Sub-Theme 1 | Development of New High-yielding Rice Varieties
The comprehensive work of rice variety improvement was initiated with a systematic collection of native rice varieties and their pure-line selections followed by exotic introductions and their adaptability tests during the early period of 20th century. These were replaced by domestic-bred varieties through hybridization within the traditional temperate japonica varieties since the late 1930s. During 1970s, the indica and japonica types were hybridized and Tongil types were developed with a view to achieve Green Revolution in Korea.
Tongil type is designated from “Tongil”, the first variety developed from a selection from hybridization between indica and japonica in 1971. It was selected from the progeny of IR667, which was derived by 3-way cross (IR8//Yukara/Taichung Native 1) and released to the farmers in 1972. Afterwards, improved Tongil type varieties like Milyang 23, Geumgang, Raekyeong, etc. were released that rapidly increased the area under their cultivation. The acreage reached 76.2 percent of the total rice area in 1977, resulting in Green Revolution in Korea. Forty varieties of Tongil type rice were developed and cultivated during 1970s and 1980s. Successful cultivation of Tongil type rice varieties opened not only a new milestone for future improvement of rice varieties but also offered a practical opportunity to utilize indica germplasm in temperate environments. Major characteristics of Tongil type rice varieties were short stature in their plant architecture with erect leaves, high yield potential, tolerant to heavy doses of nitrogen and lodging and resistance to major diseases and insect pests, particularly more or less neutral responses to photoperiod and longer period of basic vegetative stage of rice growth. However, there were some shortcomings too such as susceptibility to low temperature, easy shattering of grains and unacceptability of grain quality and palatability to Korean consumers.
The milled rice yield potential of rice varieties that were domestic-bred by hybridization and were first cultivated in the late 1930s, progressed to 4.06~4.57 MT/ha for the leading varieties such as Palkweng, Jinheung and Palgeum by 1970 and greatly increased to 3.3 MT/ha as the national average on the farmers’ field due to improvement of both varieties and cultural practices and to 3.7 million MT/ha for total production. Although productivity of rice varieties increased significantly by the 1960s, it was still behind in meeting self-sufficiency in rice production as a staple food crop in Korea.
The development of “Tongil” rice variety, the first variety derived from indica/japonica hybridization in 1971, lifted up milled rice productivity to 5.13 MT/ha which was 28 percent higher than that of the best japonica rice variety at that time. The productivity of subsequent Tongil type varieties steadily increased to 5.76 MT/ha for Milyang 23 in 1976 and 6.05 MT/ha for Yongmubyeo in 1985. The national average of milled rice yield in the farmer’s field dramatically increased to 4.93 MT/ha ranging 4.37~5.53 MT/ha in 1977 as compared with japonica varieties yielding 3.37~4.69 MT/ha of milled rice. Total rice production reached 4.67 million MT in 1976 which was the first self-sufficiency of rice in Korea, and 5.21 million MT in 1977 and 6.01 million MT in 1978 which was the first time to exceed 5 million MT of rice production in the history, resulting in a significant achievement for green revolution in Korea.