Root phenotypes of young wheat plants grown in controlled environments show inconsistent correlation with mature root traits in the field.

Sarah M Rich,Michelle Watt,Richard Richards,Jack Christopher,Ian Dodd

doi:10.1093/jxb/eraa201

Abstract

Using a field to lab approach, mature deep-rooting traits in wheat were correlated to root phenotypes measured on young plants from controlled conditions. Mature deep-rooting root traits of 20 wheat genotypes at maturity were established via coring in three field trials across 2 years. Field traits were correlated to phenotypes expressed by the 20 genotypes after growth in four commonly used lab screens: (i) soil tubes for root emergence, elongation, length, and branching at four ages to 34 days after sowing (DAS); (ii) paper pouches 7 DAS and (iii) agar chambers for primary root (PR) number and angles at 8 DAS; and (iv) soil baskets for PR and nodal root (NR) number and angle at 42 DAS. Correlations between lab and field root traits (r2=0.45-0.73) were highly inconsistent, with many traits uncorrelated and no one lab phenotype correlating similarly across three field experiments. Phenotypes most positively associated with deep field roots were: longest PR and NR axiles from the soil tube screen at 20 DAS; and narrow PR angle and wide NR angle from soil baskets at 42 DAS. Paper and agar PR angles were positively and significantly correlated to each other, but only wide outer PRs in the paper screen correlated positively to shallower field root traits. NR phenotypes in soil baskets were not predicted by PR phenotypes in any screen, suggesting independent developmental controls and value in measuring both root types in lab screens. Strong temporal and edaphic effects on mature root traits, and a lack of understanding of root trait changes during plant development, are major challenges in creating controlled-environment root screens for mature root traits in the field.

Highlights

Value and expression of root traits in the field at maturity in wheatRoot traits offer a largely untapped resource for improved yield in wheat
Wheat seedling root phenes inconsistently correlate to mature traits | 4753. Those emerging from foliar leaf nodes, termed leaf nodal roots (LNRs) or those arising from the coleoptile node just above the seed, termed coleoptile nodal roots (CNRs)
Root development progressed in a similar manner across genotypes, illustrated using photos of Indian line C306 in Fig. 3.The timing of root development varied slightly between genotypes; and generally the primary root (PR) had emerged at 13 days after sowing (DAS) (Fig. 3A) and CNRs developed between 13 and 20 DAS, during which all genotypes started to develop LNRs.The period between 20 and 34 DAS showed continued elongation of all root types and further initiation of LNRs (Figs 3, 5), with some genotypes having up to 25 LNRs by 34 DAS [genotypes with a mean higher than 20 LNRs were Gregory, COW(W)-1 and HS420]

Summary

Introduction

Value and expression of root traits in the field at maturity in wheatRoot traits offer a largely untapped resource for improved yield in wheat. Roots to depth in the field is possible (Wasson et al, 2014; Rich et al, 2016); it is constrained by the time wheat takes to reach maturity and the strong influence of the soil physical and chemical conditions on the mature root system phenotype (Manschadi et al, 2006; Wasson et al, 2012; Rich and Watt, 2013). Controlled-environment screens for traits such as deep rooting focus on seedling and young plant vegetative stage phenotypes, because beyond that point the roots are too large for most laboratory pots and glasshouse facilities.To inform our understanding of roots, seedling root phenotypes should be correlated with root architecture in later development stages and performance in the field, in spite of all these enviromental and developmental influences

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