جستجوی مقالات مرتبط با کلیدواژه « ليگنين » در نشریات گروه « گیاهپزشکی »

 As a very important and widely used construction material, wood is easily decomposed by biological agents such as bacteria, fungi and termites. However, some wood species are more resistant to these destructive factors, while others are very susceptible to destruction. The aim of this study was to investigate the effective factors on the resistance of the wood of four species of poplar, maple, chinaberry and Cypress against the attacks of the subterranean termite Microcerotermes diversus Silvestri. Since the tropical provinces of Iran, including Khuzestan, are among the regions where different species of termites are considered as the main factors in the destruction of lignocellulosic materials, therefore, knowing resistant woods, which in their natural and untreated state can have high durability compared to the attacks of this insect can help to choose better wood for making wooden products and structures.

 To check the natural durability of the four mentioned species, first, wooden samples were selected and cut from healthy trunks without visible defects. Then, with the aim of collecting termites to conduct selective and non-selective feeding tests, an abandoned palm grove was considered in Dodangeh village, located 20 km from Behbahan city, and then beech wood with dimensions of 2.5 x 4 x 20 cm were planted in the soil as bait for two weeks. After this period of time, the bait sticks were removed from the soil and transferred to the laboratory. Then, the cut wood was subjected to M. diversus termite infestation according to AWPA-EI:06 2008 standard obtained from baits. After the desired period of time, the chemical and physical properties of wood such as the percentage of extractive materials, specific gravity, lignin and cellulose content of each species were calculated according to the standard.

 The results showed that the percentage of extractive substances in maple species has a significant difference compared to other species and is lower than other species, while the highest amount of extractive substances is related to Cypress. Among the investigated species, cypress exhibited the highest lignin content, while poplar displayed the lowest. Notably, both cypress and poplar significantly differed in lignin content compared to the other two species. Cellulose analysis revealed a significantly higher percentage in spruce compared to all other species (p< 0.05). Conversely, no significant differences in cellulose content were observed between the remaining three species. The lowest amount of specific mass belongs to spruce and the highest It belongs to the maple species. This difference is significant at the 95% level. The results of selective, non-selective and field tests of termite feeding on wooden samples are shown in figure number five. The results show that Cypress and chinaberry samples showed the lowest percentage of weight loss and poplar and maple samples showed the highest weight loss.

 What increases the natural durability of wood species against termite attacks and other destructive factors are wood anatomy, wood density, lignin and cellulose content, moisture content, and the composition of extractive materials in the wood. Examining the extractives of the researched species, it can be seen that maple has the lowest percentage of extractives and Cypress has the highest amount, and this problem can have a serious effect on the intensity of termite attacks. Extractive substances play a critical role in enhancing wood's natural resistance to destructive agents, particularly insects. Their significance is evident in certain durable wood species. Removing these extractives renders the wood susceptible to decay. Furthermore, the weight loss observed in both selective and non-selective decay tests, along with field trials, demonstrates a clear correlation with the content of lignin and cellulose in the wood. By increasing the percentage of lignin, the desirability of wood for termites decreases, and on the other hand, with the addition of cellulose percentage, the desirability of the species for termites increases. Lignin is a polymer that, as the second component of wood after cellulose, plays an important role in wood, and due to its phenolic groups, it is considered a toxic substance for destructive agents and has repellent properties. When lignin coats the cell wall, it forms a more impermeable matrix, making the cellulose less accessible and making the wood more resistant to biodegradation. In this research, the highest amount of lignin belongs to Cypress and the lowest amount belongs to poplar, and a significant difference between the amount of lignin in these two species is observed. Physical characteristics such as specific mass is also considered as determining factors of durability against termite attacks, and species with lower and lighter specific mass are more likely to be attacked by termites. According to the obtained results, poplar is different from other species in terms of specific gravity and is considered a lighter species, and this issue, along with the high percentage of cellulose, which is the material preferred by termites, can increase the vulnerability of this species. Based on the obtained results, the effect of factors such as chemical composition and physical characteristics of the studied species on the intensity of subterranean termite attacks M. diversus and according to the mentioned parameters, Cypress species was the most resistant and poplar was the weakest species to the attack of this termite species.

