Document Type : Research Articles
Department of Animal Science, Faculty of Agricultural Sciences, University of Guilan, Gilan, Iran
Department of Sericulture, Faculty of Agricultural Sciences, University of Guilan, Gilan, Iran
Iran Silk Research Center, Agricultural Research, Education and Extension Organization (AREEO), Gilan, Iran
Department of Textile Engineering, Faculty of Engineering, University of Guilan, Gilan, Iran
Introduction: So far, many researches have been conducted to compare the productivity of different silkworm hybrids in Iran, which were just based on the evaluation of cocoon traits, eg. cocoon weight, cocoon shell weight, cocoon shell percentage, pupation rate, etc. In the present study, with the aim of obtaining information on the quality characteristics of silk thread in Iranian silkworm hybrids, 80 Iranian silkworm hybrids were examined for silk thread characteristics.
Materials and Methods: 72 of the new silkworm hybrids in addition to 8 current commercial hybrids were evaluated for the six silk thread characteristics including filament size (FS), filament length (FL), filament tensile strength (FTS), filament elongation percent (FEP), filament weight (FW) and raw silk percentage (RSP) based on dry weight. 200 good cocoons from each hybrid were sampled at the Iran Silk Research Center and sent to the Fiber Physics Laboratory of the University of Guilan. After re-evaluating the individual cocoons based on form and size of them, 3 repetitions of 21 cocoons (based on the capacity of the spinning machine) were spun and dried. According to reciprocal crosses in this research, the data were analyzed using 40x2 factorial analysis (40 hybrids and two kinds of crosses) using the GLM procedure of SAS software version 4.9.
Results and Discussion: Mean comparison of the studied traits based on the combined reciprocal data (40 hybrids) showed that the highest average of the FS trait (73.3 deniers) was for the hybrid IRA3×IRA10 and the lowest average (58.2 deniers) for the commercial hybrid 153 ×154. The highest FL trait(771.4 m) was for hybrid IRA5×IRA8 and the lowest (441.18 m) for the commercial hybrid IRA2×IRA3. The highest average of the FTS (3.47 g/denier) was for commercial hybrid 104×103 and the lowest average (2.9 g/denier) was for hybrid IRA2×IRA3. The highest average for the FEP trait (17.6%) was reported for the commercial hybrid 154×151 and the lowest average (12.83) was related to the hybrid IRA2×IRA3. The highest average for FW (5.59 grams) belonged to the IRA5×IRA8 hybrid and the lowest average (3.34 grams) belonged to the IRA2×IRA3 hybrid. Also, for the RSP trait (the most critical trait of silk characteristics), The IRA5×IRA8 hybrid had the highest average (41.4%) and the IRA2×IRA3 hybrid had the lowest average (25.86%). IRA5×IRA8 hybrid had superior performance than all commercial hybrids. The RSP of the IRA8×IRA9 hybrid was 39.47%, which was superior to the three commercial hybrids. The hybrids that were excellent in at least three of the six characteristics were: all commercial hybrids and three new hybrids including IRA5×IRA8, IRA11×IRA12 and IRA8×IRA9. Analysis of the variance of the traits showed that the reciprocal-cross effect was not significant for the FS and FTS traits (P>0.05). Despite the close competition of new hybrids with current commercial hybrids, many characteristics of commercial hybrids were significantly higher than new hybrids. However, the new hybrids including IRA2×IRA9, IRA2×IRA11, IRA3×IRA4, and IRA4×IRA11, which have shown superiority in terms of cocoon traits, also performed favorably in terms of all yarn characteristics. However, two hybrids were among the superior hybrids in terms of cocoon production and cocoon traits, but the results of the present research showed that they are not superior in terms of yarn characteristics and raw silk yield and productivity, including IRA2×IRA3 and IRA4×IRA7. The IRA2×IRA3 hybrid has an unfavorable performance in terms of weight, strength, and raw silk percentage and cannot provide the interests of silk spinners.
Conclusion: In the final selection of new hybrids based on the performance of both cocoons and silk thread, it is necessary to pay attention to the strength and weakness of the silk yarn obtained from the cocoons of each hybrid. But it will not be the case that hybrids with better cocoon performance are necessarily among the best in terms of all silk yarn traits or even some of them. For example, hybrids IRA2×IRA9, IRA2×IRA11, IRA3×IRA4, and IRA4×IRA11 had better cocoon performance, but they had a middle performance for yarn characteristics. In other words, if they are not among the weaker group, they can be considered. Generally, it is necessary to decide about new hybrids after rearing them in rural conditions and evaluating the produced cocoons and yarns.
Keywords: Filament size, Raw silk percentage, Silk yarn, Superior hybrid, Tensile strength