Induction of tetraploidy in garden cress: morphological and cytological changes

Abstract

Garden cress (Lepidium sativum L., Brassicaceae) is one of the most popular leafy vegetables which is widely used, and has also various medicinal properties and industrial usage. Small and very delicate leaves of this short period and fast growing species cause lots of crop losses along production to consumption; so it was supposed that increase in thickness and size of the leaves via induction of polyploidy possibly will improve post-harvest quality. Primary trial proved that seed treatments, via immersion of dry and wet seeds in different concentrations and durations of colchicine, were completely ineffective. Thereafter dropping method was conducted on apical bud of cotyledon and two true leaf stages with different concentrations of colchicine (0, 0.05, 0.1, 0.2, 0.5 and 0.75% w/v). Treatment on cotyledon stage was not fruitful because of sensitivity to colchicine and dying of small seedlings; but apical bud treatment in two true leaf stage resulted in inducing some polyploid plants. The best result was obtained by 0.5% colchicine concentration, inducing 9.33% tetraploid plants. Chromosome counting and flowcytometric analysis of morphologically putative plants confirmed chromosome doubling in garden cress from 2n = 2x = 16 to 2n = 4x = 32. Tetraploid plants comparing diploid ones specified by increasing in leaf size and thickness, stem diameter, stomata size, number of chloroplasts in stomata guard cells, seed weight and on the contrary, decreasing in stomata count and height of plants, percentage of seed germination and also germination rate. In this research, we have tested various methods and different levels of colchicine for the polyploidy induction in garden cress, and the results of polyploidy induction have been studied.