A study of grain filling in barley

Abstract

Two field experiments were conducted during the years 1980-81 and 1981-82 to investigate the effect of carpel weight at anthesis on potential grain weight of barley (Hordeum vulgare L.). In the first experiment three high yielding spring barley cultivars of contrasting grain size, namely Ark Royal, Kaniere and Manapou were grown at 400 and 800 seeds m² with row spacings of 15 and 7.5 cm. Ark Royal was thinned at anthesis by removing alternate rows to investigate the influence of post-anthesis source strength on final grain size.

In the second experiment crops of Ark Royal and Kaniere were shaded to 50% of full sunlight at Zadok's growth stage 43 in an attempt to decrease the carpel size at anthesis. To try to increase carpel size on the mainshoot ears, some plants had all their tillers removed at Zadok's growth stage 24. The supply of assimilate was enhanced by plant thinning at anthesis to examine the post-anthesis source limitation in final grain size. The dry weight of carpels or grains from node 8 on the mainstem ears was measured regularly from shortly before all-thesis until maturity of the crops.

From 6-9 days after anthesis, the grains grew at a constant rate for about 23-30 days. The grains of large-grained cultivar had a faster rate of dry matter accumulation during linear phase than in small-grained ones but there was no difference in the duration of the linear phase. The cultivars were different in the rate of grain growth during the linear phase. The other treatments had no significant effect on grain growth rate during linear phase in any experiments although a decreasing trend was associated by shading in the second experiment. There was a highly significant positive correlation between the rate of grain growth and final grain weight in both experiments.

The large-grained cultivar produced the heavier carpel and final grain weight. Planting density and row spacing had no effect on either carpel weight or final grain weight.

In the second experiment, shading decreased and detillering increased both carpel dry weight at anthesis and final grain weight. Thinning had no effect on either the rate of grain growth or final grain weight in any experiment. There were highly significant positive correlations between carpel dry weight at anthesis and final grain weight and between husk weight and final caryopsis weight in both experiments.

For 6-9 days after anthesis the grains grew exponentially. The cultivars did not differ for relative grain growth rates, although they did so in caryopsis weights in the post-anthesis exponential phase. In the second experiment, the pre-anthesis treatments did not produce differences in relative grain growth rate but they did so for carpel dry weight at anthesis.

Before anthesis, the carpels grew exponentially. The treatments produced differences in carpel dry weight at the initial measurements and these differences were maintained until anthesis, rate of grain growth during the linear phase and final grain weight.

These results suggest that within the limitations of the present study there was an adequate supply of assimilate during the grain filling period and that final grain weight was already determined by some factors operative before anthesis. These factors caused differences in carpel dry weight at anthesis; carpel dry weight was significantly correlated with final grain weight.