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Research Project: Management of Temperate-Adapted Fruit, Nut, and Specialty Crop Genetic Resources and Associated Information

Location: National Clonal Germplasm Repository

Title: Small genomes in tetraploid Rubus L. (Rosaceae) from New Zealand and southern South America

Author
item Hummer, Kim
item Bassil, Nahla
item Alice, Larry - Western Kentucky University

Submitted to: Journal of American Pomological Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2016
Publication Date: 1/15/2017
Citation: Hummer, K.E., Bassil, N.V., Alice, L. 2017. Small genomes in tetraploid Rubus L. (Rosaceae) from New Zealand and southern South America. Journal of American Pomological Society. 7(1):2-7.

Interpretive Summary: Most of the raspberry and blackberry species have multiple sets of chromosomes. The usual is 2 x 7 or 14 chromosomens. Some species have 4, 6, 7, 8, 10, or 12 sets of 7, or up to 84 chromosomes in their nuclei. Some species that are crop wild relatives for raspberries are native to New Zealand, Australis, and Southern South America. he U.S. Department of Agriculture, National Clonal Germplasm Repository houses a diverse Rubus genebank of living plant collections, including five of these species. These species are known to have 4 sets of chromosomes. Our objective was to determin the amount of nuclear DNA in these species. We used flow cytometry to make this determination. These species had very small chromosomes and a significantly smaller amount of DNA than other raspberry or blackberry species that have 4 sets of chromosomes. In fact, these species had about the amount of DNA that one mite expect of a raspberry species that had 3 sets of chromosomes. This seems to imply that over evolutionary time a raspberry ancestral species with small amounts of DNA combined with itself or another small genome species. After that some of the DNA was reduced to make the present day species. Further molecular research will determine the nature of the nuclear DNA of these species.

Technical Abstract: About 60 to70% of Rubus species are polyploids. Ploidy in this genus ranges from diploid through tetradecaploid , with aneuploids. The gametic chromosome number is x = 7. Taxa in Rubus Subgenera Micranthobatus and Comaropsis are endemic to the Southern Hemisphere in trans-Pacific Ocean environments of Australasia, southern South America, and the Falkland Islands. The U.S. Department of Agriculture, National Clonal Germplasm Repository houses a diverse Rubus genebank of living plant collections, including five species representing subgenera Comaropsis and Micranthobatus. These species were determined previously by chromosome counts to be tetraploid (2N = 4x = 28). Our objective was to examine the nuclear DNA content (C values) of the tetraploids R. cissoides, R. parvus, R. schmidelioides, R. squarrosus, and R. geoides in contrast with those of diploid and tetraploid black raspberries (R. occidentalis) and diploid red raspberry (R. idaeus subsp. strigosus). Nuclear DNA content was determined using flow cytometry. Surprisingly, the C values of these subgenera Micranthobatus and Comaropsis species were significantly smaller than an autotetraploid of R. occidentalis and other tetraploid Rubus species, and seemed numerically equivalent to less than the size of a triploid. The small genomes detected in this study may provide clues concerning the evolutionary history of subgenera Comaropsis and Micranthobatus.