Sclerotinia sclerotiorum white rot white mold in the USA

Control of this pathogen is extremely difficult because of its wide host range and formation of persistent sclerotial resting bodies. Resistance is recessive and quantitative. The introduction line PI206942, a non-heading cabbage from Turkey, has shown superior levels of resistance (Dickson and Petzoldt, 1996). Resistance was transferred to cabbage, broccoli and cauliflower. Sharma et al. (1995) reported that cauliflower cv. Early Winter Adam's White Head and EC 162587 were highly resistant, and RSK 1301 and MRS1 were moderately resistant. Harindar and Kalda (1995) indicated that EC 103576,

EWAWH and EC 177283 were resistant. Some systemic pesticides offer protection from white rot, but tolerant strains can develop with remarkable speed. Cultural controls such as soil cultivation, aeration and flooding are helpful in combating the pathogen. Forms of nitrogen fertilizer such as calcium cyanamide are also associated with diminished pathogen activity. Control of storage rots incited by S. sclerotiorum is aided by retaining fresh produce in a turgid state and reducing the temperature to 5°C. Some encouraging results have been achieved using biological control, particularly with hyperparasites such as Coniothyrium species that attack the sclerotia of S. sclerotiorum.

White rot is a serious pathogen of Indian mustard (B. juncea) (Sharma and Sharma, 2001), attacking the stems before and after flowering, leading to substantial yield losses through reductions in height, fewer siliquae in the primary and secondary inflorescence branches, fewer pods and shrivelled seed. Even where seed matures it has reduced germination capacity with diminished radicle and plumule growth. Similar effects are reportedly caused by Alternaria spp. on brown sarson.

Sclerotial survival of S. sclerotiorum was evaluated in the field following amendment with whole crops of white mustard or oats incorporated by rotary tilling (Thaning and Gerhardson, 2001) (Table 7.4). Sclerotial survival was reduced significantly by plastic covering and amendment with brassica residues, and in one instance by mycoparasitism with Coniothyrium minitans. The controlling effects of brassica residues result from sulphur compounds - glucosinolates which by enzymic breakdown produce antimicrobial substances. Soil solarization is widely practised in Mediterranean countries where sufficiently high soil temperatures can be achieved. In more northerly areas, a combination of plastic covering and crop residues has proved a valuable form of control (Kirkegaard et al., 1998). Use of plastic sheeting in cool climates, although sublethal, retards the dissipation of volatile derivatives of the glucosinolates and keeps oxygen concentrations low; these conditions add stress to the sclerotia and hence increase the control of this pathogen.

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