Inheritance of Root Characters and their Relations to Drought Resistance in Rice¹

Abstract

The ability of rice plants to tolerate drought stresses is associated with root system characters. However, the genetics of root traits are not well understood. Hence, the inheritance of six root characters of rice (Oryza sativa L.) was studied using the parents, F1, F2, and F3 populations of the cross IR20✕MGL‐2. Plants were grown in a hydroponic culture solution in a phytotron glasshouse and in an upland drought screening nursery. A polygenic system of inheritance was indicated for the root characters. The F1 plants had root systems characterized by thick, deep roots with a higher lateral and vertical distribution than the low parent (IR20), and the heterosis was significant and positive. The additive and dominant genetic effects contributed equally to the expression of all root traits. Both progeny parent regression of F3 and F2, and the narrow sense heritability estimates in F3 were high for root thickness (0.61 and 0.80), root dry weight (0.56 and 0.92) and root length density (0.44 0.77). Selection of root types, based on individual plant performance, should be successful in early segregating generations if selection is practiced on these characters. Associations between root characters and plant height, tiller number, and shoot weight were positive and significant. Five root characters were significantly correlated with the visual field drought resistance scores and with leaf water potential, confirming the role of root characters in maintaining high leaf water potential under water stress.

Genotypic Variation in Response of Rainfed Lowland Rice to Drought and Rewatering

“…Increased carbon supply to roots (Aguirrezabal et al, 1993;Bingham and Stevenson, 1993) or exogenous applications of plant growth regulators (Torrey, 1986), have been shown to increase root branching. However, such morphological adaptations of deep roots have not previously been characterized among relevant genetic materials according to the level of water stress, in spite of many genetic studies on rice roots (Ekenayake et al, 1985 ;Loresto and Chang, 1994) . By new molecular techniques, we may now be able to identify quantitative trait loci ( QTL) for such adaptive root traits under differing water-stress levels, which could be helpful in incorporating such traits into elite cultivars for improvement of drought tolerance.…”

QTLs underlying natural variation in stele and xylem structures of rice root

“…In general, the roots of upland rice cultivars are morphologically thicker and penetrate more deeply than those of lowland cultivars. These traits are controlled by multiple genes (Ekanayake et al 1985). Many analyses of quantitative trait loci (QTLs) of root morphological traits have been carried out using different mapping populations (reviewed by Price et al 2002a).…”

Overexpression of the OsERF71 Transcription Factor Alters Rice Root Structure and Drought Resistance

“…Previous studies also have elucidated structural adaptations of root architecture to overcome drought stress. For example, rice inbred lines (IR20 3 MGL-2) with long, thick roots showed enhanced drought tolerance (Ekanayake et al, 1985), and root-specific overexpression of OsNAC10 promoted radial root growth, which in turn enhanced drought tolerance . In addition, overexpression of DEEPER ROOTING1 conferred drought avoidance capacity by altering rice root architecture (Uga et al, 2013), while drought stress was reported to cause an accumulation of lignin in roots, thereby modifying cell wall architecture to enhance growth under drought conditions (Yoshimura et al, 2008).…”