II.9. Effect of light intensity on expression of leaf pubescence.
George Fedak, Research Branch, Canada Agriculture, Ottawa, Ontario, Canada.
Various combinations of pubescent leaves and sheaths were found in hybrids between H. vulgare (2x) x H. bulbosum (2x) produced by S. Symko of this station and in strains of H. spontaneum collected in the Middle East by T. Rajhathy also of this station. During the course of genetic studies of this character it was noticed that intensity of pubescence varied with growing conditions. Light intensity differences produced most conspicuous variation. To quantify the differences four plants of each of the five strains were grown at lite intensities of 1,000 and 4,000 foot candle while temperatures and relative humidity were kept constant.
Counts were taken as number of single hairs per randomly selected field of a microscope (15.6 m.m.2). The values shown in Table I represent the means of two measurements per leaf on a total of four plants.
Table I. Number of single hairs per 15.6 m.m.2 of leaf area
The youngest leaf was analysed at the five leaf stage. As shown in Table I the H. bulbosum derivatives showed the greatest density of pubescence on lower and upper leaf surfaces plus leaf sheaths. These strains also showed the greatest reduction in pubescence when light intensity was increased from 1,000 to 4,000 f.c. The greatest reduction was observed on the tips of the upper leaf surfaces. This environmental variation in density of pubescence should be taken into account when material is being screened for resistance to insects or in inheritance studies.
