The effects of root angle on root growth and yield of wheat in the Australian cereal belt

Abstract

Genetic variation in seminal root angle exists in wheat. It has been suggested that narrow root angles contribute to adaptation to summer–dominant rainfall zones and wide angles are important in the Mediterranean climates of southern Australia. This hypothesis was tested by measuring root angles in wheat and examining its relationship with yield and root distribution. Root angles of 52 genotypes, defined as the angle subtending the first pair of seminal roots of 14-day old seedlings, were measured in a root box. Field experiments were conducted in successive years to measure the depth and distribution of roots. The importance of root angle to yield over a wider range of sites was assessed by an analysis of yield variation among the 52 varieties in 12 years of breeding trials. Root angle varied significantly from 56° to 113° and there was no consistent difference between genotypes from South Australia (mean ± SEM = 82 ± 2.9°) and Queensland (82 ± 5.4°); genotypes from Western Australia had a slightly wider angle (90 ± 2.2°). In the two field trials, maximum depth of rooting did not differ significantly among the genotypes. Narrow root angle was weakly associated with more roots at 60 to 70 cm, but there was no relationship with yield. Within breeding trials, varieties with narrow root angles tended to produce slightly higher (c. 5%) yields, but this occurred in all states. The hypothesis that root angle is associated with adaptation to different parts of the cereal zone was not supported.