Abstract

It is thought that the man xylem vessel in the seminal roots of wheat crop will regulate crop water use if water is available in the subsoil but the top soil is dry. This should result in more water being used after anthesis, and a higher harvest index and yield. A backcross breeding program using two Australian commercial wheat varieties is described that reduced their xylem vessel diameter from about 65 8m to less than 55 8m. In field trials conducted on fallow land in eastern Australia over five years, comparing selections with narrow xylem vessels against unselected controls, narrow vessel selections yielded between 3 and 11% more than the unselected controls, depending upon their genetic background, in the driest environments. Yield differences in the wetter environments were largely not significant. This yield increase in the narrow vessel selections was associated with a significantly higher harvest index, also higher biomass at maturity and kernel number.