Morphology and Crossing Ability of Tetraploid Species Closely Related to Sweetpotato
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Jpn. J. Trop. Agr. 43 (1) : 42-48,1999 Morphology and Crossing Ability of Tetraploid Species Closely Related to Sweetpotato Katsumi KOMAKI National Agriculture Research Center, 3-1-1 Kannondai, Tsukuba, Ibaraki 305-8666, Japan Abstract Twenty five accessions of tetraploid Ipomoea species that are closely related to sweetpotato were used for the analysis of morphological variation and evaluation of crossing ability. Based on the principal component analysis of 47 char- acters, the accessions were morphologically classified into four groups. One of the groups consisted of five accessions which had small, thick and leathery or membranous leaves and markedly different from other three groups. However, crossing rates were not significantly different in inter- and intra-group cross combinations, suggesting that there was no significant biological isolation. Morphological variation in the progeny resulting from inter-group crossing, covered almost all range of the variations of parental accessions. All the tetraploid accessions used in this study were considered to belong to one taxon, as indicated in the taxonomical studies carried out in U. S. A. Therefore these accessions should be designated as I, batatas. Key words Crossing ability, Ecological variation , Ipomoea species, Tetraploid 四倍 体 のサ ツマ イ モ近 縁 野 生植 物 の 形 態 と交雑 性 小 巻 克 巳 農 業 研 究 セ ン ター 〒305-8666茨 城 県 つ くば 市観 音 台 3-1-1 要 約 四倍 体 の サ ツ マ イ モ近 縁 野 生 植 物25種 類 を供 試 して,花 器,萼 片,及 び 茎 葉 に 関 す る57形 質 を 調 査 し,変 異 の 認 め られ た47形 質 に つ い て主 成 分 分 析 法 に よ りそ の 変 動 様 相 を 明 らか に した.供 試 した25種 類 は こ れ に よ り四 つ の グ ル ー プ に 分 類 す る こ とが で き,そ の一 つ は 葉 が 小 さ く,厚 く,膜 質 あ る い は 革 質 で あ る とい う特 徴 を も っ て お り,他 の3つ の グ ル ー プ とは 著 し く異 な って い た.し か し,グ ル ー プ 内 あ る い は グ ル ー プ 問 で行 っ た交 配 実 験 の 結 果,い ず れ の グ ル ー プ との 交 雑 に お い て も交 雑 率 に 有 意 な差 が 認 め られ な い こ とが 明 らか とな っ た.こ れ は 形 態 的 に 差 が あ っ た と して も生 物 学 的 な 隔 離 は 十 分 に進 ん で い な い こ とを 示 唆 す る も の で あ っ た.ま た,グ ル ー プ 問 の 交 雑 の 後 代 の 形 態 は 両 親 の 中 間的 な 特 徴 を 示 し,変 異 は 連 続 的 に な っ た.こ れ に よ り,サ ツマ イ モ と交 雑 が 可 能 な 四 倍 体 近 縁 野 生植 物 は 分 類 学 的 に は一 つ の 種 に 属 す る と判 断 さ れ た.サ ツ マ イ モ近 縁 野 生 植 物 の 形 態 分 類 を精 力 的 に行 っ て きた 米 国 の 研 究 グ ル ー プ に よ る研 究 蓄 積 と今 回 得 ら れ た 形 態 変 異 及 び 交 雑 性 に 関 す る知 見 か ら,わ が 国 で こ れ ま でI. trifidaで あ る と して きた これ ら の植 物 はI. batatasと す るの が 妥 当 で あ る と結 論 し た. キー ワ ー ド 形 態,交 雑 性,サ ツ マ イ モ近 縁 野 生 植 物,四 倍 体 I. batatas6,7). Introduction Morphological variation and crossing Ipomoea trifida (H. B. K.) G. DON. is a ability of tetraploid Ipomoea species have species most closely related species to sweet- not yet been analysed in detail. Thus, this potato. It is principally distributed in the study aimed at analyzing various aspects of Carribian region and may consist of both morphological variation in the tetraploids diploid and tetraploid races4). Japanese scien- and classifying them based on multivariate tists10,16)have recorded diploid, triploid, and analysis. Crossing experiments were conducted hexaploid types. The morphological charac- to detect reproductive isolation among the teristics of the tetraploid types are highly groups classified based on the morphological distinctive, in terms of leaf size and thickness characteristics. Morphological and crossing or plant type16). This type of tetraploid is rep- studies were also carried out in progenies resented by K 233 collected at Veracruz, from the cross of the tetraploids. Mexico, which has small, thick and leathery Materials and methods or membranous leaves. K233 and other morphologically identical Twenty five tetraploid Ipomoea accessions accessions were designated as I, littoralis.20), were used for the analysis of morphological I. gracilis.8,13), a hybrid between sweetpotato variation and evaluation of crossing ability and diploid species1,2), I. trifida9, 10,15, 16, 18, 19) or (Table 1). The accessions were grafted onto Received Aug. 28, 1998 a dwarf type morning glory (I. nil cv. Kidachi) Accepted Nov. 13, 1998 grown in 24 cm clay pots because only a KOMAKI: Variation of tetraploid