A Study of Resistance to the Sweet Potato Wilt Pathogen, Fusarium oxysporum Schlecht f. batatis (Wr.) Snyder & Hansen, and of Histological Aspects of the Host-pathogen Complex
A Study of Resistance to the Sweet Potato Wilt Pathogen, Fusarium oxysporum Schlecht f. batatis (Wr.) Snyder & Hansen, and of Histological Aspects of the Host-pathogen Complex
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Date
1963
Authors
Wells, John Milton
Advisor
Kantzes, James G.
Citation
DRUM DOI
Abstract
Research on Fusarium wilt of sweet potato, a vascular disease
caused by Fusarium oxysporum Schlecht f. batatis (Wr.) Snyder & Hansen,
was undertaken to determine the susceptibility of various sweet potato
lines to Maryland isolates of the pathogen under field and greenhouse
conditions. Highly resistant lines would be useful as sources of
resistance to Fusarium wilt in sweet potato breeding programs.
In 2 years of field and greenhouse trials, 94 different lines of
sweet potato were inoculated with a composite spore and mycelial suspension
of 5 Maryland isolates of F. oxysporum f. batatis. Results
indicated that the following lines were highly resistant to the pathogen:
the foreign plant introductions P.I. 153655 ("Tinian"), P.I. 153906,
P.I. 153907, and P.I. 251602; the variety Pelican Processor; and the
breeding selections B-6842 from the United States Department of Agriculture
Plant Industry Station at Beltsville, Maryland, and T-7 from the
Georgia Coastal Plain Agricultural Experiment Station at Tifton, Georgia.
Greenhouse experiments showed that the host range of Fusarium
oxysporum f. batatis should include an additional species of Morning
Glory, lpomoea pandurata (L.) G. F. w. Mey. Furthermore, no symptoms of infection were obtained on various crop plants commonly grown in
rotation on land used for sweet potato culture.
Physiological studies in the laboratory and greenhouse indicated
that no significant levels of fungitoxic substances were present in either
uninoculated or inoculated ''Tinian" plants. Nor could a fungal metabolite
be detected, under the existing experimental conditions, which was toxic
to a susceptible variety of sweet potato (Porto Rico) but not to the
resistant ''Tinian".
A study was made of the basis for resistance of the foreign plant
introduction "Tinian" (P. I. 153655). Histological examinations of
serial stem sections of the susceptible sweet potato variety Porto Rico
and of the resistant foreign plant introduction ''Tinian" were made from
plants collected at 3-day intervals following inoculation with spores
of the pathogen. It was found that "Tinian" responded to infection by
the production of tyloses in advance of the fungus. Twelve days after
inoculation, 75 - 88% of the vessels which were 22 - 32 mn above the
invasion site at the base of the plant were completely filled with
tyloses. This compared to only 0 - 3% in the uninoculated control plants.
Furthermore, no mycelia or spores could be detected in tnis region but
were present in 25 - 50% of tne vessels within 11 mm of tne invasion site.
In the variety Porto Rico the occurrence of tyloses in the inoculated
plants was not significantly greater than in the uninoculated controls,
except near the invasion site where after 12 days 3 - 6% of the vessels
contained small 1 tyloses. The pathogen was not limited, as in ''Tinian",
to the immediate invasion site. Tnis suggests that tne production of
tyloses in "Tinian may represent an important defense mechanism against
Fusarium wilt.