Genetic diversity within and between sulfonylurea‐resistant and susceptible populations of Schoenoplectus juncoides in Japan

To reveal the effects of herbicide selection on genetic diversity in the outcrossing weed species Schoenoplectus juncoides, six sulfonylurea‐resistant (SU‐R) and eight sulfonylurea‐susceptible (SU‐S) populations were analysed using 40 polymorphic inter‐simple sequence repeat loci. The plants were collected from three widely separated regions: the Tohoku, Kanto and Kyushu districts of Japan. Genetic diversity values (Nei's gene diversity, h) within each SU‐S population ranged from h = 0.125 to h = 0.235. The average genetic diversity within the SU‐S populations was H_S = 0.161, and the total genetic diversity was H_T = 0.271. Although the H_S of the SU‐R populations (0.051) was lower than that of the SU‐S populations, the H_T of the SU‐R populations (0.202) was comparable with that of the SU‐S populations. Most of the genetic variation was found within the region for both the SU‐S and SU‐R populations (88% of the genetic variation respectively). Two of the SU‐R populations showed relatively high genetic diversity (h = 0.117 and 0.161), which were comparable with those of the SU‐S populations. In contrast, the genetic diversity within four SU‐R populations was much lower (from h = 0 to 0.018) than in the SU‐S populations. The results suggest that selection by sulfonylurea herbicides has decreased genetic diversity within some SU‐R populations of S. juncoides. The different level of genetic diversity in the SU‐R populations is most likely due to different levels of inbreeding in the populations.     

Genetic variation among populations of Pythium irregulare in southern Australia

Isolates of Pythium irregulare were sampled from seven cereal crops throughout South Australia to determine the extent of genetic diversity within this pathogen and the scale of genetic differentiation among populations. Data derived from 29 individual restriction fragment length polymorphism (RFLP) loci differentiated 54 DNA fingerprints among the 92 isolates analysed. Some isolates had two alleles at several RFLP loci and were scored as heterozygous. One such isolate was selfed in vitro and segregation ratios in the progeny were not significantly different from those expected for allelic variation in a diploid. These data provided evidence that outcrossing occurs within P. irregulare and may contribute to the high level of genetic variation within the species ( D _T = 0·502). Allelic frequencies were significantly different among all seven populations and G _ST values showed significant genetic differentiation between populations. The average genetic identity among populations was low and hierarchical cluster analysis provided no clear evidence that populations formed geographically related groups. These analyses indicate low levels of interpopulation gene flow within P. irregulare and imply that population differentiation results from genetic drift.     

应用微卫星分子标记估算毛竹的异交率

选用自行开发引物的、具有较高遗传多态性的8个微卫星位点，分析来自独立的3株开花毛竹半同胞家系各50个子代个体。结果表明：位于3个不同地点的开花植株都能够通过与外源花粉杂合产生具有不同的微卫星基因型特点的半同胞家系子代，各个家系子代内均存有一定的遗传多样性，估算的平均异交率约为0.089。这说明毛竹主要以自交为主，并兼顾有一定比例的异交以确保其后代种群的遗传多样性。     

Efficiency of various insects in germplasm regeneration of carrot, onion and turnip rape accessions

Seed regeneration is one of the most important tasks in genebank work. To regenerate germplasm of allogamous, entomophilous plant species in isolation facilities, insects are often used as pollen vectors. The objective of this study was to determine the effect of pollinator species, pollinator densities, pollinator combinations, and flower preferences on the seed quantity and quality of Daucus carota, Allium cepa, and Brassica rapa. The isozyme phosphoglucoisomerase (PGI) served as genetic marker in determining outcrossing rates and pollen dispersal distances. Field plots and isolation cages without insects were used as controls. The pollinators studied consisted of the following insect species from German native fauna: red mason bees (Osmia rufa L.), hoverflies (Eristalis tenax L.), and blowflies (Calliphora sp. and Lucilia sp.). In D. carota and B. rapa, higher seed yields were achieved in isolation cages than in field plots, but in A. cepa lower seed yields were obtained in the isolation cages. Although O. rufa showed no liking for A. cepa, unintentional pollination was effected by this insect in isolation cages. Lower insect densities were necessary for O. rufa than for the various fly species.     

Use of isozyme analysis in the breeding of synthetic rapeseed cultivars

Eleven winter rapeseed inbred lines (I₄) were characterized according to isozyme banding patterns from seven polymorphic enzyme systems. All lines could be qualitatively and quantitatively distinguished using two enzyme systems, shikimate dehydrogenase (SDH) and diaphorase (DIA). Genetic distances were calculated among lines and 15 selected two-line hybrids were planted as experimental synthetics in field-trials. Syn-0 populations produced seed yields between 0.4% lower and 12.9% higher than the mean yields of the respective parental lines. Syn-1 seed yields were 11–24.1% higher than the respective parental lines and the yield improvement was positively correlated with the genetic distance between the parental lines. This tendency suggests that genetic distances between cross components, calculated from isozyme polymorphism, can be used in prognosis of yield performance of synthetic rapeseed cultivars. Isozyme analysis was also applied to study fertilization behaviour in line mixtures, and differences among parental lines were observed with regard to the tendency for self-pollination or out-crossing. The partially very high outcrossing rate suggests the possible existence of a self-incompatibility system.     

