Drought resistance in ryegrass involves morphological plasticity–osmotic adjustment interplay

Weerarathne LVY1, Dong W2, Nie M2, Wang Y2, Lopez I1 and Matthew C1

  1. School of Agriculture and Environment, Massey University, PB 11-222, Palmerston North, New Zealand 4442.
  2. Ningxia University, 489 Helanshan West Rd, Yinchuan, Ningxia Hui Autonomous Region, China 750021.

Recent Massey University research into improving water-use efficiency (WUE)-assisted drought resistance in commercial perennial ryegrass varieties is outlined. Two clonal replicates of 220 genotypes of three market-leading cultivars were evaluated to identify elite genotypes possessing high WUE (g DM/g H2O used). Plants aged two months, after root system development in soil at near field capacity, were grown on for a month under strong moisture deficit, and then water relations traits were measured, including: dry matter yield (DM, g), pot water use per gram of DM (WU, g/g), leaf water potential (LWP, bars), leaf osmotic potential (LOP, bars), leaf relative water content (RWC, %), relative growth rate (RGR, g/g/day), root mass (for 4–20 cm and 20–50 cm soil depths), soil moisture content at 30–40 cm depth and, post-cutting regrowth score. Data were subjected to a principal component analysis (PCA) to evaluate trait associations of drought-response. For selected contrasting groups of genotypes chosen by PCA scores, WU ranged from 278±12 g/g (averaged for the best 25 genotypes) to 578±49 g/g (averaged for the least efficient 15 genotypes). The elite germplasm was characterized by more negative LOP (–24 bars) and higher RWC (67%) than for least efficient genotypes, under low LWP (–11 bars); indicative of osmotic adjustment (OA). In this experiment, plants demonstrating high RGR in soil near field capacity, also formed comparatively high below ground root mass, which, coupled with turgor maintenance by OA, enhanced water acquisition as the drought resistance strategy in the elite perennial ryegrass genotypes. Key words: perennial ryegrass, WUE, OP, RGR.