Seasonal variation in the herbage yield and nutritive value of perennial ryegrass (Lolium perenne L.) cultivars with high or normal herbage water-soluble carbohydrate concentrations grown in three contrasting Australian dairy environments

Two lines of perennial ryegrass (Lolium perenne L.), cv. Aurora and breedin g line Ba 11351, from the United Kingdom with elevated concentrations of wa ter-soluble carbohydrates in the shoot were compared with the standard cult ivars, Ellett, Vedette and Kangaroo Valley, in pure grass swards under irri gation at Kyabram, Victoria, and Gatton, Queensland, and under natural rain fall at Condah, Victoria, during 1995-97. Near infrared reflectance spectro scopy was used to predict the water-soluble carbohydrate, crude protein, in vitro dry matter digestibility, neutral and acid detergent fibre, and Klas on lignin concentrations of the perennial ryegrass herbage. Herbage yield a nd water-soluble carbohydrate differed between cultivars at each site at mo st harvests, with the high water-soluble carbohydrate lines usually yieldin g less and having higher water-soluble carbohydrate concentrations than the 3 standard cultivars. However, the high water-soluble carbohydrate lines a lso had higher water-soluble carbohydrate concentrations at harvests where their yield was equal to the standard cultivars. The other nutritive value traits differed significantly at more than half of the 32 harvests: the hig h water-soluble carbohydrate lines had higher crude protein and dry matter digestibility, and lower neutral detergent fibre, the neutral detergent fib re containing less acid detergent fibre and lignin than did the standard cu ltivars. The high water-soluble carbohydrate lines were more susceptible to crown rust during spring and summer than the standard cultivars at Kyabram and Gatton: heavy infections reduced yield, water-soluble carbohydrate, dr y matter digestibility and crude protein. Higher water-soluble carbohydrate may depend on only a few genes, as does rust resistance and it seems likel y that high yielding, high water-soluble carbohydrate cultivars can be deve loped by recombination and selection.