| In this study, we used 93 introgression lines derived from L .hirsutum LA1777 together with E6203 and 77 introgression lines derived from S. lycopersicode LA2951 together with VF36 to map and characterize quantitative trait loci (QTLs) conferring resistance to late blight. At the same time, we used the cytological methods to follow infection of tomato leaves by Phytophthora infestans. The main results obtained in this research were concluded as following:(1)Microscopic analyses suggest that:First, we can follow the process which sporangiums were places on the surface of the leaf, formed germ tubes and eventually germ tubes through epidermis stomata and cell in 48h after inoculation using samples after the staining procedure. Second, there are extremely significant less sporangiums formed germ tubes on the leaf surface of tomato materials with Ph-2 genes than of cultivated species M82 in 14h after inoculation. There are extremely significant less sporangiums formed germ tubes on the leaf surface of tomato materials with Ph-2,Ph-3 genes than of cultivated species M82 in 38h after inoculation.(2) We used 93 introgression lines derived from L .hirsutum LA1777 together with E6203 to gain 5 QTLs named hgm4-1, hgm4-2, hgm7-1, hgm8-1, hgm12-1 showed the resistance to late blight. These QTLs were located on chromosome4, 7, 8, 12respectively. Among them, one QTLs hgm7-1 on chromosome 7 gave more resistance than the other. The area of the disease lesion was reduced 25.25% comparing to E6203 after inoculation.(3)We found inoculation data is normal distribution, so the trait of tomato resistance to late blight is the quantitative trait. And 3 QTLs named sgm2-1, sgm4-1, sgm9-1 showed the resistance. Among them, one QTLs sgm1-1 on chromosome 2, 4,9 gave more resistance than the other. The area of the disease lesion was reduced 37.11% comparing to VF36 after inoculation.
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