Path Analysis of Root/Shoot Traits and Grain Yield in Winter Wheat in Texas Wintergarden and High Plains.

Knowledge of interrelationships between crop root/shoot traits and grain yield will help improve crop breeding through the appropriate selection of crop growth indicators. In winter wheat (Triticum aestivum L.), what root/shoot characters influence high grain yield under stressed conditions is still unclear.  We tested ten wheat varieties in 2016, namely ‘Duster’, ‘Fannin’, ‘Fuller’, ‘Gallagher’, ‘TAM 112’, ‘TAM 114’, ‘TAM 304’, ‘TAM 305’, ‘TAM 401’, and ‘WB Cedar’. Testing was done under two irrigation regimes, full irrigation (100% of crop evapotranspiration) and deficit irrigation (60% of crop evapotranspiration) to identify the interrelationships between root/shoot traits and crop yield in two semi-arid regions of Texas- Uvalde (Wintergarden) and Amarillo (High Plain). Three combined trait indicators, specific flag leaf area (SLA), specific root length (SRL) and root/shoot ratio (RS) were chosen to represent above- and below-ground characters. Multiple linear regression and path analysis were used to analyze the relationships of SLA, SRL, and RS with grain yield.  Then bootstrap analysis (1000 samples) was used to test the significance. Multiple regression analysis showed that only RS was significantly related to grain yield, with a negative effect under full and positive effect under deficit irrigation. Path analysis also showed that RS had more negative direct effects on grain yield than did SLA and SRL under full irrigation, which was further verified by bootstrap analysis that the relation between RS and grain yield was significant (P < 0.05). Under deficit irrigation, however, RS had the highest (P < 0.05) direct and positive effect on grain yield among the three characters tested. Though SRL did not have a significant direct effect on grain yield (P > 0.05), it had a significant (P < 0.01) negative indirect effect through RS on grain yield, which was not identified by multiple regression. This study showed that low SRL and high RS could be used as physiological markers to aid in selection of drought-resistant wheat varieties in the Wintergarden area. Analysis of data from Amarillo is in progress.