Genetic and Physiological Variability of Sclerotinia sclerotiorum Isolates from Different Plant Hosts and Their Biocontrol Using Biological Methods

Abstract

Thirteen isolates of Sclerotinia sclerotiorum causing white mold disease were collected from various host plants across different regions in Salahuddin Governorate, Iraq. Results obtained showed physiological variability among isolates in sclerotia formation, time of emergence, and colony diameter. When sequences of the ITS region were compared, it was evident that closest isolates originated from the same host plant regardless of geographic location. The most aggressive isolates on pepper were K-1, K-4, K-5, and K-9 from Samarra, Al-Dur, Al-Dhuluiya, and Al-Duz locations, respectively; isolates K-2, K-7, and K-11on tomato from Al-Dur, Al-Alam, and Tikrit locations, respectively; isolates K-3, K-6, K-10, and K-13 on eggplant from Al-Alam, Samarra, Tikrit, and Baiji locations, respectively, and K-12 isolate on aquash from Al-Sharqat location. Six Streptomyces sp. isolates from healthy pepper rhizosphere showed that Streptomyces-6 (identified as Streptomyces albidoflavus strain Kefaa-1, GenBank PP486249.1), had the strongest inhibition (2.12 cm zone) against the pathogen S. sclerotiorum. Fermented organic fertilizers (10%) inhibited fungal growth, with okra stalk compost being the most effective (1.66 cm colony diameter vs. 3.5 cm for the control) and reduced sclerotia counts. Findings showed host-specific virulence of S. sclerotiorum and identified S. albidoflavus Kefaa-1 and okra compost as effective biocontrol agents. All tested organic compost extracts suppressed fungal growth, with okra stalk compost demonstrating the strongest inhibition. The mean colony diameters were 1.66, 2.34, 2.55, and 2.69 cm for okra, reed, wheat, and Alhagi sp. composts, respectively, compared to 3.5 cm in the control. Furthermore, Streptomyces albidoflavus Kefaa-1 and okra-based compost were the most effective in suppressing S. sclerotiorum growth under laboratory conditions.

Keywords:

White mold disease, genetic variability, biological control, compost, Streptomyces, Sclerotinia sclerotiorum.