Exploring root traits associated with increased yield under water deficit in perennial ryegrass (Lolium perenne L.) germplasm of Mediterranean and European origins.

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Exploring root traits associated with increased yield under water deficit in perennial ryegrass (Lolium perenne L.) germplasm of Mediterranean and European origins Sajjad Hussain1, Cory Matthew2, Muhammad Naeem3, H. Sydney Easton4 1Plant Genetic Resources Institute, National Agricultural Research Center, Islamabad, Pakistan, 2Institute of Agriculture and Environment, Massey University, Palmerston North, New Zealand, 3Federal Seed Certification and Registration Department, Islamabad, Pakistan, 4AgResearch, Palmerston North, New Zealand. Contact: shmalik25@hotmail.com Introduction Perennial ryegrass (Lolium perenne L.) is now one of the most widely used forage grass species in temperate pastoral agriculture and in recent years breeding for improved performance in summer drought conditions has become a focus. Germplasm of Spanish origin has been widely used in New Zealand plant breeding (Stewart, 2006), but another possibility that has attracted comparatively little research to date is introgression of summer dormant germplasm of North African origin with material of European origin. Methods Plants of a New Zealand-bred perennial ryegrass cultivar “Grasslands Samson”, a summer dormant Australian cultivar “Medea” developed in the 1960’s from germplasm of Mediterranean origin (Silsbury, 1961), and the F1 and F2 progenies of the two parents were compared during summer 2010-11 in a glasshouse study at Palmerston North, New Zealand. The experiment compared rooting behavior and herbage yield of the two cultivars and studied the pattern of inheritance of those traits to F1 and F2 progeny. Plants grown in 100 cm lengths of soil-filled PVC pipes were initially bottom-watered in 200 liter drums and then drought was imposed by gradually lowering the water table until plants survived on water retained in the soil profile. At a concluding destructive harvest, herbage yield (DW) and tiller number (TN) were recorded, while total root mass (Rt), coarse root mass (Rc) fine root mass (Rf) and gravimetric soil moisture % (SMC) were all measured for three soil depths (0-30, 30-60 and below 60 cm). From these data root:shoot ratio (R:S), deep root (below 30 cm): shoot ratio (DR:S), an index of deep rooting (% total root below 30 cm, IDR), and DW/(0.2 – SMC) as an index of efficient water use (IEWU) were derived. Results and Discussion Medea exhibited deep rooting compared to Grasslands Samson indicated by higher R:S, DR:S and IDR, that had never been studied since its release in Australia. However, it had lower IWU, 83% lower DW and 87% lower TN than Grasslands Samson – a characteristic of Mediterranean origin pasture species. On the question of introgressing root traits of Medea to Grasslands Samson: in the F1 generation, some plants surpassed Medea for some root traits (eg DR:S and IDR), while F2 plants were similar to Grasslands Samson parents, However, within Grasslands Samson itself some plants showed high IEWU. Conclusion Introgression of Medea genes into Grasslands Samson will not be straight forward. However, direct selection for maintenance of growth under moderate water deficit with reduced soil moisture extraction per unit DW is an immediate option for improving drought tolerance in perennial ryegrass, providing the trait proves sufficiently heritable. Stewart AV (2006) Genetic origins of perennial ryegrass (Lolium perenne) for New Zealand Pastures. Pp11-20 In: Breeding for success: diversity in action, (ed, CF. Mercer) Proceedings of the 13th Australasian Plant Breeding Conference, Christchurch, NZ. Silsbury JH (1961) A study of dormancy, survival and other characteristics in Lolium perenne L. at Adelaide, SA. Aust. J. Ag. Res.12:1-9.