Seed number as a function of growth. A comparative study in soybean, sunflower, and maize

Seed number, the main yield component of cereals and oil-seed species, stro ngly depends on the physiological status of the crop during a critical peri od for seed set. Using a comparative approach including three species with contrasting reproductive strategies, we investigated the relationship betwe en seed number per plant (SNP) and plant growth rate during the critical pe riod for seed set (PGR(C)). Indeterminate soybean [Glycine mar (L.) Merr.], sunflower (Helianthus annuus L.), and maize (Zea mays L.) crops were grown under a wide range of plant densities to generate contrasting availability of resources per plant. Growth of individual plants was estimated by a nov el, nondestructive method based on relationships between actual shoot dry m atter and morphometric variables, including stem diameter, plant height, an d dimensions of reproductive structures. Seed number per plant ranged from 0 to 890 in soybean, 0 to 4096 in sunflower, and 0 to 1348 in maize and PGR (C) (g d(-1)) from 0.01 to 4.3 in soybean, 0.3 to 17.6 in sunflower, and 0. 4 to 12.3 in maize. Our study showed that (i) the relationship between SNP and PGR(C) was linear in soybean, reflecting the reproductive plasticity of this species, and curvilinear in sunflower and maize, reflecting morphogen etic restrictions to generate reproductive sinks under favorable growing co nditions; (ii) the PGR(C) threshold below which no seed was set varied amon g species, being negligible in soybean, close to 0.35 g d(-1) in sunflower, and I g d(-1) in maize. Quantitative relationships between seed number and plant growth rate during the critical period of seed set could be useful f or crop modeling.