Early Season Drought Largely Reduces Grain Yield in Wheat Cultivars with Smaller Root Systems

Abstract

In the Australian grainbelt, early winter rainfall has declined during the last 30 years, and farmers sow their crops dry, increasing the risk of early season drought. This study aimed to examine whether differences in the root systems were associated with tolerance to early season drought. Three wheat cultivars with different root systems were grown in 1 m columns in a glasshouse. Immediately after sowing in dry soil, 440 mL water (equivalent to 25 mm rainfall) was supplied to each column, and no water was added to induce the early-season drought for the next 30 days. Shoot and root traits were measured at the end of the early season drought, anthesis and at maturity, respectively. The restricted water supply reduced Ψleaf, stomatal conductance, leaf photosynthetic rate, shoot and root biomass. Early season drought delayed phenology in all cultivars, but there was recovery of root and shoot biomass at anthesis in all three cultivars. Leaf area and shoot biomass at anthesis in Bahatans-87 (large root system) recovered better than Tincurrin (small root system). At maturity, early season drought reduced grain yield more in Tincurrin than Bahatans-87. The slow phenology of Bahatans-87 allowed greater recovery after the drought in leaf area and shoot biomass, which may explain the smaller reduction in grain yield after early season drought.

Wheat Cultivars With Contrasting Root System Size Responded Differently to Terminal Drought

“…Terminal drought reduced grain yield in both cultivars, with the differences reflected in phenological development. Bahatans-87 had slower phenological development allowing root and shoot growth to continue for longer ( Figueroa-Bustos et al, 2019 ). Early flowering allows grain filling to be completed before the onset of severe water stress ( Shavrukov et al, 2017 ).…”

“…Breeding programs for improving wheat grain yield in dry environments and dry seasons have mainly focused on improving tolerance to terminal drought ( Siddique et al, 1990a ; Asseng and van Herwaarden, 2003 ; Golabadi et al, 2010 ; Senapati et al, 2018 ) by selecting for early vigor and early flowering to minimize frost damage and escape the effects of terminal drought ( Perry and D’Antuono, 1989 ; Rebetzke and Richards, 1999 ; Richards et al, 2014 ). This advantage seems to diminish when cultivars selected for early anthesis experience early season drought, which main effect is to delays phenology, particularly time to anthesis ( Figueroa-Bustos et al, 2019 ). With the slow onset of climate change, early winter rainfall in the Mediterranean-type climate of Australia has been decreasing; as a result, more than 82% of wheat growers are dry sowing their crops ( Fletcher et al, 2015 ).…”

“…The pots (0.15 m diameter and 1.0 m deep) contained 26 kg of soil (volume 0.01766 m3). Several studies have reported that the above volume of soil and particularly depth (1 m) did not show root development restrictions in wheat ( Aziz et al, 2016 ; Saradadevi et al, 2017 ; Figueroa-Bustos et al, 2019 ; Pooniya et al, 2019 ). In addition, Turner (2018) suggested that large tall pots better simulate water extraction and root development similar to field conditions than smaller pots.…”

“…Cultivars with larger root systems had greater grain yield than cultivars with smaller root systems in rain-fed experiments in Central Europe ( Motzo et al, 1993 ; Středa et al, 2012 ). Early season drought reduced grain yield less in Bahatans-87 (larger root system size) than Tincurrin (smaller root system size) due to slow phenology that allows better recovery in leaf area and shoot biomass at anthesis ( Figueroa-Bustos et al, 2019 ). However, it is not clear whether a strategy of higher water use (higher biomass production and transpiration rate) of the cultivar with larger root system size or the saving water strategy (lower water use combined with a lower leaf area) of cultivar with smaller root system size are superior under terminal drought.…”

Does plant root architecture respond to potassium nutrition under water stress? A case from rice seedling root responses

“…Treatments water productivity (mg/ml) was estimated as total dry weight of seedling (mg) divided by total water applied (ml) during the experimentation. Indirectly root thickness was estimated by specific root length (SRL)(m/g) as root depth divided by root dry weight 20 .…”