| Potato (Solarium tuberosum L.), is the fourth biggest crops in both the world and China. Late blight, caused by the oomycete Phytophthora infestans (Mont.) de Bary, is a major disease of potato cultivation which can lead to complete loss of the crop yield. Resistances of potato to late blight have two types; vertical resistance and horizontal resistance. Vertical resistance is generally monogenic easily overcome. However, horizontal resistance is partial, polygenic and more durable. Based on the principle, current breeding strategies focus on horizontal resistance.True potato seeds of 26 combinations from CIP were employed, derived from B population with horizontal resistance to late blight. We desired to get lines with stable horizontal resistance to late blight and good agronomic traits, which can be used as intermediate breeding materials or directly used in potato production. In our experiments, we primarily selected and evaluated seedling by artificial incubation in net house in 2001. Furthermore, we studied field resistance of foliage, leaf resistance in vitro and molecular marker-assisted selection. The major results are as following:1. There were 5795 of 13000 true potato seeds germinated from 24 combinations. The frequency of emergence varied from 0.80% to 74.40% (average 44.58%) among the combinations. 1616 plants were selected with an average selection rate of 27.87%. The selection rate had big difference among the combinations with 0.39-63.94%. The plants from the combinations 395019. 395021, 395050 and 399005 showed strong growth vigor while the others were weak to middle.2. The identification of field resistance to late blight showed that the rate of resistance varied from 33.36% to 100%. The plants from the combinations 395007, 395017, 395018, 395029, 395052 and 399003 showed high horizontal resistance to late blight, with 100% resistance rate. The resistance rate of the other combinations was 55.57% to 97.14%.3. The resistance to late blight of the selected plants varied from the combinations. The rate of high resistance varied from 0% to 72.15% (average 33.47%), middle resistance varied from 0% to 50.00% (average 20.71%), low resistance varied from 0% to 26.80 % (average 15.78%). This indicates that horizontal resistance to late blight is quantitative trait. Percentage of plant resistance to late blight of 22 combinations is 69.76%.4. QTL of the total 729 plants from 22 combinations were analysed by 4 molecular markers. The results demonstrated that 6 plants (0.8%) had one QTL, 34 plants had twoQTL (4.66%), 103 plants had three QTL (14.13%), 586 plants had four QTL (80.38%). This showed that QTL closely linked with marker could be detected in most hybrid progenies.5. The relationships among field assessment of foliage resistance to late blight, laboratory assessment of leaf resistance to late blight and molecular marker-assisted selection were disscussed. There were extremely significant correlations between field resistance and total bands of marker selection. Field resistance to late blight had significant correlation with the marker prpl, and extremely significant correlation with the bands of 570bp and 800bp, however, had no significant correlation with other markers. This indicated that foliage resistance to late blight was linked with marker prpl. There were significant correlation among foliage identification in vitro, field assessment and marker-assisted selection. |
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