Effect of Inoculum Density of <i>Stromatinia cepivora</i> on the Ability of Sclerotial Mycoparasites to Suppress White Rot in Garlic

Abstract

White rot, an garlic disease caused by the soil-borne fungus S. cepivora, is a serious problem of garlic productions in Egypt. This study examines the potential of controlling the disease biologically by using three sclerotial mycoparasites i.e., Chaetomium globosum (Chg6), Clonostachys rosea (Cr12) and Penicillium oxalicum (Po9) employed either alone or in combinations. In in vitro assays, these sclerotial mycoparasites showed high antagonistic effect against S. cepivora isolate (Sc8). In greenhouse experiments, the chemical treatment of tebuconazole was the most effective, with the lowest incidence of white rot in garlic compared to the control. Sclerotial mycoparasites either alone or in combinations significantly reduced the incidence of white rot in garlic. In general, dual and triple combinations of the sclerotial mycoparasites were more effective than these isolates used individually. In field experiments, under low (40 sclerotia/kg of soil) and high (600 sclerotia/kg of soil) inoculum levels, the standard fungicide programme gave statistically significant white rot control, decreasing disease incidence by 67.7 & 32.4% in 2016/2017 season and 72.6 & 31.1 % in 2017/2018 season, respectively. Under low inoculum levels, significant control, equal to the fungicide treatment, was achieved with the triple combination of three sclerotial mycoparasites. However, no sclerotial mycoparasites employed alone give significant control of garlic white rot under high inoculum levels. The triple combination of three sclerotial mycoparasites decreasing disease incidence by 70.8 &25.9 % in 2016/2017 season and 73.7 & 27.6 % in 2017/2018 season, under low and high inoculum levels, respectively. The activities of defense enzymes, i.e. peroxidase, polyphenoloxidase and chitinase due to application of sclerotial mycoparasites were enhanced in garlic plants either grown under low or high inoculum levels. Reduction of white rot disease incidence was accompanied by increasing growth parameters and bulbs yield of garlic plants grown under field conditions. These results concluded that the performance of sclerotial mycoparasites may be influenced as much by the absolute disease pressure. At the low disease pressure site, the low level of S. cepivora inoculum enabled sclerotial mycoparasites to bring about disease control.

Reduction of Stromatinia cepivora inocula and control of white rot disease in onion and garlic crops by repeated soil applications with sclerotial germination stimulants

“…White rot disease caused by the soil borne fungus Stromatinia cepivora (Berk.) Whetzel is a serious threat to onions and garlic worldwide and is a major limiting factor in the production of both crops in Egypt (Hunger et al., 2002; Metcalf et al., 2004; Elshahawy et al., 2017a,b,c; Elshahawy et al., 2018a,b). The first reference of white rot in Egypt was in 1922.…”

“…The first reference of white rot in Egypt was in 1922. Since then, the incidence of disease has risen progressively and nowadays the disease rate can exceed 80.0% in some commercial onions and garlic fields resulting in significant yield losses (Elshahawy et al., 2018a,b). Loss estimates are difficult to ascertain because once the disease is identified in a field, growers are forced to grow other non susceptible (non- Allium ) crops.…”