Allelopathy of purple nutsedge (Cyperus rotundus L.) on cotton (Gossypium).

摘要

The effects of extracts from purple nutsedge tubers were determined on the germination, growth, root leakage, water status, and photosynthesis of an Upland cotton, DPL 5415, and a Pima cotton, Pima S-7. Tubers extracts inhibited secondary root growth of seedlings more than primary root growth. At 500 ppmw, primary root growth was inhibited 44 percent whereas inhibition of secondary root growth was 64 percent. Non-polar extracts were more inhibitory to growth than polar extracts. Cotton plants grown in soil treated with hexane extracts of tubers containing non-polar allelopathic substances also lost electrolytes from their roots indicating an effect on root function. The effects on root function resulted in perturbations to the capacity of the plants to maintain efficient water status. At 250 ppmw of the hexane extract, the plant water potential, the leaf water content, and the leaf osmotic potential decreased from {dollar}-{dollar}0.7 to {dollar}-{dollar}1.3 MPa, from 89 to 79 percent, and from {dollar}-{dollar}0.8 to {dollar}-{dollar}1.0 MPa, respectively. In addition, the photosynthetic capacity of cotton was decreased 50 percent in both cotton cultivars in the second and third day after transplanting to soil treated with 62 ppmw of the hexane extracts. Leaf dehydration to below 70 percent relative water content and a reduction of quantum yield was detected in DPL 5415 at 125 ppmw of the hexane extracts. However, Pima S-7 was capable of tolerating higher levels of dehydration and did not show the reduction of quantum yield. Leaf expansion and epicotyl growth were also inhibited by 30 and 37 percent, respectively, by the hexane extracts at 250 ppmw. Purple nutsedge tubers released volatile substances that inhibited growth when trapped and tested on cotton seedlings, and caused root leakage. GC analyses showed that both the hexane extracts of purple nutsedge tubers and the volatile compounds released from the tubers contained substances with retention times that are characteristic of sesquiterpenes. These results demonstrate that purple nutsedge tubers contain allelopathic substances capable of inhibiting the growth of cotton by interfering with membranes of root cells, disrupting water status, and affecting photosynthesis.