Field Screening and Marker Assisted Selection of Late Blight Resistant Potato Lines

Late blight (LB), caused by Phytophthora infestans (Mont.) de Bary, is the most destructive disease of potato. The main objective of this study was to evaluate 72 potato lines, derived from crosses of the recipient cv. ACI Pakri-1 (female) and a LB resistant donor variety (male), against LB disease. Parent materials, LB susceptible varieties Diamant and BARI Alu-40 and LB resistant variety BARI Alu-77 were used as check varieties. The experiment was conducted with three levels of inoculums pressure (i) LB inoculation & no fungicide, (ii) No LB inoculation & no fungicide and (iii) No LB inoculation & fungicide. LB infection was assessed at 10 day intervals by scoring the percentage of foliage destruction. Subsequently, the area under the disease progress curve (AUDPC), relative AUDPC and susceptible scale value were estimated. Three categories of potato lines were selected considering level of LB infection and tuber appearance - (a) LB resistant - 8 lines, (b) LB tolerant - 14 lines, and (c) LB susceptible - 14 lines. The foliage destruction of selected LB resistant lines was considered to be between 1 to 25%, in LB tolerant lines between 25 to 50%, and in LB susceptible lines between 51 to 90% at 85 DAP. The recipient ACI Pakri-1 had 100% foliage destruction at 63-65 DAP. In LB resistant lines low AUDPC, rAUDPC and susceptible scale value were found. The highest susceptible scale value 9 was recorded mostly in LB susceptible cv.ACI Pakri-1 and BARI Alu-40; where the range of susceptible scale value of LB resistant lines was 0.1 to 2.13. LB resistance genes Rpi-abpt and Rpi-blb1, amplified by PCR using primers R2-F1/R2-R3 and 1521/518 respectively, were identified through marker assisted selection (MAS) in the donor variety and crossed LB resistant line 13, 41, 61, 72 and 54 but absent in susceptible ACI Pakri-1.Round tubers, mostly of uniform size, deep to light red and white skin, red and deep eye were found in 8 resistant lines. The highest number of tubers/ hill (20) was recorded in line 8 under natural inoculums pressure, and the highest weight of tuber/hill (460 g) was found in line 61 projecting a yield of 38.3 Mt/ha, which was higher than the donor variety (31.5 Mt/ha) and the recipient ACI Pakri-1 (29.0 Mt/ha) under fungicide application treatment. However, resistance breeding for resistance against potato diseases is developing day by day in Bangladesh. In this regard, our study might contribute in resistance breeding to LB resistance potato variety development.