Growth Responses of Various Ryegrass Cultivars to Drought Stress.

Eight ryegrass (Lolium perenne L.) cultivars [Covet, OSC129 (Covet II), Galileo, OSC127 (Galileo II), Michelangelo, Newton, Whitney, and OSC126 (Whitney II)] were studied in a greenhouse to evaluate their shoot length, clippings fresh and DM weights, and grass general quality under drought stress. Grasses were grown in cups (9 cm diameter and 7 cm height) placed in galvanized cans (45.72 cm diameter and 55.88 cm height) containing fritted clay as the culture medium. After 2 months of the establishment period (normal growth, daily irrigation, weekly fertilization and clipping at 2 cm height), the grasses were evaluated for 4 weeks under drought stress. Five replications of each cultivar were used in a RCB design trial. Shoot length and clippings fresh and DM weights were determined weekly. After the fresh weight determination, shoots were oven-dried at 60º C and DM weights recorded. Grass general quality was daily evaluated. The results show shoot length and clippings fresh and DM weights of all the cultivars decreased linearly as drought period progressed. However, at each harvest, there were only some numerical differences found in the shoot (clippings) length or fresh and DM weights of the various cultivars. There was no measurable growth by any plants after 3 weeks growth under drought stress. Grass general quality followed the same pattern (decreased) as the shoot length and clippings fresh and DM weights. General quality scores were 9 for all the cultivars at the initiation of the drought stress phase of the study. These values decreased to 8 for all the cultivars after a week of drought stress. Two weeks after exposure to drought stress, these values ranged between 6 to7 for various cultivars. The scores ranged between 4 and 6 after 3 weeks of exposure to drought. Then, the scores sharply decreased daily and on day 22 after exposure to drought all cultivars scored less than 5 for general quality. Based on the results of this study, the tested cultivars exhibited a similar level of drought tolerance with only some numerical differences between the study parameters at each harvest.