Comparative adaptation of canola (Brassica napus) and Indian mustard (B-juncea) to soil water deficits: Plant water relations and growth

The work reported in this paper was designed to describe how mustard achieves,greater dry matter production and yield compared to canola under water-deficit conditions. The work was based on three field experiments which each used at least three cultivars or lines of each species. Mustard leaves had greater turgor pressure than those of canola (up to 0.36 MPa greater). Mustard's growth advantage increased with increasing stress with total leaf area duration being longer (1.5 times) and crop growth rates greater (up to 2 times) than those of canola under high water deficits. These differences in growth were positively correlated with leaf turgor. Mustard also grew better under low water deficits particularly early in the season; these differences were associated with differences in early season leaf morphology (lower specific leaf weights) rather than with differences in the partitioning of assimilate to leaf growth. However, the early growth differences were also linked with differences in turgor, suggesting that mustard's turgor advantage at least partially explained its superior early vigour. It is concluded that the greater leaf turgor of mustard is a key factor in this crop's adaptive advantage under high water deficits, allowing it to maintain longer leaf area duration and thereby greater dry weight and seed yield compared to canola.