Molecular contribution to selection of intergeneric hybrids between sugarcane and the wild species Erianthus arundinaceus

Erianthus arundinaceus has great potential as a germplasm source for better ratoonability, vigour, tolerance to environmental stresses, and disease re sistance in sugarcane. Many unsuccessful attempts have been made to introdu ce these characters into modern sugarcane cultivars. We report on significa nt progress made since molecular tools were implemented. Sequence-tagged PC R, revealing size variation in the 5S rDNA cluster, was performed on intact leaf tissue to identify genuine hybrids six weeks after germination. This early screening of seedlings avoids the loss of genuine hybrids due to comp etition with selfed progeny. Of 96 crosses made involving female Saccharum officinarum or sugarcane cultivars (Saccharum spp.) and male E. arundinaceu s, 26 were fertile producing 1328 seedlings. Thirty-seven genuine hybrids w ere unequivocally identified but only 19 have survived. Genuine hybrids wer e produced from only three crosses, all involving S. officinarum as the fem ale parent. Chromosome elimination was observed in all seven hybrids analyz ed using genomic in situ hybridization (GISH). Very little cross-hybridizat ion was observed between the genomes of the two species after GISH, confirm ing recent molecular studies which showed that E. arundinaceus is quite dis tant from the genus Saccharum. The major limitation in the introgression of E. arundinaceus resides now in the apparent sterility of the hybrids.