One of the most important species of termites in the southern provinces of Iran is Microcerotermes diversus Silvestri, which is considered as subterranean termite and has the ability to attack the trees and the construction of timber. Due to the fact that Lignocellulosic material can be eaten easily by termite, this can cause great damage to buildings, so identifying resistant wooden species can help us to select suitable materials in areas where termite infestation is high. The aim of this study was to evaluate the tendency of M. diversus termite for different woods by using selective and non-selective nutritional tests in laboratory conditions. For the collection of termites, beech wood with dimensions of 2.5 × 4 × 20 cm was buried for two months inside the soil in an abandoned palm farm, 20 km from the city of Behbahan. After that, the woods were removed from the soil and transferred to the laboratory. Then, parameters such as percentage of extract material, specific gravity, lignin and cellulose content were calculated for each wooden sample. Determination of cellulose and lignin content of woods was carried out according to the T-264cm-88 and T-222cm-88, TAPPI standard, respectively. The measurement of extractive materials was carried out in accordance with the TAPPI Regulation No: T 204om-88ISO-3131 standard to measure dry specific gravity.
The data was analyzed by Tukey's test using SPSS software version 17, and the significance test was performed at 95% level using Pearson correlation test. According to the results, the percentage of eucalyptus extractives is higher than other species and all three species have a significant difference at 95% level. All three species have a significant difference at 95% level in amount of lignin and the highest and the lowest one was related to cypress and the beech species, respectively.
Also, the results showed that there is no significant difference between the three species in terms of cellulose content.
The highest level of dry specific gravity is also found in beech and the least of that belongs to the cypress. All three species have a significant difference at 95% level. The results of non-selective test of wooden samples showed that the cypress samples had the least weight loss and the highest weight loss was observed in the beech samples. Eucalyptus specimens were interstitial and had a significant difference with samples cypress and beech. Comparison of weight loss percentage in wooden samples illustrated that the lowest and the highest percentage of weight loss belonged to cypress species and beech, respectively. However, there is no significant difference between eucalyptus species and two other species. Selective and non-selective feeding of termites revealed that in both tests, there was a significant difference between the weight loss of cypress and beech, and the eucalyptus samples did not have a significant difference with the other two samples. Increasing the lignin decreased wood utilization for the termite. There is a significant difference between lignin content in these two species, the highest amount of lignin was obtained in cypress and the least one belongs to beech. Lignin which is composed of phenyl propane units, is known as malicious factors for pests due to the presence of aromatic groups in its structure. . The presence of extractives in eucalyptus should not be ignored in resistance to termites too. There are a wide variety of extractive materials in wooden species that affect wood properties such as the natural durability. The amount of extractives along with lignin can prevent the pest infestation. In the present study, the specific gravity among the three species was significant, and the highest and the lowest one belongs to beech and cypress, respectively. According to the results of other researchers, it was expected that the higher specific gravity would reduce the desirability for termites to consume wood, while our study demonstrated the effect of lignin and extractives are more meaningful in terms of termite deterrence.

Termites play a major role in reducing and decomposing woody materials within terrestrial ecosystems by degrading lingo-cellulosic materials with the help of the microbial community of their guts. We isolated the lignin-degrading bacteria from Anacanthotermes vagans (Hagen) using liquid and solid media containing wheat straw and lignin hydrochloric acid. Cellulose-degrading bacteria were also isolated using liquid medium containing filter paper، agar-cellulose and Congo red agar-cellulose. By conducting various experiments، 16 bacterial species were isolated and subjected to different biochemical tests for comparing their growth rates. The genera Enterobacter and Klebsiella showed the highest growth rate among the rest species of isolated lignin-degrading bacteria. The species Staphylococcus lentus and Bacillus subtilis were isolated from the media containing cellulose.