Differences in the aphid transmission of cucumber mosaic and some potyviruses.

The transmission by Myzus persicae of cucumber nmsaic virus (CMV) and three potyviruses - amaranthus leaf mottle (AMV), bean yellow mosaic (BYMV), potato Y (PVY) - was studied. Plants were inoculated with either CMV or PVY and used as virus source for aphide 1.2.3 and 4 weeks later. Virus concentration in the leaves was checked each time by infectivity and serology.The rate of transmission of CMV decreased while that of PVY increased in successive transmission tests. In both cases no clear correlations were found between rate of transmission and virus concentration in the source plante. Aphids were given ashort acquisition probe (<1 min) and were then tested individually after a postacquisition fasting period (PFP) ranging from 0 to 16 hr. CMV was transmitted after 2 but not 3 hr PFP and the transmission rate decreased linearly with log PFP. ALMV, BYMV and PVY were all transmitted up to12 but not 16 hr PFP. The transmission rate decreased in the first hour of PFP but then all cases showed a secondary maximum between 2 and 4 hr PFP. Infected aphids were transferred individually to a series of plants and allowed to make a short probe on each, with fasting in betveen. The retention of CMV by the aphids did not exceed 40 min. Generally, only one plant in each serieswas infected and occasionally two, always consecutively and within the first three probings. ALMV was transmitted up to 5 plants by the same aphid and was retained for up to 7 hr. Transmission was sometimes intermittent. It is concluded that other factors concerned with source plants, besides virus concentration, influence the transmission of non-persistent viruses. The different transmission patterns of CMV and the potyviruses studied may reflect already noted differences in virus-vector relationships.