), and Acacia catechu (30%). PEG-200 caused a marked decline in germination, although Hardwikia binnata and Butea monosperma retained relatively higher tolerance. PEG-300 induced severe osmotic stress, resulting in complete inhibition of germination in Pithecellobium dulce. Significant species and treatment interactions indicated differential sensitivity to water stress among species. The findings demonstrate that water availability is a critical determinant of seed germination in tropical forest tree species, with pronounced species-specific tolerance thresholds. The relatively higher tolerance of Hardwikia binnata and Butea monosperma under moderate stress suggests their potential suitability for afforestation and restoration programs in drought-prone regions. This study provides valuable insights into early-stage drought tolerance mechanisms, supporting the selection of climate-resilient tree species for sustainable forest management.