Morphological, phenological and reproducitve characteristics of the invasive weed species Abutilon theophrasti Medik as affected by various plant densities

Background and purpose: Abutilon theophrasti Medik (velvetleaf) is an invasive plant well spread in Croatia as noxious weed species. The aim of this study was to provide morphological, phenological and reproductive information of velvetleaf grown under various densities: 2, 5, 10 and 20 plants m-2. Material and methods: The field experiment was conducted in 2014 at University of Zagreb Faculty of Agriculture as complete randomized blocks design. Throughout the vegetation morphological (hypocotyl and epicotyls length, number of leaves and branches, plant height, shoot dry weight and diameter), phenological (beginning of flowering end of flowering and first capsule formation; GDD to beginning of flowering end of flowering and first capsule formation) and reproductive (capsules plant-1, seed capsules -1, seeds plant-1, seeds m-2, 1000 seeds weight and germinability) characteristics were measured. Results and conclusion: Mostly all morphological and reproductive characteristics were significantly affected by plant density. Increase of velvetleaf competition from 2 to 20 plants m-2 hasreduced number of capsule and consequently almost five fold decreased seed production per plant. However, plants which have been growing at densities > 5 plants m-2 produced in average 50% more seeds per land area than plants at the lowest density. Low germinability at harvest (2%) and six month later (15%) indicate on primary dormancy and possibility for longevity in soil if plants are left uncontrolled in the field. In contrast to morphological and reproductive changes, plants in high density did not showed increasing growing degree days requirements.