In vitro inhibition of potato fungal pathogens using isothiocyanates David Kenyon & Fiona Taylor
Potatoes are the world s 4 th largest crop 3 rd largest food crop Potatoes Very susceptible to infection from a vast range of pathogens Traditional control broad range pesticides and soil fumigants but for some disease there are no control options Legislation of the use of pesticides is tightening
Black Scurf
Rhizoctonia solani Black Scurf Thrives on organic matter All stages of potato development Predominantly infects below ground parts Black Scurf Black sclerotia masses Rejected fresh market Stem Canker Early attack of germinating sprouts before emergence Delayed emergence & weakened plants Reduction in crop vigour
Black Scurf Control Integrated approach to control is necessary as no single measure is entirely effective. There are no resistant varieties but seed should be clear of infection or fungicide treated. Measures which promote early emergence such as planting in warm, well drained seed beds minimise infection as vigorous plants will outgrow the infection. Long rotations reduce disease levels in the soil.
Silver Scurf
Helminthosporium solani Silver Scurf Infection can originate from seed tubers or the soil. The longer tubers remain in the soil, the more likely silver scurf is to develop. Control Fungicidal treatment of tubers prior to planting or at harvest (into store) may prevent infection. Early lifting can reduce the incidence of silver scurf.
Black Dot
Colletotrichum coccodes Black Dot One of the most problematic blemish diseases of washed, pre-packed potatoes. The disease can be seed borne but is more commonly soil-borne. Control Long rotations & using clean seed prevent soil contamination. Varietal susceptibility varies. Fungicidal soil treatment (azoxystrobin) can delay disease.
Bioassay Allyl, Benzyl, Isopropyl, Methyl, 1-Naphthyl, 2-Phenylethyl, Propyl Isothiocyanates Incorporated into Potato Dextrose Agar plates 3.1, 6., 12., and mg L -1 Plates innoculated with 7mm fungal plug, from mature colony Radial growth measured.
Black Scurf R. solani colony growth after exposure to ppm (b) benzyl, (c) 2-phenylethyl, (d) allyl Isothiocyanate, in comparison to (a) control colonies
Mean Radial Growth (mm) Mean Radial Growth (mm) Black Scurf 4 4 3 1 allyl isothiocyanate 2 4 6 8 12 14 4 4 3 2-phenylthyl isothiocyanate 1 2 4 6 8 12 14
Mean Radial Growth (mm) Mean Radial Growth (mm) Black Scurf 4 4 3 benzyl isothiocyanate 1 2 4 6 8 12 14 4 4 3 methyl isothiocyanate 1 2 4 6 8 12 14
Silver Scurf H. solani colony growth after exposure to ppm (b) methyl, (c) allyl, in comparison to (a) control colonies
Mean Radial Growth (mm) Mean Radial Growth (mm) Silver Scurf isopropyl isothiocyanate 1 4 6 allyl isothiocyanate 1 4 6
Mean Radial Growth (mm) Mean Radial Growth (mm) Silver Scurf benzyl isothiocyanate 1 4 6 2-phenylethyl isothiocyanate 1 4 6
Black Dot C. coccodes colony growth after exposure to ppm (b) benzyl, (c) 2-phenylethyl, (d) methyl Isothiocyanate, in comparison to (a) control colonies
Mean Radial Growth (mm) Mean Radial Growth (mm) Black Dot 4 4 3 1 isopropyl isothiocyanate 2 4 6 8 12 14 4 4 3 1 allyl isothiocyanate 2 4 6 8 12 14
Mean Radial Growth (mm) Mean Radial Growth (mm) Black Dot 4 4 3 1 benzyl isothiocyanate 2 4 6 8 12 14 4 4 3 1 methyl isothiocyanate 2 4 6 8 12 14
Conclusions Pathogens respond differentially to the ITC screened.
Conclusions Isothiocyanate Black Dot Black Scurf Silver Scurf Allyl Benzyl Isopropyl Methyl Napthyl Phenylethyl Propyl
Conclusions Pathogens respond differentially to the ITC screened. Benzyl, Methyl & 2 Phenylethyl Isothiocyanate show greatest activity A range of both fungistatic and fungitoxic responses have been observed
Further work Expand the range of pathogens to include fusarium, common scab, powdery scab, etc Comparison of results with ITC profiles of cultivars. Inoculated pot trials. Field evaluation.