Abstract
Field experiments were conducted to compare methods of evaluating the tolerance of upland cotton (Gossypium hirsutum L.) to Verticillium dahliae Kleb. by visual symptoms. Good differentiation between susceptible and tolerant cultivars was obtained by observing foliar symptoms after the middle of the flowering period.Correlation studies indicated that foliar symptoms explained 31 to 45% of the variation in lint yield among cotton breeding lines and cultivars in a wilt‐infested field, vascular discoloration at the base of the stem explained 25 to 29%, and vascular discoloration at a height of 40 cm explained 6% or less of that variation. Similar results were obtained when the dependent variable was the difference between lint yield in the infested field and mean lint yield of the same lines grown in two wilt‐free locations. Effective screening for wilt tolerance in Israel appears possible by observing foliar symptoms during the second half of the flowering period, provided the field is relatively uniformly infested by the fungus and suitable temperatures prevail.

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