Comparison of the Iranian and Chinese commercial silkworm hybrids with the aim of planning for continuity of production and import

Introduction: In general, in silkworm breeding, a set of traits including production traits related to produced cocoon, reproductive traits, and resistance or survival traits are of particular importance, which are directly related to the profits of this profession. Considering the production of new silkworm hybrids in China, as the hub of the world's silkworm industry, and the existence of international connections for the annual import of some of these hybrids into the country, it is necessary to evaluate the performance of existing hybrids in Iran in comparison with imported hybrids from Chian in terms of various economically important traits. So that correct decisions can be made to replace imported hybrids with domestic hybrids, and to select the most appropriate type of hybrid in terms of functional traits and to determine the priority of imports. In the present study, performance of Iranian commercial silkworm hybrids, including old and new commercial hybrids, along with hybrids imported from China, was investigated for the most important production, reproduction and longevity traits. Given the 80% share of dependence on imported hybrid seeds, the importance of imported hybrid types is very essential. Therefore, given the country's foreign exchange restrictions, a large effort is made every year to provid imported hybrid seeds.
Materials and methods: Six old Iranian commercial hybrids including 104×103, 103×104, 154×151, 151×154, 154×153 and 153×154, nine new Iranian commercial hybrids including IRA2×IRA3, IRA2×IRA9, IRA2×IRA11, IRA3× IRA2, IRA3×IRA4, IRA4×IRA3, IRA7×IRA4, IRA11×IRA4, IRA9×IRA2, IRA11×IRA2, IRA4×IRA7 and IRA4×IRA11 along with nine hybrids imported from China including S×M, M×S, B×Q, Q×B, BB×QA, QA×BB, 7532×781, Lianggang No2 and Guican No5 were reared in a completely randomized design with four replications of 200 larvae and their performance for the studied traits (including hatching percentage (HA), mean weight of a best cocoon (MWBC), mean weight of a best cocoon shell (MWBCS), percentage of a best cocoon shell (PBCS), total cocoons weight produced per 25,000 larvae (TCW), number of cocoons per liter (NCPL), weight of cocoons per liter (WCPL) and mortality rate (MR) was recorded. The generalized linear models (GLM) procedure of SAS software version 9.4 was used for statistical analysis. Data obtained in respect of the studied traits were subjected for further analysis by a multiple trait evaluation index (E.I.) using the following formula: E.I. = (A-B/C×10) + 50, where A is value of a particular hybrid for particular trait, B is mean value for a particular trait of all the hybrids, C is standard deviation of a particular trait for all the hybrids, 10 is standard unit and 50 is fixed value. Minimum / average of the E.I. value fixed for selection of a hybrid is >50.
Results: The results of comparing the averages showed that there was a significant difference between the hybrids for all investigated traits (P<0.01). The minimum and maximum values of the traits are not the same in different hybrids and some hybrids show higher performance for a larger number of traits. Among them, the traits related to weight, shell weight and shell percentage of cocoon are the most important traits in breeding purposes with high economic value and are used to improve cocoon performance. The highest hatching percentage as the most important reproductive trait with a value of 97.97% and the lowest percentage of mortality rate as a survival index with a value of 4.25% was reported for Chinese hybrid Lianggang No2. The Iranian new hybrid IRA11×IRA4 had the highest values for most production traits related to cocoons (P<0.01). Also, evaluations based on a group comparison of Iranian hybrids (new and old) versus Chinese hybrids showed that there is no significant difference between the two groups in terms of hatching percentage, although for production traits including the mean weight of a best cocoon (MWBC), mean weight of a best cocoon shell (MWBCS), percentage of a best cocoon shell (PBCS), total cocoons weight produced per 25,000 larvae (TCW), Iranian hybrids have a higher performance than Chinese hybrids, but for the characteristic of moratality rate as the most important indicator related to longevity, Chinese hybrids are superior than Iranian hybrids. Based on an evaluation index used in the present study, which is based on the average of two-way crossings for pairs of hybrids, both pairs of which were used in the experiment, the new Iranian hybrids IRA2×IRA3, IRA3×IRA4 and IRA11×IRA4 had an acceptable level of the evaluation index and showed superiority. Based on this index, for the trait of hatching percentage, only the old Iranian hybrid 153×154 and Chinese hybrids with direct and inverse crossing (including B×Q, BB×QA and M×S), and for the larval mortality percentage trait, the majority of new Iranian hybrids with direct and reverse crosses of the old Iranian hybrid 104×103 had a higher average than the other hybrids.
Conclusion: In conclusion, the results of comparison of the means, group comparison between Irainian and Chinese hybrids, and values of the evaluation index showed that new Iranian hybrids had better performance for traits related to produce cocoons than the Chinese and old Iranian hybrids, but Chinese hybrids were significantly different from the Iranian (old and new) for hatchability and longevity trait. However, in the next step, it is necessary to conduct these comparisons at the level of farmers and rural conditions in order to draw a final conclusion. This information is reviewed annually by the country's Sericultural Strategic Committee to plan the necessary measures for breeding commercial hybrid parents, producing commercial hybrids, and importing for the coming year.