Abstract
A new disease of carrots showing a stunted, unthrifty appearance suggestive of mineral deficiency has been noted in Kanto District since 1951. Foliage symptoms consisted of irregular chlorotic mottle, yellow veinclearing, and distortion or reduction in size of leaflets. Sometimes growth stunting and rosette were severe. No necrosis was observed on leaflets, stems and roots.
The disease was proved to be caused by a virus, which is transmitted by the aphid Brachycolus heraclei, a common infestant on carrot in Japan, but not by Myzus persicae. Negative results were obtained by mechanical inoculation with carborundum or pin-puncture method, and there was no evidence of transmission through carrot seed.
The vector acquired the virus after an infection feeding period of 1 to 24 hours and viruliferous aphids could transmit with an inoculation feeding for 24 hours. The virus was of a persistent type and viruliferous vector remained infective for a period of up to fifteen days in a series of transfer experiments. There appeared to be no evidence of the presence of a latent period in its vector.
Carrot was the only known natural host of the virus. Celery was experimentally infected, but Cryptotaenia canadensis and parsley were not infected.
From the symptoms, the mode of transmission, restricted host range, long persistence in its vector etc., the virus, in consideration, may be closely related with the carrot motley dwarf virus described by Stubbs (1948) in Australia.
With cucumber mosaic virus from petunia, mechanical inoculation to carrot failed to produce infection.
