Mainstem leaf stage and its relation to single plant grain yield in spring wheat

Mainstem leaf stage (MLS), determined with the Haun scale, has been used to indicate plant development in small grain crops, but it is not clear whether MLS can be used to predict final grain yield. A field study was conducted on a Neuhorst clay loam (fine-loamy, frigid, Aquic Haploboroll) at Portage la Prairie, MB, Canada, in 1990 and 1991, to determine the relationship between MLS and single plant grain yields within a canopy of spring wheat (Triticum aestivum L.). Plants were grown with small (2.2-2.4 mm wide), large (3.0-3.2 mm wide), and mixed (>2.2 but <3.2 mm wide) seed sizes. The MLS was determined 2, 3, 4, and 5 wk after initial seedling emergence (the date of the first seedling emergence in a plot), and grain yields were determined at maturity, on a single plant basis. Seed size had a significant effect on MLS only during the early seedling stages; plants grown from large seeds had greater MLS and lower plant-to-plant variation in MLS than those from small or mixed seed sizes. Within a canopy, early-emerging plants had greater MLS and were more uniform than late-emerging plants. Plant grain yields linearly responded to the MLS determined 2, 3, and 4 wk after seedling emergence. The MLS determined 230 degree-days from planting most accurately reflected final grain yield. With the Haun scale, MLS measured 2 to 4 wk after seedling emergence can be used to predict single plant grain yield in hard red spring wheat.