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Thermostability of Cassava Green Mite Mononychellus Mcgregori(Tetranychidae:Mononychellus):an Important Invasive Pest Mite

Author: LuZuoPing
Tutor: FuYueGuan
School: Hainan University
Course: Crop pests learning
Keywords: Mononychellus mcgregori thermostability development and reproduction protective enzymes activities Hsp70 gene expression
CLC: S435.33
Type: PhD thesis
Year: 2012
Downloads: 55
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Abstract


Cassava green mite Mononychellus mcgregori is a newly invasive pest mite of cassava in China. It mainly harms the green components of buds, young leaves and stems of cassava, with damaged leaves deformed by yellow blot, which results in leaf chlorosis, dried branches and even plant death in serious cases, a40~60%reduction in production in the case of serious damage. It was firstly reported in Danzhou, Hainan province, China in2008and has since become more widespread. It is known to occur currently in important cassava-planting areas such as Guangxi, Guangdong and Yunnan where it causes significant damage to cassava. Since it’s invasive in tropical area of China, the populations have increasing quickly. The adaptation to its invasive environment are the fundamental for the population expansion of M. mcgregori, although the population growth have something to do with the deficiency of natural enemies and that it dose not have other pest mite species with the same ecological niche to compete with. The continually survey showed that, the green mite were very difficult to collected in2008, but in2010, the mites developed to vast areas of land and occurrence not only in spring and winter, but also in summer and autumn. Therefore, the cassava green mite M. mcgregori has gradually developed adaptation to the climate of tropical area of China.Whether a alien species can survive the temperature stress after its invasive had important influence on its dispersal in the new environment as well as its population expansion. The physiological, biochemical as well as the molecular mechanism for an alien species to adapt the high temperature have important significance in theory and practice to reveal the population expansion, population replacement as well as the population prediction. The origin M. mcgregori is South America and as a tropical native mite, the adaptation to high temperature was the significant foundation for its occurrence and damage and was also the most fundamental material for us to predict the distribution, disperse as well as the population occurrence mechanism of the pest mite after its invasion in China. The study on the adaptation to high temperature of M. mcgregori can lay the groundwork for investigate further the ecological adaptation, population expansion mechanism as well as the forming of its effective control and management measures.Therefore, to understand more of the mechanisms behind the invasion and spread of M. mcgregori in China, as well as the adaptation of this mite to a tropical environment, the mainly ecological factors affected the development and reproduction of the mite were firstly studied, then the effects of high temperature exposure on the development and reproduction, protective enzyme activities and the relative expression of protective enzyme genes as well as the heat shock protein70(Hsp70) gene via spectrophotometry method and realtime fluorescence quantitative PCR(RTFQ PCR) were also studied, so that the thermostability as well as its mechanisms were revealed based on the biology, physiology as well as the molecular. The results will provide a theoretical basis and precondition for further research on the molecular mechanisms of the thermostability and ecological adaptability of M. mcgregori.The main results are as follows:1. The suitable temperature, humidity, photoperiod and host for the development and reproduction of M. mcgregori were24~27℃,70%~90%,12~14h and the local cassava cultivars "Bread", respectively. Under the above suitable conditions, the development duration of M. mcgregori were as follows:eggs durations was4.17±0.29d, larvae duration was2.67±0.29d, protonymphs duration was2.17±0.29d, detonymph duration was2.33±0.29d and eggs to adults duration was11.34±0.29d. The eggs hatchability was100%, the fecundity of per female was9.00±1.00, the female percentage was89.36%±1.53%and the female adult mite lifespan was19.00±0.50d.2. High temperature significantly affected the development and the reproduction of M. mcgregori.42℃was the extremely high temperature for the development and the reproduction of M. mcgregori and under the temperature the eggs could not hatch and not fullfill their subsequent development. With the increasing of the temperature from30℃to39℃, the development duration and the female adult mite lifespan decreased significantly. The development