Document Type

Article

Publication Date

10-25-2024

Keywords

Corynespora cassiicola, digital measurement, disease screening

Abstract

Target spot (TS), caused by the fungus Corynespora cassiicola, is a foliar disease
of increasing importance to soybean in the United States. Identifying cultivar re-
sistance to TS is challenging. The objective of this research was to determine the
reactions of a diverse collection of soybean genotypes to TS using a detached
leaf inoculation method. A detached unifoliate leaf of each soybean genotype
was placed in a Petri dish on moist filter paper, wounded at three locations, inoc-
ulated with 10 μl of a 10 5 -conidial suspension of C. cassiicola, and incubated at
room temperature (23°C). The percent leaf area with TS symptoms (TSS) was
measured digitally at 7, 10, 14, and 17 days after inoculation (DAI), and the area
under the disease progress curve (AUDPC) was calculated. Thirty-seven soy-
bean genotypes and three soybean cultivars were evaluated in three replicated
trials. At 17 DAI, TSS ranged from 2 to 84%. Significant differences occurred be-
tween soybean genotypes at each rating time in each trial. Across the three trials,
the reaction of most soybean genotypes ranged from resistant to susceptible.
These soybean genotypes were evaluated in the field with natural inoculum at
two locations in 2022. TS developed late but differed significantly between geno-
types, averaging from 0.35 to 3.35% TSS. Field results were not significantly cor-
related to the detached leaf results. The detached leaf assay is another tool for
screening soybean genotypes for resistance to TS but needs field validation.

Additional Files
phytofr-05-24-0057-r.st1.pdf (386 kB)
Supplementary table I
phytofr-05-24-0057-r.st2.pdf (245 kB)
Supplementary table II
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