The utilization of germplasm of the wild species in sweet-potato breeding has been conducted for the last three decades. Such attempts brought some remarkable achievments in improving root yield, starch content and resistance to the nematodes of sweet potato. Some wild plants in polyploid series may have many genes potentially important for further improvement of the agronomic traits. However, the genomic relationship between the wild relatives and hexaploid sweet potato (2n=6x=90) has been unrevealed. Meiotic studies were carried out on the hexaploids synthesized with diploids and tetraploids and on the F1 hybrids, when possible, with sweet potato. Chromosomes in pollen mother cells (PMC's) and root tip cells were fixed in New-comer's solution and stained according to Feulgen reaction with Schiff's reagent. The present report was concerned wlth two kinds of the synthetic hexaploids. The first was the hexaploids derived from chromosome doubling of triploid hybrids between Ipomoea lacunosa (K61, 2n=30) and I.tiliacea (K134, 2n=60). the synthetic hexaploid exhibited mostly regular meiosis with bivalents at the metaphase I stage (MI), and it was considered an allo- or segmental allo-hexaploid. The synthetic hexaploids were fertile, but failure in obtaining hybrids by crosses with sweet potato suggested a critical reproductive barrier between them. The second synthetic hexaploids with 2x I, trifida (K221, 2n=30) and 4x I, trifida (K233, 2n=60) showed the chromosome configurations characterized by the occurrence of tetravalents and hexavalents. Such multivalent associations, high in frequency and number per cell, suggested the presence of the genomes at least in quadruplicate. Similar pattern of the chromosome configura-tions was observed in a cultivar of sweet potato and the F1 hybrid between the synthetic hexaploid and sweet potato. Consequently, the genomic formula for sweet potato was proposed as B1B1B2B2B2B2, in which B1B1 was given to 2x I.trifida and B2B2B2B2 to 4x I. trifida. However, it is necessary to clarify the degree of homology between B1 and B2 genomes for more conclusive genomic constitution of sweet potato. A brief account was given for the taxonomic identification of the wild Ipomoea strains used in the present study.
1. This work is one of the studies in which the writers intend to make clear the mode of quantitative inheritance in main crops from the view ppint of breeding. Materials used are the same as those used for the studies of inheritance of the panicle length and culm height in the preceding experiments(SYAKUDO, et. al. 1952-a, b) namely -, the F1-F4 generations from the hybnds of "NABESIMA" and "KAlRYO-AIKOKIJHEN-DAIKOKUGATA", which were crossed in 1945 at the plant-breeding laboratory of the Kyoto Univ. The total numbers of lines and individuals ob, served are 467 and 49, 223 respectively. 2, , NABESIMA" is a normal variety showing a medium length of panicles and a medium height of culm with small grains, three dimensions of which are about 5.3mm, 3.0 mm, and 2.1 mm. "KAIRYO-AIKOKUHEN-DAIKOKUGATA" is a dwarfish variety with short panicles, short culm and small round grains, three dimensions of which being 4.5 mm, 3.2 mm and 2.3 mm. 3. The conditions of cultivation and the methods, of investigation are the same as those already, described in the writer's reports (SYAKUDO, 1948-b, 1951). . 4. The progeny test in regard to the grain length was made considering the mean value, standard deviatian, coefiicient of variabilityand the range of variance. The results show that the gene Gr3 and the dwarfish gene D1 determine the grain length. Thus the genotypes of the parents will be assumed as follows:
1. In this work, the writers intend to make clear the modes of quantitative inheritance in main crops from the view point of breeding.For this object, ' a part of the hybrids of " NA BESHIMA" x "KAlRYO-AIKOKUHEN-DAIKO-KUGATA" was used namely-the F5-F7 generations from the F4No. 70 and F4No. 106 of the hlybrid. The total numbers of lines and individuals are 27.2 and 15244 respectively. 2. The conditions of cultivation are the same as those already described in the previous reports (SYAKUDO, 1948), excepting the dates of sowing and transplantation. The date of heading indicates the first day when the top of one ear emerged from the leaf-sheath. And the heading duration indicates the nunrber of days from sowing to.heading. 3. As the result of the progeny test, the genes E1, E2 and the dwarfish gene D1 determine the heading duration accumulatively. Ptobably the effect of E1 may be of perfect dominance, while that of E2 of inperfect dorrLinance. The gene-interactions are recognized b.etween E1 and E2, though their qualifying effects are neither additive nor multiplicative. 4. The qualifying values of the genes which indicate the medium type of heading duration are the same in the two years, but those of th.e genes which indicate the early and the late typ, es are not the same respectively. These differences seeni to be due to the difference of the daily mean temperature during the heading of each type. 5. The gene El for the heading duration seems to be the same as the gerne H2 for the culm height (SYAKUDO, et.all. 1952-b), while the gene E2 for the heading duration has no effect to the culm height.
