SMIC DOCUMENT SORGHUM AND MILLETS INFORMATION CENTER tntmmional Cropa Rosorrcb Institute for tho Gomi-Arid Tmpl~ ICRISAT PrtmImu P.O. Andhrr PtW India 502 324 DOWNY MILDEWS OF TROPICAL CEREALS I. In~r(wiut.~inrl II. Thr Pa~lii~qcrlsiir~rl their 110~1s Krl~iti~~r~\l~if~siirnony tl~v /'~ro~ro~~/rro~por(r S]I,,<it,, H. \'ariatior1 in .Y~~lrrniportlpronlrnr<oln (:, Kv\riirc 11 Rr~c~~~irrrr~~~r~t~OII P.II~III~I,~Ililrr~ti~\ 111. GvograpI~i(.!I I~~~trrl~t~tionancl 01igi11, 11'. S! nlptorns \'. E,.onornic Loss \'I. Slaizr rlrr l'niquc I)OWII\ 1lildc.u Sua<t.l~t .A. Tht, 1)<1ur1\\filclru v 01' \l;ii~t, B. Thr Tllrtxt 11) tlrc \l.ii/r. (:II~I\~~I'.\lri~~~ <III(I tllc .\IIIC \']I. Biolo~)and tpidrrriiol~~g\ A. Thr Iilli.cri\,r I'ri~piigull..; 8. ~~l~.;~lOl'." C;. .\sexual Sporr* I). Infi.ctic~nand (:(~lilrrirati(~r~ E. Syst~~rni<S\rnptorrr I)t.vt.lol~nrerlt F, Disc,isv lr~i~i~~tr~~r~,Builci-LI~I,111d S]~rv>id (;. Seed 'I'rii~isniis\ior~ VIII. (:c~r~~r(~lol t11v (;rar~~ir~~~tt,oubI~JWII\ Slil(l~,\v\ .\. Haric Cone t.pth R. (:orltrol 'I'hrouql~(:ulrural Pr;~rtl(r\ C:, C;o~~trulwilh \lirro(~rg:~nisrns D. (:nrlrrol uith Funglcidra E. (:onrrol wit11 Host-Plarlt Kt,s~rtan(c I. Resiatancr Sc,rrrning l'vc.hniqurs 2. Evaluation of l'lant and \'arirtal rral tronr 3. Thr Qurstion of Irnrnunit) 4. Reaistanrr to Ooal~oresand Ahr~ualSpr1r1.s 5, Resirtanrr lo I.~rcalarld Syv cmic C:olurri~dtion 6. Soureps of Rrsistiltlcc 7. Stabilit) and Durability of Re\isran~v 8. Prc~sprcrsfor Hori7.ontal Krsistanrr F. Integrated control IS. Thr Challenges hr thr Future R. J Williams I. INTRODUCTION 'l'hc c.c.rc,als maizes [<PO nrgy~I,. 1, sorghum [Jhr,chumhirolor I I.. I llocnch]. iirltl prarl millrt [l'mni.rr~um ornrrir.urrunr 1,. 1 I,cekc, syn. I1rrrtri\rturn !~phoide~I Burnm., Stapl', & Hul~l).),togcthu \cith the ro-c,;~llrdminor rnillvts sl~c,has Li)x[ail rnillet [S~lariciilalicci 1.. Bcauv.]. Proso rrmillet il'crniiutt~ miliclcuunr I.itil14, and fingrr millvt (E/YU.I~NYi~iururri~ I,., (;;lrrtn.l. 1)rovide the staple c1ic.t oI';i v;tit pri.~portionof Im~~niatlkind livir~gill tr:opic,al and suh;roI)ici~lless-drvc~lo,c~d'courmtrirs. 111 nlarly ol' tt1c.c. c.our~rrics,particularly in 12f'ric.a and :l\;i;i, larqc. r~~~mhcrsofpc~oplc ;Irct rlow aufT(*rir~gli.olim 1mulmgc.r itt~dnlall~~~tririo~~, thr !,irldr 01' thr I~iisic li)od crops art. ~l't(,n;il)piilIi~lgl~~ IO\Y~ ;IIICI III(. i~~(,r(,;iwsin li)od ~)rodu~.tio~~iirr fl~llit~g t~ehincl ~lmt' i~lilrrnirmqil~crc;~seh in ~)op~~l;~tiori ~'l';il~lrsI ;ilmd 1 11. 