PROGRESS IN OHIO SOFT RED WINTER-WHEAT BREEDING - GRAIN-YIELD AND AGRONOMIC TRAITS OF CULTIVARS RELEASED FROM 1871 TO 1987

Significant increases in worldwide wheat (Trilicum aestivum L.) grain yield (GY) over years have been due to the release of newer, genetical ly improved cultivars that are earlier maturing, shorter in stature, a nd more resistant to lodging. Some analyses of wheat GY trends have le d to conclusions that future genetic gains could be limited and that, in some cases, a GY plateau would soon be approached. Soft red winter wheat (SRWW) field trials, which included cultivars re leased from 187 1 to 1987, were conducted for 4 yr at Wooster, OH, USA. Trials were co nducted to document any changes in GY to determine if a yield plateau was being approached for Ohio SRWW. Grain test weight (GTW) and plant height (PH) measurements and time to heading (TTH) and lodging evaluat ions were made to determine if changes in these traits were associated with the development of newer cultivars. Linear regression of mean GY on cultivar years since release (YSR) over the four trial years, was significant. Linear regression on YSR accounted for 42% of the variati on of mean GY. Mean GY changed 15.5 kg ha(-1) yr(-1) as YSR decreased. Testing a nonlinear relationship for GY and YSR, indicated that a yie ld plateau was not being approached. There was no significant change f or mean GTW on YSR. Linear regressions for mean TTH, PH, and lodging o n YSR were significant. Linear regressions on YSR accounted for 78, 33 , and 27% of the variation in mean TTH, mean PH, and mean lodging, res pectively. Mean TTH changed -0.05 d yr(-1), mean PH changed -0.4 cm yr (-1), and mean lodging changed -0.7% yr(-1) as YSR decreased. Progress has been made in breeding Ohio SRWW cultivars that produce higher GY. The release of newer, higher yielding SRWW cultivars that are earlier -heading, shorter, and more resistant to lodging, has contributed to a mean GY increase, across Ohio, of approximately 2259 kg ha(-1) over a period spanning eight decades, 1910 to 1991.