(49(2):1-13)Genetic Studies on the Brown Rice Characteristics in the Progenies Derived from the Hybrid and Backcross between Oryza sativa L. and O. nivara Sharma et Shastry

野生稻O. nivara (IRGC Acc.104705)穀粒細長具褐色種皮為貢獻親，中國型稻臺梗1號(TK1)及臺農67號(TNG67)穀粒短圓為輪迴親行雜交及回交，由各所得之F1、F2、BC1F1、BC1F2、BC2F1、BC2F2、BC3F1、BC3F2族群為材料探討糙米種皮顏色、粒長、粒寬及粒形等性狀的遺傳及育種行為。結果顯示：野生稻之褐色種皮為單一顯性基因所控制，且與其他三個糙米性狀無連鎖關係。兩組合F1之粒長具部份顯性，F2超親分離者少。回交後代族群明顯集中且偏向輪迴親本，但恢復輪迴親本的程度因組合不同而有所差異。粒寬則僅TK1 X O. nivara 具雜種優勢，但F2兩雜交組合均有超親分離現象；回交後代在TNG67 X O. nivara 之粒寬變異均大於TK1 X O. nivara 。兩組合F1之粒形均屬中粒形，顯隱性作用不明顯，F2無超親分離，回交後代TK1 X O. nivara 粒形之頻度分布較為集中。F2及各回交世代之粒長、粒寬及粒形等性狀之平均皆低於F1，顯示此三性狀基因累加性效應高。粒長、粒寬及粒形等三性狀於早期世代F2及BC1F2的廣義遺傳率較高，呈現回交次數增加而遺傳率減少的趨勢，但TNG67 X O. nivara 之粒寬於BC3F2世代，其廣義遺傳率仍高。在各F2世代粒形與粒長呈正相關，而與粒寬呈負相關；粒長與粒寬於早期世代F2及BC1F2無顯著相關性，於BC3F2呈正相關。Two sinica cultigens, Tainung 67(TNG 67) and Taiken 1(TK 1), and a wild rice, O. nivara (Acc.104705) were used as the recurrent parents and donor parent, respectively, to investigate the genetic behaviors for the seed coat (brain) color, grain length, grain width, and grain shape (length-width ratio) of the interspecific hybrid progenies of Oryza species. The F1, F2, BC1F1, BC1F2, BC2F1, BC2F2, BC3F1 and BC3F2 populations of two cross combinations were simultaneously planted at the experimental farm of Taiwan Agricultural Research Institute in the first crop of 1996. In normal growth conditions, the seed coat color of O. nivara is brown, and the shape of grain is slender, on the other hand, two sinica cultigens are light brown in seed coat color and bold in grain shape. It is indicated from our data that the seed coat color is conditioned by one major gene, and brown seed coat is dominant. Furthermore, linkage was not found between seed coat color and grain length, width and shape of brown rice. Heterosis was found in grain length in both cross combinations. Few are transgressive in both F2 populations, and the frequency distributions of grain length in various backcross populations are peaked and leaned toward the recurrent parents, cultigens. For grain width, heterosis was only found in TK 1 X O. nivara combination. However, transgressive segregation was indicated in both F2 populations. Variation of grain width in various backcross populations TNG 67 X O. nivara combination appeared to be larger than those in TK 1 X O. nivara. As for grain shape, bold shape was observed in both F1 populations. Transgressive segregation was observed in both F2 populations, and frequency distribution was peaked only in various backcross populations of TK 1 X O. nivara cross combination. In general, the mean performance for length, width, and shape of brown rice in F2 and various backcross populations were lower than those in F1 populations, indicating that the genes concerned might be additive. The broad sense heritabilities estimated for the three grain traits were relative high in both F2 and BC1F2, and heritabilities appear to lower along with increase in the number of backcross except grain width in BC3F2 population in TNG 67 X O. nivara combination. In F2 populations of both cross combinations, it was found that there is a positive correlation between grain shape and length, and a negative correlation between grain shape and width in various populations. Data were also observed that there is no significant relationship between grain length and width in both F2 and BC1F2 populations, however, a positive correlation was observed in BC3F2 populations