Toshinobu Morikawa

Characterization of two morphological groups of isolates of Pythium ultimum var. ultimum in a vegetable field

Comparisons were made between two morphological groups ofPythium ultimum var.ultimum strains isolated in a vegetable field in Japan. The groups were distinguished as having smaller or larger sexual organs by the sizes of their antheridia and oogonia. Morphological study indicated that the two groups comprised a single taxon,P. ultimum var.ultimum, by the current taxonomical keys. The smaller group grew faster in the lower temperature range of 4–15°C, whereas the larger group grew faster in the higher temperature range of 25–37°C. Random amplified polymorphic DNA (RAPD) and isozyme analyses revealed genetic dissimilarity between the two groups. Cluster analysis of the isozyme banding patterns with four otherPythium spp. demonstrated that the genetic dissimilarity between the two groups was equivalent to species level. In the field survey, the smaller group was frequently detected in February, May and September but not in July, while the larger group was detected mainly in July and September. The two groups were not distinguishable by their pathogenicity to spinach seedlings.

Classification of Pythium ‘group F’ based on mycelial protein and isozyme patterns

Taxonomic characteristics were compared among 10 isolates ofPythium ‘group F’ in tems of the electrophoretic patterns of their mycelial proteins and isozymes. These isolates were obtained from water of three ponds in different seasons and have an identical morphology of zoosporangia. Attempts to cross the isolates with each other themselves and with other isolates from the same group failed.Pythium ‘group F’ is the most dominant of the pythia in the aquatic ecosystem and is difficult to identify because of the lack of sexual reproductive structures. Isozyme analysis proved useful in this respect. Comparisons of banding patterns of total soluble proteins and isozymes revealed five subgroups inPythium ‘group F’. Two isolates obtained from water of different ponds in different seasons showed the same protein and isozyme patterns. Our findings indicate that the use of total soluble protein and isozyme patterns for determining the variation withinPythium ‘group F’ could become a valuable adjunct to the morphological and physiological criteria.

Isozyme Polymorphism and Genetic Differentiation in Natural Populations of a New Tetraploid Species Avena agadiriana, from Morocco

A new wild tetraploid oat Avena agadiriana Baum et Fedak was collected from the five populations along the Atlantic coast in Morocco. Variations in six enzyme systems were surveyed and allele frequency, percentage of polymorphic loci, number of alleles per locus, observed and expected heterozygosities, and unbiased genetic distance were calculated. Phenotypic frequencies were scored representing 11 polymorphic loci. The mean percentage of polymorphic loci was 46.25, the mean number of alleles per locus was 1.502, and the mean expected heterozygosity was 0.1526. Two heterozygotes resulting from outcrosses were found in the progeny from M60 and M71. The population of M71 had peculiar alleles Est-4A not present in the other populations. Most of the genetic diversity of this species was between populations with little existing within populations. Geographic and genetic distances between populations were positively correlated with each other and the correlation coefficient was 0.7031. Cluster analysis showed two strongly differentiated groups were apparent, M71 and M74, and the remainder. The former group appears to be adapted to man-made habitat, such as road side or eucalyptus plantation, and the latter to a distinct dry, sandy habitat. To make wide intra-specific variation in this species, the modified mating system would be indispensable.

Protocol for Producing Synthetic Polyploid Oats

A protocol to produce synthetic oats by introducing alien genetic variations into cultivated oats is proposed based on suitable genetic relationships between Avena species. Furthermore, artificial hybridization procedures between different ploidy species are explained. Amphiploids can be produced by rescuing aborted embryos and treating the F1 hybrids with colchicine to overcome sterility between interspecific plants. Furthermore, I present the cytological methods for observing somatic and meiotic chromosomes in the treated hybrids.