Chlorophyll content as an index of the productive capacity of selfed lines of corn and their hybrids

1. In a study of methods, it was found that the area of corn leaf blades could be determined as accurately by the formula length X greatest width X 0.75, as by planimeter readings of blue-printed leaf outlines. Leaf areas may conveniently be determined from growing plants by this method without injury. 2. Both chlorophyll and carotin were most concentrated in the uppermost leaves and least in the bottom leaves. The gradient between the uppermost and lowest leaves was fairly regular, and the middle leaf or leaves of the plant exhibited practically the same concentration of pigment as the average for the whole plant. Xanthophyll values were erratic and no significance was attached to such observations. 3. Estimates of total chlorophyll content per plant based on the concentration of the pigment in the middle leaf and on the leaf area determined by the formula were practically as reliable as complete analyses of all leaves. Carotin content of plants was also estimated satisfactorily by this method. A Ganong leaf punch which clips circles 1 sq. cm. in area was used to sample leaf blades without appreciably disturbing the living plant. 4. A group of 12 newly homozygous selfed lines selected basis of observed greenness of leaves in 1929 varied in chlorophyll concentration from 5.14 mgms. of chlorophyll per 100 sq. cm. of leaf for the lightest strain to 11.30 mgms. for the darkest green strain when grown in 1930. Total chlorophyll per plant ranged from 106 to 407 mgms., although no strain showed obvious chlorophyll defects. The 12 strains also differed widely in leaf area, total yield of dry matter, and shelled grain. 5. Eighteen first generation hybrids involving the 12 selfed lines were chosen to represent all combinations of greenness. The chlorophyll concentration within this group ranged from 6.23 to 11.61 mgms., and the total chlorophyll from 332 to 607 mgms. From the chlorophyll content of these hybrids, it appeared that chlorophyll concentration of a given strain may either be genetically recessive, dominant, partly dominant, or cumulative in relation to that of other selfed lines. 6. The mean values of the attributes for the, parents of each hybrid suggest that chlorophyll inheritance is controlled by a relatively small number of genetic factors in contrast with leaf area and yield. Chlorophyll concentration in leaves of the hybrids was only slightly greater than the mean value of the parents, whereas leaf areas and yields were 50 to 100% higher. 7. Correlation coefficients between attributes of the 12 selfed lines indicated that total chlorophyll was significantly related to chlorophyll concentration, leaf area, yields of total dry-matter, and shelled grain. Chlorophyll concentration was correlated with shelled grain and leaf area, but not with total dry matter. 8. Within the group of 18 hybrids, total chlorophyll was more highly correlated with yields of total dry matter and grain, leaf area, and chlorophyll concentration than any other attribute. Chlorophyll concentration was significantly correlated with production of total dry matter, but not with leaf area. 9. Mean values of the parental attributes of total chlorophyll, chlorophyll concentration, and leaf area were all significantly correlated with total dry weight of the hybrids. Mean chlorophyll concentration of the parents was also closely related to chlorophyll concentration and total chlorophyll of the hybrids. 10. The mean values for chlorophyll concentration and total chlorophyll of selfed lines are reasonably reliable indexes of the total yield that will be produced by their hybrids. Light green inbreds with other desirable attributes should be mated with dark green rather than light green strains for best results. Selection of dark green plants in successive generations of segregating strains should be an aid in isolating prepotent lines.