We examined a method for evaluating the root lodging resistance in soybean by the measurement of the pushing resistance and top weight moment using five cultivars differing in their lodging resistance, which are common in the Tohoku Region. We tried to use the pushing moment ratio calculated by the formula (top fresh weight×height of gravity center)/(pushing resistance×pushing height), as a criterion for root lodging resistance. The ratios of the lodging-resistant cultivars were lower than those of the lodging-susceptible ones. There was a high correlation between the pushing moment ratio and lodging degree in the field tests. The cultivars and lines with high pushing moment ratios in 1999 experienced more pronounced lodging than those with low ratios under the severe lodging field conditions in 2000. Therefore, it is considered that the pushing moment ratio can be used as an index of root lodging resistance. The optimum time for the investigations was the beginning or the middle part of August. Since the plant stems must be cut to measure the top weight moment or the height of the gravity center for calculating the index of root lodging resistance, progeny seeds cannot be obtained from the plants investigated by this method. We observed that the parameter (main stem length×major axis of the middle section across the first internode), which can be easily determined without breaking the plants, could be substituted for the top weight moment, if progeny seeds from the evaluated plants are needed.

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The objective of this study was to analyze the relationship between Japanese tea varieties and Korean wild tea populations based on their morphological characteristics. About seven hundred Korean wild tea seedlings grown in NIVOT fields were used as materials in this study. The seeds were collected from six different temples and a farmer’s field in 1993. The morphological characteristics were examined from 1998 to 2001 based on the descriptors for characterization and evaluation of plant genetic resources. In seven Korean tea populations, there was only one variegated leaf plant and Koro type plants could not be observed. As a result of cluster analysis, the Korean populations clustered into two large groups. The mature leaf width of the Korean tea plants was smaller and the leaf index (length/width) was larger than those of the Japanese plants. The length of the area extending from the pistil to the stamens was relatively longer in many Korean tea plants. In about two-thirds of the plants, some or all the styles were constricted. In the Korean wild tea plants examined in this study, pubescence generally fully covered the new shoots, while in 6.8% of the clones only partially.

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Double ovules (polyovules) which contain two or some true seeds (ovules) in a seed canopy of a monogerm fruit, and bigerm fruits which consist of two monogerm fruits fused at the pericarp are undesirable characters for sugar beet (Beta vulgaris L.) production as they require thinning, a laborious operation. In this experiment, the frequency distribution of double ovule rates and bigerm rates, and the possibility of individual selection using a self-fertilized O-type line and F₂ populations were investigated. For the double ovules, the mother population of a self-fertilized O-type line showed a large and continuous variation. The progenies selected from this population were fixed to the high, middle and low double ovule rates, and the standardized heritability was 0.55. Furthermore, F₂ populations developed from lines derived from crosses between these progenies showed a continuous distribution from the mid-parent. There were statistically significant differences between these F₂ populations. These results indicated that the rates of double ovules of monogerm sugar beet are controlled by a polygene system, and that, by individual selection, it is possible to develop lines with genetically different double ovule rates. For the bigerm rates, the variation was smaller than that for double ovules, but it was possible to select for low bigerm rates, and the standardized heritability was 0.43. Based on these results, it was suggested that bigerm rates are also controlled by a polygene system.

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Interspecific hybrids of Nicotiana debneyi Domin.×N. tabacum L. cv. Hicks-2 displayed hybrid lethality that it one of the mechanisms for reproductive isolation. Apoptotic changes were detected in the cells of hybrid seedlings expressing lethality at 28°C but not under high-temperature conditions (34°C), when the lethality was suppressed. Condensation of chromatin and fragmentation of nuclei observed by fluorescence microscopy characterized the changes in the hybrid cells associated with the expression of lethality. Fragmentation of the nuclei was confirmed by flow-cytometry. One peak corresponding to the nuclei at the G1 phase of the cell cycle became less prominent and additional peaks with lower fluorescence values appeared in the roots, followed by the shoots of the hybrid seedlings. Agarose gel analysis of DNA extracted from 10 days-old (days after germination) hybrid seedlings revealed a specific ladder pattern in the roots suggesting the existence of nucleosomal fragmentation unlike in the shoots of the hybrid seedlings. These results indicate that lethality process in the interspecific hybrids of Nicotiana debneyi×N. tabacum is associated with apoptosis.

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We detected occasionally maternally inherited RAPDs (randomly amplified polymorphic DNAs) in F₁ populations derived from reciprocal crosses of tea. We detected 18 from 1040 random primers and 1 while obtaining emphasized RAPD (e-RAPD) from bands given by other primers. These results confirmed the maternal inheritance of the RAPDs. The electrophoresis bands of the RAPDs were significantly larger than the other major bands derived from the same random primers. We consider that this size difference was due to the amplification of high copy-number sequences such as chloroplast or mitochondrial DNAs. Five maternally inherited RAPDs were cloned and sequenced. One of them showed a high homology to a mitochondrial sequence of Arabidopsis thaliana, whereas the others did not exhibit a high homology to other sequences in the public databases. Generally, chloroplast DNA is highly conserved, whereas the sequence and size of mitochondrial DNA are variable. Therefore, the maternally inherited RAPDs were presumably derived from mitochondrial DNA. Maternally inherited RAPDs are useful for evaluating the diversity of cytoplasmic DNA among varieties and cultivars, which is important in breeding. Tea seeds weigh about 1 g—too heavy for wind dispersal—and contain saponins, which are toxic to animals. Consequently, they are not easily spread under natural conditions, compared with pollen grains, which are spread by insects. Hence, tea cytoplasmic DNA, which is maternally derived, is evolutionarily well conserved compared with tea chromosomal DNA, which is derived from both parents. Maternal RAPDs are thus useful for analyzing the origin and spread of tea populations.

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