The fifty-one diploid (2n=2x=30) Ipomoea strains, which have been named I. triloba. I. lacunosa and I. trifida in Kyoto University and Mie University, Japan, and I. triloba. I. lacunosa. I. ramoni and I. cordatotriloba (syn. I. trichocarpa) in the University of Georgia, USA, were studied for further identification by means of multivariate analyses. A total of forty-one characters distributed over various parts were used: (a) stems and leaves 10, (b) inflorescence 8, (c) corollas 10, (d) sepals 6, and (e) capsules and seeds 7. The initial data-base of 51 strains × 41 characters was subjected to the WVGM (weighted variable-group method) cluster analysis. Subsequently, the data-base of the same 51 strains with 25 characters was processed accordlng to principal components analysis. The 25 characters included one addltional root character but other 24 characters were selected from those used in the WVGM analysis. These two analyses represented that the 45 strains are divided into six phenetic groups, A1, A\2, B, C1, C2 and D. The other 6 strains including. I. trifida strain K221 remained ungrouped. Further, the result of analyses demonstrated that the I. trificla strain in question has the most phenetic similarity to group D and the next most similarity to group B. By making a morphological comparison between the phenetic group and taxonomically described species, three groups A1, A2 and B were identified as I. trlfloba L., C1 as I. lacunosa L. and D as I. cordatotriloba DENN. The intermediate position of group C2 in the taxonomic space suggested that the strains of this group are natural hybrlds, I. × leucantha JACQ. To clarify the interspecific relationships based on crossability within and between the phenetic groups, crossing studies have been carried out. Intragroup hybrldiza-tlon among the stralns In group B or group D showed various degrees of crossabllity, however, none of these strains produced hybrids in crosses with the I. trifida strain K221. The low crossability in intergroup hybridization between the strains of group D and one strain of A1 suggested the possible genetic divergence of these taxa, I. cordatotl'iloba and I. lacunosa. Crosses of the I. trifida strain K221 with four strains each from group A1, A2, C1 or C2 were also unsuccessful in obtaining hybrids. These results indicated the presence of a significant reproductive isolating barrier between diploid I. trifida and the other diploid lpomoea taxa studied.
1. This work is one of the studies in which the as followswriters intend to make clear the modes of the quantit, ative inheritance in main crops from the view point of breeding. Materials used in this work are the F1-F5 generations from the hybrids of the two varieties, of rice, "NABESIMA" and "KA1RYo-AIKoKUnEN-DAIKO-KUGATA", which were crossed in 194 at the Plantbreeding laboratory of the Kyoto Univ . The total :numbers of the lines and individuals observed are 1. 137 and 85.616 respectively. 2., 'NABESIMA" is a normal veriety showing a medium stem length and also a medilm length of pa nicles (about 21 cm), while "KAlRYO-AIKOKUHEN-DAIKOKUGATA" is a dwarfish variety with short stems and short penicles (about 17 cm). 3 . The methods of investigation are the same as those already described in the senior writer's previous feports (SYAKUDO, 1948, 1950). 4, The progeny test in regard to the. panicle length was made eonsidering the mean value, standard deviation, coeificient of variability and the range of variance. The. results ., show that the two multiple, genes P4 and P5., and a dwarfish gene D1 determine the panicle length. The accumulative effect of the genes P4 and P5 to the panicle length are of inperfect dominance, while that of D1 is of perfect dominance. Consequently the genotypes of the parents will be assumed as follows:
Ipomoea fnfida (H.B.K.) DON. forms a polyploid complex with a range from diploid to hexaploid. The synthesized hexaploids (SH, 2n=6x=90) with I. trlfida d{ploid (K221, 2n = 2x=30) and tetraplold (K233, 2n=4x=60) have been considered to have the same genomic structure (B1 B1 B2 B2 B2 B2) as the sweet potato (SP, 2n=6x=90). To determine the genomic structure of the derived hexaploids (DH) frorn intercrosses of I. trzfida triploid (K222, 2n=3x=45), and the genomic structure of I. trzfida hexaploid (K123, 2n=6x=90), F1 hybrids from DH×SH, DH×SP, SH×K123, and DH×K123, and their backcross (BC1) and double-cross progenies have been cytologically examined. When the genomes existing in quadruplicate in the parental hexaploids are non-homologous, such non-homology may cause failure of chromosome pairing in a BC1 or double-cross progeny. Meiotic analyses of these hexaploid hybrids showed almost complete chromosome pairing at the matephase I (MI), suggesting that the hexaploids DH and K123 have the same genomic structure just as do SH and the sweet potato. Further, to clarify the genomic structure of the sweet potato and the I. tnfida hexaploids by estimating the degree of homology between the B1 and B2 genomes, meiotic pairing was observed in the tetraploid hybrids (B1 B1 B2 B2) from DH×K221 and tetraploid hybrids (B1 B2 B2 B2) from (DH×K221)×K233. Both tetraploid hybrlds demonstrated a reasonable frequency of tetravalents to support the autoploidy of their genomic constitution. These results led to the conclusion that the sweet potato and the I trifida hexaploids are autoploids with respect to the B genome of the I. trlfida diploid (K221). The use of wild germplasm of I. trtfida to incorporate its valuable traits into cultivars was undertaken and 'has brought some remarkable results in sweet potato breeding. A significant role of the autoploidy in possible gene flow through inter- and intraploidy hybridization between the sweet potato and I. trlfida was discussed.
