The aim of this research was to use a natural component, renewable and environmentally friendly material (silk cocoon) as reinforcing component for urea formaldehyde resin in the plywood manufacturing and investigate its influence on physical and mechanical properties of plywood. For this purpose, silk cocoon was used as filler and reinforcement at four levels of 0, 10, 20 and 30 percent (based on dry weight of urea formaldehyde resin). The physical and mechanical properties of samples including water absorption and thickness swelling after 2 and 24 hours immersion in water, bending strength parallel and perpendicular to the surface layer grain and shear strength were measured. The results show that increasing the content amount of silk cocoon decreased water absorption and thickness swelling after 2 and 24 hours immersion in water and increased bending strength parallel and perpendicular to the surface layer grain and shear strength. So that, using 30 percent of silk cocoon improved dimensional stability, bending strength and shear strength.

Genetic parameters of cocoon weight, cocoon shell weight and cocoon shell percentage was estimated in two commercial lines during three generations under individual selection and random selection schedule. The individual selection program included (A) individual selection based on cocoon weight and (B) individual selection based on cocoon shell weight. The data collected from two commercial lines 153 and 154 were used in the Iran Silkworm Research Centre. Genetic parameters of cocoon weight and cocoon shell weight were estimated using WOMBAT software and REML algorithm. For both selection methods, high heritability were estimated for cocoon weight and cocoon shell weight. Both lines had higher heritability for traits under individual selection. Since there are high and positive genetic correlation between cocoon weight and cocoon shell weight, so it is showed we can improve one trait using selection based on another trait. Generally based on obtained results, it must be noted we can improve cocoon weight average in the short term using strategy A. If our purpose is improvement of the cocoon shell weight in the hybrids, strategy B is effective and can be recommended. Also strategy A improved cocoon shell percentage.

A total of 22268 records from 10 commercial silkworm lines reared in Iran Silkworm Research Center including Chinese lines of 32, 104, 152, 110 and 154 and Japanese lines of 31, 103, 107, 151 and 153 collected during 3 years in 4 rearing periods in spring and autumn were used for study of effect of inbreeding on economic traits. Two statistical models were used for analysis of the data. In the first model, inbreeding coefficient was considered as a covariate variable along with fixed effects of line, rearing year and season. In the second model, inbreeding effect considered as a classified fixed effect along with other mentioned fixed effects. All effects had highly significant effects (P<0.0001) on all traits. However, the non-significant effect of inbreeding on cocoon shell weight in the first model was an exception. Tukey-Kramer test was used for comparison of means. The means of different levels of each fixed effect were significantly (P<0.01) different for all traits. In the first model, partial regression coefficients on inbreeding were significant for cocoon weight (P< 0.0001) and cocoon shell percentage (P<0.01) and not-significant for cocoon shell weight. The results of this study showed that increasing of inbreeding significantly increases the cocoon weight and decreases the cocoon weight percentage, but its effect on cocoon shell weight is not significant. Regarding to the results of this study, it could be concluded that increasing of inbreeding has no noticeable effect on silk quantity. Therefore, increasing of inbreeding, at least, at the studied level of this population, is probably acceptable.

