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Era of semi-dwarf high yielding varieties

Era of semi-dwarf high yielding varieties
13
Jul

The era of semi dwarf high yielding varieties

Taichung (Native)1-the first semidwarf indica: Taiwanese breeders had been serious since the World War II to improve the productivity of their very low yielding tall native indica and of the introduced japonica varieties. The breeding strategy has been to reduce plant height to lessen their pronness to lodging, to enhance fertilizer responsiveness and to make them early maturing and photo-thermo insensitive enabling double cropping of rice. The effort of years led to the successful development of Taichung (Native)1, the worlds’ first high yielding semidwarf indica variety. Evolved of the cross involving Dee-geo-wugen, a short statured mutant of spontaneous origin and the popular tall variety Tsai-Yuan-Chung, it is considered rightly to represent a ‘giant stride’ in the global effort to raise the ceiling to genetic yield level in indica rices (Huang et al., 1972). Characterized by semidwarf stature with strong culms and upright foliage, short growth duration with photo-insensitivity, fertilizer responsiveness and non-lodging, T(N)1 yielded more than two times that of the locally popular tall varieties. In a few years since its introduction, over 0.8 million ha were planted to it in tropical Asia (Chander, 1966; Huang et al., 1972).
                                          Introduced in India in 1964, it marked the beginning of the ‘era of yield revolution’ (Chander, 1972; Shastry, 1968). It was reported to have yielded 8.0 and 5.0 t/ha respectively in dry and wet season as against 3.4 and 2.5 t/ha by the local variety Mtu15. Sadly, on account of its high susceptibility to bacterial leaf blight (BLB), blast, Rice Tungro Virus (RTV) and brown planthopper (BPH), its cultivation came to an abrupt end by late sixties. IRRI developed IR8 then started gaining ground all-over by virtue of its higher yield edge over T(N)1 and higher level of tolerance to BLB and BPH. Though T(N)1 could survive only for a short period, it provided the dwarfing gene source and base for development and promotion of plant type based high yielding varieties. Ponlai varieties of improved plant type: Taiwanese breeders simultaneously improved japonica varieties popularly known as ‘Ponlai’ by continuous selection for high yield, short duration and adaptability to both the seasons of subtropical Taiwan. The effort led to the development of a series of high yielding varieties like Taichung65, Chianung242, Tainan-3, Tainan5, Taichung 180, Taichung 186, Hsinchu56, Kaohsiung53 etc. Performing consistently well with yield levels ranging from 6 to 7 t/ha, they were very popular with farmers in many countries outside Taiwan.
                                         Many of them introduced in several Afro-Asian countries including India were found well adapted yielding 5-7 t/ha. For instance, Tainan3, Taichung 65 and Kaohsiung53 introduced in southern states of India, were very successful, because of their high yield potential. Yet, like T(N)1 they too could not be sustained on account of their cooking quality not acceptable to consumers and susceptibility to major pests. The modern varieties that heralded Green Revolution: An important development that accelerated breeding research at global level was the establishment of IRRI in the Philippines in 1960. Breeding activities began the very next year with the primary objective of evolving non-lodging semidwarf varieties with higher yields, led to the development and release of IR8 in 1966. A rare recombinant from the cross between Peta, the popular javanica (tropical japonica) variety of Indonesia and Dee-geo-wugen, the dwarfing gene source from Taiwan, IR8 was the ideal plant type with the highest yield potential the breeders had been dreaming for. The pace at which it was adopted in a short span of time almost in every rice growing continent, provided the momentum for development of a series of high yielding semidwarf varieties at IRRI and NARS.
                                           While serving as an improved plant type donor in place of earlier used T(N)1 and DGWG, IR8 helped breeders develop precise ‘selection eye’ for genotypes of high yield - the panicle number type and high panicle density per unit area. Thousands of crosses of IR8 or its immediate derivatives from crosses with popular tall varieties of the rice world, especially of Asia made at IRRI had led to the evolution and release of a series of high yielding varieties for irrigated ecosystem, which included IR20, IR26, IR28,IR30, IR36, IR42, IR50, IR64, IR72 and IR74 over the years. Simultaneously the rice growing countries in Asia, came up with hundreds of high yielding dwarf varieties, many bred by them and sizeable of IRRI developed varieties/breeding lines. As IRRI has accessed and used germplasm of value from NARS for developing progressively improved varieties, NARS too have used abundantly both basic and improved germplasm of their need from IRRI through the unique global testing network viz., IRTP/INGER that facilitated free and speedy two-way flow of germplasm. Since the advent of the miracle variety IR8, NARS along with IRRI have evolved and released for general cultivation over 4000(?) modern varieties suiting major rice ecologies with emphasis on irrigated production system which accounting for over 55% of the global rice area contributes the maximum to rice production.

 

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