هیبرید

One of the goals of new programs for silkworm breeding is to investigate the ability to withstand environmental fluctuations. Silkworms are cold-blooded organisms, meaning that their body temperature and metabolic processes are affected by the temperature of the environment. Silkworms are sensitive to temperature changes, and exposure to cold temperatures can affect their growth, development, and overall health. So far, no special attention has been paid to improving compatibility traits in Iranian silkworms. The requirement of this goal is to improve the traits related to resistance to stresses and adaptation to new conditions. Achieving this regard requires expanding the country's silkworm gene bank, especially in the field of commercial lines. New genetic resources should also be made available while identifying the genetic capabilities of the existing lines. In the meantime, producing eggs that are resistant to cold stress is one of the proposed solutions to deal with this stress. For this purpose, it is necessary to determine the level of resistance or susceptibility to cold stress in commercial lines used in the production of commercial eggs, and the desired lines should be rated from this aspect. With this rating, recommendations can be made to create crosses between the mentioned lines aiming at producing commercial eggs resistant or sensitive to cold stress and distributing each batch of these eggs in different geographical areas with different climates. In the present study, the performance of commercial lines of Iranian silkworms including 31, 32, 103, 104, 151, 153, and 154, under cold stress was investigated in control and challenge treatments.

After the steps of preparation for breeding, silkworm eggs were kept in a hatching room under standard temperature and humidity conditions for 12 days. The standard conditions for breeding were temperature (25 ± 2 °C), relative humidity (75 ± 5%), and photoperiod (16 hours light/ 8 hours dark). Mulberry leaves of modified varieties were used to feed the larvae. To induce cold stress, 300 larvae on the third day of the fifth instar (in the form of three replicates of 100 larvae) were incubated at 0 °C for 12 hours and then returned to the standard rearing conditions at 25 °C. The production traits the characteristics of cocoon weight, cocoon shell weight, cocoon shell percentage, number of cocoons per liter, cocoon weight per liter, the average weight of a cocoon, the average weight of the best cocoon, the average weight of a middle cocoon, the  average weight of a weak cocoon, and the average weight of a double cocoon, as well as some traits related to longevity, including the percentage of live larvae, the percentage of dead larvae, the percentage of pupal losses, and the percentage of produced butterflies, were investigated in each cold stress and control treatments. For statistical analysis, the generalized linear model (GLM) procedure was used in SAS software, and means were compared with Tukey's statistical test at a significant level of 0.05.

In general, the highest and lowest values of traits were not the same among the genotypes and under applied stress conditions, but some genotypes showed higher performance for a larger number of traits. Among the studied traits, those related to cocoon weight, cocoon shell weight, and cocoon shell percentage are the most important traits for breeding purposes, which have high economic values and are used to improve cocoon performance. Meanwhile, the live and dead larvae percentage traits, along with death pupae percentage and productive moth percentage, are important indicators related to viability, which showed significant differences between the studied lines. The results of mean comparisons showed that the larvae of the control group generally had better performance in all the examined traits than the larvae under cold stress, with a significant difference (P < 0.001). However, two lines 153 and 154 from the cold stress group had higher performance in many production and longevity traits than the other lines under cold stress and even some lines of the control group.

The temperature of the breeding environment is one of the factors that, in the case of fluctuation, leads to the deviation of breeding conditions from the optimal state and damage. In general, cold stress and low temperatures have different effects on insects, considering the intensity and duration of the insect's exposure. In addition, the stage of life, the evolution degree of adaptation mechanisms, and adaptation to the environment greatly affect the insect's response to cold stress. The results of the present research show that the performance of commercial lines of Iranian silkworms is affected under cold stress conditions, and lines 153 and 154 have higher resistance than the other lines. Hence, they can be prioritized in the production of commercial hybrids in terms of resistance to cold stress and production and survival records. Further studies are suggested to measure the molecular and biochemical characteristics of some proteins related to temperature stress in different treatments.

