Two dimensional in-vitro phenotyping of root system architecture using Poly Ethylene Glycol in backcross inbred lines harboring drought tolerant QTLs of rice (Oryza sativa L.)

The present investigation was made to validate the effect and expression of multiple drought QTLs from Apo in the background of high yielding drought susceptible variety IR 64 under two dimensional in-vitro root architecture studies. The genotype CB 229 (DTY2.2, DTY3.1 and DTY8.1) recorded a higher network bushiness, network width, specific root length and network distribution of roots under PEG treatment (stress) and in network area CB 193-3 outperformed than CB 229. This clearly shows that introgression of multiple drought QTLs in various combination in the same genetic background enhances different level of expression of QTLs and tolerance to varied intensity of drought. Under field screening for drought, CB 229 out performed in both spikelet fertility percentage and yield than the remaining BILs. The traits viz., major ellipse axis, maximum number of roots, network bushiness, specific root length, network convex area and network width are positively correlated with spikelet fertility percentage and single plant yield under drought experiment. Principal component analysis accounted for 78.47 per cent of variability among root traits in PC1 and was loaded with all the traits observed under in-vitro condition. Hence, an understanding on complex nature of QTL expression associated with root system architecture under in-vitro stress in rice may help the breeder to develop new cultivars with enhanced level of tolerance against water limited situations in near future.