Detection of Alternaria radicina andA. daucifrom imported carrot seed in New Zealand

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Abstract
Seven laboratory methods and a glasshouse test used to determine the incidence of two seed-borne pathogens, Alternaria radicina and A. dauci, are compared and discussed. Incidence ranged from 0–26% and 0–1%, respectively. The two most efficient methods of detection were a heat treatment and the Copenhagen germinator test. The heat treatment was the only method that detected internal infections of the seed. Disease symptoms were expressed in the filter paper, Copenhagen germinator, and pot tests. In glasshouse tests there was no correlation between seed infection and seedling emergence. Hyphae of A. radicina were carried in the inner pericarp layers of the seed and in the testa. It is suggested that seed infection by A. radicina develops from infection of umbel parts through the pedicel and ovary wall.