Abstract
Rice (Oryza sativa L.) is the most important staple food crop of the world; nearly half of the global population depend on it for majority of their dietary intake. Many stresses (biotic and abiotic) have critically affected rice production throughout the world due to global warming, changing climatic conditions and in addition non-durability of biotic resistance gene(s) incorporated into cultivars. Yield increase is not as per the required rate and becomes yield rate is in stagnation. Primary reason of yield stagnation is due to the narrow genetic base in the released varieties. Minimum number of parental lines were utilised to develop new crop varieties which ultimately leads to narrow genetic base. The narrow genetic base in the improved varieties is going to be a main bottleneck for crop improvement program which shield the yield increase. Genetic bottleneck during domestication causes erosion of the genetic diversity in the well adapted cultivars which leads to yield stagnation. Yield plateaus can be surmount through genetic gain by combining the yield related genes/QTLs from different genetic resources of rice germplasm both from local landraces (CLR) and crop wild relatives (CWR). Wild species are the reservoir of genetic diversity with wide adaptability and tolerance to many biotic and abiotic stresses. It is utmost necessary to characterize and conserve rice germplasm for evaluation and effective use of the genetic diversity prevailed in the rice gene pool. Genetic variability in respect to biotic/abiotic resistance is inadequate in the genetic resources of cultivated rice; however, these traits specific genes are available in the unexplored wild species of Oryza which are considered as rich source of agronomically important traits including biotic/abiotic traits. Therefore, breeders are trying to identify and transfer of these valuable genes from wild Oryza species to improve varieties through pre-breeding method and with the assistance of molecular breeding technology.
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