YIELD POTENTIAL IN MODEM WHEAT-VARIETIES - ITS ASSOCIATION WITH A LESS COMPETITIVE IDEOTYPE

Field experiments were conducted with modern semidwarf spring wheat cu ltivars representing a range of yield potential in order to compare th eir adaptation to levels of interplant competition for resources. Leve ls of competition were altered, in both leaf canopy and underground, b y manipulating rows of plants in eight-row yield plots. Competition fo r light was decreased by bending adjacent rows away from the central t wo rows thus permitting greater penetration of light to lower leaves o f the central rows (light treatment). Reduced competition underground was realized, simultaneously with reduced competition for light, by up rooting the plants adjacent to the central two rows (root/light treatm ent). These treatments were implemented at the developmental stage of flag-leaf ligule emergence (FLLE), when interplant competition was ass umed to become maximal. While the average yield responses were 25%, an d 40% to the light and root/light treatments respectively, there was a significant interaction with genetic material. Low-yield-potential(LY P) lines responded more to reduced competition than high-yield-potenti al (HYP) lines suggesting that the greater efficiency of the HYP lines , reflected in their higher yield, is related to their better adaptati on to interplant competition. Physiological bases for improved perform ance are examined and discussed in relation to ideas about crop ideoty pes and possible implications to breeding. These data appear to suppor t the idea that genes conferring yield potential through improved adap tation to the crop environment are associated with a less competitive phenotype.