The Journal of Heredity 2002:93(3)
© 2002 The American Genetic Association 93:185-192
Occurrence and Cytological Mechanism of 2n Pollen Formation in a Tetraploid Accession of Ipomoea batatas (Sweet Potato)
From the International Potato Center (CIP), P.O. Box 1558, Lima 100, Peru. We are grateful to the International Potato Center (CIP) for financially supporting this research. L. A. Becerra Lopez-Lavalle is currently at the Centre for Plant Biodiversity Research, CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia. G. Orjeda is currently at Genoscope, 2 rue Gaston Cremieux, CP 5706, 91057 EVRY CEDEX, France.
Address correspondence to L. A. Becerra Lopez-Lavalle at the address above or e-mail: Augusto.BecerraLopez-Lavalle@csiro.au.
We evaluated a 4x accession of Ipomoea batatas (L.) Lam. and four 2x accessions of Ipomoea triloba for 2n pollen production. Approximately 90% of the genotypes of accession 81.2 (I. batatas, 4x) produced 2n pollen with different frequencies. In contrast, none of the genotypes of I. triloba produced 2n pollen. The diameter of the 2n pollen was approximately 30% (
) larger than that of the n pollen, making it easy to identify, measure, and quantify. The correlation (r = 0.93**) between the frequency of giant pollen and the frequency of dyads and triads was highly significant, strongly suggesting that the giant pollen grains were 2n pollen. The 2n pollen producers presented either a parallel or tripolar spindle arrangement (Y shaped) at anaphase II instead of the normal 60° crossed spindle orientation. These two abnormal spindle configurations produced dyads and triads, with different frequencies (1367%), instead of tetrads. Occasionally a metaphase II spindle variation was found with a single fused spindle, which also forms a dyad. The correlation (r = 0.89**) between the frequency of 2n pollen and the frequency of parallel, fused, and tripolar spindle arrangements was also highly significant, suggesting that these abnormal spindle configurations are involved in the production of 2n pollen in I. batatas. When we evaluated the efficiency of 2n pollen in polyploidization using 4x x 4x (2n) crosses, all progenies were 4x, suggesting the existence of barriers to crossability between 4x genotypes and their 2n pollen-producer counterparts.
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