Considering the production of new silkworm hybrids by prominent countries in the sericulture industry such as China and the import of these hybrids to the country in recent years, it is necessary to update these evaluations so that correct decisions can be made to choose the most suitable type of hybrid in terms of functional traits. Therefore, such comparisons are done annually and the results are sent to the Iran Sericultural Corporation- Silk Worm Research Center as an executive body for final decision. The present study aimed to investigate the performance of eight Chinese commercial silkworm hybrids, including Suju×Minghu (S×M), Minghu×Suju (M×S), Baiyue×Qiufeng (B×Q), Qiufeng×Baiyue (Q×B), BaiyueB×QiufengA (BB×QA), QiufengA×BaiyueB (QA×BB), 874×873, and 874×873. Hybrids 872×871 and 872×871 also were among the studied hybrids, but due to the decrease in the performance of cocoon-related traits compared to other hybrids that had a big difference in terms of the obtained values, they were removed and excluded from the final analysis. The desired hybrids for 14 traits including best cocoons weight produced per 26,000 larvae (BCW), total cocoons weight produced per 26,000 larvae (TCW), number of cocoons per liter (NCPL), weight of cocoons per liter (WCPL), percentage of pupa viability (PPV), mean weight of a cocoon (MWC), mean weight of a cocoon shell (MWCS), mean of cocoon shell percentage (MCSP), mean weight of a male cocoon (MWMC), mean weight of a male cocoon shell (MWMCS), mean of male cocoon shell percentage (MMCSP), mean weight of a female cocoon (MWFC), mean weight of a female cocoon shell (MWFCS), and mean of female cocoon shell percentage (MFCSP) were reared in the spring of 2022 after hatching and according to standard methods and under the same conditions in Iran Silk Research Center and their performance was recorded. Each silkworm hybrid was reared in three replications of 200 larvae (total number of observations including 600 records per hybrid for all traits) in a completely randomized design. The analysis of the obtained data was done by SAS software by using the procedure of generalized linear model (GLM), and the average performance of the traits was compared to each other using Tukey's range test at the probability level of P<0.05. The results of the analysis of variance for the studied traits showed that the effect of the hybrid type for most of the studied traits including best cocoons weight produced per 26,000 larvae (BCW), total cocoons weight produced per 26,000 larvae (TCW), number of cocoons per liter (NCPL), the weight of cocoons per liter (WCPL), mean weight of a cocoon (MWC), mean weight of a cocoon shell (MWCS), mean of cocoon shell percentage (MCSP), mean weight of a male cocoon (MWMC), mean weight of a male cocoon shell (MWMCS), mean of male cocoon shell percentage (MMCSP), mean weight of a female cocoon (MWFC), mean weight of a female cocoon shell (MWFCS) and mean of female cocoon shell percentage (MFCSP) was significant (P<0.05). In the meantime, only traits of the percentage of pupa viability (PPV) as the most important index related to survival and the mean of male cocoon shell percentage (MMCSP) were not affected by the hybrid type (P<0.05). The average performance of the hybrids showed a significant difference (P<0.05) for all the traits except for the percentage of pupa viability (PPV) and the mean of cocoon shell percentage (MCSP). The BB×QA hybrid showed a higher performance than other hybrids for six traits including the best cocoons weight produced per 26,000 larvae (BCW), the total cocoons weight produced per 26,000 larvae (TCW), the weight of cocoons per liter (WCPL), the mean weight of a cocoon (MWC), the mean weight of a male cocoon (MWMC), and the mean weight of a female cocoon (MWFC) (P<0.01). Also, the M×S hybrid showed a higher performance than other hybrids for the five traits of the mean weight of a cocoon shell (MWCS), mean of cocoon shell percentage (MCSP), mean weight of a male cocoon shell (MWMCS), mean weight of a female cocoon shell (MWFCS), and the mean of female cocoon shell percentage (MFCSP) (P<0.05). In addition, the M×S hybrid showed the lowest value compared to other hybrids for the number of cocoons per liter (NCPL), which the lower values of this trait are preferred (P<0.01).  Based on the results of the present research, the priority of importing and rearing silkworm eggs in 2023 is suggested for BB×QA and M×S hybrids. Although the performance of these two hybrids with other hybrids, except for the 874×873 and 874×873 hybrids, is not significant in most of the examined traits, they can still be considered as next-import priorities. The desired hybrids for 14 traits including: best cocoons weight produced per 26,000 larvae (BCW), total cocoons weight produced per 26,000 larvae (TCW), number of cocoons per liter (NCPL), weight of cocoons per liter (WCPL), percentage of pupa viability (PPV), mean weight of a cocoon (MWC), mean weight of a cocoon shell (MWCS), mean of cocoon shell percentage (MCSP), mean weight of a male cocoon (MWMC), mean weight of a male cocoon shell (MWMCS), mean of male cocoon shell percentage (MMCSP), mean weight of a female cocoon (MWFC), mean weight of a female cocoon shell (MWFCS) and mean of female cocoon shell percentage (MFCSP) were reared in the spring of 2022 after hatching and according to standard methods and under the same conditions in Iran Silk Research Center and their performance was recorded. Each silkworm hybrid was reared in 3 replications of 200 larvae (total number of observations including 600 records per hybrid for all traits) in a completely randomized design. The analysis of the obtained data was done by SAS software (version 9.4) by using the procedure of generalized linear models (GLM) and the average performance of the traits was compared to each other using Tukey's range test at the probability level of P<0.05. The results of the analysis of variance for the studied traits show that the effect of the hybrid type for most of the studied traits including best cocoons weight produced per 26,000 larvae (BCW), total cocoons weight produced per 26,000 larvae (TCW), number of cocoons per liter (NCPL), the weight of cocoons per liter (WCPL), mean weight of a cocoon (MWC), mean weight of a cocoon shell (MWCS), mean of cocoon shell percentage (MCSP), mean weight of a male cocoon (MWMC), mean weight of a male cocoon shell (MWMCS), mean of male cocoon shell percentage (MMCSP), mean weight of a female cocoon (MWFC), mean weight of a female cocoon shell (MWFCS) and mean of female cocoon shell percentage (MFCSP) is significant (P<0.05). In the meantime, only traits of the percentage of pupa viability (PPV) as the most important index related to survival and the mean of male cocoon shell percentage (MMCSP) were not affected by the hybrid type (P<0.05). The average performance of the hybrids showed a significant difference (P<0.05) for all the traits except for percentage of pupa viability (PPV) and the mean of cocoon shell percentage (MCSP). The hybrid BB*QA showed a higher performance than other hybrids for six traits including the best cocoons weight produced per 26,000 larvae (BCW), the total cocoons weight produced per 26,000 larvae (TCW), the weight of cocoons per liter (WCPL), the mean weight of a cocoon (MWC), the mean weight of a male cocoon (MWMC) and the mean weight of a female cocoon (MWFC) (P<0.01). Also, the M*S hybrid showed a higher performance than other hybrids for the five traits of mean weight of a cocoon shell (MWCS), mean of cocoon shell percentage (MCSP), mean weight of a male cocoon shell (MWMCS), mean weight of a female cocoon shell (MWFCS), and the mean of female cocoon shell percentage (MFCSP) (P< 0.05). Also, the M*S hybrid showed the lowest value compared to other hybrids for the number of cocoons per liter (NCPL); the lower values of which are preferred (P<0.01). Based on the results of the present research, the priority of importing and rearing silkworm eggs in 2023 is suggested for BB*QA and M*S hybrids. Although the performance of these two hybrids with other hybrids, except for the 874×873 and 874×873 hybrids, is not significant in most of the examined traits, and they can still be considered as next import priorities.

