Cucurbit Genetics Cooperative Report 1:15 (article 14) 1978
Spontaneous Mutation in the Cucumber
R. W. Robinson
New York Agricultural Experiment Station, Geneva, NY 14456
A search was made for spontaneous mutants among 30,030 plants of 13 cucumber cultivars. Several chlorophyll deficient mutants were found, each conditioned by a different single recessive gene. Surprisingly, male sterile mutants occurred in a frequency much greater than that of all other visible mutants combined.
The overall frequency of male sterile plants was 0.9 per thousand plants. Seed lots of the same cultivar from different seed companies often were similar in male sterile frequency, but cultivars differed significantly. The frequency of male steriles per thousand plants was 2.1 for 'Wisconsin SMR 18' and 2.3 for 'SMR 58', but no male steriles were found among 2,828 plants of 'Pixie'.
The male sterile plants were easily recognized by abortion of their staminate flowers. Pistillate flowers of male sterile plants appeared normal, but the few staminate flowers that developed to anthesis had rudimentary anthers. Fruit set and development of the male sterile plants was normal, and thus male steriles would not be detected when seed production fields are rogued at harvest time. Despite the normal appearance of the pistillate flowers, the mutants had a high degree of female as well as male sterility. The average number of seed per fruit from open-pollinated 'SMR 18' male steriles was only 0.7, and many fruit were parthenocarpic. In controlled pollinations with the same source of pollen, male sterile plants produced an average of 0.3 seed per fruit while normal plants in the same F2 had 157 seed per fruit.
Monogenic ratios were obtained in F2 and back cross generations with each male sterile mutant tested. Nine different male sterile mutants of spontaneous origin were sib-mated with normal plants of the same cultivars, and then different F1's were crossed inter se. In every case, the next generation segregated 3 normal:1 male sterile. Thus, each of the nine male steriles is conditioned by the same single recessive gene.
Cultivar differences in frequency of this gene may be related to differing proportions of plants heterozygous for this gene in the initial seed released. The high frequency of this gene in commercial seed lots of different cucumber cultivars, despite the selection pressure against homozygotes because of their poor fertility, suggests this may be a very mutable gene.