How im­por­tant is potato virus S (PVS)?

Potato virus S (PVS) is a virus caus­ing very mild (of­ten not vis­i­ble) symp­toms in a potato crop. Its ef­fect on a crop may be en­hanced with a co-in­fec­tion (mixed in­fec­tion) with other viruses such as Potato virus Y (PVY) and Potato Virus X.

NZ Grower - - Future Focus - John Fletcher of Plant & Food Re­search of­fers his per­spec­tive on the im­por­tance of Potato virus S (PVS.

PVS is par­tic­u­larly con­ta­gious and may be trans­mit­ted me­chan­i­cally, for ex­am­ple from tu­ber to tu­ber through dam­age, by equip­ment pass­ing through crops, or from tu­ber cut­ting. The virus is also trans­mit­ted by aphids. Psyl­lids are not known to trans­mit potato viruses. Re­in­fec­tion of seed lines is a con­cern, as we have found that re-in­fec­tion can oc­cur from zero to 20-50% over one seed gen­er­a­tion.

Re­search in The Nether­lands cal­cu­lated that if 100% of plants were in­fected with ei­ther PVS or PVX there would be a yield re­duc­tion of 10%. In Poland PVS in­fec­tion de­creased yield of tu­bers by be­tween 11 and 20% com­pared with that in healthy plants. In the Philip­pines re­duc­tions in yield due to PVS were recorded at be­tween 4 and 9%.

Sim­i­larly in the USA tu­ber num­bers and spe­cific grav­ity of the tu­bers were un­af­fected by mot­tle and la­tent strains of PVX or by PVS, whereas PVX alone and la­tent PVX + PVS re­duced tu­ber size and yield be­tween 2 and 5%. In Cze­choslo­vakia, yields fell by 15-34% and the num­ber of tu­bers by 16-25.7%. From the fig­ures re­ferred to above, an av­er­age value of 12% loss in yield can be cal­cu­lated.

In the con­text of a striv­ing to im­prove potato yields from 50 - 60 t/ha to 80 or 90t/ha un­der the ‘Potato Yield Gap’ project un­der­way here in Can­ter­bury, how­ever, this po­ten­tial loss is a con­cern. It is essen­tial in this con­text that seed tu­bers planted must be of the high­est virus health. In the Yield Gap ex­per­i­ment, lines tested sub­se­quent to plant­ing were es­ti­mated to have 10100% in­ci­dence of PVS. Other viruses were also present but at a lower over­all in­ci­dence: PVX (1-4%), PVY (1%), PVM (1-100%), PLRV (1%).

How is re­in­fec­tion with PVS oc­cur­ring so rapidly?

Cut­ting seed is known to spread me­chan­i­cally trans­mit­ted viruses. At­ten­tion to the use of suit­able sani­tis­ers on cut­ters be­tween lines and at breaks to min­i­mize trans­mis­sion is essen­tial. Other con­trib­u­tors to me­chan­i­cal trans­mis­sion can be through sprout dam­age caused by rough han­dling, es­pe­cially wet stor­age or plant­ing con­di­tions and the move­ment of ir­ri­ga­tors through seed crops. A fur­ther con­trib­u­tor to virus spread seems to be the in­creased move­ment of spray equip­ment through crops in re­sponse to the tomato potato psyl­lid (TPP) out­break.

It is ad­vised that spray lanes or tram­lines for ir­ri­ga­tor move­ment are es­tab­lished to min­i­mize this method of trans­mis­sion. >

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