Abstract:
Iron toxicity is recognized as one of the most widespread soil constraints for rice production,
particularly in the Low Country Wet Zone (LCWZ) of Sri Lanka. Underwater logged conditions,
soluble iron present in the soil solution is absorbed by paddy roots and is accumulated in the
leaves, resulting in poor plant growth, lowering of tillers and severe yield reductions. These
characteristics are often accompanied by apparent leaf discoloration or bronzing. The aim of this
study was to assess the use of the Leaf Bronzing Score (LBS) to assess its suitability as an
indicator of Fe toxicity tolerance/susceptibility. The suitability of LBS of the rice varieties were
monitored against the grain yields of each tested variety. This simple and practical approach will
result in identifying promising rice varieties that could be used in breeding programs aimed at
improving iron toxicity tolerance. The experiment was carried out in the Maha seasons of
2017/2018, at the research field of the Regional Rice Research and Development Center
(RRRDC), Bombuwala, located in the LCWZ. The selected location consisted of sandy loam
which had a relatively high level of total Fe (589.0±16.51 ppm) and acidity (pH:4.47±0.20).
Three rice varieties of unknown iron tolerance, and a further two varieties of known
tolerance/susceptible traits, were used as test entries. Varieties were arranged in the field in a
Randomised Complete Block Design (RCBD), with three replicates. The Leaf Bronzing Scores
(LBS) were determined at different stages of growth while the grain yields were determined at
maturity. Observations revealed that there were significant differences in the LBS values
between the tested varieties across the different stages of growth. The varieties Kahata Wee and
Bw267-3 were the most tolerant as indicated by the lowest LBS value (LBS-1), followed by
Bw372 and Bw360. The highest LBS value was recorded in Bw272-6b (LBS-7), indicating its
susceptible nature. The grain yield of the five varieties also differed significantly (one-way
Anova: F=18843.034, p<0.05). Three rice varieties (Kahata Wee, Bw372, Bw360) consistently
recorded higher yields than the other two. The highest grain yield (9.9145 t/ha) was recorded in
Kahata Wee, followed by Bw372 (5.1086 t/ha) and Bw360 (4.0462 t/ha). The lowest grain yield
of 1.9968 t/ha was recorded in Bw267-3. The trends further showed that the LBS values were
negatively correlated with grain yield (Regression Analysis: R2=14%, F=2.112, p<0.05). This
observation indicates that the Leaf Bronzing Score could be used as a simple trait to detect iron
toxicity tolerance in rice varieties.
