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Estimation of Parthenogenesis Frequency in Kentucky Bluegrass with Auxin-Induced Parthenocarpic Seeds

Istituto di Miglioramento Genetico Vegetale, Università degli Studi di Perugia, Borgo XX Giugno 74, 06100, Perugia, Italy

Anton P. M. den Nijs

DLO-Centre for Plant Breeding and Reproduction Research (CPRO-DLO), P.O. Box 16, 6700 AA, Wageningen, the Netherlands

^* Corresponding author (imgvsas{at}ipguniv.unipg.it).

To estimate the frequency of apomixis in Kentucky bluegrass (Poapratensis L.) by use of traditional embryo sac classification and progeny testing methodologies is difficult and time consuming. This study was conducted to test the applicability of the auxin test, a recently developed technique that allows the asexual potential to be estimated quickly as the frequency of auxin-induced, endospermless grains containing one or more parthenogenetic embryos. Frequency of parthenogenesis was estimated by the auxin test for eight clones in two seasons and two locations. The 2,4-D (2,4-dichlorophenoxyacetic acid) induction of endospermless grains ranged from 50 to 100%. Two clones were 100% sterile, while the others presented sterility ranging from 2 to 63%. Expression of parthenogenesis was fairly stable within and between environments, suggesting a strong genetic control. Differences in parthenogenesis frequency between clones were evident. Statistical analysis based on pooled data discriminated highly (87–89%), intermediate (78%), and moderate (69–73%) parthenogenetic clones. Estimates of parthenogenesis frequency obtained by embryo sac analysis were similar to or lower than those from the auxin-induction test. Estimates of apomictic reproduction by progeny tests were usually higher than both estimates of parthenogenesis. Auxin-induced grains of one clone were analyzed by histological sections. Most of the embryos in the parthenogenetic ovules and grains (80%) seemed normal with regard to position, shape, and cell pattern. It is therefore concluded that the auxin test is a workable technique for determining the percentage of parthenogenesis in breeding programs.

Received for publication March 28, 1994.