(15(3):1-23)STUDIES ON THE POPULATION GENETICS IN WILD RICE

本研究利用日本國立遺傳學研究所，岡彥一博士在印度、泰國及筆者在臺灣所採集的野生稻系統為材料，就各種性狀調查野生稻集團間及集團內之變異，並與栽培稻變異比較，又就含有野生，栽培及其中間型之Jeypore系統，考察由野生稻變為栽培稻之進化路徑。又觀察Spontanea型野生稻與栽培稻間之導入雜交及Perennis型野生稻與栽培稻間之Hybrid swarm等，所得結論中主要者有如下幾點： 1. 所有Perennis型集團均為強感光性，但Spontanea型集團亦有弱感光性者。Perennis型之界限日照時間，以集團內變異為大，而Spontanea型之感光性指數以集團內變異為大。 2. 種子休眠性與與脫粒性，野性型較栽培型為大。野生稻中Spontanea型之種子大，花粉稔性高再生力弱。穗長、植高、葉舌長、花藥之長度等而言，Perennis型較大。Perennis型對此等性狀一般集團內變異大而集團間變異小。Spontanea型集團間變異大，而集團內之變異小。 3. 由野生稻集團內變異所推算之雜交率因推算方法不同而不同，但假定遺傳因子間有顯性作用，同時有淘汰作用時所計算的結果為30-40％。 4. 就野生稻集團間及栽培稻品種變異，計算性狀間之相關係數，用要因分析法由相關行列抽出第1及第2成分。將之各為縱軸與橫軸，並將調查性狀分佈於圖面時，即可看出野生型與栽培型之間有共同與不同部分，由兩者之性狀變異可知其遺傳的背景略為不同。 5. 由印度Orissa州山地之Jeypore地區所採系統，可分為野與栽培二型，但均包括野生～栽培之中間型，自野生稻至栽培稻之變異為連續變異。製作野生型對栽培型及印度型對日本型之判別式，調查Jeypore系統之變異。野生稻及Jeypore系統接近於野生稻者看不出印度型與日本型之分化，但愈接近栽培型者可發現少數的日本型稻。 6. 將印度Raipur地區以水田雜草狀態所生長的野生稻（Spontanea型），與典型的Spontanea及栽培稻作比較。雜草化野生稻之各性狀屬於栽培及野生之中間型，因此認為由栽培與野生稻之導入雜交（Interogression）之結果所生者。比較此等集團之環境條件，認為野生稻與栽培稻之雜交所生集團，隨生長當地之栽培壓力而漸變為栽培型。 7. 在印度Cuttack郊外所見Perennis型之1集團Chiengmai郊外（糯米地帶）之1集團及臺灣野生集團（Perennis型）已認為屬於與栽培稻之Hybrid swarm。可行無性繁殖的Perennis型野生稻，在集團內保存由於自然雜交所吸收的栽培型遺傳因子，因此繁殖種子時，可分離出屬於Perennis型，Spontanea型之野生型至栽培型之種種植物。Perennis型野生稻之此種性質對栽培稻之起源有重要的貢獻。 8. 基於上述之觀察結果，對野生稻之Perennis型與 Spontanea型之分化曾加討論，並認為栽培型係以Perennis型為祖先，再向Spontanea型之方向變化同時發生非脫粒型之變化，兩者相互作用後所產生。 Studies on the origin of most crop plants have been cytogenetically put forward In rice, however, no polyploid relation is found between the cultivated species, Oryza sativa, and wild ones in close relation to it. O. perennis and other. They have the same chromosome number, n = 12, and the F1 hybrids do not show a disturbance in chromosome pairing. On the other hand, variations in various characters are quite rich. Population genetic study of the variation may then be an important line of approach to the origin of cultivated rice. From this view-point, the writer has engaged in this work in cooperation with the National Insti-tute of Genetics, Japan. The wild rices used were collected by Dr. H.I. Oka of the above mentioned Institute, from varions localities of India in October-December 1957, and from Thailand in Nevember-December, 1958. The wild rice of Taiwan was collected by the writer in October, 1957. In addition, about 80 rice strains from various Asian countries (including both the indica and japonica types) were used for the sake of comparison. Further, a number of strains collected from Jeypore Tract, India, in which many intermediate plants between wild and cultivated types were included, were observed. The seeds taken from many plants of respective wild populations, as well as those taken on a single plant basis, were grown and investigated in experimental fields of the Taiwan Prov. Chung-Hsin University, Taichung, in 1958, 1959 and 1960. Records were taken for various characters on an individual plant basis. According to Dr. Oka, the plants seemingly belonging to O. perennis were in water reservoirs of deep swamps and had rhizomes, while those showing the characteristics of O. sativa f. spontanea were found in relatively shallow swamps and had no rhizomes. Between the two species, however, many intermediate forms were found so that the two species could not be clearly distinguished from each other. Therefore, the populations observed were classified into perennis, intermediate and spontanea types according to the classification of Morishima and Oka (1960), and were com-pared. The main conclusions reached were as follows: 1. Plants of the perennis type showed a strong response to photo-period, while those of the spontanea type had relatively weak responses. The former type showed wider range of winthin-populational variation in critical day-length than the latter. The spontanea type, however, showed a wide variation in photoperiodic sensitivity. From these facts, differences of the two types in the mode of adaptation to habitat was discussed. 