CYTOLOGICAL EVALUATION OF TOBACCO DOUBLED HAPLOIDS FOR PRESENCE OF AMPLIFIED HOMOLOGOUS CHROMOSOMAL REGIONS

Atypical quadrivalents, resulting from pairing between homologous ampl ified chromosome segments, have been observed in hybrids between low-y ielding, second-cycle doubled haploid (DH) lines of tobacco (Nicotiana tabacum L.) and their source cultivars. The first objective of this s tudy was to determine if homologous amplified chromosome segments are present in other DHs, such as those that have been through only one cy cle of anther culture and those that are only moderately depressed in yield. The second objective was to trace the development of amplified chromosomal regions through consecutive cycles of anther culture. Chro mosome pairing was studied in DH x cultivar hybrids involving high- an d low-yielding first-cycle DHs and second-cycle DHs derived from the h igh-yielding first-cycle DHs. There appeared to be no correlation betw een multivalent formation and yield. The one DH that was found to cont ain homologous amplified chromosome segments was a low-yielding first- cycle DH, NC95 DHL. NC95 DHL was then crossed to two second-cycle DHs derived from it that had previously been determined to have homologous amplified chromosome segments. Cytological analysis of these DH x DH hybrids indicated that the amplified chromosomes in NC95 DHL passed un changed to one of its second-cycle derivatives. In contrast, a number of modifications occurred in another of its derivatives during the sec ond cycle of anther culture.