A freeze/thaw technique for estimation of nitrogenase activity in detached nodules of Vigna mungo

The Ivory Coast and Nigerian strains of okra mosaic virus (OMV) were transmitted by the flea-beetle Podagrica decolorata, a serious pest of okra in the southern Ivory Coast. The Ivory Coast strain was also transmitted by the orthopteran, Zonocerus variegatus. The Ivory Coast strain was acquired faster than it was inoculated by P. decolorata. When groups of five beetles were given acquisition and inoculation access periods of 24 and 48 h, respectively, 60% of the okra test plants were infected. OMV-carrying P. decolorata remained infective for up to 6 days. The virus was readily detected in extracts of crushed beetles that had fed on infected plants for 20 h. The beetle was also able to transmit to and from plants of Hibiscus sabdariffa and Corchorus olitorius; as a food source it preferred C. olitorius to okra or H. sabdariffa. The beetle is active throughout the year, and presumably can spread OMV at any time between plants of these species. A considerable and unexplained decrease in frequency of transmission was observed in experiments done in the rainy season. The revised cryptogram of OMV is R/l:*/32:S/S:S/Ve/Cl.