ARS | Publication request: Cucumis zambianus (Cucurbitaceae): A New Species from Northwestern Zambia

Submitted to: Systematic Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2008
Publication Date: N/A

Interpretive Summary: A 1984 germplasm exploration to Zambia collected seven seed samples of Cucumis (the genus of melons and cucumbers) that were not identified to species. Two of these collections were grown out and carefully studied at the USDA-ARS North Central Regional Plant Introduction Station in Ames, Iowa. An identification to species was attempted based on current scientific keys and species descriptions. These collections did not fit any known species. Detailed notes were taken describing the morphological features of these plants, and DNA samples were taken for gene sequencing. The gene-sequence data showed that these collections differed from all other Cucumis species tested, but were closely related to Cucumis insignis, C. pustulatus, C. dipsaceus, and C. anguria. Morphologically, these collections differed from those other four Cucumis species by the following characters: plants pilose (softly hairy), male flowers held in panicles with 6¿30 flowers, male calyx lobes linear, and female flower stalks very long and cylindrical. Controlled crosses were among these plants and between them and and C. pustulatus, to see if they were reproductively isolated. Fruits were produced from crosses made within and between these plants, but all attempts involving C. pustulatus were unsuccessful. In this paper, we describe the two collections as a species new to science, Cucumis zambianus. Four of the other unidentified Cucumis collections from Zambia are also identified as C. zambianus. These six collections all came from the northwestern corner of Zambia, but the new species is also expected to occur in eastern Angola and southern Zaire. This new species may provide valuable traits for insect and disease resistance of use to breeders for melon and cucumber crop improvement.

Technical Abstract: During germplasm explorations within Zambia in 1984, seven Cucumis accessions were collected that could not be identified to species. Two of the accessions were studied in-depth. Based on phenotypic characters, they were closest to Cucumis pustulatus. In ITS analyses of all available Cucumis species and the accessions, the two accessions formed a clade with 100% bootstrap support, sister to a clade that also included C. insignis, C. pustulatus, C. dipsaceus, and C. anguria. The accessions differed from these four Cucumis species by the following characters: plants pilose, male inflorescences paniculate with 6¿30 flowers, male-calyx lobes linear, and female-flower pedicels long and cylindrical. Controlled crosses were made within and between the two accessions and between each of them and C. pustulatus. Fruits were produced from crosses made within and between the two accessions, but attempts involving C. pustulatus were unsuccessful. The two accessions are described as a new species, Cucumis zambianus. Six of the seven unidentified Cucumis collections from Zambia are identified as C. zambianus herein. They were all collected in the northwestern corner of Zambia, but the new species is also expected to occur in eastern Angola and southern Zaire.