Evaluations and Correlated Responses for Resistance to Chloramben Herbicide in Cucumber

Abstract

The U.S. cucumber germplasm collection (753 accessions) and U.S. adapted processing cucumber (Cucumis sativus L.) inbreds and hybrids were surveyed for response to 6.7 kg ae/ha of chloramben. Nine plant introductions (PI 165952, 173892, 179676, 275411, 277741, 279464, 279465, 436609, and 482464) were classified as tolerant to chloramben, based on percentage and rate of field emergence and seedling vigor. All adapted strains evaluated were susceptible to chloramben injury. The chloramben-tolerant accessions (C0) were subjected to two cycles of recurrent half-sib family selection that resulted in 11 C2 families. These families, a susceptible adapted line (WI 2870), and the resistant PI 436609 were evaluated in the field (6.7 kg ae/ha) and laboratory (0.0, 0.01, and 0.0001 M) for response to chloramben challenge. Significant (P = 0.05) differences between families were observed for percentage emergence and phytotoxicity ratings. Correlations between emergence and phytotoxicity ratings at two dates were low (r2 = -0.32 and – 0.05). Significant (P = 0.05) interfamily differences were also recorded for percentage germination, hypocotyl length, primary root length, and number of lateral roots in the laboratory. Correlated responses between these growth variables were high (r2 = 0.78 to 0.84), but correlations between field and laboratory observations were low (r2 = -0.31 to 0.24). We hypothesize that the genetic response to chloramben challenge under laboratory conditions depends on the concentration of the chemical administered. Chemical name used: 3-amino-2, 5-dichlorobenzoic acid (chloramben).