Esterase 1 and Hordein C allelic and genotypic frequencies in CC XXXI,a male sterile barley population

Summary Seeds from the 5th, 6th, 12th and 18th generation of enforced outcrossing in CCXXXXI-B, a barley (Hordeum vulgare L.) population containing genetic male sterility, were assayed for genotypic distribution of Est 1 and Hor C alleles. The result suggest that natural selection was effective in altering allelic frequencies at both loci and that genotypic frequencies were often different from what would be expected if allelic frequencies solely determined genotypic frequencies. Departures of actual from expected genotypic frequencies occurred in that shifts in allelic frequencies were detected.Joint contribution of the USDA-ARS and published with the approval of the Director of the Montana Agric. Exp. Sta. Journal Series No. 2281.     

Self-pollination in swedes (Brassica napus ssp Rapifera) and its implications for cultivar production

Summary The degree of selfing on open pollination was examined in four swede cultivars. Three cultivars had over 80 per cent selfing, whilst the fourth had less than 55 per cent. The inbreeding coefficient with these levels of selfing, assuming the cultivars were at equilibrium, would be 0.69 and 0.37 respectively. The cultivar with the high level of outcrossing was found to possess a degree of self-incompatibility. The structure of such populations is demonstrated, and the implications for cultivar production are discussed.     

蓝桉树木园异型杂交及花粉污染的微卫星分子标记研究

本文应用4对微卫星分子多态引物,对利用优株嫁接建立的蓝桉(E.globulus)树木园中的118个自由授粉子代的DNA微卫星指纹进行了分析.结果表明:选用的引物具有高度多态性,各个位点扩增得到的平均等位基因数为14.25,树木园中母株的异型杂交率为15%(95%,整体异型杂交率为47.9%,外源花粉污染率为17.6%.由于该树木园的异型杂交率低,其自由授粉的种子应用价值不高,因此应采用大规模人工授粉来制种或选用树木园中异型杂交率高的母株采种.     

Natural outcrossing in common buckwheat

Common buckwheat is an obligate cross pollinating crop because of its sporophytic self-incompatibility system. Therefore a study to assess the extent of natural outcrossing was undertaken for two years at Morden and Portage la Prairie, Manitoba using the semi-dwarf character, which is due to a homozygous genotype with regard to a single recessive gene, as a marker. The semi-dwarf genotype was grown in 100 m rows running in four directions at 90 ° from a central 36 m² plot of a normal, tall variety. At maturity, seed samples were taken from the semi-dwarf population at designated intervals. At least 200 F₁ seeds from each sample were grown in the greenhouse to the 3-4 leaf stage and the proportion of tall plants was used to determine the percentage of outcrossing. Approximately 50% outcrossing occurred where the semi-dwarf plants were immediately next to the normal plants and then the proportion decreased with increasing distance. Although outcrossing occurred throughout the distance tested, there were no significant differences from 12 m onward from the pollen source. Lack of directional influence in outcrossing and a sharp reduction in the proportion of tall plants within a 3 m distance from the pollen source suggested that wind was not a major factor in dispersing the buckwheat pollen over long distances. Although a substantial cross pollination was limited to a few metres from the pollen source, nearly 1% outcrossing occurred even at 100 m. Since the distance in this experiment was limited to 100 m from the pollen source, the present results do not allow us to recommend the minimum isolation distance required to meet certain standards for buckwheat seed production. This revised version was published online in July 2006 with corrections to the Cover Date.     

RAPD analysis reveals a low rate of outcrossing in burr medic (Medicago polymorpha L.)

Although burr medic (Medicago polymorpha L.) is commonly considered a self-pollinating species, intrapopulational variation for morphological, biochemical and molecular markers is relatively high. To investigate whether part of this variation is the result of outcrossing, we designed RAPD analysis experiments to reveal both inter- and intra-accession crossing. No cases of inter-accession hybrids were documented, but an intra-accessional crossing rate of 0 to 4% was estimated for one of the four accessions studied. Therefore, a rare outcrossing event between local individuals and migrating genotypes may contribute to high genetic variability observed in natural M. polymorpha. A better understanding of the factors which influence outcrossing in M. polymorpha is pertinent both for medic breeding programmes and for assessing risks associated with releasing transgenic herbicide-resistant crops.