Giant reed is one of the most widespread invasive species in riparian habitats in California and other coastal states of the United States. This species is thought to spread primarily asexually by flood dispersal of stem and rhizome pieces; viable seeds have not been found in the United States. Research was conducted to quantify genetic variation in giant reed along the Santa Ana River in California and to investigate the pattern of distribution of variation along this watershed. Populations at least 3.2 km apart were collected along the length of the Santa Ana River from the headwaters to the Pacific Ocean. One additional population from a different watershed was collected to serve as an out-group. Genetic analyses were conducted using both starch gel electrophoresis for isozyme analysis and random amplified polymorphic DNA (RAPD) analysis. Both isozyme and RAPD analyses revealed levels of genetic diversity comparable with those in the literature for clonal species, suggesting that asexual reproduction is the primary means of spread of giant reed. Most phenotypes were spread along the Santa Ana River, which is expected if water is the primary means of spread of vegetative propagules. Among the unique phenotypes found, two isozyme phenotypes and one RAPD phenotype were dominant and were found spread along the river, which may indicate greater fitness or competitive superiority to the other phenotypes that were less common. The dominant phenotypes were also found in the out-group population, possibly because of spread by humans. Because spread occurs mainly asexually, management efforts should focus on preventing establishment and spread of vegetative propagules. A moderate level of genetic diversity also suggests that biological control of this weed could be successful.
In order to determine the pattern of genetic diversity within and among the species of Cicer and to estimate interspecific genetic relationships, allelic variation was assayed for 23 isozyme loci in 63 accessions of 11 species of Cicer using starch gel electrophoresis. The total allozymic variation observed in the genus (H t )was equal to 0.60. When partitioned (G st), 96% of this allelic diversity was found among rather than within species. The allelic diversity among species (D st)and allelic diversity within species (H s)were equal to 0.58 and 0.02, respectively. Cicer reticulatum and C. pinnatifidum had the highest proportion of polymorphic loci (17.39%) and the highest mean number of alleles per locus (1.22 and 1.17, respectively). UPGMA cluster analysis of Nei's unbiased genetic distance revealed four genetic groups. One includes C. reticulatum, C. arietinum and C. echino spermum where the first 2 species represent a putative derivative-progenitor pair. A second cluster contains C. bijugum, C. pinnatifidum and C. judaicum. Cicer yamashitae, C. chorassanicum, C. anatolicum and C. songoricum form a third group. Finally, C. cuneatum, which has a very distinct isozyme profile and peculiar morphological features, is the only member of a fourth species group. This species grouping agrees partially with those obtained from crossability and cytogenetic studies. The results suggest that the annual habit arose from perennial progenitors at least twice in the genus Cicer.
The identities of two novel perennial nutsedge biotypes collected near Bakersfield, CA, were assessed using isozyme and random-amplified polymorphic deoxyribonucleic acid markers in conjunction with morphological analysis. The two biotypes, designated as CK (Cyperus rotundus cv. ‘Kempeni’) and CR (Cyperus esculentus cv. ‘Robusta’), morphologically resemble purple nutsedge and yellow nutsedge, respectively. Plants from both biotypes exhibited more prolific growth than the typical forms and possessed some traits that are not characteristic of the species they resemble. The morphological study was conducted on a total of 15 purple nutsedge, yellow nutsedge, CK, and CR populations collected in the first year and on 20 additional nutsedge populations were collected in the second year. The genetic analysis was performed on populations from the first year only. In general, there was agreement among the results obtained from the morphometric, isozymatic, and deoxyribonucleic acid studies. Populations of CR clustered with yellow nutsedge populations, indicating that CR is within the normal range of variation of this species and may represent a new introduction. Populations of CK, however, were distinct from both purple nutsedge and yellow nutsedge populations. Considering the low level of genetic variation reported in purple nutsedge and its strict vegetative mode of reproduction, CK might represent a sexually reproducing ecotype of purple nutsedge or a hybrid with yellow nutsedge.
Somatic karyotypes of the nine annual species of Cicer (2n = 16) were analyzed using C-banding. Highly significant differences in haploid genome length and C-band positive heterochromatin content were observed. The haploid genome length ranged from 20.0 μm in the wild species C. judaicum to 28.7 μm in the cultivated species C. arietinum, and significant differences for this character were observed between accessions within several species. Based on their heterochromatin content, the species were divided into two groups: low heterochromatin content (average of 41.7%), which included C. arietinum, C. chorassanicum, C. echinospermum, C. judaicum, C. pinnatifidum, C. reticulatum, and C. yamashitae, and high heterochromatin content (average of 59.5%), which included C. bijugum and C. cuneatum. Within-group variation for heterochromatin content was insignificant, while differences between groups were highly significant. There seemed to be a trend for reduction in C-heterochromatin content in the course of evolution in Cicer. In all species studied, C-bands were located proximally around the centromere with occasional bands in intercalary and distal positions. C-banding patterns allowed for chromosome identification and matching pairs of homologues in all species analyzed.
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