DROUGHT STRESS Comparison of osmotic adjustment, leaf proline concentration, canopy temperature and root depth for yield of juncea canola under terminal drought B. R. Pandey 1 | W. A. Burton 2 | P. A. Salisbury 1,3 | M. E. Nicolas 1 1 Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Melbourne, Vic., Australia 2 Grains Innovation Park, Seednet Australia, Horsham, Vic., Australia 3 Centre of AgriBioscience, Agribio, Department of Economic Development, Jobs, Transport and Resources, Bundoora, Vic., Australia Correspondence B. R. Pandey, Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Melbourne, Vic., Australia. Email: babu.pandey@ecodev.vic.gov.au Funding information Australian Commonwealth Government; Australian Government Research Training Program Scholarship Abstract Two glasshouse and two field experiments were conducted in 2013 and 2014 to compare the relative importance of four physiological traits: osmotic adjustment (OA), leaf proline concentration, canopy temperature depression (CTD) and root depth on drought performance of canola quality B. juncea (juncea canola). Glass- house experiments were conducted at The University of Melbourne, Parkville, and field experiments were conducted at Horsham, Victoria. The experiments used jun- cea canola hybrids and their parental lines and were laid out in a randomised com- plete block design with three replications. The glasshouse experiments consisted of two treatments, well watered and water deficit from first open flower to maturity, whereas the field experiments were sown at a site that received 266 mm annual rainfall in 2014. In the glasshouse, canopy temperature depression was the only trait to show a positive and consistent association with drought performance of juncea canola. Cooler canopy temperature was also associated with improved yield in field experiments. Root depth was positively correlated with CTD in 2014 in glasshouse, whereas no correlation of root depth with OA and leaf proline was observed. The results indicated that CTD was the only reliable trait among those tested to screen juncea canola for drought tolerance. Root depth of juncea canola hybrids was a constitutive trait and probably was a result of hybrid vigour. KEYWORDS canopy temperature, juncea canola, osmotic adjustment, root depth, terminal drought 1 | INTRODUCTION Brassica oilseeds are likely to face drier and hotter growing environ- ments in future with changing climate (Torrey, 2007; Watkins, 2008). Brassica juncea could expand the options for Brassica oilseeds in the low rainfall cereal belt of southern Australia. Canola quality Brassica juncea (juncea canola) is being bred for low rainfall environ- ments of southern Australia that are not suitable for cropping B. na- pus. As the current open-pollinated cultivars of juncea canola need yield improvement (Gan, Malhi, Brandt, Katepa-Mupondwa, & Kutcher, 2007; Gunasekera, French, Martin, & Siddique, 2009), hybrid cultivars of juncea canola are being developed and tested in Australia to improve yield potential of the crop. Inconsistent and unpredictable environmental conditions cause difficulty in direct selection for yield in southern Australia. Selections based on physiological traits can improve efficiency of breeding pro- grammes for yield improvement (Araus, 1996; Reynolds, Hays, & Chapman, 2010; Richards, 1996; Slafer & Araus, 1998). Physiological traits have been shown to improve drought performance (as mea- sured by relative biomass, yield, or other traits under drought stress compared with well-watered conditions) of cereals and other crops. For example, increased osmotic adjustment in wheat (Morgan, 1991, 2000), reduced anthesis–silking interval in maize (B€ anziger, Setimela, Hodson, & Vivek, 2006; Bruce, Edmeades, & Barker, 2002), stay- green in sorghum (Borrell, Hammer, & Henzell, 2000; Rosenow, Quisenberry, Wendt, & Clark, 1983) and deeper rooting in rice Accepted: 6 February 2017 DOI: 10.1111/jac.12207 J Agro Crop Sci. 2017;1–9. wileyonlinelibrary.com/journal/jac © 2017 Blackwell Verlag GmbH | 1