Quantifying rooting at depth in a wheat doubled haploid population with introgression from wild emmer (PhD)

Abstract

Wheat root systems may not be optimal for the acquisition of subsoil water, due to excessive root growth in surface layers and inadequate soil exploration at depth. The aim of this project was to study the phenotypic and genetic diversity of rooting at depth within the wheat doubled haploid population of Shamrock x Shango. Shamrock has recent introgression from wild emmer (Triticum dicoccoides) and exhibits a non-glaucous trait mapped to the short arm of chromosome 2B (2BS). The population was genotyped using the Wheat Breeder’s 35k Array, and a linkage map produced to facilitate study of the association of rooting and wild emmer introgression. Rooting in doubled haploid lines was measured in the field (below 50 cm), at and shortly after anthesis, in addition to canopy traits of photosynthetic capacity, spectral reflectance indices and canopy temperature. Root traits of field-grown plants were compared to lines grown in a seedling screen and within rhizotrons to the end of tillering.

Shamrock had greater root length density (RLD) than Shango at depth in the field and within the rhizotrons. The DH population exhibited diversity for rooting traits within the three environments studied. QTL were identified on 5D, 6B and 7B, explaining variation in RLD post-anthesis in the field. Effects associated with the non-glaucous trait on RLD interacted significantly with depth in the field and some of this interaction mapped to 2BS. The effect of genotype interacted greatly with the context of root assessment: e.g. glaucousness expressed in the field was negatively associated with RLD in the rhizotrons, but positively associated with length in the seedling screen.

Non-glaucous lines yielded more than glaucous lines, associated with a stay green trait inherited from wild emmer. RLD in the field at anthesis had a significant negative association with canopy temperature. Significant relationships were found for spectral reflectance indices measured at ear emergence and rooting at depth. However, these relationships were dependent on the glaucousness of the canopy.

Wheat root systems may not be optimal for the acquisition of subsoil water, due to excessive root growth in surface layers and inadequate soil exploration at depth. The aim of this project was to study the phenotypic and genetic diversity of rooting at depth within the wheat doubled haploid population of Shamrock x Shango. Shamrock has recent introgression from wild emmer (Triticum dicoccoides) and exhibits a non-glaucous trait mapped to the short arm of chromosome 2B (2BS). The population was genotyped using the Wheat Breeder’s 35k Array, and a linkage map produced to facilitate study of the association of rooting and wild emmer introgression. Rooting in doubled haploid lines was measured in the field (below 50 cm), at and shortly after anthesis, in addition to canopy traits of photosynthetic capacity, spectral reflectance indices and canopy temperature. Root traits of field-grown plants were compared to lines grown in a seedling screen and within rhizotrons to the end of tillering.

Shamrock had greater root length density (RLD) than Shango at depth in the field and within the rhizotrons. The DH population exhibited diversity for rooting traits within the three environments studied. QTL were identified on 5D, 6B and 7B, explaining variation in RLD post-anthesis in the field. Effects associated with the non-glaucous trait on RLD interacted significantly with depth in the field and some of this interaction mapped to 2BS. The effect of genotype interacted greatly with the context of root assessment: e.g. glaucousness expressed in the field was negatively associated with RLD in the rhizotrons, but positively associated with length in the seedling screen.

Non-glaucous lines yielded more than glaucous lines, associated with a stay green trait inherited from wild emmer. RLD in the field at anthesis had a significant negative association with canopy temperature. Significant relationships were found for spectral reflectance indices measured at ear emergence and rooting at depth. However, these relationships were dependent on the glaucousness of the canopy.