Shade avoidance syndrome in Rottboellia exaltata and Leptochloa filiformis (Gramineae-Poaceae)

Shade effects among and within weed and crop plants is an important part of integral control practices. To study shade quality (wave length) and quantity (Photon flux density, PFD 400-700 nm) effects on two noxious weeds in sugarcane (Saccharum spp hybrid) crops, plants in groups of ten, were grown in pots containing soil shaded by cabinets covered with red, blue and green cellophane paper and under a low PFD neutral shade while another group of plants was left uncovered. Cabinets were directly exposed to davlielt. Previous to the experiment, cellophane paper samples were scanned. Tramittance (A = -log T) from 380 to 800 nm using a spectrophotometer. Treatment effects were compared separately for each species (Kruskal-Wallis non-parametric test) when plants in any of the groups showed visual symptoms of deterioration. Results showed different shade avoidance strategies in biomass production, tillering, leaf area, plant height and flowering revealing different capacity of acclimation to shade in these two species. L. filiformis, was more sensitive to shade, thus it may be controlled by canopy closure. R. exaltata showed a higher shade avoidance response rendering it capable of competing for a longer time with the sugarcane crop under cultivation.