Chondrilla juncea in Australia. 4. Root morphology and regeneration from root fragments

Abstract

The morphology of the root system of Chondrilla juncea and its response to changes in soil type near Wagga Wagga, New South Wales, is described. The root system is described as consisting of vigorous long roots capable of vegetative reproduction at any depth and short roots, apparently without secondary thickening, of limited life span. The long root system consists of a simple tap root and a number of surface laterals, which increase in frequency and extent of lateral spread as soil clay content decreases. The relationship between plant age, growth stage, and depth of origin, as well as depth of planting and soil type, on shoot production from root fragments also was studied. Root fragments from depths to 80 cm and more did not differ appreciably in regenerative capacity. But, whereas shoot buds formed on some seedling roots two to four weeks after germination, all such roots formed buds five weeks after germination. Soil type and depth of planting did not affect shoot production from root fragments per s e, but establishment of new plants fell as depth of planting increased. A comparison of vegetative and reproductive plant roots of similar age showed that regenerative capacity was minimal during the reproductive growth phase. The inhibition of shoot bud formation on the roots, however, was confined to the proximal 40 cm. It is suggested that weed control operations are likely to be more effective when carried out shortly after stem initiation than at other times.