Studies on Seed Germination of Coscinium fenestratum (Gaertn.) Colebr. - A Threatened Medicinal Plant

Abstract

Mature seeds of Coscinium fenestratum recorded 92.20% germination after pre-treating the seeds by exposing to direct sun light for 6 hours (sun cracking) followed by dipping seeds in 2250 mg/L Gibberelic Acid (GA3) solution for 24 hours. Seeds subjected to sun cracking followed by water soaking for 24 hours (59.2%) resulted significantly (P< 0.05) low germination rate. Seeds subjected sun cracking followed by water soaking for 24 hours started to germinate four months after sowing and continued up to six months while GA3 pretreatments significantly (P< 0.05) reduce the time taken for germination from six months to three months. Germination was facilitated on sand:coir dust (1:1 ratio) medium after improving the micro climate by maintaining the temperature above 30°C, minimizing fungal contaminations, regular watering and under total dark conditions. Highest in vitro seed germination (39%) was achieved at 32±2°C temperature under total dark conditions where seeds were surface sterilized using 20% Clorox (5.25% NaOCl) followed by 70% Ethanol for 2 minutes and subsequently cultured into sand:coir dust medium aseptically. Seeds on water agar medium consisting lg/L Activated Charcoal (AC) achieved 35% mean germination rate which was not significantly different (P< 0.05) with the previous. Seeds were not germinated on MS medium due to the presence of sucrose which facilitates microbial contaminations. Seeds of C. fenestratum coupled with exogenous (physical, chemical and mechanical) seed dormancy created by hard seed coat, inhibitory substances presence in the seed coat and the endosperm and endogenous (physiological) dormancy created by some other physiological factors as high Abscisic acid (ABA)/GA3 ratio. Temperature above 30°C and dark conditions facilitate germination of mature seeds of C. fenestratum after split opening the hard seed coats by exposing to direct sun light for 6 hours followed by removing inhibitory chemicals, facilitating embryo growth to reduce the time taken for germination and reducing inherent ABA/GA3 ratio by dipping the seeds in 2250 mg/L GA3 solution for 24 hours.