Does leaf manipulation affect leaf appearance in italian ryegrass (Lolium multiflorum Lam.)

Authors: Williams, Robert; Bartholomew, Paul

Submitted to: Proceedings of Southern Weed Science Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2010
Publication Date: 12/20/2010
Citation: Williams, R.D., Bartholomew, P.W. 2010. Does leaf manipulation affect leaf appearance in italian ryegrass (Lolium multiflorum Lam.). Proceedings of Southern Weed Science Society. 63:57-69.

Interpretive Summary: When plants are exposed to mechanical stimuli such as wind, touching, rubbing or flexing, several changes may occur in the plants’ development. Reduction in plant height and size, smaller leaves, and increased stem thickness are typical changes. During plant experiments the physical movements caused by repeated plant measurements are often enough to alter the plant’s growth. These changes are called “observer effects” and are generally ignored in plant experiments. We are interested in leaf and tiller development as an indication of pasture grass productivity and persistence. Currently we are determining the effects of temperature, soil moisture, and trampling on seedling growth and often take repeated measurements during these studies. To determine if the repeated measurements might affect the growth of the seedlings, Italian ryegrass seedlings were placed into one of three groups. One group was the control with minimal movement. The second group was only handled every two to three days when the leaves and tillers were counted. The final group was counted as the second group plus the group was physically shaken for 30 minutes each morning. After 30 days the plants were harvested. There were only small differences in plant growth among the three groups. Regardless of treatment, leaf and tiller number, and mean total, shoot and root dry weights, were similar. This means that seedling movement by leaf counting during other studies will not alter the results.

Technical Abstract: Mechanical stimuli such as rubbing, shaking, or flexing plants can alter their growth rates and morphologies. Plant response to mechanical stress can result in delayed plant growth, reduced leaf size, shorten and thicken stems, and reduced yields. Repeated measurements, such as leaf counting or measuring leaf length or area, can also affect plant growth. In earlier field and growth chamber studies leaf and tiller appearance rates were greater in Italian ryegrass (Lolium multiflorum Lam.) seedlings grown in chambers. Differences between the field and chamber studies may be attributed in part to differences in soil moisture, soil bulk density and temperature. However, the effects of wind disturbance or mechanical stimulation due to leaf manipulation during counting have not been determined. Here we report the results of a growth chamber study where Italian ryegrass seedlings were undisturbed, periodically disturbed by leaf counting, and shaken for 30-min daily in addition to the periodic leaf counting. There was no significant difference in the leaf or tiller appearance or number between the counted and counted plus shaking treatments. Nor was there a significant difference among the treatments as to total, shoot or root dry weights.