B. Leite1, J.J. Marois2, D.L. Wright2, Enoch Osekre2, T.W. Katsvairo2, and P.J. Wiatrak2. (1) Univ of Florida, 155 Research Rd., Quincy, FL 32351, (2) University of Florida, 155 Research Rd., Quincy, FL 32351
Hardlock is a cotton disease characterized by
the increase in density of cotton boll fibers. These compacted bolls are
difficult to harvest,
resulting in considerable losses to growers. Yield is usually reduced by
20 to 60% by the end of the season if hardlock is present. Fusarium
verticillioides is the most common fungus isolated from
affected plant parts. Utilizing PCR based methods; we have sequenced the
internal transcribed spacer (ITS) region of the Fusarium isolates T2, T5 and T6. ITS
sequence analysis demonstrated that isolate T2 is F. verticillioides and
T5 and T6 are F. proliferatum. Morphological analysis
of spores also demonstrated the similarities between T5 and T6 isolates. In
cottonseed-agar, F.
verticillioides and F. proliferatum produce around 1% and 10 % of
macroconidia among the conidia population, respectively. We are
currently evaluating the involvement of each of these species in hardlock. The
combined inoculation of the two species is also being tried. A positive
correlation was found between seed weight and fiber quality. Healthy seeds
always exhibit more dry weight than diseased cottonseeds. Low cottonseed weight
is associated with severely hardlocked cotton bolls. These results suggest that
the casual agent of hardlock is consuming lipid cottonseed reserves, since there is a
decrease in oil reserves with the disease. Fumonisins (B1, B2 and B3) were
assessed. Fumonisins are not easily produced in cottonseed-based media; however, it was detected in
isolates growing on PDA plates. We hypothesize that cottonseed oil or its
byproducts may suppress toxin production. Dark field and phase contrast
microscopy have been used to monitor symptom development. Microscopic
observations revealed fungal debris, hyphae involving
cotton fibers and Fusarium-like macroconidia. This is the first direct
observation of Fusarium-like conidia in affected tissues. The
progress of this work may unequivocally place Fusarium sp. as the causal
pathogen for cotton hardlock.
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