A PROCEDURE FOR ISOLATION AND DETERMINATION OF INCIDENCE OF SCLEROTINIA MINOR IN PEANUT SEED (REENTRY--ORIGINAL 115 1/25/93 NO LONGER ON RMIS FOR REVISION)

Authors: Melouk, Hassan; BOWEN, CAROLYN - OKLAHOMA STATE UNIVERSITY; ABOSHOSHA, S - ALEXANDRIA UNIV., EGYPT

Submitted to: Alexandria Journal of Agricultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Sclerotinia blight, caused by the soilborne pathogen Sclerotinia minor Jagger, is an important disease on peanut in Virginia, North Carolina, Texas, and Oklahoma. Sclerotinia blight has rapidly become the most important disease on peanut in Oklahoma, and causes severe economic losses to peanut growers. Infected peanut seed and debris may serve as sources for rthe spread of S. minor into clean fields. Due to a lack of effective controls, we must minimize the spread of S. minor by way of infected seed. Therefore, better seed detection methods are needed to aid in the identification of infected seed lots. Several fungi are commonly associated with peanut seed that may interfere with the positive identification of S. minor from infected peanut seed. Many of these fungi are not removed from the seed by washing in soapy water. We found that soaking infected peanut seed in clorox solution for 2 min reduced the recovery of contaminating fungi and increased the recovery of S. minor. We used this procedure routinely and successfully for the last two years to determine the incidence of S. minor in commercial peanut seed lots and from growers fields in Oklahoma.

Technical Abstract: Sclerotinia minor exists in peanut seed as dry mycelium and/or sclerotia. Several fungi are commonly associated with peanut seed that may interfere with positive identification of S. minor from infected peanut seed. Soaking infected Okrun peanut seed in 1.05% NaClO for 2 min reduced the number of contaminating fungi and increased the recovery of S. minor. Dry mycelia and dsclerotia of S. minor were submerged in 0, 0.26, 0.53, 1.05, 1.58, or 2.10 aqueous solution of NaClO for 2 min, blotted dry, and then plated on potato dextrose agar containing 100 ug/ml streptomycin sulfate (SPDA). A decrease in viability of dry mycelial fragments occurred with increasing concentration of NaClO. There was no significant difference in viability of sclerotia that were submerged in the above concentration of NaClO. Okrun peanut seed naturally infected with S. minor was washed in 0.2% liquid ivory soap, rinsed twice in deionized water, and immersed in 0, 0.26, 0.53, ,1.05, 1.58, or 2.10% aqueous solution of NaClO for 1 min, air dried for 15 min, then plated onto SPDA. There was a reduction in the number of contaminating fungi isolated from seed exposed to concentrations greater than 0.53% NaClO. Recovery of S. minor from naturally infested Okrun seed increased with NaClO concentration up to 0.53%. Okrun peanut seed infected with S. minor were sized as large, medium, or small. Sized seed were submerged in 0.2% liquid ivory soap, rinsed twice in deionized water, and immersed in 1.05% NaClO for 2 min, air dried, and plated onto SPDA. The infection of these seed ranged from 3.58% to 3.68% and there was no significant difference between seed sizes in the percent seed infection with S. minor.