Characterization of WSSV resistance in selected families of Litopenaeus vannamei

Disease outbreaks caused by the white spot syndrome virus (WSSV) have resulted in high economic losses in the shrimp-culture industry worldwide. After three generations of selective breeding for WSSV resistance, 29 families of Litopenaeus vannamei (G3) were selected and divided into three groups: relatively high-resistance, moderate-resistance, and susceptible families, which had average survival rates of 22.7 +/- 12.30, 9.08 +/- 1.46, and 0.78 +/- 1.70%, respectively, after WSSV infection. Appearance of the mortality peak in the relatively high-resistance families was postponed by 2-3 days compared to the same in susceptible families and unselected shrimps. Using real-time quantitative polymerase chain reaction, the copy number of WSSV DNA in the muscles of surviving shrimps from the relatively high-resistance family 14 was significantly lower than that of the moderate-resistance family 17, the susceptible family 4, and the unselected family of shrimps at 36 hours postinfection (hpi) and thereafter; for example, at 48 hpi, the DNA copy number was (23.87 +/- 2.56) x 10(6) copies g(-1) in the high-resistance families against (40.03 +/- 2.54) x 10(6), (65.70 +/- 3.44) x 10(6), and (47.87 +/- 3.95) x 10(6) copies g(-1) body weight, respectively, in the other groups. The WSSV copy number in the muscles of dead shrimps from the relatively high-resistance family 14 was significantly higher than that of the moderate-resistance family 17, the susceptible family 4, and the unselected family of shrimps at 48 hpi and thereafter; for example, at 72 hpi, the DNA copy number was (54.1 +/- 3.9) x 10(6) copies g(-1) compared to values of (31.5 +/- 2.6) x 10(6), (11.6 +/- 2.9) x 10(6), and (25.4 +/- 2.7) x 10(6) copies g(-1) body weight in the other groups, respectively. The results indicated that shrimps from the relatively high-resistance families could inhibit the replication of WSSV and therefore had apparent WSSV resistance. These results provide a direction for the future selective breeding of shrimps for WSSV resistance. (C) 2010 Elsevier By. All rights reserved.