Some factors affecting the relative incidence, distribution and importance of beet yellows virus and sugar‐beet mild yellowing virus in eastern England, 1955‐62

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Abstract
SUMMARY: Sugar‐beet mild yellowing virus (SBMYV) was much more common than beet yellows virus (SBYV) in beet in south‐eastern England during 1961 and 1962. SBYV strains and strain‐mixtures, typical of those in East Anglia between 1958 and 1961, decreased sugar yield of a commercial sugar‐beet variety inoculated in the field slightly more than did SBMYV isolates. Simultaneous inoculation with SBYV and SBMYV decreased yield more than did either virus alone. SBMYV probably caused about three times as much sugar loss as SBYV in England during 1961 and about ten times as much during 1962. Aphis fabae Scop. did not transmit SBMYV from sugar beet to sugar beet or to Claytonia perfoliata and this aphid seems not to spread SBMYV in the field. The surveys of 1955‐62 showed that SBW is common in most years only in parts of Essex and Suffolk; it is suggested that the main overwintering sources of SBYV were confined to those areas, where Beta maritima is probably an important source of SBW. The sources of SBMYV were probably very much more widespread and numerous. The facts that SBMYV persists longer than SBYV in Myxus persicae Sulz. and is not lost during moulting apparently also favour the wider distribution of this virus.