Rice cultivation in tropical Asia is susceptible to drought and flood and the need is high for stress resistant genes. Wild rice Oryza rufipogon Griff., grows in close sympatric association with cultivated rice in various habitats across the globe and possesses traits for survival under challenging environments. The species adapts according to the level of soil moisture available and modifies phenology, biomass production and grain yield. Variation in tiller dynamics of the species between contrasting environments gives an estimate of the adaptation. The species possesses AA genome, which permits genetic compatibility for cross breeding with cultivated rice. Utility of the species as possible repository of stress resistant genes is evaluated in this review by examining variation in assimilate partitioning between different classes of tillers of ecotypes growing across a gradation of habitats against background knowledge available for cultivated rice. Models have been constructed to explain mechanisms of tillering and tiller dynamics, and reveal the genotypic permissibility for resilience in sub-optimal environments. It is concluded that environmentally cued alteration in assimilate production and partitioning mask genetic potential for tiller production and survival. Tiller number in excess of resource capacity is corrected by senescence of late-tillers possibly through an ethylene-mediated signal. 1. Introduction The Poaceae family of monocot angiosperms constitutes of grasses which provide food and fodder for man and other animals on earth. In this family, contribution of the genus Oryza is of high economic importance to man and domestic animals. This genus consists of two cultivated species, namely Oryza sativa L. and Oryza glaberrima Steud and 20 other related non-domesticated species [1]. Oryza species are related more to the bamboos [2] than to other cereals [3]. Hence for cultivated rice, the wild species of Oryza are the only source for useful traits for genetic recombination. Vaughan [1] divided the Oryza species into two major complexes, such as O. sativa and O. officinalis (also O. latifolia) on the basis of genomic diversity. The cultivated species of rice belong to the former complex along with non-domesticated species like O. nivara Sharma et Shastry, O. rufipogon Griff., O. barthii A. Chev, and O. longistaminata Chev. et Roehr. O. meridionalis Ng. Species belonging to this complex possesses AA genome group and 24 chromosomes. The genomic group of the species of the second group is BB, CC, DD, and EE in plants with diploid chromosome
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