Introduction: Silkworm (Bombyx mori) is an important economic insect which is used as experimental material for the evolution of economically important silkworm breeds. Breeds/strains thus evolved are maintained in germplasm stations for breeders and researchers to use (Chiang 1980). Silkworm germplasm resources have a very important role not only for use in sericulture and silkworm breeding, but also for experimentation in genetics and molecular biology research. Based on several parameters like nutrition, genetics, and biochemistry, silkworms have been classified into different inbred strains (ESCAP 1993). However, few studies are reported for classification of silkworm based on larval growth potential. The Islamic Republic of Iran has valuable silkworm genetic resources which differ in cocoon shape. The present study was carried out to evaluate and identify oval cocoon bivoltine breeds suitable for rearing as germplasm resources under climatic conditions in Iran. Material and method: The present study was conducted in the Iran Silkworm Research Center (ISRC) and Islamic Azad University, Qaemshahr Branch, Iran. Fifty-four oval cocoon strains maintained by the Iran Silk Research Station (ISRC) were analyzed for the estimation of evaluation index to study their genetic divergence. Silkworm rearing was carried out as a single batch rearing system. Disease free laying of these strains were incubated in a controlled environmental chamber. When the eggs attained the head pigmentation stage on the 8 th day of development, they were shaded with a black gobo for 48 hr to shield them from light, so as to obtain uniform hatching on the 10 th day. Neonates were brushed and reared separately on fresh mulberry (Morus alba) leaves. st Young 1 rd to 3 instar larvae were reared at 27– 28° C and 85-90% relative humidity. Late age larvae th viz., 4 th and 5 instars, were reared at 24-26° C and 70-80% relative humidity. The larvae were fed mulberry leaves ad libitum three times a day. 250 larvae each from all batches of all strains were retained for completion of the life cycle. Feeding and other conditions of larval rearing were conducted following standard procedures. Larval growth weight was recorded on day 1, 3, and 5 of th the 5 instar (3 replicates each), using a precision digital balance. Evaluation index and subordinate function values were calculated for performance indices based on changes in larval weight at the last larval instar. The Evaluation index and sub-ordinate function values for all traits were calculated separately and average index value was obtained. Silkworm strains were ranked based on the average of evaluation index method and sub-ordinate function method. Hierarchical agglomerative clustering was done by using NTSYS-pc, version 2. 02e based on complete, single, UPGMA, UPGMC, and FLEXI approaches, and SAS-pc based on WARD and average approaches. However, the method of average linkage between groups (Romesburg 1984) under UPGMA (Unweighted Pair-Group Method using Arithmetic average) was considered as the major and final protocol for data conclusions and the resulting clusters were expressed as dendrograms. Results and discussion: ANOVA based on a completely randomized design indicated significant variations among the silkworm strains (P<0. 01). On the fifth day, strains 104×110, Shown, 102[Shown], 124-16-9[116] and Shaki A×D had significantly higher larval weights ranging from 4. 153– 3. 965 g (P<0. 01). Larval growth parameters revealed higher evaluation index and higher sub-ordinate function values for strains 104×110 (197. 272 and 2. 857), 1001 (193. 268 and 2. 780), BH-4 (186. 365 and 2. 647), 124-16-9[116] (183. 023 and 2. 602), and Shown (180. 744 and 2. 556). In the present study, by adopting quantitative approaches, 54 silkworm oval strains with different geographical distribution were analyzed. Based on these results it was observed that strains of the same origin did not group together, indicating they have different biological background. Main groups were divided into various sub-groups. Some oval strains were grouped together and were placed far away from other silkworm strains, indicating they might be suitable for future crossing, maintenance of parental strains, and hybridization with peanut cocoon strains so as to maximize heterosis and to avoid inbreeding depression. Because of the low effective population size and each female mating only with one male (thus, all her offspring were full-sibs), the inbreeding rate for this study was very high. This could cause more differentiation among these strains. The grouping methods allowed us to subdivide observations into several subgroups in such a way that we obtained homogeneity inside the subgroups and heterogeneity between the subgroups. Present results confirmed and complemented the results of previous studies about the importance of evaluation and classification of Iranian silkworm strains based on economical and biological characters (Zhao et al. 2007; Zanatta et al. 2009). Silkworm oval strains could be clustered into different groups according to the geographic areas initially observed. Present results confirmed and complemented the results of previous studies about the importance of evaluation and classification of Iranian silkworm strains based on economical and biological characters (Sohn 2003). During selection of two parents for hybridization, some characters should be matched, including high silk yield, adversity-resistance, good combining ability, and excellent silk quality, so that hybrids have good characters of both parents. Effective utilization of selected germplasm plays an important role in saving time in the synthesis of new hybrids. Critical assessment of variability present in the breeding material is a pre-requisite for paving the way of combining most of the desirable traits present in different genotypes into a single hybrid combination. Generally, hybrids from distant background have high heterosis. The study of diversity is important for selection of useful races, use of the heterosis advantage and generating new races. The selection of high yielding breeds with wider adaptation and stable performance are important goals in breeding programs.

