Abstract:
Plant nutrients play a significant role in the growth and development of the
rice plant (Oryza sativa L.). Today rice cultivation including those grown the tank
cascade systems, is heavily dependent on chemical fertilizers. Breeding rice varieties
for improved nutrient use efficiency (NUE) is one of the most feasible ways to in-
crease grain yields without losses to the natural ecosystems. Therefore, the study fo-
cused on the root architecture enhancing the NUE of different rice varieties under
nutrient-sufficient and deficient conditions. A field experiment was conducted under
nutrient-sufficient and deficient conditions with 17 rice varieties with the objective of
selecting rice varieties with a high number of S-type roots, which are crucial to in-
crease the NUE of plants. The root system was studied at the panicle initiation stage
from uprooted plants. Rhizotrone structure was prepared to observe and analyse the
variations in root architecture. Results of root scanning indicated that the number of
S-type roots was significantly higher (P<0.05) in nutrient-sufficient conditions com-
pared to the nutrient-deficient conditions. In the rhizotrone study, the root system ar-
chitecture of selected rice varieties was analysed and grouped into 0°-30°, 30°-60°,
and 60°-90° angles. The highest number of S-type roots in 0°-30° was observed in Bg
375. The H4 variety showed the highest number of S-type roots in 30°-60° and 60°-
90° angles. The ratio between L-type roots to S-type roots of H4 at a 60°-90° angle
was 1:20. The ratio between main roots to S-type roots of H4 at a 60°-90° angle was
1:175. Therefore, H4 and Bg 375 varieties have the potential to be used as parents for
the breeding of rice varieties with high NUE. This research outcome will help to en-
sure future food security while considering safe rice-based ecosystem in the major
rice growing areas in Dry and Intermediate zone in Sri Lanka.
