Pre-sowing treatments for improving emergence of bitter gourd seedlings under optimal and sub-optimal temperatures

Abstract

Bitter gourd (Momordica charantia L.) requires high temperature (between 25 and 28°C) for successful seedling emergence, and poor emergence is common at sub-optimal temperature. This study evaluated the effect of suboptimal temperature on seedling emergence and several physiological characteristics related to seedling growth in bitter gourd cultivar Special Six. Priming was achieved by mixing the seeds with moist No. 3 vermiculite, incubating at 25°C for 36 h, then air-drying to the original moisture level. Warm water soaking was achieved by soaking the seeds in water at 50°C for 60 min, and then air-drying to the original moisture level. Seedling emergence from vermiculite was determined at 25, 20 and 15°C. The emergence of non-treated seeds at 25°C was 50%. No seedlings emerged at 20 or 15°C. However, both priming and warm water soaking improved the emergence responses of bitter gourd seeds under 25 and 20°C. The observed decrease and delay in emergence at sub-optimal temperature were linked to the reduced activity of enzymes (i.e. isocitrate lyase, malate-synthase and malate dehydrogenase) involved in lipid and sucrose conversion. Both priming and warm water soaking improved the low temperature (20°C) seedling emergence. These improvement were attributed to the increased enzyme activities. Nevertheless, the morphological changes and softening in seed coat and seed treatment-stimulated embryo growth might also play crucial role in speeding up the seedling emergence.