In order to study of the effect of inbreeding on economic traits, 22494 records were collected from 10 commercial silkworm lines of Iran Silkworm Research Center including Chinese lines of 32, 104, 152, 110, 154 and Japanese lines of 31, 103, 107, 151, 153 during 4 generations from 2005 to 2007. In the linear statistical model, inbreeding was considered as covariable along with the fixed effects of line, sex and generation. All the effects included in the model were highly significant on cocoon weight, cocoon shell weight and cocoon shell percentage (P>0.0001) except inbreeding covariable for cocoon shell weight. Lsmean method was used for mean comparisons. Mean differences among levels of fixed effects and covariables were significant in all the traits (P>0.0001) so that Chinese lines of 32, 152, 104 and Japanese lines of 153, 103, 31 showed good performance. The highest heritability for all the traits was observed in 31 line and the lowest in 153 line. For cocoon shell percentage, the lowest values belonged to 152, 104 and 32 lines. The average inbreeding coefficient was 0 in the first and second generations and 0.03644 and 0.07327 in third and fourth ones. This demonstrated that inbreeding coefficient becomes twice in the fourth generation due to not controlling relative matings.

Introduction: 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.Materials and methods: 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.Results and discussion: 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.Conclusions: 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.

Identification of Gilkworm genetic stocks of each country and their potential have large imprtace.Due to lack of sufficient information about the three commercial silkworm pure lines of 31, 103 and 107 under Iranian condition, this research was conducted to assess the effects of gender, generation and line on cocoon economical traits. Phenotypic data for these three lines was collected from Iran Silkworm Research Center (ISRC) in three generations since 2001-2003.The used data included eight families ´ 3 × generations ´ 3 pure lines ´ 3 traits ´ 2 gender ´ 25 individuals (equals to 10, 800 records). Mean comparisons were conducted for each line, generation and gender in total and each pure line separately. Fixed effects of pure line, generation and gender were significant in level 0.01 for cocoon weight, cocoon shell weight and cocoon shell percentage (P<0.01). Trait average of three pure lines were statistically significant difference (P<0.05); so that the average of cocoon weight and shell cocoon weight for pure line of 31 (1.60±0.28 gram and 0.35±0.05 gram) and pure line of 103 (1.62±0.28 gram and 0.36±0.05 gram) were more than pure line of 107 (1.39±0.21gram and 0.28±0.03 grams), but shell cocoon percentage mean in pure line of 103 (22.76±2.75 gram) was more compared to the other pure lines. This trait for pure line of 107 was less then other pure lines (20.90±2.31 gram). In total pure lines of 31 and 103 had most quantitative traits pure line of 107 had less quantitative traits. Generation effect on differences between the cocoon weight, cocoon shell weight and cocoon shell percentage was significant (P<0.05). Second generation in comparison to other generations had more cocoon weight (1.648 gram) and cocoon shell weight (0.353 gram), but the average of cocoon shell parcentage (%21.651) was minimum compared previous and next generations (P<0.05). Also cocoon weight, cocoon shell weight and cocoon shell percentage were significantly different in two gender of female and male. Cocoon weight and cocoon shell weight of female individuals were higher than male individuals (P<0.05).

selection method using DNA markers is an assured method in breeding process via preparation of linkage map and QTLs determination of effective genes on quantitative traits control. This method can be used in the silkworm, since it has economical-productive and polygenic traits. It was used in this research for determination of QTLs of shell cocoon percentage by AFLP markers, 20 compounds of two primers (TaqI & PstI) that selected from 81 compounds in 33, 36 and 34 of F2 individuals of three mulberry silkworm populations which these progency was produced by mating of two Lemon Khorasan (as female) and 107 (as male) lines as pure parents. The extraction of DNA was done using phenolchloroform and extracted DNA was digested by TaqI and PstI restriction enzymes, so they linked to suitable adaptors and selected propagation of all samples of DNA was done by means of all of the primer compounds. The propagated samples were transferred to the acrylamid gel 6% and the linkage maps of studied populations were drawn based on matrix formation (number of progency of F2 population× number of appeared poly-morphic bands) by Map Manager and Cartographer ver.2.5 Softwares after genotyping of individuals and ultimately is identified number of possible locations of studied trait controller based on QTL analysis through Composite Interval Mapping in Likelihood Ratio Test (LRT) >13 and detected 4, 2 and 5 QTLs respectively within recessive-overdominance limitation.