Estimation of the mode of inheritance of thermal tolerance in the guppy <Emphasis Type="Italic">Poecilia reticulata</Emphasis>

High water temperature influences the survival, growth, and maturation of fish. Genetically characterizing thermal tolerance is one of the most important subjects in fish culture. To identify the genetic characterization of thermal tolerance, this characteristic was compared among strains, and among parents and their offspring, in the guppy Poecilia reticulata. In the strain comparison, significant differences in survival rate were observed among the five strains examined, and between females and males. Females exhibited greater tolerance than males in four of five strains examined. In the comparison between parents and their offspring, stronger influence of female parent than of male parent was observed. Offspring obtained from surviving females exhibited greater tolerance than those from dead females. This tendency was typically observed in male offspring. The survival rate in male offspring obtained from dead female parents was lower than that of those from surviving females. The high-temperature tolerance of male parents did not influence this characteristic in offspring as strongly as that of female parents. These results suggest that the major gene or genes, which has a dominant resistant allele and a recessive sensitive allele, are probably passed on by sex-linked inheritance, located on the X chromosome.     

3,4-dihydroxyproline: a new amino acid in diatom cell walls

An analog of proline, 2, 3-cis-3, 4-trans-3, 4-dihydroxy-L-proline, was found in the cell walls of the eight species of diatoms studied and was isolated from the proteinaceous material of the wall of Navicula pelliculosa. The properties of this substance are described; its structure was confirmed by nuclear magnetic resonance spectros-copy.     

Inhibitory effects of pesticides on growth and respiration of cultured cells

Effects of various drugs including pesticides on the growth and respiration of cultured cells were evaluated comparatively using cell lines derived from mosquito ovary and subcutaneous mouse tissues. The concentration producing 50% inhibition of cell growth, I₅₀ (M), was determined for each of 42 drugs. Inhibitors of respiration and nucleic acid and protein biosyntheses such as rotenone, piericidin A₁, actinomycin D, and puromycin had very high pI₅₀ values of approximately 8. Except for the compounds known to be uncouplers of oxidative phosphorylation, the drugs suppressed the respiration rate of the cultured cells to various degrees. The pI₅₀ value (and the pEC₁₅₀, 150% enhancement of the control, value for uncouplers) was determined for each compound. By examining the relation of pI₅₀ (and pEC₁₅₀) values between cell growth and respiration, the compounds could be classified into two groups according to their modes of inhibitory action against the cultured cells. One mode relates to the inhibition of energy synthesis and the other, perhaps, to interference with the biosynthesis of biomacromolecules.     

Use of chrysanthemum plantlets grown in vitro to test cultivar susceptibility to white rust, Puccinia horiana P. Hennings

An efficient incubation and inoculation system for white rust was established using plantlets of chrysanthemum growing in vitro. The internal conditions of a culture vessel (plant box) were maintained at a humidity of 90‐100% and an optimum temperature of 20‐25°C, which are suitable conditions to germinate teliospores and basidiospores of the pathogen. Telia were maintained continuously on plants in the plant box and were used as an inoculum for infection experiments throughout the year, allowing differences in susceptibility to white rust among chrysanthemum cultivars to be detected. Susceptibility to white rust in the plant‐box evaluation showed a good correlation with the rating of sporulation on plants grown in a greenhouse. The method described here is a simple, space‐saving inoculation system to evaluate the susceptibility of chrysanthemums to white rust.     

Ultrastructural studies of spermatia of grey mould (<Emphasis Type="Italic">Botryotinia fuckeliana</Emphasis>)

To investigate maturation of spermatia of Botryotinia fuckeliana, we examined micro-structural changes in spermatia in liquid culture. Three to four spherical lipid bodies were seen in the center of the cell at the start of culturing. After 3–7 days, maturing spermatia had developed large mitochondria along with extensively developed granular endoplasmic reticulum. In contrast, the lipid bodies decreased not only in number but also in size over time. The results obtained here suggest that the maturation of spermatia involves active cell metabolism using the energy supply from lipid bodies.     

Effect of infection timing on fusarium head blight and mycotoxin accumulation in open- and closed-flowering barley

ABSTRACT Barley has two flowering types, chasmogamous (open-flowering) and cleistogamous (closed-flowering). We examined the effect of the timing of Fusarium graminearum infection on Fusarium head blight (FHB) and mycotoxin accumulation in barley cultivars with different flowering types using greenhouse experiments. In the first experiment, 13 cultivars were spray inoculated at two different developmental stages, and the severity of FHB was evaluated. The effect of the timing of infection differed among cultivars. Cleistogamous cultivars were resistant at anthesis but susceptible at 10 days after anthesis, whereas chasmogamous cultivars were already susceptible at anthesis. In the second experiment, five cultivars were inoculated at three different developmental stages and the concentrations of deoxynivalenol (DON) and nivalenol (NIV) in mature grain were analyzed. Cleistogamous cultivars accumulated more mycotoxins (DON and NIV) when inoculated 10 or 20 days after anthesis than when inoculated at anthesis, whereas chasmogamous cultivars accumulated more mycotoxins when inoculated at anthesis. Thus, the most critical time for F. graminearum infection and mycotoxin accumulation in barley differs with cultivar, and likely is associated with the flowering type. Late infection, even without accompanied FHB symptoms, was also significant in terms of the risk of mycotoxin contamination.