The present invention relates to a mutant ACO2 gene allele, which leads to a plant of the family of Cucurbitacea, in particular a cucumber plant producing only male flowers. The invention also relates to a plant of the family of Cucurbitacea, in particular a cucumber plant, comprising the mutant ACO2 gene allele. The mutant ACO2 allele provides plants that only produce male flowers. The invention further relates to the use of the mutant allele of the ACO2 gene for the identification and development of a plant of the family of Cucurbitacea, in particular a cucumber plant, producing only male flowers.