Graduate Thesis Or Dissertation
 

Morphogentic studies of intraspecific hybrids of Microseris laciniata (Hook.) Sch.-Bip.

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  • Microseris laciniata is a perennial, self-incompatible species classified in subgenus Scorzonella. It is morphologically the least specialized species in the genus, in contrast to the members of subgenus Microseris, which are morphologically advanced, self-compatible annuals. First-generation hybrids were available from crosses involving eight populations of two subspecies of Microseris laciniata from southwestern Oregon and northwestern California. This study focused on the morphology and reproductive behavior of twelve different intraspecific crosses of this group. One of the morphological characters investigated was the number of pappus-parts per achene. This trait was chosen not only for the ease with which it can be analysed, but also because it was used in recent studies on evolutionary genetics of Microseris. All the ten families of hybrids tested, except four, showed significant variation in the distribution of pappus-part numbers within themselves. Most of the distribution patterns resembled the "high determining" genotypes reported in the literature. The other morphological trait investigated was the number of phyllaries of the involucre. The phyllaries are an important character in distinguishing the two sub-species of M. laciniata. The proportion of outer versus inner phyllaries was tested statistically to determine whether there were significant differences among the siblings of each hybrid family. This characteristic was found to be uniform in each family, although different families seemed to differ among themselves. The results could not be compared with earlier published accounts, due to differences in cultural conditions for the plants. The reproductive behavior of the intraspecific hybrids was studies with respect to (1) seed fertility, (2) pollen stainability, and (3) chromosomal behavior at meiosis. The test plants were crossed in the greenhouse with siblings and sometimes with half-sib plants. The percentage of pollinations that yielded fruits with normal embryos was calculated. The results of these hand pollinations showed widely varying success in seed formation. Sometimes a particular sibling cross would yield one capitulum with no fertile fruits and a second capitulum with mostly normal fruits. There was no tendency for F l's within the same subspecies to be more fertile than F l's between subspecies. The low seed productivity of many sibling crosses, despite their high pollen fertility, is suggestive of shared self-incompatibility factors among sister plants. Pollen stainability was investigated for eight intraspecific and three interspecific hybrids of M. laciniata. Among the intraspecific hybrids studied only two had markedly reduced pollen stainability. Pollen germinability in vitro failed in several attempts. In vivo only a few pollen tubes were observed on the styles of two of the four hybrids crossed to their siblings, indicating a strong rejection reaction in all four hybrids tested. Chromosomal behavior at meiosis in intraspecific hybrids was mostly normal, but minor irregularities were seen especially from prophase to first anaphase. No gross structural changes in the chromosomes of M. laciniata were observed, despite the probable antiquity of the species and spatial isolation of its populations.
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