111 order to ;illr\.i;itcnI~unl;trl sulti3ril~~. ;i11(I to rrduc,c rhc 1,;1ui11Illctors ol'soci;~luI1r(lst ;ind c~)r~sccluc~nt~x~litic;~l (onflier, there is ;in urgcnr nerd to irlc,rr;~srth(* produc,tion ol'll;~sicli~od crops ill the trol,ic,al Irhs-dr\,c- loptd (~ou~m~rit~siLla!rr, I!Ji'ti: \\'ortrnar~.l!J761. \Yhilr in parrsol':lfrica i111d South :lmcric.i~tllcqrr nm;t). I)? oppurt~~~iitit~sto itmcr~iisr tht* totiil arra 01' I;ctld c,ropl)ed, t lierc is 110 dol~l)t111;it arl i~mcreilsc*in production ~)cr' u~mirol'iirca crc1p1)c.d \\.ill 1)c of\.it;tl in~por~;~r~cc~.'1'0 achit~vc sig~lific.al~t inc.rrnsr ill virlds tlirl,r. is a rlerd to: li: i~lcrrascthr yirld potc.~lti;tlol'il~di\.iciuirl \,;iricric*s; ;ii I d(9c~rt~asrtlir c*lY(,cthof liotic yirld rctlucc~rs: :iii\ dcc.rc;isr thr rtti.cts ol'ahiotic yicald rrduc,t.rr; and f i\ i inmprovc crop m;iri;igrrnclit. Amoiig the t~ioticyicald rc~ducersthe plant pathogrns arc ol' major sigtiifica~~cr,and li)r the itrlporran~trapical drylarlii crreals maize. sorghum and thc tnillets'l, tllc dow~mymildcws art* a widesprrad and lii~I11ydcs[~.ucti\,r group of pathogrns. Although the downy rnildrws have brt\n rceogtizt3d its ilnpor~nritctbrcal pathogrns sincr thr early part of his crntury, they recei~rdrelatively little attention until the early 1960s. Evrn ~odaythere art, many important gaps in our knowlcdgt. of the biology and epidemiology ol'thrse pathogrns and the diseases thcy Table I.' Population. food supply and food production dataa of selected countries. Average Annual Crude Dally Per Capita Per Capita Population Birth- Calor~eSupply as Food Production Growth (%) rate/1000 % of that Required Index 1975-77 Region Country 1970-77 1977 1974 (1 969-71 = 100) - West Africa Senegal 49 Mali 49 Upper Volta 48 Niger 52 Chad 45 Ghana 48 Nigeria 50 East Africa Sudan 45 Kenya 51 Tanzania 48 Ethiopia 49 Zambia 50 South Asia Nepal 45 Pakistan 45 India 35 The Americas Ecuador 41 El Salvador 39 Venezuela 36 Brazil 36 Mexico 38 USA 15 'Source World Development Report. 1979. The World Bank. Wash~ngton.D C Table 11. The total arable area, the area cropped with millet, sorghum. and maize. and the yields of these cereals in selected countries in Asia, Africa and the Americas. Total Arable Area (mn ha) 1978 Yields (kg ha-') Land (mn ha) Cropped with in 1979 for Region Country 1978 maize sorghum miller maize sorghum millet West Africa Senegal Mali Upper Volta Niger Chad Ghana Nigeria East Africa Sudan Kenya Tanzania Zambia South Asia Nepal Pakistan India The Americas Ecuador El Salvador Venezuela Brazil Mexico USA -- - Source FA0 Pr+uct!on Yearbook. Vol 33 1979 FAO. Rome Downy Mildews of Trop~celCereals 5 causr, that inhibit our efi~rtsto control thrni. In ordrr to fill tlirsc* gaps much rrsrarch is nrrdrd on an intrrnational co-oprr,~ti\.rI~asis. This review attrmpta to dr,~\\ntrrntion to thr import;~ncroS thc graminaceous downy mildrwr, to summarirc the stat? ol'kr~o\vIrdgc.on many of ~hrimportant aspects ol'thrst~pi~rhe~gc.ns ;~nd tht, diszasrs thry incite in tropical crrrals, and to highlight the inipcrrtat~rnrt%as tliiit still rrquirr rc.sc+arrh.Ir