Commercial silkworm hybrids comparison based on cocoons and silk thread performance of Guilan sericulturists

The assessment of commercial silkworm hybrids based on cocoon characteristics will provide only profit to the sericulturists. However, the profits of sericulturists and silk spinners can be guaranteed by paying more attention to quality and quantity characteristics in both cocoons and fibers. In silkworms, the paternal and maternal lines of commercial hybrids are crossed reciprocally. That is the reason that hybrids of silkworms raised by sericulturists are not so identical. This genetic difference causes a difference in the final quantity and quality of the productive cocoon and silk thread. This study aimed to compare commercial silkworm hybrids based on cocoons and silk thread performance of Guilan sericulturists. In this study, the silk filament characteristics of 12 imported silkworm hybrids and two domestic hybrids were compared in two regions of Guilan province. The weight, size, length, and strength (Tensile strengths and Elongation percentage) of the silk filament in addition to the raw silk percentage were investigated. The cocoon characters were the performance of each box, cocoon weight, cocoon shell weight, cocoon shell ratio, the percentage of good cocoons, the number of cocoons per liter, pupal mortality, cocoon length, and cocoon width. Statistical analysis was done using the GLM procedure of SAS software. The hybrids from reciprocal mating were compared by t-test. To clustering, the WARD method was applied based on the deviation from the standardized number (Z-score) using the SPSS software. Variance analysis of traits showed that geographical region has a significant effect on thread diameter (P<0.05). The highest silk filament weight was related to hybrid 871×872, and two Iranian hybrids (154×153 and 104×103) with 5.01, 4.89, and 4.88 grams, respectively, and the lowest for BxQ hybrid with 3.57 grams. For filament diameter, the Iranian hybrids (104×103 and 154×153) had the highest filament size with 69.63 and 61.05 deniers, respectively. Higher diameter in Iranian silk filament fits the silk thread consumption type in Iran. The silk thread in Iran is used to produce silk carpets and rugs, therefore, it needs a larger thread diameter than when the goal is to produce high-quality silk fabrics that require fine thread. The Iranian hybrid 154×153 was excellent in terms of all the important features of the silk filaments, including strength, weight, diameter, and length. M×S, HB×JA, and B×Q hybrids had the smallest thread diameter with 53.72, 54.60, and 54.76 deniers, respectively. Hybrid Q×B was superior to some hybrids but for reciprocal hybrid (B×Q), the overall performance was not favorable. This hybrid had the lowest yield of silk filament weight, diameter, and length. A comparison of hybrids resulting from reciprocal crossing showed that the famous hybrids Q×B and B×Q had the highest differences among six-pair imported hybrids. The difference was observed between the two hybrids for six characteristics including cocoon shell weight, cocoon weight, the number of cocoons per liter, the percentage of good cocoons, the weight and size of the silk filament, and the raw silk percentage. It certainly affects the profits of both sericulturists and silk spinners. The classification of hybrids based on the WARD method led to three groups and the Iranian hybrids were in one group. Q×B and B×Q hybrids and their rejuvenated hybrids (BB×QA and QA×BB) were in the third group. M×S and S×M along with 871×872 and 872×871 hybrids were in the same group. Therefore, if necessary replacing hybrids within the group will be possible. The cocoon production of imported hybrids showed that there is a big difference between the performance mentioned in the catalog and what was produced under the conditions of rural silkworm rearing in Guilan province. Elongation percentage,  raw silk percentage, filament length, cocoon width, pupal mortality, cocoon weight based on total good cocoons, and number of cocoons per liter had no significant difference between domestic and imported hybrids. Due to the better performance of BB×QA and QA×BB, especially the similarity of reciprocal hybrids, these rejuvenated hybrids can replace the old ones (Q×B and B×Q). M×S and S×M hybrids, which had the advantage of uniformity between direct and reverse hybrids, can be considered more due to more silk filament weight and raw silk percentage. The results of this study showed that the most important factors in silkworm rearing are the performance of the silkworm box and the raw silk percentage to be improved for Iranian hybrids.