Complementation Between Two Perfect Flowered Mutants in Cucumber

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Cucurbit Genetics Cooperative Report 3:12-13 (article 7) 1980

A.F. Iezzoni and C.E Peterson
University of Wisconsin, Madison, WI 53706

G.E. Tolla
Campbell Institute of Agricultural Research, Napoleon, OH 43545

In 1928, Rosa reported simple inheritance for flower type in cucumber: M/- plants have pistillate flowers and m/m plants have perfect flowers. Over the past several years, we have developed perfect flowered lines from backcrossing programs using two sources of the perfect flowered gene. The sources were the American cv. ‘Crystal Apple’ and a Polish breeding line from Kubicki. Both of these lines showed the characteristic clusters of perigynous perfect flowers with small rounded ovaries. When lines derived from the same m/m source are crossed, the prefect flowered phenotype is observed. However, when two perfect flowered lines originating from different sources are crossed, the F1s have one epigynous long ovaried pistillate flower per node. This appears to be a classical example of genetic complementation in which two mutants are crossed and the wild type phenotype is obtained. we have arbitrarily assigned the ‘Crystal Apple’ derivatives allele m1 and those from the Polish breeding line, m21. In this study, the apparent complementation between two perfect flowered types was investigated. The simply inherited dominant gene for bacterial wilt resistance which is tightly linked to the M/m1 locus (~1% CO) was used as a genetic marker.

Two different crosses which exhibited complementation in the F1 were investigated in the F2 and BC1 populations. In the F2 population, a 1 perfect:1 pistillate flowered plant ratio was obtained (Table 1). The perfect flowered types could further be separated into bacterial wilt resistant or susceptible plants which indicates whether they are homozygous for m1 or m2 . Upon backcrossing to the susceptible parent, a 1 perfect:1 pistillate flowered plant ratio was obtained and as expected, all the perfect flowered types were susceptible and all the pistillate types were resistant (Table 2).

Both flower type and ovary shape show complementation. Unfortunately, this system does not lend itself to further analysis of the chromosome segment. Therefore, it is impossible to conclude whether the m1 and m2 mutants represent different genes (non-allelic complementation) or whether they are different mutational sites within the same gene (allelic complementation).

1This nomenclature is temporary and will be revised following further investigation.

Table 1. F2 data from two populations exhibit complementation in the F1.

(m1Bw/m2/bw)

Phenotype
Genotype
Population A
Population B
Perfect, resistant m1Bw/m1Bw 91 83
Pistillate, resistant m1Bw/m2bw 204 160
Perfect, susceptible m2bw/m2bw 87 71
Total 382 314
X2 (1:2:1) 1.85 1.03
Probability 25-50% 50-75%

Table 2. BC1 data from two populations exhibiting complementation in the F1.

(m1Bw/m2bw) x (m2bw/m2bw)

Phenotype
Genotype
Population A
Population B
Pistillate, resistant m1Bw/m1bw 21 67
Perfect, susceptible m2bw/m2bw 29 51
Total 50 118
X2 (1:1) 1.28 2.78
Probability 20-25% 5-10%

Literature Cited

  1. Rosa, J.T. 1928. The inheritance of flower type in Cucumis and Citrullus. Hilgardia 3:233-250.