Genetic effects influencing salinity tolerance in six varieties of tilapia (Oreochromis) and their reciprocal crosses

Abstract

Six tilapia varieties were used in two 6 × 6 diallel crosses. Salinity was increased in daily increments of 7 g L−1 in five replicate trials to estimate the salinity tolerances of 2205 F1 juveniles from parental varieties and their reciprocal crosses. Genetic effects potentially influencing salinity tolerance were estimated, including line effects, maternal effects, reciprocal and specific reciprocal effects, direct heterosis, specific combining abilities (SCAs) and general combining abilities (GCAs). The mean heterosis, , for salinity tolerance was 4.46 g L−1 (P<0.01). The average mean salinity tolerance (MST) of the parental varieties was 35.2 g L−1, and yet, MSTs above 36 g L−1 were found in 21 of 34 variety crosses produced. In some instances, maternal effects offset line effects, while in others, these influences were complementary. Ten variety combinations exhibited significant (P<0.05) or highly significant (P<0.01) direct heterosis, and SCAs were significant (P<0.05) or highly significant (P<0.01) in five combinations. Reciprocal and specific reciprocal effects also influenced the salinity tolerance in some variety combinations. Direct line effects generally reflected MST rankings. The variance of cross means was 30.1% due to variety GCAs (primarily additive effects) and 69.9% due to SCAs (primarily dominance effects).