Fruiting Efficiency in three Bread Wheat (Tritkum aestivum) Cultivars Released at Different Eras. Number of Grains per Spike and Grain Weight

Increasing sink size (i.e. number of grains m^?2) has been the way of the genetic improvement for obtaining higher grain yield of wheat. We have studied under field conditions the number of fertile florets and grains per spike and individual grain weight of three bread wheat cultivars ( Klein Favorito, Eureka FCS and Buck Pucara ) which were previously selected to represent cultivars released at different eras (1920, 1940 and 1980, respectively) in Argentina (S lafer and A ndrade 1989).
The three cultivars Buck Pucara, Eureke FCS , and Klein Favorito averaged 56.9, 48, and 34.5 grains spike^?1. Differences were observed in both main shoot and tiller spikes. The number of fertile florets at anthesis was greater in the modern cultivar than in the other two cultivars; however, the intermediate and old cultivars did not significantly differ in this trait. Differences in number of florets and number of grains spike were independent of the number of spikelets spike^?1; spikelet numbers did not vary among the three cultivars. Therefore, both the number of fertile florets produced per spikelet and the ability of the cultivar to set grains in those florets were responsible for the different number of grains spike^?1 among cultivars. The modern, high yielding cultivar had a lower individual grain weight than the old, low yielding cultivar when the average of all grains were considered; but basal grains of its central spikelets were as heavy as those of the other cultivars.
We suggest (i) that the modern cultivars of Argentina have increased their ability both to produce fertile florets and to set grains, and (ii) that the lower individual grain weight of the modern cultivars does not imply an increased competition for resources as a consequence of their higher number of grains.