Seed production potential dormancy and seed storage behaviour in sida spp.

Abstract

The study entitled “Seed production potential, dormancy and seed storage behaviour in Sida spp.” was undertaken at the Department of Plantation Crops and Spices, College of Horticulture, Vellanikkara during 2012-2014. The study aimed to assess seed production potential and characterize dormancy in three Sida species (Sida alnifolia, Sida acuta and Sida cordifolia) and to standardize ideal pre-treatment for improving germination and to study seed storage behaviour in Sida alnifolia. Flowering and fruiting in Sida species was staggered and started four months after planting. Flowering and fruiting was earliest in Sida acuta and latest in Sida alnifolia. Maximum seed rain and seed production potential was exhibited by Sida acuta. The fruits and seeds were biggest in Sida cordifolia. Physical characterization of dormancy by analysis of seed coat thickness and embryo size of three species revealed that hard thick seed coat comprising endoderm, mesoderm, periderm and presence of thick corrugated impermeable cuticle was a major limiting factor restricting the exchange of water and gases. Acid scarification brought out reduction in all layers of the seed coat with maximum reduction in cuticle thickness. Upon storage, the total thickness of the seed coat and individual layers was slightly reduced but embryo area, perimeter and cuticle thickness increased slightly. The physiological conditions tried such as exposure of seeds to different temperatures, light and dark and exposure to stress by hydration and dehydration failed to promote germination in fresh seeds. Irrespective of the species, seeds whether fresh or stored, also failed to germinate without pre-treatment. Germination studies under field conditions indicated that seeds exposed to natural weathering showed a spontaneous response on receipt of rain and the germination was completed in ten days with highest germination (74.50 per cent) in Sida acuta followed by Sida alnifolia (67.50 per cent) and least in Sida cordifolia (42.50 per cent). Biochemical analysis of seeds revealed that species differed in the content of total extractives, total phenol and total alkaloid and Sida acuta recorded higher contents of total extractives and total alkaloid whereas total phenol content was higher in Sida alnifolia. Analysis of the seed leachates indicated species difference in the content of minerals and electrical conductivity. Sida acuta recorded the highest potassium and EC values. Among the eighteen pre-treatments tried for improving germination, chemical scarification using Conc. H2SO4 was significantly superior and recorded higher germination per cent and speed of germination. Untreated seeds failed to germinate. Scarification of seeds with Conc. H2SO4 for higher duration of 30 minutes was selected as the best treatment considering improvement in water imbibition, germination per cent, speed of germination, growth and vigour of seedling and significant reduction in the intensity of dormancy. Storage studies revealed that upon storage, germination, vigour of seedling and reduction in dormancy factors were at a positive side compared to fresh seeds. Storage of seeds under cooler atmosphere either refrigerator or freezer was found to improve the water imbibition, content of minerals, germination and vigour of seedling compared to ambient storage. The present investigations could thus establish that seeds of Sida species exhibit coat imposed dormancy and require two months of after ripening period, posing problems in germination. Pre-treatment of seeds with Conc. H2SO4 for 30 minutes is suggested to bring down dormancy and improve germination and vigour of seedlings. Exposing the seeds to natural weathering is a simple way of improving germination. The seeds can be effectively stored under cooler conditions in refrigerator / freezer for one year or longer which also lowered dormancy and improved germination and vigour of seedlings.