Ipomoea species 43 Table 1. Tetraploid Ipomoea species used for morphological analysis and crossing *,**: renamed I . trifida by KOBAYASHI 9,10) and SHIOTANT 16), respectively. small number of flowers were formed under sis (PCA)processed by SPSS Base 7.5 J natural conditions. The plants were kept in a (SPSS Inc.,Chicago, Illinois,U.S.A.). green house at Ibusuki Branch, Kyushu Na- Crossing was mainly performed for 25 tional Agricultural Experiment Station, flowers in each cross combination. Seed set- Kagoshima, Japan. ting was calculated by the formula(No. of Data were gathered for 57 characters re- mature seeds×100)/(No. of pollinations× lated to corolla, sepal, leaf, vine, and others 4)and expressed in percentage. A one-way (Table 2). Measurements were based on 3 to analysis of variance(One-way ANOVA)was 5 samples per accession. Qualitative charac- employed to detect differences in the seed ters involving color, pubescence, shape or setting among the types of cross combina- texture were rated on a numerical scale ac- ti ons based on the classification of the acces- cording to their levels. Two ratings were sions by PCA and testing of the homogeneity adopted for the characters, one for presence of variance within the type of cross combina- and zero for absence. Since no variations tion by the Levene test. Mature seeds ob- among the accessions were observed among tamed from 16 cross combinations were the 10 characters such as: presence of star grown in the greenhouse and the plants were shape inside of corolla tube bottom and ex- grafted to the dwarf type of morning glory ternal nectary, corolla tube shape, color of to induce flowering as described above(Ta- stigma, style, and anther, apex shape of ble 3). Morphological data were collected in outer and inner sepal, vine twining, and pres- the same way as in the parents. Each plant ence of adventitious root primordia at node, was crossed with the parents or other plants data matrix of 25 accessions×47 characters and crossing rate was also calculated. was used for the principal component analy- 44 Jpn. J. Trop. Agr. 43 (1) 1999 Table 2. Characters measured or observed in this study leaf thickness (-0.850), leaf lobing (-0.717), Results and adaxial pubescence of leaf (0.752). The Morphological classification of tetraploid second principal component (Component II) accessions had high loading values for the pedicel Around 25 and 12% of total morphologi- length (0.784), longest stamen length (0.802), cal variation of 47 characters in 25 acces- and shortest stamen length (0.753). There- sions could be explained by the first and sec- fore, the Component I mainly explained the ond principal components, respectively. In combination of variation among whitish the first principal component (Component I), flowers, small sepals, large, round, thin and high factor loading values (<-0.7 or >0.7) hairy leaves, and thin pedicel vs. pinkish were observed for the corolla limb color (- flowers, large sepals, small, lobed, thick and 0.881), corolla tube color (-0.791), stamen glabrous leaves, and thick pedicel. On the pubescence (0.713), outer sepal width (- other hand the Component II mainly ex- 0.731), inner sepal length (-0.720), inner se- plained the variation of stamen length and pal width (-0.748), pedicel diameter (- arrangement of the inflorescence. 0.772), leaf length (0.864), leaf width (0.787), The scatter diagram of the first and sec- KOMAKI: Variation of tetraploid Ipomoea species 45 ond principal component scores showed that One-way ANOVA was applied on the accessions fell into four different groups. basis of the Levene test, which did not reject The first group (Group A) which had a the hypothesis of equal variances across the smaller Component I score (<-1.5) and in- 14 types of cross combinations, and it did not termediate Component II score (around 0) any difference in the means among the type consisted of 5 accessions including K 233. of cross combination between the different The second group (Group B) included 2 ac- groups classified by morphological analysis cessions, the third group (Group C) had 5 ac- (Table 3).