Screening for eri silkworm ( Samia ricini Donovan) ecoraces using morphological characters, growth, yields, and ISSR marker

摘要

The selection of eri silkworm ecoraces with high yield and distinct morphological characters is necessary for variety improvement. The five ecoraces SaKKU1, SaKKU2, SaKKU3, SaKKU4 and SaKKU5 were derived mostly by international academic cooperation. They were cultured using castor leaves of TCO 101 cultivar as food plant at 25±2°C, 80±5% R.H. Based on morphological characters, they are similar, except the body of the 5 th instar larva of SaKKU1 is clearly covered with more creamy white powder and the mature larva has a shiny dominant yellow color. The duration of the life cycle among ecoraces was also similar; 46-53 days (SaKKU1), 42-53 days (SaKKU2), 42-52 days (SaKKU3), 40-56 days (SaKKU4) and 41-52 days (SaKKU5). SaKKU1 had the highest survival rate at larval stage (1 st – 5 th instar) (100.00%) and larva (1 st – 5 th instar) - adult (88.89%), including the predominant heaviest average larva weight of all instars, 0.0317 g (2 nd instar), 0.2206 g (3 rd instar), 1.0788 g (4 th instar), 4.0102 g (5 th instar), and 8.9940 g (5 days of 5 th instar), which was significantly different (P<0.05) to other ecoraces. Moreover, this ecorace gave the highest average yields: fresh cocoon weight (3.8016 g), pupa weight (3.2532 g), shell weight (0.5287 g), shell ratio (14.01%), fresh cocoon weight/10,000 larvae (38.01 kg), eggs/moth (531.13 eggs), total eggs (6,375.27 eggs) and total hatching eggs (6,006.13 eggs), which was also significantly different (P<0.05) than other ecoraces. Of those properties, especially survival rates and yields, this ecorace (SaKKU1) is favored for further varietal improvement program. In parallel, genetic relationship analysis of eri silkworm ecoraces using inter-simple sequence repeat (ISSR) technique was also carried out. The result revealed from dendrogram analysis that SaKKU1 was the farthest distance than other ecoraces, especially against SaKKU3. Based on all above results, the SaKKU1 ecorace was considered to be the most suitable for heat tolerant variety improvement.