Edible Bean Bacterial Blight Test
Field symptoms of common bean bacterial blight include water soaked lesions on leaves and pods that later develop into larger brown necrotic areas on leaf surfaces and into circular brownish lesions on pods. Severely infected leaves may have a “burnt” appearance. Infected seed may be shrunken, shriveled, and discolored. Halo blight symptoms on leaves give the appearance of a yellow ring around each lesion. Pods develop water soaked brown lesions similar to common bacterial blight. Halo blight also causes seed to become shriveled and discolored.
Effective control measures include:
The bacterial blight test, known as the dome test, has been used by the department for a number of years to detect bacterial blight in dry edible beans. The dome test provides a blight rating score for each sample, permitting an easy comparison of seed lots. Lower dome scores equate to lower amounts of blight in the seed. Dome scores of four or less are considered acceptable for certification.
The dome test actually measures the symptoms of blight in the form of water soaked lesions on the undersides of primary bean leaves. These results are calculated on the basis of the number of lesions observed on the primary leaves of 13-day-old plants. The average lesion number is determined on 30 plants and samples are typically run in duplicate. The average lesion number corresponds to the average area of the leaf surface covered by lesions.