b'WHAT IS ASIAN SOYBEAN RUST? 1 Because of the lack of resistance in soybean and the4 ASR first appeared in the Western Hemisphere in a explosive nature of the disease, it carries the potentialfew fieldsin Paraguay in South America in 2001. In to cause significant yield losses (30% to 80%). the summer of 2004, entomologists identified ASR in Columbia. A few months later, it was found for the first 2 According to the American Phytopathologicaltime in the continental United States in Louisiana.Society, two closely related fungi cause soybean rust: Phakopsora pachyrhizi, referred to as Asian or Australian soybean rust, and P. meibomiae. However, it5 Soybean rust does not appear to overwinter in areas is P. pachyrhizi that causes a challenge for growers. with freezing temperatures.P. pachyrhizi was first described in Japan in 1902. Its6 A least 160 host species in 53 genera have been identified 3 presence appears to be limited to Asia and Australia untilas alternative hosts. Kudzu, an invasive species known 1997 when it was found in Uganda in East-Central Africa.colloquially as the vine that ate the South, acts as a Within four years, it had spread to Zimbabwe and then togreen bridge for ASR between soybean crops across South Africa. seasons in the Southeastern United States.blocks of repetitive, appar- Opening Doors ofthe pathogen to underminepea, a related legume species. ently undifferentiated DNAUnderstandingsoybeans defense system.However, given the pathogens in plant and animal species,Finding genetic resistanceThese effectors often disableadaptability, multiple genetic this material was early onin soybeans against thissoybean receptors that are amodes of action need to be considered nothing morepathogen has been a hugepart of the non-self-detectioncombined to ensure a longer-than useless, junk material.challenge, partly becausesystem, van Esse says. Nowterm solution.Over time, however, a func- there are not many resistantthat we have a complete tion could often be ascribedsoybean breeding lines thatcatalog of all the proteinsLooking for Achilles Heelto this type of DNA. Similarly,contain novel resistance in thethat are in the ASR genome,Now that ASRs genetic van Esse and his colleaguesfirst place. Van Esse says thatwe can start to study thoseroadmap is known, the are very interested in find- to develop ASR resistance,components that are used bynext step is to learn how ing why P. pachyrhizi hasresearchers must begin withthe pathogen to suppress thethis pathogen works and to such a large genome with anwhat is already known. soybeans immune system. find its Achilles heel. This extreme amount of repetitiveWe begin by using theOne way forward is tocould enable researchers to sequences.best available data to identifymake a transgenic trait com- target the pathogen with a We believe that most ofmolecules that we know arebining resistance genes fromnew combination of genet-the genomic content has abeing used by the patho- other legumes in a stackics, chemicals or other novel function. In the case of thegen to cause disease. Plants,which enables soybeans totypes of solutions. This new repetitive DNA, it may haveincluding soybean, have anrecognize ASR. This novelgenomic information could something to do with theexcellent immune system thatrecognition would tilt the bal- help tremendously, even ability of the pathogen tois dismantled and suppressedance in these new soybeanthough some of these solu-adapt more rapidly to differ- by ASR. We know pretty wellplants favor. They wouldtions may be reached years in ent conditions. The repeti- from basic research how thatdetect ASR again, switch onthe future.tive elements may enhanceworks. Soybeans have antheir immune system andSome of the traits we are the fluidity of the genome toexcellent self/non-self-recog- take care of the invader. Wegenerating are still in the lab-make adjustments that arenition system, but ASR makesalready demonstrated that thephase, but I anticipate they necessary to survive, vanproteins called effectors andprinciple is sound by transfer- will be available in the next Esse says.components that enablering a receptor from Pigeondecade, van Esse predicts. JUNE 2020SEEDWORLD.COM /45'