The purpose of line production is to increase yields and good behavior of bee colonies. Using inheritance, heritability, heritability, genotypic correlation between them, selection line and production are planned. In each line, important traits are measured and the top queens are selected by kinship and performance test. If pure queens intersect with purebred bees, they create a pure line, and if they intersect with other male bees, a hybrid is produced. At least three independent lines are needed to increase heterozygosity and decrease inbreeding. There is a dilemma between choosing an attribute to improve performance and reducing the cost of breeding. In line production, kinship and mixing methods are used, the combination of which is Diallel cross.The purpose of managing bee lines; Maintaining genetic diversity and improving the performance and behavior of bees, reducing colony losses and reducing dependence on drug treatments. By evaluating the offspring, the response rate to selection and genetic progression will be determined. Queens of high-yielding breeds and commercial lines are also valued and sold based on the evaluation of the desired traits. In creating a bee line with high production of royal jelly, first Italian bees were bred and after six generations, a bee line called znd1 was produced with high production of royal jelly and even high honey production. Quantitative genetic advances and the use of molecular markers over 35 years improved the bee line by producing very high royal jelly.

City of Torbat Heydarieh in the northeast of Iran is one of the most important region in rearing silkworm in country. In Iran, two types of silkworm are used for rearing, mostly hybrids produced in center of Iran silkworm research, also in some regions some of imported hybrids using for rearing. Understanding the resistance and sensitivity of these hybrids is essential for choosing the best hybrid in each region and for understanding their genetic capabilities to apply future breeding hybrid. In addition, considering the conditions in the traditional and industrial field of silkworm breeding, which is suffering from many contamination and morality reasons, the selection of resistant strains and hybrids is important for preventing a severe drop in production. The goals of many of pervious experiments were to identify the proper hybrid for each region. Results of studies in Iran showed that Iranian hybrids as 103 x 104, 104 x 103, 31 x 32 and 154 x 151 are proper for rearing in some region in Iran. Seven Iranian commercial silkworm hybrids were hatched and reared during the spring 2016 in center of silkworm development of Torbat Heydarieh. Propose of the study was compare of performance for silkworm hybrids.

