2.1. Plant Materials

Four potato cultivars of tubers, namely Dianshu 47 (DS47), Dianshu 23 (DS23), Qingshu 9 (QS9) and Lishu6 (LS6), were obtained from the Tuber and Root Crops Research Institute, Yunnan Agricultural University. These potato cultivars are widely cultivated crops with high yields in Yunnan Province. Potato cultivars were planted in pots and kept in the greenhouse of Yunnan Agricultural University, P. R. China, with no pesticides and no other pests involved during the growth period. All the potato cultivars were planted on the same date except DS47 (with low germination), and 30 plants of each were planted (3 plants in one pot). The same genotype was planted every week until the larvae pupated, and the leaves were fed after they were picked to ensure that the larvae had access to fresh and tender leaves. When the plant grew to 30 cm, the middle leaves were cut to allow PTM larvae to feed on them. Then, the third or fourth potato leaves were collected. Three replicates per variety were weighed and then frozen in liquid nitrogen for SGA content analysis.