| The resistance of Bt transgenic cotton to cotton bollworm and the physiological mechanisms thereof are probed into by methods of field experiment, chamber bioassay, biochemical and immune determination. The main results are summarized.1. The insect-resistant comparison and evaluation of Bt transgenic cottonThe resistance to cotton bollworm of Bt transgenic cotton "Guo-kang-mian No.l", the first cultivar of tansgenic cotton breed in China, is compared with that of "Bao-ling-mian 32B" introduced from America. Their resistances both show the same time and space dynamic. The resistance descends significantly with the development of cotton growth stages. The resistance also differs with the differences of cotton structures; that is, the resistance of tender leaves is superior to that of tender squares. The resistance of "Guo-kang-mian No.l "is inferior to that of "Bao-ling-mian 32B" at every corresponding growth stage, and the same as every corresponding cotton structure. Their resistant degrees are evaluated at RESISTANCE and HIGH RESISTANCE respectively.2. The resistance to cotton bollworm of Bt trnsgenic cotton during its former growth stagesBt transgenic cotton during its former growth stages shows magnificent insecticidal activity to the lower-instar larvae of cotton bollworm, but the resistance shows dynamic variation with the development of cotton growth stages. The resistance at cotyledon stage is superior to that at any other stage; when the first true leave sprouts the resistance descends slightly, and then increases gradually during the whole seedling stage, until reaches the top at 10-leaf stage; henceforth the resistant descendent starts. The abnormal climates, such as storm, low temperature, consecutive overcast and rainy, can cause the sharp resistant descendent, and it will take several sunny days to restore.During the first generation occurrence stage of the cotton bollworm larvae in Yanjiang Cotton Area, Bt transgenic cotton shows considerable insecticidal efficacy against 1st and 2nd instar larvae, however the efficacy against 3rd and 4thinstar larvae descends significantly; and the efficacy against 5th instar larvae is so poor that part of the larvae can survive to pupa, but the pupation rate is significantly lower than that of CK.The quantity supervision of the first generation larvae should be stressed, especially in the fields interpersed with normal cotton and other host crops preferable to cotton bollworm, so that the chemical control can be operated timely. The suggestive control index is 20 second-instar and above larvae per 100 cotton plants. The powerful and quick chemical pesticides are favorite to be sprayed, when necessarily, the higher-instar larvae with strong adaptability should be killed artificially. Bt Preparations are not recommended in view of the probable mutual resistance of pest.3. The influence of fertilization, soil drought and water-logging, environmental temperature on the insect-resistance of Bt transgenic cottonThe insecticidal activity and the growth inhibition action of Bt transgenic cotton increase with the enhancing of rates of fertilization, and decline sharply at lower-rate. The excess and weakness of water in soil both show detrimental influence on the resistant expression, meanwhile the influence of drought is less than that of water-logging. Lower-temperature can descends considerably not only the expressive activity of Bt gene transformed in transgenic cotton, but also the insecticidal activity of the insecticidal protein having expressed in transgenic cotton. Higher-temperature can also cause the expressive descendent of Bt gene, but its influence is less than that of lower-temperature. However, the insect-resistant activity of the insecticidal protein having expressed in transgenic cotton, under higher-temperature, to the lower-instar larvae of cotton bollworm increases significantly.The management of water and fertilizer in transgenic cotton field is crucial to the efficient insect-resistant expression. The rate of fertiliz...
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