| Non-heading Chinese cabbage (Brassica campestris ssp. chinensis Makino) is a variety with great diversity and an important leafy vegetable in China. The damage caused by diamondback moth (Plutella xylostella) (DBM) has been more and more serious to the cruciferous vegetable in recent years. It can decrease the product quality, reduce the production and even produce no yield. Various chemical pestides have been used to control pests for many years;The abuse of pesticides has caused severe pollution to the environment and pest's resistance to pesticides without control. Therefore, it is very important to mine the resistant genes of the plant itself and breed insect-resistant variety. In this study, two elite non-heading Chinese cabbage germplasms resiatant to DBM were used, and insect-resistance inheritance was analyzed from the aspects of antibiosis and avoidance. Meanwhile, two molecular genetics maps were constructed based on different F2 segregating populations and QTLs of resistance to DBM were identified and the allelism of insect-resistant genes analyzed in different resistance sources. The results were as follows:1. The insect-resistant inbred lines '508 'and '599 'of the non-heading Chinese cabbage as female parents respectively and the susceptible inbred lines '114 ' as male parent were used to construct two six-generation populations of P1,P2,F1,BC1P1,BC1P2 and F2. The resistances of all the populations to DBM were evaluated by in vitro methods separately, and the joint analysis method for six generations was used to analyze the inheritance of insect-resistance. The results showed that the insect-resistance was partly recessive in the two combination of '599 '×'114' and '508 '×'114' both under net and in vitro conditions. Inheritance of insect-resistance in '599 '×'114' fitted to the E-0 genetic model which is two major genes with additive-dominant-epistatic effects plus poly-genes with additive-dominant-epistatic effects. The additive effects of two major genes were negative (i.e. it could increase the resistance). The dominant effects were positive. The dominant effect for the first major gene was predominant. The additive effect for the second major gene was foremost. There was some interaction between the two major genes. In the BC1P1, BC1P2 and F2 populations, the heritability of major genes was 69.52%, 74.09% and 75.49% respectively, and. In the BC1P1 generation, the heritability of poly genes was 12.25%, the heritability of poly genes in BC1P2 and F2 were 0. Inheritance of insect-resistance in '508 '×'114' fitted to the D-1 genetic model which is one major additive-dominant gene plus additive-dominant polygene. The additive effect and the dominant effect of the major gene were all positive. The dominant effect of polygenes was positive and? overdominant.? In the BC1P1, BC1P2 and F2 populations, the heritability of major genes was 51.13%, 65.87% and 79.06% respectively. In the BC1P1, BC1P2 and F2 populations, the heritability of poly genes was 32.69%, 17.21% and 0. Based on the same populations, the resistances to DBM were evaluated in net, and the joint analysis method for six generations was used to analyze the inheritance of insect-resistance. The results showed that the insect-resistance was partly recessive in the two combination of '599 '×'114' and '508 '×'114', and all fitted to the D-1 genetic model, which is one major additive-dominant gene plus additive-dominant polygene. In the combination of '599 '×'114', The additive effect of major gene was negative and the dominant effect was positive. The additive and dominant effects were all positive (i.e. decreasing the resistance). In the BC1P1, BC1P2 and F2 population, the heritability of major genes was 53.59%, 46.21% and 78.35% respectively. In the BC1P1, BC1P2 and F2 generation, the heritability of poly genes was 18.64%, 21.65% and 0. In the combination of '508 '×'114' , the additive effect and the dominant effect of major gene were opposite. In the BC1P1, BC1P2 and F2 population, the heritability of major genes was 57.21%, 25.87% and 76.05% respectively. In the BC1P1 and BC1P2, the heritability of poly genes was 6.24% and 27.79%, in the F2 generation, the heritability of poly genes was 0. All these demonstrated primarily that the genetic backgrounds for the insect-resistance of two ellite germplas were different. The genetic mechanisms for antibiosis and avoidance were also not the same. Therefore, more attention should be paid to the selection of the resistant plants in the early regenerations in breeding, and fully use of the genes with the enhancing additive effect and dominant effect for increasing the insect-resistance of new varieties.2. Two molecular genetics maps was constructed with two F2 populations of 252 plants and 213 plants respectively from the cross of'599'×'114'and'508'×'114'. Four kinds of markers of SSR, SRAP and InDel were adopted. The molecular genetic map of'599'×'114'contained 122 markers, including 51 SSR, 20 InDel, and 51 SRAP markers, and was consisted of 10 linkage groups. It covered 1019.93cM. The length of different linkage groups was 31.43cM～182.46cM,and the mean distance was 8.29cM between markers. The molecular genetic maps of'508'×'114'contained 123 markers, including 66 SSR, 2 InDel and 55 SRAP markers, and was consisted of 10 linkage groups and covered 1093.36cM. The length of different linkage groups ranged 33.60cM～221.35cM, and the mean distance is 8.67cM between markers. All the markers distributed on linkage groups evenly. The fact that there were a few sharing makers between the two genetic maps, which were distributed on different linkage groups meant that the genetic bases of two elite germplsm were different.3. Based on the two linkage maps constructed with F2 populations from'599'×'114'and'508'×'114', and the resistance data of two F2 populations identified by different methods, fourteen QTLs related to the insect-resistance trait were mapped. From the aspect of antibiosis of by in vitro identification on the F2 population of'599'×'114', four QTLs were mapped, which located in LG7, LG8 and LG9 , the contributions were 10%, 7.04%, 5.63% and 5.21%, which can explained 27.88% of the total variation. From the cross of'508'×'114', three QTLs were mapped, which located in LG1 and LG10 , the contributions were 22.88%, 10.70% and 5.40%, which can explained 38.98% of the total variation. QTLs from the two resistant germplasm were different in the distrubution on linkage groups, the mode of gene action and the genetic effect, which meant that the resistant genes controlling the antibiosis may not be the same. From the aspect of avoidance of'599'×'114'by the identification in net, three QTLs were mapped, which located in LG1, LG5 and LG8; the contributions were 29.58%, 27.65%, 38.90%, which can explained 96% of the total variation. From the cross of'508'×'114', three QTLs were mapped, which located in LG3, LG4 and LG7; the contributions were 10.4%, 19.28% and 6.83%, which can explained 36.51% of the total variation. It could be inferred that the resistant genes controlling avoidance in different germplasms may also not be the same. In addition, the antibiosis and the avoidance revealed by in vitro method and net method may be different in one germpalsm. The avoidance contributed more to the insect-resisitance in"599", but the antibiosis in"508"was greater. The genetic distances of the nine QTLs in total which were mapped by the aspects of antibiosis and avoidance to one of the flanking loci was less than 5cM.These markers can be used to molecular assistance selection and lay a foundation for molecular insect- resistance breeding.From all the above, it could be concluded that the insect-resistance genes from two resistance germplasms were different. The insect-resistance genes in the genetic mechanism for antibiosis and avoidance were not the same. The result are helpful for us to effectively utilize different resistance germplasms to breeding the new varieties with high resistance by traditional and MAS breeding.
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