Field Root Biomass, Morphology And Nitrogen Use Efficiency Of Pavon 76 And Its Wheat-Rye (1RS) Translocations

Abstract

The need to curb increased pollution of environmental resources caused by excessive nitrogen (N) fertilizer application and N fertilizer use inefficiencies in wheat (Triticum aestivum) production systems warrants an inexpensive, sustainable, environmentally sound solution, the root system. Wheat germplasm containing the short arm of rye chromosome 1 (1RS) has recently been found to have larger root system sizes in pot experiments in addition to previously documented higher yields and resistance to leaf, stem and yellow rust. These 1RS lines could therefore be useful in wheat breeding efforts targeting superior root system traits for yield improvements as well as environmental and economic benefits. This dissertation evaluated field root biomass production of Pavon 76 and its wheat-rye (1RS) translocations, effects of root biomass on nitrogen use efficiency, and the temporal variation in their root morphological traits and early growth vigor. The translocation 1RS.1BL had 9 and 23 % higher total root biomass than Pavon 76 at jointing and physiological maturity respectively. Root N uptake peaked at the jointing, where it comprised 22-34% of the total plant N uptake and was lowest at physiological maturity for all genotypes. The inclusion of root N uptake reduced the N utilization efficiency and N harvest index by 6-14 and 7-15% respectively, indicating that the use of only the above ground plant parts over estimates these parameters. In pot experiments, the translocation 1RS .1AL had 12 and 39% higher root biomass than Pavon 76 at anthesis and maturity respectively. 1RS.1BL had 38% higher root mass and 16% longer roots than Pavon76 at physiological maturity. This suggests the existence of differences among the genotypes in below ground partitioning of assimilates at peak nutrient demand (anthesis) for grain filling, and also in rates of root decay and senescence. The lack of differences in root morphological traits among genotypes at early growth stages (6-46 days after sowing) indicates that there are minimal differences in early root growth vigor. The 1RS translocations could therefore expand the wheat breeder's tool box in selections for superior root traits for improved NUE without adverse effects on grain yield.