FRUITING EFFICIENCY IN 3 BREAD WHEAT (TRITICUM-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 t he genetic improvement for obtaining higher grain yield of wheat. We h ave studied under field conditions the number of fertile florets and g rains per spike and individual grain weight of three bread wheat culti vars (Klein Favorito, Eureka FCS and Buck Pucara) which were previousl y selected to represent cultivars released at different eras (1920, 19 40 and 1980, respectively) in Argentina (SLAFER and ANDRADE 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 m ain shoot and tiller spikes. The number of fertile florets at anthesis was greater in the modern cultivar than in the other two cultivars; h owever, the intermediate and old cultivars did not significantly diffe r in this trait. Differences in number of florets and number of grains spike-1 were independent of the number of spikelets spike-1; spikelet numbers did not vary among the three cultivars. Therefore, both the n umber of fertile florets produced per spikelet and the ability of the cultivar to set grains in those florets were responsible for the diffe rent number of grains spike-1 among cultivars. The modern, high yieldi ng cultivar had a lower individual grain weight than the old, low yiel ding cultivar when the average of all grains were considered; but basa l 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 gra ins, and (ii) that the lower individual grain weight of the modern cul tivars does not imply an increased competition for resources as a cons equence of their higher number of grains.