Crop floret number per unit area and, to a lesser extent grain set, are the determinants of yield that are associated with the increase in sunflower oil yield at crop densities greater than the most frequently used in Argentina of 3–5.1 pl.m⁻². A better understanding of the responses of these two yield determinants to crop density and their intra-specific variability could contribute to the development of higher yielding cultivars suited to higher crop densities. In an initial experiment, we measured the aboveground biomass partitioning to leaves and stems between emergence and the end of floret differentiation, the weight and length of the basal internodes whose growth overlapped with the floret differentiation phase, plant height at the star visible (R1) and anthesis (R5.5) stages, and florets per plant in response to crop density across a 0.7–14.3 pl.m⁻² range. In Exps. 2 and 3, designed to explore intra-specific variability for responses to crop density we measured, in five hybrids, the last four variables plus oil yield in crops grown at 5.1, 10.2 and 14.3 pl.m⁻². Lastly, in Exp. 4, we measured the responses of the basal internode of four of the hybrids used in Exps. 2 and 3 to three levels of red/far red ratio (R/FR) in the light incident on spaced plants. Plant height at the R1 stage and above-ground biomass partitioning to the stem increased significantly with crop density, contrasting with a fall in floret number per plant in Exp. 1. The length and weight of the fourth internode, the internode whose growth period overlapped the most with the floret differentiation phase, increased with crop density, while floret number per plant showed a significant decrease with increasing weight of the fourth internode. The hybrids examined in Exps. 2 and 3 exhibited intraspecific variability in their responses to crop density for plant height at R1 stage, fourth internode length, floret number per plant, in the relationships between floret number per plant with fourth internode length and plant height at R1 stage, and in oil yield. The length of the first internode of the four hybrids examined in Exp. 4 increased consistently with reductions in the R/FR ratio of the light incident on the plants, suggesting that perception of the R/FR ratio by phytochrome may play an important part in the responses of floret number per plant to crop density and its intraspecific variability. The lack of association in some hybrids of the responses of floret number and oil yield per square meter to crop density showed that grain set and unit grain weight are additional yield determinants that require attention when considering intraspecific variability in yield responses to high density.

每单位面积的作物小花数，在较小程度上，谷物集是产量的决定因素，当作物密度大于阿根廷最常用的 3–5.1 pl.m ^{-2 时，}与葵花籽油产量增加相关. 更好地了解这两个产量决定因素对作物密度的响应及其种内变异可能有助于开发适合更高作物密度的高产栽培品种。在最初的实验中，我们测量了在出现和小花分化结束之间分配给叶和茎的地上生物量、生长与小花分化阶段重叠的基部节间的重量和长度、可见星处的植物高度 (R1)和开花 (R5.5) 阶段，以及每株植物的小花以响应 0.7-14.3 pl.m ^{-2 的}作物密度范围。在 Exps. 2 和 3，旨在探索对我们测量的作物密度响应的种内变异性，在五个杂交种中，最后四个变量加上以 5.1、10.2 和 14.3 pl.m ^-2生长的作物的油产量. 最后，在Exp。4，我们测量了实验中使用的四个杂种的基底节间的响应。2 和 3 到三个水平的红色/远红色比 (R/FR) 在入射到间隔植物上的光中。R1 阶段的株高和地上生物量分配到茎的比例随着作物密度显着增加，与实验中每株植物的小花数下降形成对比。1.第4节间的长度和重量，即生育期与小花分化期重叠最多的节间，随着作物密度的增加而增加，而单株小花数随着第4节间重量的增加而显着降低。在 Exps 中检查的杂种。2 和 3 在 R1 阶段的株高、第四节间长度、每株小花数、R1期单株小花数与第四节间长度与株高的关系，与油产量的关系。实验中检查的四个杂种的第一个节间的长度。4 随着入射到植物上的光的 R/FR 比率的降低而持续增加，表明光敏色素对 R/FR 比率的感知可能在每株植物的小花数对作物密度及其种内变异性的响应中起重要作用. 在一些杂种中，小花数量和每平方米油料产量对作物密度的响应缺乏关联，这表明粒数和单位粒重是额外的产量决定因素，在考虑对高密度的产量响应的种内变异性时需要注意。