| Abstrakt: |
Numerous chromosome‐doubled haploids (dihaploids) were obtained from cultured anthers of a tobacco (Nicotiana tabacumL.) hybrid with multiple disease resistance. Field plot tests of dihaploid progenies were made in 1977 (in the absence of diseases), and some of the highyielding entries observed in 1977 were included in a 1978 planting. The selections grown in 1977 consisted of four groups based on their resistance or susceptibility to Tobacco Mosaic Virus (TMV) and Potato Virus Y (PVY). Unlike dihaploids from inbreds, some of the dihaploids from the hybrid yielded significantly more than the midparent (MP). Four yielded more than the MP 1977, and six yielded more in 1978. Most of the entries that produced high yields in 1977 were also high‐yielding in 1978. Alkaloid values were extremely variable among dihaploid lines and highly uniform within them. Values for agronomic traits, averaged among entries in the group that was susceptible to TMV but resistant to PVY, indicated that the gene for PVY resistance was associated with increased yields and high grade indexes (values). Resistance to TMV or root knot (RK), caused by Meloidogyne incognita(Kofoid and White) Chitwood, was not particularly beneficial to the groups of entries that possessed those genes. However, individual entries with the same combinations of genes for resistance/susceptibility were found to be high‐yielding; some, contrary to expectation, also had high grade indexes. This finding suggests that large numbers of dihaploid lines should be evaluated to assure identification and selection of exceptional individuals for use as breeding stocks or as varietal candidates. The occurrence of exceptional in. dividuals from a hybrid anther source, coupled with the fact that a dihaploid is a true‐breeding, homozygous diploid, obtained in a single generation, offers encouragement for progress in breeding high‐yielding, disease: resistant tobacco. |
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