2. Variations in various other characters were observed comparing wild and cultivated types. Characters most sharply differentiating the two types were dormancy of seeds and grain shedding. Comparing the perennis and spontanea types, the latter had larger seeds, higher fertility and lower regenerating ability than the former. It was found further that in plant height, lengths of panicle, ligule and another, and in other characters, perennis had larger within-populational variance than spontanea, but the latter varied among populations on wider range than the former. 3. The percentage of out-crossing, estimated from the results of analysis of variance components for seed size and other characters, differed according to the biometrical methods used. The values estimated taking the effects of dominance and natural selection into consideration were 30-40% in wild rice. 4. The multi-variate variations in these wild populations and cultivated varie-ties were then studied by factor analysis methods. From matrices of correlation coefficients between characters, principal components were extracted, and the characters were scattered on the plane defined by the component axes. The wild and cultivated types showed different distribution patterns, suggesting that they have different genetic backgrounds. 5. Strains collected from the Jeypore Tract, India, comprised both wild (not controlled by man) and cultivated ones, but in both of the two groups many inter-mediate wild-cultivated types were found forming a continuous array of intergrades between the two types. The variation was then studied by using two discriminant functions, one for classifying wild and cultivated typed, and the other for classify-ing the indica and japonica types. Differentiation into the indica and japonica types was found among strains approaching cultivated rice. The same was also found from the variation in pollen fertility of their F1s with certain test strains of cultivated type. 6. Populations of perennis type growing in a grassland, near rice fields and in a rice field as a weed, and the cultivated variety in the rice field, were collected from a village near Raipur, India. The wild plants growing in or in proximity of the rice fields appeared to be intermediate between wild and cultivated plants in various characters. This situation might have resulted from introgression of genes of cultivated rice, while the envirommental conditions of those intermediate popu-lation would be near that in rice fields. It was hypothetically postulated that a population of hybrid origin may acquire characters of cultivated rice in accordance with the “pressure of cultivation” under which the population grows. 7. A population of perennis type found in the suburb of Cuttack, India, and another in the suburb of Chiengmai, Thailand as well as the wild rice populations of Taiwan were found to be hybrid swarms. It was pointed out from studies of those population that a population of perennis type, which can be propagated asexually, might have an ability to preserve a great amount of genetic variability which, if released, could cover the wide range from wild to cultivated types, and this ability might have played an important role in the origin of cultivated rice. It was then inferred that perennis could be a more plausible ancestral species of cultivated rice than spontanea