duration decreased fromll.34d (25℃) to9.83d (39℃), the female adult mite lifespan decreased from19.00d (25℃) to3.00d (39℃) and the fecundity of per offspring female decreased significantly, from49.00(25℃) to7.00(39℃). The eggs could completely hatch when temperature increase from30℃to33℃. but the hatchability significantly decreased at36℃with32.05%and39℃with13.42%, respectively. At24℃, the female percentage was the highest with89.36%, but significantly decreased30℃with76.67%and33℃with76.40%, respectively. In addition, there was no difference in the female percentage at36℃and39℃.3. Exposure of eggs, larvae, protonymphs, deutonymphs and adults to high temperature significantly affected the development and reproduction of M. mcgregori. With the increase of the temperature and exposure time, the development duration significantly prolonged, but the eggs hatchability, female percentage and longevity of female adults were all significantly decreased. The tolerance of M. mcgregori to high temperature was some improved with the increased of instars, however, the tolerance of pronymphs were some higher than deutonymphs, for that not only the fecundity but also the offspring hatchability of the exposed protonymphs were higher than deutonymphs. The tolerance of all the development stage to high temperature were ranked in the sequence:adults> protonymphs> deutonymphs> larvae> eggs. However, they usually recovered more slowly after the high temperature exposure termination.4. Exposure of eggs, larvae, protonymphs, deutonymphs and adults to high temperature for different time significantly affected the activities of polyphenol oxidase (PPO), peroxidase (POD), ascorbate peroxidase (AsA-POD) and catalase (CAT) in M. mcgregori. Activities of PPO, POD, AsA-POD and CAT in protonymphs and adults some varied with the increase of temperatures and exposure time, and were the highest at1h-exposure, and then decreased except in larvae in which the CAT activity decreased to the lowest after exposed to the extremely high temperature (42℃) for1h. Howerve, there were no significant difference in changes of activities of PPO, POD, AsA-POD and superoxide dismutase(SOD) in larvae and deutonymphs.Howerer, the activities of CAT increased significantly in larvae and decreased in detonymphs after exposed to the extremely high temperature (42℃) for1h. No significantly changes were observed in SOD activities after all the development stages were exposed to high temperature for different time.5. Exposure to high temperatures for1hour was the most sensitive time for M. mcgregori. The fecundity and the offspring eggs hatchability decreased significantly and the the activities of PPO, POD, AsA-POD and CAT in protonymphs and adults changed significantly after exposure to high temperatures for1h. After exposure to extremely high temperatures of42℃for1h especially, the fecundity per female decreased to9.00for larvae,18.67for protonymphs,11.33for deutonymphs and21.00for adults; the offspring hatchability decreased to30.82%for larvae,57.33%for protonymphs,54.11%for deutonymphs and61.19%for adults; and the activities of PPO, POD, AsA-POD and CAT were0.92,5.85,2.9and1.56times (larvae),1.91,1.00,1.00and0.14times (protonymphs),0.92,0.99,1.00and0.17times (deutonymphs),1.81,12.52,9.00and1.75(adults).6. The relative expression of PPO, POD, AsA-POD, CAT and SOD gene via RTFQ PCR were increased in adults after they were exposed to extremely high temperature (42℃) for1h, which increased5.19,4.38,152.23,321.42and3.41times that of the control, respectively, and were in accord with their enzyme activities. These results suggested that protective enzymes of POD, AsA-POD, CAT and SOD were associate with the thermostability of M. mcgregori and they might have synergistic effect on protect the mite against toxic oxygen intermediates and perhaps were associate with the resistance of high temperature in M. mcgregori.The increasing of PPO activities as well as its gene expression were associate with the immunity improvement of the mite to high temperature stress. These results provide a theoretical basis and precondition for further research on the molecular mechanisms of the thermostability and ecological adaptability of M. mcgregori.7. The relative expression of heat shock protein70(Hsp70) gene via realtime fluorescence quantitative PCR (RTFQ PCR) were increased to56.85times that of the control after exposure adults to extremely high temperature (42℃) for1h. It suggested that the elevated expression of HSP70gene was related to the adaptation of M. mcgregori to high temperature.

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CLC: > Agricultural Sciences > Plant Protection > Pest and Disease Control > Crop pests and diseases and their prevention > Tuber Crops Pests and Diseases > Cassava ( manioc ) pests and diseases
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