Viroses of annual larkspurs

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Annual larkspurs are naturally infected with many virus diseases, in a few of which the identity of the virus has been determined. Annual and perennial larkspurs, or delphiniums, both belong to the genus Delphinium, and hence in connection with investigations of diseases and leaf variegations of perennial species ⁽²⁾, ⁽³⁾, ⁽⁴⁾, ⁽⁵⁾, ⁽⁶⁾3 a study was undertaken to determine whether delphinium viroses ⁽²⁾, ⁽³⁾, ⁽⁶⁾ also affect annual species under natural conditions.

In this paper the following virus diseases of annual larkspurs are discussed: California aster yellows, celery calico, curly top, tomato spotted wilt; and western cucumber mosaic.

California Aster Yellows

Annual larkspur was demonstrated to be naturally infected with California aster yellows. The virus was recovered from naturally infected annual larkspurs grown for the cut-flower trade, in home gardens, and on seed farms. The virus was recovered from naturally infected annuallarkspurs and transferred to asters by the short-winged and long winged forms of aster leafhopper, Macrosteles divisus (UhI.), and was transferred to celery by the mountain leafhopper, Thamnotettix montanus Van D., and by the geminate leafhopper, T. geminatus Van D.

Since short-winged and long-winged aster leafhoppers were not efficient vectors of the virus to perennial delphiniums and a high mortality occurred within 24 hours, an attempt was made to infect annual larkspurs with these leafhoppers experimentally. Table 1 gives a list of annual larkspurs which were infected with the virus. Both short-winged and long-winged aster leafhoppers infected 19 of the 24 plants inoculated, or 79.2 per cent. The virus was recovered from infected annual larkspurs by these leafhoppers and transferred to asters.

The longevity of short-winged aster leafhoppers on varieties of annual larkspur varied from 9 to 26 days for the males and from 15 to 22 days for the females; that of the long-winged aster leafhoppers varied from 8 to 13 days for the males and from 8 to 21 days for the females. Nymphs of both leafhoppers emerged from eggs deposited in larkspurs but none lived to become adults.