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Pre era of plant type varieties

Pre era of plant type varieties
13
Jul

Breeding prior to plant type varieties

Immediately after the World War II, the major problem the world faced was serious shortages of food. The deficiency ranging between 15 and 20%, especially in the rice dependant Asia, leaving a large population die of undernourishment and malnutrition made the United Nations Organization (UNO) to identify ‘increasing food production by scientific means’ among its priorities. The founding of the Food and Agriculture Organization (FAO) and establishment of the International Rice Commission (IRC) under its framework in 1949 was the major step forward towards this mission. Series of Asiawide research programmes initiated by this institutional mechanism to step up rice production included collection, cataloguing and maintenance of germplasm, Cooperative Varietal Testing, Variety-Fertilizer Interaction and Indica-Japonica Hybridization. Whereas the cooperative multi country evaluation of promising entries from different countries enabled identification and introduction of the best performed in the participating countries, the study of variety x fertilizer interaction in the identification and exploitation of fertilizer responsive genotypes in breeding programmes. The collection and cataloguing of cultivar germplasm into varietal groups and maintenance of indica germplasm at Cuttack in India and Bogor in Indonesia, Japonica at Hiratsuka in Japan and the USA and the floating rices at Habiganj in Pakistan now in Bangladesh proved a valuable and readily accessible source of variability for use by breeders all over. These early initiatives of the FAO/IRC were, in a way the forerunners for the coordinated variety testing programmes of the NARS and the International Rice Testing Programme (IRTP) International Network of Germplasm Evaluation and Utilization of Rice (INGER) of the IRRI since 70s and the International Rice Gene Centre (IRGC) at IRRI respectively.

Early breeding research in tropical Asia began with the improvement of native varieties by ‘pureline selection’, the strategy for purification of highly heterogenous farmer varieties into readily recognizable ones of uniform stature, maturity and grain type. Though the strategy had helped greatly to restrict the number of varieties, it hardly helped raise appreciably the genetic yield level. The rediscovery and elucidation of Gregor Mendel’s Laws of Inheritance, a hundred years back was the defining moment in the history of biology. It was the understanding of the laws of genetics that convinced crop breeders hybridization as the most effective means to generate more variability, on which selection could be practiced in desired direction. Application of this knowledge in rice was however, restricted to improvement of simply inherited traits rather than the genetically complex yield. If pureline selection had helped raise the yield level by 5-10% over the landraces, the gain through hybridization had been another 10-15%. Rice yields thus remained practically very low and stagnant until the launch of the Indica/Japonica Hybridization Programme by the FAO in 1952 aimed at recombining the fertilizer responsiveness of japonica rices and wide adaptability and preferred grain quality of indica rices. It was the earliest international effort to explore the possibilities of breaching the yield barrier in tropical rices.

A decade long ambitious Indica-Japonica project with CRRI at Cuttack (India) as the primary hybridization centre and major rice growing countries in the region for study of segregating populations of interest proved, however a disappointing experience. Persistent hybrid semisterility and skewed segregation towards parental types because of restricted recombination attributable to the failure, are now traceable to inappropriate choice of parents. Instead of temperate japonica, had breeders used sexually more compatible tropical japonica, the success level would have been closer to the targeted objective of yield enhancement. Mahsuri and Malinja selected and adopted in Malaysia and Adt 27 in India were the only products of value from this project. Mahsuri, the medium late semitall variety introduced later in India continues to be popular and ideally suited to long wet season and rainfed lowland ecologies. Its excellent grain quality being the preference of consumers, traders and millers alike, it is the choicest donor source of breeders all over for improvement of grain quality of varieties and hybrids. The high yielding varieties like Samba Mahsuri (GEB24/T(N)//Mahsuri) attracting premium price in the domestic market and occupying a very large area and ‘Swarna’ (Vasistha x Mahsuri), the widely popular in the irrigated long season and rainfed shallow lowland ecologies planted over 8 mill. ha in India and the adjoining countries like Bangladesh and fast spreading hybrids like DRRH 44, Sahyadri 4, etc are products of crosses involving Mahsuri as a parent. Adt 27, by virtue of its earliness and relatively higher response to high doses of fertilizer proved an ideal choice for the short ‘Kuruvai’ season in Tamil Nadu. Despite the disappointing outcome, the lesson learnt from the indica-japonica hybridization project that the key to raise the yield level of rice lies in making it fertilizer responsive and non-lodging, had in a way helped conceive and develop the semidwarf ideo type in the sixties.

 

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