Field screening of advanced potato clones for foliar resistance to late blight (Phytophthora infestans) in two agro-climatic regions

Late blight caused by the pathogen Phytophthora infestans is regarded as the most important oomycete disease responsible for causing economic loss to potato production in Mauritius. This study was carried out to evaluate the field resistance of 18 advanced potato clones to late blight in two agro-climatic regions representative of the super-humid and humid zones of the island. Control susceptible cultivars were Spunta and Safari while varieties Vigora and Belle Isle were used as resistant controls. Disease severity, area under disease progress curve (AUDPC), relative area under disease progress curve (rAUDPC), tuber yield and relative yield loss were assessed to identify clones with foliar resistance to late blight under natural conditions. Significantly lower percentage disease severity was recorded in the breeding series 142/161, 29/5 and 161/142 compared to the susceptible controls which reached 100% leaf defoliation. Clones of the 29/5 and 142/161 series recorded the lowest final disease severity of 20% across both locations. Thirteen clones were identified as highly resistant to late blight with AUDPC and rAUDPC values ranging from 0.3 to 119.4 and 0.002 to 0.048 respectively. Among them, three clones (142/161/2, 29/5/3 and 29/5/14) recorded the highest marketable tuber yields of 23.6 t/ha, 22.4 t/ha and 21.3 t/ha respectively. The relative yield loss in the susceptible controls over the highly resistant clones averaged 274%. This suggests that the highly resistant clones were less affected in their yield by late blight and are potential candidates for cultivation under conditions where P. infestans is a recurring problem.