Assessment of Laboratory Methods for Evaluating Potato Tubers for Resistance to Late Blight.

Two laboratory methods (whole tuber and tuber slice) were evaluated and compared with field assessment of potato tubers for resistance to late blight caused by Phytophthora infestans. Altogether, the resistance responses of 20 cultivars and advanced selections were compared by the three methods. All three assays separated materials into resistant and susceptible groups. The majority of cultivars and advanced selections did not react in the same way within the field and tuber-slice assays but did react similarly within the whole-tuber assay. Some cultivars were susceptible in the field at harvest but were resistant in the whole-tuber assay. The differences may be due to the extent of lenticel and eye development during tuber formation. In contrast, other cultivars resistant in the field at harvest were susceptible in the whole-tuber assay. In this case, placement in the hill may affect whether or not the tuber is exposed to inoculum or whether aging of tubers during storage affects susceptibility to tuber blight. Our study shows that high levels of tuber resistance are available in certain commercial cultivars and advanced potato selections. For laboratory assessments to be reliable, however, both pre- and poststorage evaluations may be necessary.