Tak­ing steps to­wards late blight re­sis­tance

Maris Piper pota­toes can be ge­net­i­cally mod­i­fied to develop late blight re­sis­tance, trial work in the United King­dom has shown.

NZ Grower - - Potatoes Nz Inc. - By Heather Briggs

Glob­ally, late blight (Phy­toph­thora in­fes­tans) is the most de­struc­tive pathogen of pota­toes, and has been iden­ti­fied as the cause of potato famines in Europe dat­ing back to the 1800s.

It’s es­ti­mated to cause an­nual losses of 15 per­cent of global potato pro­duc­tion. Ac­cord­ing to the Agri­cul­ture and Hor­ti­cul­ture De­vel­op­ment Board (AHDB Pota­toes), it costs the Bri­tish potato in­dus­try an es­ti­mated £50 mil­lion, or a lit­tle un­der $100 mil­lion an­nu­ally, in crop pro­tec­tion prod­ucts in a typ­i­cal blight pres­sure sea­son.

Pro­fes­sor Jonathan Jones of The Sains­bury Lab­o­ra­tory in Nor­wich, be­lieves ge­netic mod­i­fi­ca­tion has real po­ten­tial to of­fer grow­ers agro­nomic ben­e­fits, par­tic­u­larly in terms of de­vel­op­ing late blight re­sis­tance. Against a back­ground of ag­gres­sive potato late blight strains, com­bined with in­creas­ing losses of chem­i­cal plant pro­tec­tion tools, crops car­ry­ing genes that con­fer in­creased disease re­sis­tance would help to take the pres­sure off grow­ers.

These crops would fa­cil­i­tate op­ti­mised in­te­grated pest man­age­ment and al­though Pro­fes­sor Jones does not en­vis­age an end to fungi­cide ap­pli­ca­tions, they may not need to be added at the present rates and fre­quen­cies. He’s lead­ing a team which has de­vel­oped a new, im­proved Maris Piper potato with a stack of three genes that con­fer re­sis­tance to late blight.

These lines suc­cess­fully un­der­went field tri­als in the UK in 2017 and are on track to help fight the new blight strain 37_A2, which has es­tab­lished it­self in North­ern Europe over the last few years.

Fit, ag­gres­sive and in­sen­si­tive to the fungi­cide flu­az­i­nam, this strain com­prised 24 per­cent of UK sam­ples iden­ti­fied last year by Dr David Cooke from the James Hut­ton In­sti­tute, who car­ries out blight mon­i­tor­ing for the levy body AHDB Pota­toes’ Fight

Against Blight cam­paign. It has also been iden­ti­fied in tu­ber blight.

Each blight re­sis­tance gene can be con­sid­ered a mode of ac­tion, and re­ly­ing on just one mode of ac­tion is a risky strat­egy, he said

“As we have suc­cess­fully in­serted three blight re­sis­tance genes, there will be three modes of ac­tion against the pathogen. Fungi­cide ap­pli­ca­tions will still be used to con­trol early blight (Al­ternaria) so these will pro­vide a fourth mode of ac­tion. As a re­sult, it will be more dif­fi­cult for the pathogen to mu­tate so it can evade all of them and break the re­sis­tance.”

This com­bi­na­tion should con­fer blight re­sis­tance for a good pe­riod of time.

Also de­ploy­ing blight-re­sis­tance genes can be com­pared to an­tibi­otic use where reliance on a sin­gle mode of ac­tion even­tu­ally se­lects for mu­ta­tions that se­lect for strains that re­sist the an­tibi­otic. And the time­li­ness of fungi­cide spray­ing when blight pres­sure is high and in­ocu­lum is present will not be so cru­cial, be­cause the grower will be able to wait un­til the land is dry enough to take the weight of the spray­ing ma­chin­ery with­out risk­ing the loss of valu­able crop.

Even if the pathogen does get onto the crop, it will not be able to mul­ti­ply as quickly as it would on a non­re­sis­tant va­ri­ety, which will help slow down the speed of spread, he said.

One of the ben­e­fits of his projects is that the ge­net­i­cally mod­i­fied potato will be the UK’s most-grown va­ri­ety, Maris Piper, but with these ad­di­tional traits. This is pos­si­ble be­cause adding spe­cific genes for re­sis­tance does not af­fect the other char­ac­ter­is­tics of the va­ri­ety, he said. Us­ing sim­i­lar meth­ods, he aims to in­cor­po­rate re­sis­tance to potato virus Y and bac­te­rial wilt (Ral­sto­nia solanacearum), and per­haps even potato cyst ne­ma­tode.

The mod­i­fied Maris Piper will also carry traits which will en­hance tu­ber qual­ity and by si­lenc­ing the chem­i­cal com­pound polyphe­nol ox­i­dase, these pota­toes will be less prone to bruise dam­age. This will make it eas­ier to en­sure the pota­toes reach customer qual­ity spec­i­fi­ca­tions and will help re­duce wastage at har­vest, par­tic­u­larly in dif­fi­cult years, he said.

In ad­di­tion, by si­lenc­ing an in­ver­tase en­zyme the potato will have low­ered lev­els of re­duc­ing sug­ars and coldin­duced sweet­en­ing, re­duc­ing black­en­ing and for­ma­tion of acryl­amide when cooked at high tem­per­a­tures. In­ver­tase con­verts su­crose to a mix­ture of glu­cose and fruc­tose.

This project is not Pro­fes­sor Jones’ first work with ge­netic mod­i­fi­ca­tion in pota­toes. In 2010-12, a blight re­sis­tance gene from Solanum ven­turii was in­serted into the va­ri­ety De­siree. This gene con­ferred re­sis­tance in the field and the United States-based com­pany Sim­plot has li­censed this gene for com­mer­cial­i­sa­tion in that coun­try.

Pro­fes­sor Jones said nat­u­ral ge­netic mod­i­fi­ca­tion has been go­ing on for thou­sands of years. Agrobac­terium has evolved to insert DNA into plant cells, so there is noth­ing un­nat­u­ral about a crop that has been trans­formed by Agrobac­terium nat­u­rally in­tro­duces DNA that al­ters the plant’s hor­mones and causes galls, and mod­i­fies the plant’s own me­tab­o­lism so that it sup­ports the bac­te­rial growth. For ex­am­ple, sweet potato is the re­sult of a nat­u­ral event that in­tro­duced Agrobac­terium DNA into the crop plant.

“What we are do­ing is de­sign­ing the DNA that goes into the Agrobac­terium and then us­ing the DNA trans­fer ac­tiv­ity of these bac­te­ria to insert our de­sired genes into the plant,” he said.

“The tech­nol­ogy is easy but cur­rent reg­u­la­tions in Europe mean bring­ing to mar­ket these so­lu­tions to crop prob­lems is slower and more ex­pen­sive than it needs to be.”

For more in­for­ma­tion visit The Sains­bury Lab­o­ra­tory at tsl.ac.uk

▴ Blight symp­toms on a leaf of GM Maris Piper.

▶ Over­view of the field with dead con­trol plants next to their re­sis­tant GM pota­toes.

▶ Left to right; Pro­fes­sor Jonathan Jones and post­doc­tor­ate stu­dents Kamil Witek and Ma­rina Pais. Im­ages cour­tesy of Pro­fes­sor Jonathan Jones.

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