Sensivity of Jordanian Isolates of Alternaria solani to Manchotane

Abstract

Early blight of potato, caused by Alternaria solani, poses a significant risk to potato crops worldwide.
Fifty A. solani isolates representing a population were collected from the Jordan Valley, purified, and tested for their
sensitivity to the fungicide mancothane. The isolates were tested against a series of concentrations of 0, 0.1, 1, 10,
100, and 1000 mg mancothane ml-1 in 5% sodium dodecyl sulfate (SDS). Some A. solani isolates tolerated up to 1000
mg mancothane ml-1. Isolates treated with the various concentrations were divided into 5 groups based on the percentage
of A. solani growth achieved despite treatment: group 1 comprised isolates with mycelial growth of 0.1–
20.9%; group 2, 21–40.9%; group 3, 41–60.9%; group 4, 61–80.9%; and group 5, 81–100%. Ninety-seven percent of all
isolates grew at 0.1 mg mancothane ml-1, 94% at 1 mg ml-1, 86% at 10 mg ml-1, 66% at 100 mg ml-1, and 16% at 1000
mg ml-1. Isolates appeared to be distributed normally at 10 mg mancothane ml-1. Eight isolates were highly resistant
to mancothane and grew even at the highest test concentration. An A. solani population collected from potato fields
in the Jordan Valley exhibited a moderate level of resistance to mancothane. Growers should be careful and vigilant
when using this fungicide to control early blight.