Minoru Shimotsuma

Bio: Minoru Shimotsuma is an academic researcher from Kihara Institute for Biological Research. The author has contributed to research in topics: Citrullus. The author has an hindex of 3, co-authored 3 publications receiving 36 citations.

Cytogenetical Studies in the Genus Citrullus V

Abstract: Meiosis and fertility in six Japanese varieties of C. vulgaris and C. colocynthis No. 1 was studied with diploids and induced autotetraploids.1. Meiosis in diploid C. vulgaris and C. colocynthis was normal and pollen fertility was found to be more than 90%.2. At MI in PMC's of induced autotetraploid C. vulgaris and C. colocynthis varying numbers of quadrivalents, trivalents and univalents besides bivalents were observed, the configuration being either 11IV or its derivatives. The frequency of quadrivalents per sporocytes was higher in autotetraploid C. colocynthis than in autotetraploids of C. vulgaris. Among the autotetraploids of six varieties of C. vulgaris no remarkable difference was found. Various types of quadrivalents, most frequently zigzags and single rings were observed. Trivalents were infrequent. One or two univalents per sporocyte were frequently observed.3. At the stage between AI and quartet formation, various abnormalities were observed. Lagging and chromosome bridges were observed at AI-TI and AII-TII. Micronuclei were found at interkinesis and at quartet stage.4. Pollen and seed fertilities were higher in the diploids than in the autotetraploids. Seed fertility was higher in autotetraploids of C. vulgaris than in the autotetraploid of C. colocynthis. Seed fertility of the intervarietal autotetraploid hybrid“Fuken”was higher than that of the parental varieties.

Cytogenetical Studies in the Genus Citrullus, IV. Intra- and Interspecific Hybrids between C. colocynthis Schrad. and C. vulgaris Schrad

Abstract: Intra- and interspecific hybrids were easily obtained from crosses among two races (C. No. 1 and C. No. 3) of C. colocynthis Schrad. and a variety (V. No. 1) of C. vulgaris Schrad..Chromosome behavior of the three parental races was normal throughout the course of their meiotic divisions. Chromosome conjugations at metaphase I in PMC's of the three hybrids showed 11 bivlaents in about 50% of the cells. The remaining cells showed irregular chromosome associations such as multivalents, mostly trivalents, and univalents. The frequency of the cells with multivalent associations differs among the three hybrids (Fig. 1 and Table 2). Pollen fertility was found to be approximately 50% in all of them (Table 3 and Fig. 3).Morphological characters of the three hybrids were compared with those of their parents (Table 4, Figs. 4, 5 & 6). C. colocynthis was dominant over C. vulgaris in stripe pattern of exocarp and taste and color of flesh. On the contrary, C. vulgaris was dominant over C. colocynthis in seed and exocarp color.Although C. No. 1 and C. No. 3 belong to the same species they differ in many morphological characters. C. No. 3 was dominant over C. No. 1 in color and stripe pattern of the exocarp. On the contrary, C. No. 1 was dominant over C. No. 3 in seed color.Leaves of the three hybrids are intermediate in shape between their parents. Seeds and fruits of the three hybrids are intermediate in size and weight between their parents.Female flowers of C. No. 3 were not produced until the end of August, however, two hybrids, C. No. 1×C. No. 3 and C. No. 3×V. No. 1 produced female flowers normally as early as the beginning of July.All hybrids showed hybrid vigor and were resistant to Fusarium wilt.

Cytogenetical studies in the genus Citrullus, III. Bitter substances in fruits of C. colocynthis Schrad. and C. vulgaris Schrad.

Abstract: The bitter substance in the fruits of C. colocynthis and C. vulgaris was analysed by chromatographic technique. Only one compound was detected in the ripe fruit of C. No. 1 (2x & 4x). The junior author identified it as “Citbittol A”. The amount of bitter substance in the ripe fruit of tetraploids was nine times as high as that of diploids.In unripe fruits of C. No. 1 (2x), however, seven new bitter compounds were detected. These newly found bitter substances were called “Citbittol B, C, D, E, F, G and H”. The amount of bitter substance in unripe fruits was higher than that of the ripe fruits. The bitter substance in the unripe fruit decompose gradually as the fruits ripen. Four compounds were detected in the ripe fruits of V. No. 2 and 4. Although C. No. 4 belongs to C. colocynthis, bitter substances was not found in the ripe fruits in this exceptional case.Ripe fruits of di-, tri- and tetraploid interspecific hybrids obtained from all possible cross combinations among diploid and tetraploid strains of C. No. 1 and V. No. 1 contain a higher amount of bitter substance in the ripe fruit than C. No. 1.The segregation ratio 3 (bitter): 1 (non-bitter) for F2 population and 1 (bitter): 1 (non-bitter) for the testcross was indicated by chromatographic analysis of bitter substance in the ripe friuts of each individual. From this evidence, bitterness in the genus Citrullus was concluded to have monohybrid inheritance with dominance of the bitter character.

Founder effect in crop-plant evolution

Abstract: Seed-crop plants apparently originated from a limited number of mutants in which seed dispersal was changed from that found in nondomesticated populations. Seed nonshattering in cultivated plants may be controlled by a single gene or a small number of genes. Allopolyploid crop plants were derived from a limited number of interspecific hybridizations followed by chromosome doubling. The consequence of this founder effect is a narrow genetic variability in the crop population compared to its wild progenitor. Natural hybridization between the two is prevented by various isolating mechanisms, and gene flow, if it exists, is apparently more effective in the direction from the cultivated to the wild populations. Founder effect in crop-plant evolution indicates the value and the breeding potential of the genetic variability remaining in its wild relatives.

