1. Sajjad Hussain1, Cory Matthew2, Muhammad Naeem3, H. Sydney Easton4
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:
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.
Results:
Medea exhibited deep rooting compared to Grasslands Samson indicated by higher R:S, DR:S and IDR. However, it had lower IWU, 83% lower DW and 87% lower TN than Grasslands Samson – a characteristic of Mediterranean origin pasture species (Volaire and Norton, 2006).
Table: ANOVA p values and mean values for traits of root and shoot growth for two perennial ryegrass cultivars (Grasslands Samson, & Medea), and their F1 and F2 generations
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 (Fig. 2).
Figure 2: Five individual G. Sampson plants (circled) achieved high plant dry weight (DW) under water deficit stress (STR) without severe soil moisture depletion. Plants with these traits merit further investigation.
Variable
G. Samson
Medea F1 F2
P value TN
193.0
37.26
144.58
140.44
<0.001 DW
18.04
2.27
9.57
10.32
Rt (g)
2.92
0.83
3.29
2.93
Rt cm (g)
2.57
0.65
1.76
Rt cm (g)
0.29
0.10
1.44
0.26
Rc-below 60
0.06
0.07 ns
Rc cm (g)
2.05
0.53
1.34
2.04
0.002
Rc cm (g)
0.19
0.02
0.17
0.004
0.005
0.01
Rf cm (g)
0.56
0.15
0.42
Rf cm (g)
0.09
0.08
0.1
Rf-below 60
0.05
R:S
0.16
0.54
0.39
DR:S
0.03
IDR
0.13
0.47
IEWU
247.37
38.55
150.88
155.19
SMC cm
SMC cm
0.117
0.135
0.129
0.124
SMC-below 60 cm
0.152
0.174
0.164
0.157
<0.0001
Figure 1: Canonical 1 score from multivariate analysis of root traits plotted with plant Dry weight. Canonical 1 is effectively a score for deep rootedness and reduced soil moisture depletion, a trait combination typically displayed by Mediterranean germplasm) F1 progeny generally had a Canonical 1 score similar to or higher than the Mediterranean parent.
Aim: This experiment aimed at comparing rooting behaviour and herbage yield of a cultivar of North African origin i.e., Medea (Silsbury, 1961) with that of a cultivar of European origin i.e., Grasslands Samson) and studying the pattern of inheritance of those traits to F1 and F2 progeny.
Method: Plants grown in 100 cm lengths of soil-filled PVC pipes were initially bottom-watered in 200 litre 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, 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.
References:
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.
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.
Volaire F, Norton M (2006) Summer dormancy in perennial temperate grasses. Annals of Botany 98:
Conclusion
Introgression of Medea genes into Grasslands Samson will not be straightforward. 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.
Acknowledgements
Higher Education Commission (HEC) Pakistan, Pakistan Agricultural Research Council (PARC), T. R. Ellett Agricultural Trust
Figure: Arrangement of 1 m long PVC pots in 200 litre drums fitted with a plastic tap at the bottom