FOY, C.L., Department of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, 24061, United States
JACOBSOHN, R., Agricultural Research Organization, Volcani Center, Bet Dagan, 50250, Israel
JAIN, R., Department of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, Virginia, 24061, United States

A major screening programme was conducted to determine which Lycopersicon spp. (if any) have practical levels of resistance to glyphosate; the same lines were also tested for resistance to Orobanche aegyptiaca. A majority of the lines investigated showed high susceptibility to glyphosate applied at 37⋅5 g a.i. ha−1 in a spray volume of 250 1 ha−1. Only 41 of 1457 lines screened showed fresh weights of treated plants not significantly different from those of untreated plants at a probability level of 80%. Repeated screening of some selected Lycopersicon lines in the greenhouse and the field, however, indicated that only a few had inherent partial resistance to glyphosate. Giyphosate was less toxic to the test plants with increases in spray volume. Among 1361 Lycopersicon lines tested for resistance to O. aegyptiaca, only minor differences in susceptibility were observed. All lines were susceptible to varying degrees. The chances, therefore, of finding complete resistance in tomato to either glyphosate or Orobanche spp. alone are small. However, combining partial resistance to glyphosate and O. aegyptiaca in a breeding programme to produce new varieties might still prove to be economically useful even in fields heavily infested with the parasite. Copyright © 1988, Wiley Blackwell. All rights reserved