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The objectives of this study were to determine (i) if selection for barley yellow dwarf virus (BYDV) tolerance occurred under a modified single-seed descent (MSSD) procedure when used in conjunction with BYDV inoculation, and (ii) if changes in nuclear DNA content occurred during MSSD. Plants from four intraspecific spring oat (Avena sativa L.) crosses were grown in the greenhouse under a MSSD procedure and were infected with BYDV by inoculation with viruliferous aphids. These populations were compared with populations grown without exposure to BYDV.BYDV tolerance was evaluated in the field in the F 4:5 and F 4:6 generations. Inoculation with BYDV under the MSSD method did not selectively eliminate BYDV susceptible genotypes. To determine if the MSSD procedure induced selection for a particular nucleotype, seeds harvested from the parents (grown under the MSSD procedure) were tested for nuclear DNA content. No difference in DNA content was observed among progeny grown from seeds of stressed plants compared with progeny grown from seeds of nonstressed plants. These results suggest that even the most BYDV susceptible plants produced seeds during MSSD, and the MSSD method does not seem to induce directed changes in nuclear DNA content.

Intraspecific nuclear DNA content has been documented in various angiosperm species. The purpose of this study was to determine the nuclear DNA content variation in soybean (Glycine max(L.) Merr.). Several studies have suggested that DNA content variation exists in soybean. Ninety soybean lines representing diverse geographic locations in China were analysed by flow cytometry. Nuclei were isolated and stained with either the fluorochrome DAPI or PI. After analysis, it was determined that PI stained nuclei more accurately assessed the total DNA content in soybean. A 12% variation in nuclear DNA content was observed among the 90 lines. The amount of nuclear DNA in the lines was within the DNA range of United States cultivars previously examined. Nuclear DNA content variation in soybean is much less than the variation reported in maize. These results could be due to the lack of polymorphism in large chromosomal elements containing large blocks of repetitive DNA. In addition, unlike maize, the amounts of DNA variation did not decrease as a result of more intensive breeding in United States cultivars. Intraspecific nuclear DNA content variability is very different between these two major agronomic species.

Flow cytometry was used to characterize isolates of Phialophora gregata using the fluorescence intensity of propidium iodide-stained conidia. The isolates differed in their mean fluorescence intensity, ranging from 100.0 to 129.7 arbitrary units (AU). When the number of fluorescent events was plotted against intensity of fluorescence, a single peak was observed. Fluorescent patterns of Acremonium isolates from soybean vascular tissue were compared with those of P. gregata. Their mean fluorescence intensity ranged from 76.4 to 88.0 AU. With some of these isolates, multiple peak histograms were observed, corresponding to multiple spore sizes as well as single and double nucleated conidia. Using flow cytometry, we were able to distinguish P. gregata isolates from those of Acremonium, based on mean fluorescence intensity and/or the presence of multiple peaks. Flow cytometric analysis of propidium-iodide stained conidia of Phialophora isolates should prove to be useful for determining the relative DNA content of different isolates collected from different geographic areas.

DNA isolated from Black Mexican sweet maize populations segregating for the presence of B chromosomes was used for PCR amplifications of 320 RAPD primers. Seventeen primers produced detectable polymorphisms between populations known to carry B chromosomes and populations devoid of B chromosomes. To ensure that the primers which generated a polymorphic band were indeed identifying B chromosomes, five Arizona Indian corn populations, three tetraploid corn populations and two High Loss corn lines differing in their B chromosome composition were analysed. Four primers were selected to screen these maize populations. Root tip counts were performed on the lines to confirm the association of the RAPD markers to the presence of B chromosomes.

Ramifying hyperechogenicities within the basal ganglia were observed in two neonates followed for prematurity. The investigations demonstrated an asymptomatic cytomegalo-virus infection in both. The literature was reviewed about this association. Incidence, etiology of hyperechoic lesions in the basal ganglia of neonates and neurodevelopmental outcome of the patients were also reviewed.