Corolla Tube Length Studies in Red Clover1

Abstract

The relationship between corolla tube length and seed production was studied in two long corolla tube strains and two short corolla tube strains of red clover. Although the strains differed significantly in mean corolla tube length, the short corolla did not appear to offer any advantage for increased seed production. Because it was thought that strain differences other than corolla tube length might have been involved in the above mentioned studies, the relationships between corolla tube length, number of florets per head, seeds per head, and percentage of florets setting seed in segregating populations derived from crosses between long and short corolla tube strains were studied. In the entire population neither number of seeds per head nor percentage seed set was significantly correlated with corolla tube length. The only significant correlation was between florets per head and seed setting percentage, the r value being + 0.339. Crosses between plants of varying corolla tube lengths were made to study the relationship between the corolla tube length of parental plants and that of their progenies. Sixteen plants in each of 17 families were studied. There was a highly significant correlation between the mean corolla tube length of the parents and that of their progenies, the r value being .84. Long corolla tube tended to be dominant or partially dominant over short. One family was selected for further study of corolla tube length in F2 and backcross populations. The F2 populations derived from long X long, medium X medium, and short X short corolla tube F1 plants were significantly different in mean corolla tube length. It was possible to shift the mean corolla tube length of both the F2 and backcross populations by selecting long or short corolla tube F1 plants to produce these populations. The mean corolla tube length of all backcrosses to the long corolla tube parent was 7.55 mm and of all backcrosses to the short parent was 6.81 mm. The weights of the individual plants in the F2 and backcross populations were determined at the end of the growing season. There was a highly significant difference among the mean plant weights of the various populations. All of the backcross populations from the long corolla tube Emerson parent had a significantly higher mean plant weight than the backcross populations from the short corolla tube Zofka parent. The average plant weight of all backcross populations involving the Emerson parent was 27.02 grams and of all backcrosses involving the Zofka parent was 20.44 grams. The F2 population derived from the two short corolla tube F1 plants was significantly lower in mean plant weight than the F2's derived from the medium and long corolla tube F1 plants. In the backcrosses to both parents, the populations involving the short F1 plants also were lower in mean plant weight than the populations involving the medium or long F1 plants. The correlation between plant weight and corolla tube length on an individual plant basis gave an r value of +0.27, which was highly significant. The correlation between the mean plant weight and mean corolla tube length of the populations gave an r value of +0.83. This indicated that genes for corolla tube length apparently were associated with genes for the expression of general vigor.