Abstract:
Rice thrips, a pest causing 1.5% annual rice production loss, necessitates the development of
thrips-resistant and high-yielding rice cultivars. This study assessed the phenotypic and
genotypic characteristics of F4 breeding lines for thrips resistance at Rice Research Station,
Labuduwa, Sri Lanka during the Yala season 2023. Improved variety (At 362), thrips-resistant
mother plants (Th 55-1 and Th 12-5), and their F4 crosses (Th 55-1/At 362 and Th 12-5/At 362),
and Dahanala as reference variety (traditional thrips resistance variety) were evaluated in this
experiment. The field experiment was established according to a Randomized Complete Block
Design with two replicates. Damage severity by thrips, trichome density, and other important
yield-determining traits of rice were recorded. Genetic variability assessment for quantitative
traits was conducted to assess the relative effectiveness of selection based on phenotypic
expression of traits. The highest damage severity rank for thrips was recorded in the At 362 when
compared with both crosses while the lowest rank was recorded in the Dahanala. Both Th12-
5/At362 and Th55-1/At362 recorded higher trichome density values for long, medium, and short
trichomes rather than Th12-5 and Th 55-1 and At 362. Both Th 55-1/At 362 and Th12-5/At 362
progeny lines had greater (≥20%) genotypic and phenotypic coefficient of variation values for
panicle number, tiller number, and panicle weight. The highest (≥60%) heritability values were
found for plant height, panicle length, and weight. Agronomic characteristics with the highest
genetic advance (≥20%) were panicle weight, plant height, and number of seeds per panicle. Both
Th12-5/At362 and Th55-1/At362 progeny crosses showed moderate values of genetic advance
(10%- 20%) for panicle length and thousand-grain weight. In conclusion, both Th55-1/At 362
and Th12-5/At 362 crosses exhibit crucial characteristics for thrips resistance, warranting
further selection. Future research should explore additional morphological features, such as leaf
cuticle structure and leaf wax composition, to enhance rice resistance to thrips damage.