The field survey was conducted for determination of performance in six Iranian silkworm hybrids namely 154 x 153, 32 x 31, 104 x 103, 151 x 154, 154 x 151, 153 x 154 and one Chines hybrid. Study was carried out by feeding on the mulberry variety Kenmuchi. For the propose one box of disease-free laying of each hybrid was obtained from Iran Sericulture Research Center (ISRC) and the eggs were rearing in the center of sericulture development of Torbat Heydarieh under standard conditions of 25°C with RH of 80 and photoperiod of 16L:8D. After hatching, silkworm larvae fed base on standard rearing conditions. The larvae were fed with the healthy leaves of Kenmuchi mulberry tree. After finishing of rearing stages, the produced cocoons were collected. Some of recorded traits were including: number of live larva, number of live pupa, cocoon weight, cocoon shell weight, cocoon shell percent, color of cocoon shell and duration of larva period. Results according by CRD were analysis using procedure of GLM in SAS 9.2.

While Iranian Hybrids in this study were similar for many of quality trait, Chinese hybrid was different in most of the traits. Chinese hybrid has longer molt period for 3th instar, young larvae and longer nutritional period for 4th instar, 5th instar and adult larvae, also the hybrid has longer larvae period in compare with Iranian hybrids. Results of analysis showed that Chinese hybrid had most number of good cocoons in litter (P<0.05) due to mean good cocoon weight in this hybrid was lowest in compare with hybrids. Results showed that Chinese hybrid had the lowest good cocoon weight and good cocoon mean (P<0.05). Mean weight of a good cocoon with female pupa in 32 x 31 and 151 x 154 hybrids was more than other hybrids, meanwhile Chines hybrid showed lowest weight (P<0.05). Male pupa in different hybrids had similar weight, but female pupa in 151 x 154 hybrid and Chines hybrid showed the most and the least weight, respectively. In other hand, 32 x 31 had a higher performance for these traits. Chines hybrid and 151 x 154 hybrid showed lowest mean of cocoon shell weight meanwhile, for the trait 32 x 31 had most performance. Number of egg laying in 32 x 31 hybrids was higher in compare with other hybrids. For other traits did not observe difference between studied hybrids although, for example 151 x 154 and Chines hybrid had the least number of cocoon production and number of good cocoon. Other studies identified that using directly of imported hybrids for rearing in different region of Iran will not lead to good results.

According to the results, Chinese hybrid had the lowest value for rearing in Torbat Heydarieh region due to the hybrid has the lowest mean of good cocoon and weight of shell cocoon. Although Iranian hybrids in most of traits had similar performance but this study indicates that 32 × 31 is better for cocoon production in Torbat Heydarieh Region

This experiment was conducted to determine the effect of selection index in four iranian commercial silkworm lines (107, 110, 153, 154) on resistance of their hybrids including 107×110, 110×107, 153×154, 154×153 under stress of nuclear polyhedrosis virus (N.P.V) Infection. Selection index program was performed on 3P commercial lines during 9 generations. Later generation parents of 3P lines were selected in each generation, by forming selection matrix based on heritability parameters, correlation between cocoon weight, cocoon shell weight and cocoon shell percentage and phenotypic mean of traits. In the 10th generation, 2P populations (produced by random cross of 3P) were mated randomly and P (parent) silkworm eggs were produced by random mating of 2P population. P populations in selected and random groups were reared in village conditions (growths silkworm rearing house silkworm). Control P population was produced by crossing 2P population (produced by non-selected 3P lines). F1 hybrids of control group (non-selected) were reared simultaneously. From the obtained results, the hybrids of 110×107 and 154×153 significantly showed the highest performance for individual cocoon traits (P<0.05).The best cocoon percentage, middle cocoon percentage, low cocoon percentage, double cocoon percentage, total cocoon weight, larva survival rate and pupation rate were studied, that showed negative relationship between resistance and production characteristics. The results demonstrated that selection index method have a negative effect on resistance of silkworm hybrids as well as improving production and economic performance of silkworm hybrids. It is recommended that economical coefficients and genetically parameters are estimated for productive, resistance and quantitative cocoon characters together. Then parents would be selected on the basis of those parameters.