Fitness of Pyrisoxazole-resistant Isolate Inciting Tomato Early Blight

PurposeTo evaluate the resistance risk of Alternaria solani inciting tomato early blight to pyrisoxazole, and the fitness of pyrisoxazole-resistant isolates was studied.

MethodsThe sensitivity to pyrisoxazole, stability of resistance, and growth rate of resistant isolates were analyzed by mycelial growth rate method. And the sporulation, germination rate, spore competitiveness, pathogenicity, and toxin production were also assessed.

ResultsResistant isolates were low to moderate resistant to pyrisoxazole, and the resistance could be inherited steadily after 20 generations of subculture. The mycelial growth of resistant isolates declined along with reduction of sensitivity. Their sporulation increased and spore competitiveness became weaker, but germination rate did not vary. Their toxin production declined so that the pathogenicity turned weaker. However, the pathogenicity of resistant isolates was stronger than that of sensitive one under the impact of pyrisoxazole.

ConclusionThe pyrisoxazole-resistant isolates, whose resistance can be inherited steadily, possessed enhanced reproductive capacity, weaken viability and parasitic ability, but they can be expand their populations by the suppression of sensitive populations with pyrisoxazole. It is necessary to monitor the field resistance continually, and make the prevented strategies for development of pyrisoxazole resistance.