Root penetration ability of Vietnamese traditional upland rice varieties

Drought is the major cause of low yield of rice grown in the rainfed uplands, where has aerobic and strong soil because of water deficit. Root penetration ability (RPA) through compacted soil layers or hard-pans has been recognized as an important breeding objective for improvement of drought resistance in rice. The study was conducted to evaluate RPA of Vietnamese traditional upland rice varieties comparing with rice cultivars belonged to different ecotypes. Root penetration ability was evaluated through shallow (5 cm) and deep (10 cm) wax layers in the plastic tube. Root penetration rate (RPR), that is the ratio of the number of roots penetrated wax layers (PRN) to the total number of roots (TRN), was assumed to be an index of PRA. Although RPR through shallow wax layer was higher than that through deep wax layer, higher correlation between them was found (r=79**). Japonica upland showed the superior RPA than other ecotypes. While, there was no significant difference between RPR of Vietnamese traditional upland and other Indica upland rice. Significant correlations between RPR and TRN, PRN, root thickness (RT) and root dry weight (RDW) in deep wax layers treatment were found (r=-0.41**, r=0.82**, r=0.63**, and r= 0.51**, respectively).