Abstract
White rot, an garlic disease caused by the soil-borne fungus <i>S. cepivora</i>, 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>i.e</i>., <i>Chaetomium globosum</i> (Chg6), <i>Clonostachys rosea</i> (Cr12) and <i>Penicillium oxalicum</i> (Po9) employed either alone or in combinations. In <i>in vitro</i> assays, these sclerotial mycoparasites showed high antagonistic effect against <i>S. cepivora</i> 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.
Highlights
Garlic (Allium sativum L.) is a monocotyledonous plant and belongs to the family Alliaceae
Isolation and identification of these isolates as sclerotial mycoparasites of S. cepivora were confirmed in previous study [11]
Chaetomium globosum isolate (Chg6) produced type B reaction inhibiting the growth of S. cepivora and growing over the colony
Summary
Garlic (Allium sativum L.) is a monocotyledonous plant and belongs to the family Alliaceae. It is the second most widely cultivated vegetable next to onion and widely produced for its medicinal and nutritional properties. White rot disease caused by the soil-borne pathogen Stromatinia cepivora (Berk). Sclerotia of S. cepivora spread via mass movement of soil or water and especially on infested plant parts. In subsequent Allium crops, inoculum density increases, and disease incidence increases [7]. An inoculum density of a few sclerotia in a liter of field soil potentially can results in crop failure [7]. Loss estimates are difficult to ascertain because once white rot is identified in a field, growers are forced to grow other nonsusceptible (non-Allium) crops. Infested fields often are abandoned from further garlic production
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