Genetic analyses for TSV-susceptible and TSV-resistant Pacific white shrimp Litopenaeus vannamei using M1 microsatellite

Allelic frequency differences at the highly polymorphic M1 microsatellite of B20 locus were examined in Taura Syndrome Virus (TSV)-susceptible (Kona) and TSV-resistant (Select) lines of Pacific white shrimp Litopenaeus vannamei. DNA was screened from 1,009 cultured L. vannamei, 166 from the Kona line and 843 (97 broodstock and 746 offspring) from the Select line. A total of 34 different M1 alleles were found, 41.2% of which were shared by the two lines, and 58.2% were unique to either line. Only seven (20.6%) of the 34 alleles had similar frequencies in the two lines. The most frequent (22.4%) allele in the Select line (218 bp) was absent from the Kona line. The most frequent (9.6%) allele in the Kona line (236 bp) was not observed in the Select line. Significant genetic differentiation between the two lines was shown using contingency table analysis (chi(2) = 891.20, df = 33, P < 0.0001), the exact test (P < 0.00001), and F(st) analysis (0.06). Comparison of M1 allele frequencies between the TSV-resistant Select and TSV-susceptible Kona lines and between the top 12.5% (Top Select) and the bottom 12.5% (Bottom Select) surviving families to TSV challenge in the Select line suggested associations of M1 alleles with TSV resistance. These observations suggest testable hypotheses in future experiments aimed at finding genetic markers associated with resistance to TSV and markers that could be used for marker-assisted selection of broodstock.