Shading as an environmental factor affecting the growth of Ischaemum rugosum

Abstract

Wrinkled grass (I. rugosum Salisb.) is one of the most important weeds in irrigated rice in Maranhão, with infested fields increasing each season. The experiment was conducted in pots to study the effects of shading (0, 50 and 70%) on wrinkled grass growth. Plants were harvested at seven days after emergence (DAE), and from 14 to 112 DAE at 14-day intervals. They were separated in culms, leaves and roots, dried, weighed, and leaf area measured. Dry matter (DM) accumulation of culms, leaves and roots was reduced by shading. In roots, dry matter accumulation diminished as levels of shading increased. A sharp decline in root dry matter accumulation was observed after the beginning of flowering in unshaded plants. Leaf area, however, was greater in plants grown at 50% shading than in those that were shaded at 0 or 70%. Relative growth rate (Rw) was greater in shaded than in unshaded plants. The contrary was true for net assimilation rate (Ea). At the end of the plant cycle, however, the net assimilation rate was greater in plants shaded at 70% than in those shaded at 0 or 50%. It was concluded that there was an effect of shading on sink preference. At full sunlight the roots were the preferred sink during the vegetative phase, whereas the culms appear to be the primary sinks during the reproductive period. In shaded environments the culms and leaves were the preferred sinks. Leaf thickness was lower in plants cultivated at high levels of shading than in sunniest plants receiveing more light.