Potencial alelopático do capim-annoni-2 (Eragrostis plana Nees) na germinação de sementes de gramíneas perenes estivais

Abstract

Among plant strategies to invade and dominate the plant community, the release of alelochemicals is prominent. These compounds are present in all plant parts, principally, in root exudates, leaves and their degraded parts. They are released in the environment through volatile or soluble emanations, translocated in water. Capim-annoni-2 is an invasive exotic Poaceae of rangeland vegetation with allelopatic potential. To test this effect, plant structures from the mid part of capimannoni-2 were collected and cut in small pieces of 0.5cm and placed in three covering levels of 0, 50 and 100% in gerboxes covered with germitest blotters over the cut material. A hundred seeds of Paspalum notatum Flüggé, P. regnellii Mez, Megathyrsus maximus B. K. Simon and S. W. L. Jacobs, Setaria sphacelata (Schumach) Staff and C. E. Hubb ex Chipp and Lactuca sativa L., were placed to germinate as controls. A randomized complete block design was used with four replications. The allelopatic effect was observed on the seed germination after the beginning of capim-annoni-2 plant tissue decomposition. Seeds with high speed germination, such as M. maximus and P. reginelli as well as L. sativa, escaped the allelopatic effect. The most damaged species in their germination course were P. notatum e S. sphacelata. The germination injury was proportional to the gradient increase of the capim-annoni-2 covering tissue with the exception of P. reginelli which showed, at 50% capim-annoni-2 covering level, an increase in germination, but at 100% level there was a significant germination reduction. The capim-annoni-2 allelopathic effects occur during plant tissue decomposition. Seeds with precocious germination escape these effects. The late germination of P. notatum and S. sphacelata exposed them to the capim-annoni-2 allelopathic effects. P. reginelli germination was stimulated at 50% covering level to capim-annoni-2, but at maximum level there was a significant germination decrease in its seeds.