Duanpen Wongsorn, Weerasak Saksirirat, Sivilai Sirimungkararat, and Hathairat Urairong

pp. 499 - 505

Abstract

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 (2nd 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.