A LEAF DISK ASSAY FOR DETECTING RESISTANCE TO EARLY BLIGHT CAUSED BY ALTERNARIA-SOLANI IN JUVENILE POTATO PLANTS

Resistance to early blight, caused by Alternaria solani, was examined using leaf disks from plants of 10 cultivars of potato (Solanum tuberosum) grown in a growth chamber or greenhouse. Disks (14 mm diameter) were cut from five leaves of equivalent maturity per cultivar, 21-80 days postemergence. The leaf disks were spray-inoculated with a conidial suspension of A. solani, floated on solutions containing either 1-naphthaleneacetic acid (NAA), indoleacetic acid (IAA), 2,4-dichlorophenoxyacetic acid (2,4-D), 6-benzylaminopurine (BAP), abscisic acid (ABA), or H2O, and incubated at 22 C in the dark for 3-5 days. Estimates of susceptibility, which correlated highly with observations of early blight in Wisconsin field trials, were obtained when leaf disks were floated on 10.7-mu-M NAA (r = 0.86) or 4.0-mu-M 2,4-D (r = 0.71).