EMERGING INFORMATION ON AGRONOMIC TRAITS CONTRIBUTING TO DROUGHT RESISTANCE IN PERENNIAL RYEGRASS AND TALL FESCUE

We overview results from experiments conducted at Massey University to better define the agronomic basis of drought resistance in perennial ryegrass and tall fescue. Average November-to-April moisture deficit at Palmerston North was estimated as equivalent to 258 mm rainfall. In contrast, breeding for a 10 cm increase in root depth was predicted to provide the equivalent of 16 mm additional rainfall. Breeding for increased water use efficiency is also a possibility but such gains are also not expected to eliminate summer moisture deficit in the average year. In general germplasm of North African origin exhibited deeper rooting and reduced leaf extension rate in summer, but paradoxically increased stomatal conductance compared to germplasm originating from Europe. In one experiment some plants unwatered for 90 days remained green but we are uncertain as to the basis of this response. Measurement of gravimetric soil moisture content (GSMC) at approximately 30 cm depth was found to be informative, often more so than more sophisticated measurements like leaf water potential. With respect to current commercial cultivars of perennial ryegrass, we found evidence of variation in water use efficiency (greater plant weight associated with higher GSMC) between individual plants of Grasslands Samson, meaning that selection for this trait could be rewarding. A cultivar we examined that incorporated Spanish germplasm also exhibited similar evidence of high water use efficiency. We found evidence that Neotyphodium endophyte can improve leaf hydration in perennial ryegrass in moderate drought stress.fals