|Abstract or Summary
- Several bean yellow mosaic virus (BYMV) strains, presumably
not transmissible by aphids, were studied to determine the biological
and environmental conditions which would possibly result in aphid
transmission of these strains. Investigations were made to study the
effect of different aphid rearing conditions on the transmission
frequency of BYMV. Also, the probing behavior of Myzus persicae
(Sulzer) was studied in relation to transmission frequency of BYMV
to test plants.
Differences other than loss of transmissibility were found to
account for the failure of aphids to transmit some BYMV strains.
Five strains varied in ability to infect specific pea and bean
varieties; all strains were aphid transmissible except BYMV III.
BYMV I and II no longer produced systemic infection in Perfected
Wales pea or Dwarf Horticultural bean although both strains produced
local infection in inoculated leaves of Perfected Wales pea. Only
BYMV y21 and III produced systemic infection in Dwarf Horticultural
bean. The above changes in virus infectivity were attributed to
Both Dwarf Horticultural bean and Perfected Wales pea are
commonly used as differential hosts to identify legume viruses. BYMV
and pea mosaic virus are distinguished only on the inability of pea
mosaic virus to infect bean. Consequently, the validity of virus
classification of legume viruses based on differential host reaction
In addition to the above variation, BYMV I and II required a
high post-inoculation temperature to produce infection in Blue Lake
bean; other strains were not affected under the same conditions.
The host range of BYMV I, II, III, and IV was the same in the plants:
Trifolium pretense L., Crotolaria spectabilis Roth., Trifolium
subterranean L. variety Yarloop, Chenopodium amaranticolor Coste and
Reyn., Glycine max (L.) Merr. variety Lincoln, Melilotus alba
Desr., and Pisumm sativum L. variety Lincoln.
BYMV III, maintained by mechanical transfer since 1963, was
not transmitted to ten plant species in attempts with over 5000
aphids. Myzus persicae (Sulzer) failed to transmit BYMV III from
five different species or varieties of source plants. This was
interpreted as evidence that virus acquisition by aphids, due to
the source plant, was not involved in loss of aphid transmissibility
of BYMV III.
Five aphid species and ten test plant species were used in
an attempt to find a vector-host plant combination which would result
in aphid transmission of BYMV III. Macrosiphm albifrons Essig and
Acyrthosiphon pisum (Harris) finally transmitted BYMV III to
Crotolaria spectabilis Roth. This was the first transmission of BYMV III after attempts with more than 5000 aphids. The return of aphid
transmissibility in BYMV III could be explained only on the basis of
Indirect evidence from two experiments suggested that aphid
transmissible and non-transmissible forms of BYMV III were present
in the stock culture when Macrosiphum albifrons first transmitted
BYMV III. Aphids transmitted the isolate first transmitted by
Macrosiphum albifrons at a higher frequency than the stock culture of
BYMV III. A subsequent experiment indicated that almost any aphid
would transmit BYMV III after return of aphid transmissibility.
Transmission of BYMV IV by aphids reared on Chinese cabbage
was compared to that of aphids reared on a chemically defined diet.
The trend in frequency of transmission implied that aphids reared on
the artificial diet were inferior in transmission of BYMV IV.
The probing behavior of Myzus persicae on Pisum sativum and
Phaseolus vulgaris was evaluated in relation to the transmission
frequency of BYMV. Plant susceptibility of pea and bean was the same.
Aphids made 40 percent more probes on bean than on pea in a 15 minute
observation period. However, increased transmission to bean was not
reflected by the greater number of probes. There was no evidence that
transmission of BYMV was affected by observed differences in the
probing behavior of Myzus persicae.