Authors
L. A.
Steventon
,
Department of Plant Biology, Swedish University of Agricultural Sciences, Box 7080, S-750 07 Uppsala, Sweden
;
I.
Happstadius
,
Svalöf Weibull AB, S-268 81 Svalöv, Sweden
;
P.
Okori
, and
C.
Dixelius
,
Department of Plant Biology, Swedish University of Agricultural Sciences, Box 7080, S-750 07 Uppsala, Sweden
ABSTRACT
Extensive efforts are being made to develop oilseed rape cultivars with resistance to Verticillium wilt. Evaluation of these cultivars involves either dipping roots of young plants in a conidial suspension followed by replanting in soil, or sowing the seed directly in artificially infested soil. These methods for screening for resistance take a long time and are expensive. The objective of this research was to develop a rapid and reliable method of screening cultivars for resistance to Verticillium wilt. A box test method in which 4-day-old seedlings were inoculated and grown under sterile conditions in double magenta boxes was developed. The Brassica napus cultivars Accord, Express, Hanna, and Libraska were inoculated with isolates of Verticillium longisporum or V. dahliae. The results from the box test method were compared with root-dip inoculation of seedlings grown in a soil mixture under greenhouse conditions. In addition, plants from the box test were randomly selected and transferred to pots containing sterile soil to permit comparison of plants from the box test at similar developmental stage with plants in the root-dip method. Disease evaluation was based on the number of days after transferring seedlings into the boxes that root browning, root and shoot blackening, and wilting of cotyledons developed. Additional disease evaluation was based on a 0 to 5 disease severity scale based on the percentage of wilted leaves (number) and/or the percentage of stunting (mm) of inoculated plants compared with noninoculated plants. Disease severity was higher on Hanna than on Express, and isolates of V. longisporum were more virulent than isolates of V. dahliae. There was a significant correlation (r = 0.93) of disease rating between the traditional root-dip method and the new box test method. Analysis of variance revealed that the interaction between cultivars and isolates was highly significant (P ≤ 0.01), whereas method of inoculation did not affect the results. In the box test, plants were rated after 25 days, which is at least 3.5 times more rapid than the root-dip method.
