Vol. 72 No: 4

Title:
Methods of Screening Acer Platanoides L. Seedlings for Resistance to Wilt (Verticillium Dahliae Kleb.)

Authors:
D.A. CHAMBERS and D.C. HARRIS

pp: 601-608

Abstract:
Several methods of challenging young seedlings of Norway maple (Acer platanoides) with Verticillium dahliae were investigated to develop a method for screening seed provenances for wilt resistance. Seedlings were inoculated by pouring conidial suspension (10⁶ conidia ml^-1) over roots wounded in situ, or by dipping roots in the same conidial suspension at transplanting, or by transplanting germinated seed or seedlings into compost infested with a beet-seed or straw-cultured inoculum. On the basis of foliar symptoms during the growing season, and on seedling height, and vascular staining and the presence of V. dahliae in the wood at the end of the season, root-dipping was the most severe test; planting seeds or seedlings into straw-based inoculum was less severe than root-dipping but gave similar levels of infection. Beet seed was a less effective form of inoculum than straw, and inoculation of roots damaged in situ resulted in disease escape. A comparison of the root-dip technique using three, five-fold inoculum dilutions and transplanting seedlings to two different composts showed that a reduction of spore concentration to a fifth had no effect on disease, whilst the effects of the further dilutions suggested that spore concentration became limiting at about 4 × 10⁴ conidia ml^-1; significantly more seedlings were affected in one compost than in the other. This experiment confirmed that many plants which survive to the end of the season of inoculation die during the following winter, and that the incidence of deaths overwinter has to be considered in devising suitable screening methods for young seedlings and for making comparisons among seedling populations.

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