Better tree performance and water use efficiency through resilient root systems: rapid screening for drought and salinity stress tolerance using relative growth rate

Abstract

Abiotic stresses, such as soil water deficit and high soil solution salts, can lead to negative impacts on crop growth, productivity and quality, impacting industry profitability. The first contact of the tree with these stresses is the root system, providing the possibility of improving tree resilience by rootstock choice. Identifying almond rootstock genotypes with high stress tolerance is, consequently, of high importance in enabling the Australian almond industry to cope with these environmental challenges. This study developed and tested a potential tool to screen genotypes for tolerance to abiotic stresses, using the response of relative growth rate (RGR) to water deficit or salinity stress. Seedling plants of six almond rootstock cultivars were randomly allocated into three treatments (control, drought or salinity stress) for two months in a glasshouse. Plants in the well-watered treatment were irrigated to the point of run-off daily. The drought treatment was imposed by adding 33% of evapotranspiration of well-watered plants daily. Plants in the salinity treatment were supplied with mixed chloride solution (3.3 dS m-1) to the point of run-off daily. Plants were harvested at three time points to calculate RGR. The percentage of RGR reduction in stressed plants, relative to the non-stressed plants, was calculated and used as an index of stress tolerance. Considerable variation for stress tolerance was found among the six almond rootstock genotypes, with some genotypes being able to maintain growth rates - whereas others stopped growing - under drought or salinity stress. The impacts of the drought treatment used were generally larger than those of salinity stress. The screening approach introduced in this study provides a relatively simple and robust method to compare rootstock genotypes, contributing to horticultural management decisions, whilst also being applicable to the generation of fundamental knowledge in this area.