is hoprd that this will stimuIirt~~sc.ic~ritiststo ~vork on thr grmli'inacrous dowri\ r?lildc\(~s,li~r the), art' ;I ~;ts('itl;ltitlg srotlp 01' agriculturall!. import;irit k)arhogc.r~s.'l'licir stud!. ~villl)r(~\,idr 1101 only ;I richly rc\v;~rdingsc.irr~ti(ic. c.spc.ric.net.. 1,111 also ill1 011port11riity to coritrit)utc to tlir rolutio~i of' OIII~ 01' tlir qrciitrst prol)lrr~irlii~~iri~ hurr~ankind:that of the. 1iungc.t. iit~d rli;ili~i~tritio~lof' 1111. r;~l)idly rspiu~dingpopuliitiori.\ ol'tl~t~trol)ic,;~l I(~\s-d(.\ci~~l)c-d (,o~r~~tri(.x. 11. THE PATHOGENS AND THEIR HOSTS qcncra. ii11c1 (111. prol),~l)l~,ph>~Iogt~~~(~rii rt,l<~tioi~il;;l), ;I~II~II~ tl~c tiicniI>t~rs01' tlit* l'(~r~~r~orl)or;~lr\Fig. I ', wew, r(<(.c,1111!rts\,i~~t*(i 11y Sliav. 1!181 . I Iir t\\.o gt.llc.rit r.c,\l)ot~\il)lc,lirr III~~niclst sc.riorl+ ~.c.or~~~n~icIosws ill granlir~acrour1 rop4. .\'I/YI(I\/IIII/IS~.t~ro('t. dl, I(;ir! ;111(l /'I~IIIIIII\I/B~DL/IIIIN Ito Shirai arld Ii. I-l;~r;c,wctrc oril!. re( c*rltl\. Ii)rrn;ill>.di\~ir~guirlic.d ;is wpal.atc getlt.ra Sl~a\\,.l!liH: S~;IM;111(1 \\'i~t(,rlltrl~s(.,l!lHO, or1 tll(, 11;1si\ 'I'hc rl)rcics c.urrcnrl! rc.c.oqni7t~ci;is qr;imit~acc.oll downy rnildru.5 ;ire prcsrntrd iri 'I'al~lc111: toqc*tlicr will1 a rutnniiiry of thrir reportc.d liosts, the grnrrall!. acceptrcl corrrrnori rlarnc,\ OS tl~(.tlisc*arr\ thcay c.nusc, tlrc. typrs oTiymptoms they intlucc and ttirir al~ilit!. to ~)rodutc. oosporcasin thrir crop hosts. Kcnncth 1981 drew attentior~ro thc rclati\~c~lynarrow host rangr of .frl~ra,pora infeetirig grassc.5 iri thca tril~cI'aniccar ;inti rarely maize in thr trit~c\laydraca, arrd Prri~no.criuro\pora (pathogenic to sprcirs in thc tril)ca klaycirat. and Andropogonrar!. He suggc*sted that the Srw anomalous rrports outside thcsr limits can he ;iscrihrd mohtly to ON GRAMINEAE ON OTHER ANGIOSPERMS Per~nos~lerO~POrQ Peronowrn Peronosporo Brem~o' ~aptospsrmo ,- - - - - -. Brem~o Downy M~ldewsof Troptcal Cereals 9 error in host or patliogrn identification, or to the usr ofsonir artificial inoculation trchniquc. The sprcirs considrrrd to t~c.of t.c.oliornic significance to tropiral crrr;~ls;I[ thc prrsrnl rinic. arcs: S~~lrrm.\poro grominirolo :pearl millrt, f'ostail millet ,: IJrrnno.rc~ic.ro~porn\or,chi r sorghum, maize : P.Irutrropo~trt~~ maizc.1; I'. nr(!~c/~\1 niai~r : P. .\clcc.horr !n~aizrand sugar canta ; P. /~hili/~[~itrrrr.\i\rnaizc : I'. .\pontanra 1 niaizc.': and Sc~lrroph- thoro rqrs.,inr var. ;mc8 rnaizo . Tlir histor\ of tllr disc.o\,rry and nan~illg of'thrsc. sperirs. ~vitlithr t.sc.rpric111ol'~hr ~C(,CIIII> 11ii11irdI'. hc./~ropt<e~~t~i I Siradhanii ut 01.. !!I80 , has t)rr~~ttiorou:hl\ re*\ic.\v~-d I)! Sl~aw( 1975). 'l'hc. somc~wliatconlilhilig $ynolionl!. c.lic~ounrc~rc*din rht- lilrr;~tt~rc.is rr\,ifwrd in 'I'ablc.