| Cross combinations of hybrids were made by adopting pink boll-worm resistant varieties with different resistant mechanisms and backgrounds and non-resistant upland cotton varieties as parental materials following the way of North Carolina II (NCII). The parents, Fl generation materials together with the control variety "Ezal" were tested in accordance to the design of randomly grouped plots and repeated 3 times for the general and special combining abilities and some main agronomic characters such as yield , fiber quality, and the heterosis of Fl populations at the cotton breeding field of H.Z.A.U. in the year of 2002, and also taking the non-resistant variety"Emian 18" as another control for the evaluation of their insect resistibility in the caged plots. The main results were as following:(1) Both the lint yield and seed yield of all Fl combinations were higher than those of the control "Ezal", and reached extremely significant deviation statistically for the great majority of the cross combinations, the percentage of yield increase varied from 0.8% to 49.2%.(2) Among the yield components of the insect resistant hybrids, the mature boll number accounts for a larger propotion, whereas the boll weight and the lint percentages are equivilent to or even lower than those of the non-resitant varieties and the control. Therefore the main cause that the insect resistant varieties have a higher output is due to that they set more mature bolls.(3) The five indexes of fiber quality of the Fl hybrids fit the targets of cotton breeding and the criteria of spinning and weaving requirements, of which the fiber length fell between 29.5 and 31.2 mm, the fiber strength was between 29.5 and 32.1 cN/tex, the Micronaire values were located between 4.2 and 4.9 and the fiber uniformity was above 83%.(4) By evaluation of the resistibility to the pink bollworm in the caged plots, the result showed that all the hybrids with the backgrounds of transgenic insect resistance (Bt/CpTI and Bt) had the strongest resistibility, and those with the background of traditionally bred varieties second. The percentages of the damaged seeds from all the materials participated in the trail were lower than those of two controls "Ezal" and "Emian 18".(5) The percentage of insect damaged seeds was negatively correlated to those of the seed yield and lint yield, and reached an extremely significant level, the coefficients were -0.5688 and -0.5599 separately. Also all the insect resistant materials had a prominent hybrid vaguer in yields over the controls.(6) Analysis on the vegetative growth of all the cross combinations indicated that both the Bt/CpTI and the Bt. transgenic hybrids had a stronger growth vagour and grew faster than those of the controls before flowering stage, the coefficient of leaf acreage was also larger than that of the controls during the time of flowering and boll-setting stages.(7) The results of hybrid vagour analysis showed that the hybrids with the background of insect resistance also had a stronger heterosis on the yield of seed cotton, resistance and mature boll-setting, but had a negative heterosis on fiber quality, lint percentage and boll weight.(8)By testing the general and special combining ability of the materials, some of the cross combinations were selected to further breed into new varieties with higher yield and stronger insect resistibility.
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