Abstract :
A rapid (!O-min) tomato seedling assay was developed for determining
the wilt-capacity of cell-free culture filtrates of race 1 and race 2 isolates
of Verticillium dahliae. The assay also rapidly determined the dilTerences
in will resistance between tomato cultivars. Rapidity was attained by
manipulating incubation conditions to promote rapid wilting. These
included inducing elongated stems in the susceptible cv. Bonny Best
seedlings by growth of plants in subdued light (2.2 x 10ʹ lux) and by
concentrating two-fold the cell-free culture filtrates of the pathogen.
Further, rapid uptake of the wilt factors in the culture filtrates was
facilitated during incubation by increasing transpiration with bright
light (23.8 X 10ʹ lux), a wind stream (125-150 metres/min) across the
assay seedlings, iow relative humidity (28%) and a relatively high assay
temperature (30 C). When necessary, these conditions were altered to
extend the assay times. This assay system was used to determine optimal
incubation time, temperature and medium for obtaining culture filtrates
with increased wiit capacities. The assay also determined the relative
wilt capacities of races 1 and 2 and the comparative resistance of four
tomato cultivars to wilt caused by races 1 and 2.
