Genotypic Variation in Response of Rainfed Lowland Rice to Drought and Rewatering : II.Root growth

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Genotypic variation in the root system is a potential source for improving drought tolerance of rainfed lowland rice(Oryza sativa L.).Our work aimed at characterizing both constitutive root traits(those present under well-watered conditions)and adaptive root traits(those developed in response to drought and rewatering)among eight diverse rice genotypes in three sets of greenhouse experiments(experiments 1, 2, and 3).Under well-watered conditions, genotypic variation was observed in root to shoot ratio, root growth rate, specific root length, deep root ratio, root mass per tiller, and root thickness.CT9993 and IR58821 had a high root to shoot ratio, deep and thick root system, and high root mass per tiller.However, CT9993 had a slow root growth rate and short specific root length.In response to drought in experiments 2 and 3, the total amount of assimilate distributed to roots was reduced and roots became thinner, but the proportion of total assimilate supply assigned to deeper layers increased, thereby maintaining deep root mass and increasing specific root length.On rewatering, root to shoot ratio increased, surface roots increased, and roots became thicker.During drought, NSG19, KDML105, Mahsuri, and IR58821 partitioned a larger proportion of assimilate to deep roots and had more deep root branching.
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