Barley Treated with Ethephon: III. Kernels per Spike and Kernel Mass

Treatment of barley ( Hordeum vulgare L.) with ethephon [2‐chloroethyl)phosphonic acid)] may reduce lodging and increase kernel mass, but reductions in kernel mass and kernels per spike also are often observed. This study examined the effect of ethephon on kernels per spike and kernel mass for spikes on specific shoots which appeared before or after ethephon application. Ethephon was applied at Zadoks growth stage (GS) 35 and/or 45 at 240 g ha −1 to ‘Argyle’ conventional height and ‘Samson’ semidwarf barley grown at 100 and 300 plants m −2 at Winnipeg, MB. Tillers were tagged as they emerged on 10 plants per plot, and kernels per spike and kernel mass were determined for each spike produced. The cultivars did not differ in their response to ethephon. Kernels per spike was reduced as much as 26% by ethephon application. Such reductions were attributed to both the promotion of late‐appearing shoots with relatively few kernels, and the abortion of florets on main stems and early appearing tillers, which may be due to ethephon's gametocidal properties. Kernel mass was reduced by up to 17%, not affected, and increased by up to 12% by ethephon in 1987, 1988, and 1989, respectively. Differences in competition between developing kernels and late tillers, in lodging, and in nitrogen availability may account for the variable kernel mass responses observed. Kernels per spike and/or kernel mass reductions generally resulted in decreased yield per plant, especially for barley grown at 300 plants m −2 , but such reductions were at least partially compensated by increased spikes per plant for barley grown at 100 plants m −2 in 1987 and 1989.