The Genes of Watermelon

Abstract: Watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) is a major vegetable crop in the world, accounting for 6.8% of the world area devoted to vegetable crops. Wa- termelon is a useful vegetable crop for genetic research because of its small genome size, and the many available gene mutants. The watermelon genes were originally organized and summarized in 1944, and have been expanded and updated periodically. However, the action of some watermelon genes has not been described clearly in some cases. Also, the interaction of multiple gene loci that control similar traits needs to be described more clearly. Finally, it is necessary to identify the inbred lines having each published gene mutant, for use as type lines in studies of gene action, allelism, and linkage. The objective of this work was to update the gene list, identify the cultivar or line having each gene mutant, and collect seeds of the lines for use by interested researchers. In addition, the gene descriptions were expanded and clarifi ed, information on gene interactions was added, and errors in naming or citing previously described genes were corrected. New genes that have not previously been described (cr, Ctr, dw-3, ms-2, Ti, ts and zym-FL) were added to the list, for a total of 163 watermelon gene mutants. Watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) is a major cucurbit crop that accounts for 6.8% of the world area devoted to vegetable crops (FAO, 2002). Watermelon is grown for its fl eshy, juicy, and sweet fruit. Mostly eaten fresh, they provide a delicious and refreshing dessert especially in hot weather. The watermelon has high lycopene content in the red-fl eshed cultivars: 60% more than tomato. Lycopene has been classifi ed as use- ful in the human diet for prevention of heart attacks and certain types of cancer. Watermelon is native to central Africa where it was domesticated as a source of water, a staple food crop, and an animal feed. It was cultivated in Africa and the Middle East for >4000 years, then introduced to China around 900 AD, and fi nally brought to the New World in the 1500s. There are 1.3 million ha of watermelon grown in the world, with China and the Middle Eastern countries the major consumers. China is the largest watermelon producer, with 68.9% of the total production. The other major watermelon producing countries are Turkey, Iran, Egypt, United States, Mexico, and Korea (FAO, 2002). In the United States, watermelon is used fresh as a dessert, or in salads. U.S. production is concentrated in Florida, California, Texas, and Georgia (USDA, 2002), increasing from 1.2 Mt in 1980 to 3.9 Mt in 2002, with a farm value of $329 million (USDA, 2002). Watermelon is a useful crop species for genetic research because of its small genome size, and the many available gene mutants. Genome size of watermelon is 424 million base pairs. DNA sequence analysis revealed high conservation useful for comparative genomic analysis with other plant species, as well as within the Cucurbitaceae. Like some of the other cultivated cucurbits, watermelon

Gene List for Watermelon

Abstract: This is the latest version of the gene list for watermelon (Citrullus lanatus (Thunb.) Matsum. and Nakai). The watermelon genes were originally organized and summarized by Poole (1944). ). The list has been expanded by Robinson et al. (1976), the Cucurbit Gene List Committee (1979, 1982, and 1987), Henderson (1991 and 1992), Rhodes and Zhang (1995), and Rhodes and Dane (1999). The current list provides an update of the known genes of watermelon. This year, the list has 162 total mutants, grouped into seed and seedling mutants, vine mutants, flower mutants, fruit mutants, resistance mutants, protein (isozyme) mutants, DNA (RFLP and RAPD) markers, and cloned genes.

Enzyme polymorphism in Citrullus lanatus and C. colocynthis in Israel and Sinai

Abstract: Electrophoretic and morphological variation was studied in 13 cultivars ofC. lanatus and 31 accessions ofC. colocynthis from Israel. Twelve enzyme systems were assayed, representing 19 loci. We found 12 commercially grown cultivars to be monomorphic at all loci. OneC. lanatus accession collected from Israel is highly polymorphic and carries alleles ofC. colocynthis; this accession is probably a representative of a locally cultivated land race grown by Bedouins for animal feed. Over a range of 500 km two forms ofC. colocynthis were identified: one which grows along the coastal plains of the Mediterranean and the other in the arid Negev and Sinal deserts. A high level of electrophoretic and morphological divergence was found between plants of the two regions, whereas within the ecotypes little variation was observed.

Qualitative Inheritance of Rind Pattern and Flesh Color in Watermelon

Abstract: Watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus] is a diverse species, with fruits of different sizes, shapes, rind patterns, and flesh colors. This study measured the inheritance of novel rind phenotypes and verified the genetics of white, red, salmon yellow, and canary yellow flesh colors. For each of the 11 crosses, six generations (P(a)S1, P(b)S1, F1, F2, BC1P(a), and BC1P(b)) were produced to form 11 families. Three new genes were identified and designated as follows: Scr for the scarlet red flesh color of Dixielee and Red-N-Sweet, Yb for the yellow belly (ground spot) of Black Diamond Yellow Belly, and ins for the intermittent stripes of Navajo Sweet. The inheritance of the C gene for the canary yellow flesh color was verified as single dominant, and a new inbred type line was developed possessing that gene. Aberrations in the segregation of red, white, and salmon yellow flesh colors were recorded, raising questions on the inheritance of these traits. Finally, the spotted phenotype from Moon and Stars was combined with light green and gray rind patterns for the development of novel cultivars with distinctive rind patterns.