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Abstract Rice is one of the most important oereal orops in Egypt. It is the seoond export orop after ootton and important food orop. Rice blast incited by Pyricularia oryzae avara., is considered, one of the most des tructive disease of rioe allover the rioe growing areas in Egypt. It oauses considerable losses of the orop yearly. Results obtained from this investigati.on could be l!IUIDIIlarized •• followSl 1- During 1980 rice growing season. eleven physiologio raoes of ~. oryzae designated as: IA28 IAS7’ IBl, IBS’ ~C19’ .IC 26 , ID 2 ~ IEI’ IE.-r,IGI and Illl were identified from 94 speoimens oollected from different rice growing governorates in ARE using the set of international differential rice vari.eties. 2- Twosubraoes of ~. oryzae were identified under each of raoes IAs7’ IE.-rand Ill1 by the use of 12 local and foreign rioevarieties. g,uring season 1980..s.. 3- Eighteen physiologio raoes of ~. oryzae were identified from 103 speoimens of infeoted~leaves and necks of rioe plants col1eoted from different localities of the rioe grOWing area during 1981 season. These raoes were designated as: IA17, IAs7’ 1A64, I~21’ IB32, IB34• IBS7’ IB59, IB 62 • IC 14 , 1° 27 , 1030’ ID5, IFl, IFi’ IF), 1Gi and 1G2• -- --- - - -_.---_ .. - -_.- -- - 1}6 - 4- Using 33 local and for eign rice varie ties two subraces of Pyricularia oryzae were identified under each race of IFl and IG2 and three eLilracesunder race IF2 during 1981 growing rice aeason. s- Using the set of international differential rice varietie. s. fifteen races of!.. oryzae were identified from 107 specimens of infected leaf and necks collected from different localities of the rice growing areas in ARE during 1982 rice growing season. These races were designated as IA116• IB54• ICl, IC17, IC20, ID1, ID 9 , IE1, IE2• IES’ IE6, IF1• IFi. IG1 and IH1• During 1982 rice growing seson, three subraces of !.. otyzae were identified under each of races IEl and lEi also two subraces under each of races IES’ IFl and IF2, using 12 Japanese rice varieties and 4 local ~nes 7-All races and subraces of !.. otyzae identified during the period from 1980 to 1982 varied in their virulene on all the tested varieties. 8- Race groups IA. IB and IC are more common each year during the period 1980-1982 and there is f1.uctuation between races groups namely ID, IE, IF and IG from year to other. 9- Horizontal resistance occurred in five rice varieties i.e. • ~aby. Giza 180, CO 34. Sakha 2 and IR 36 and ten rice varieties showed vertical resistance, these varieties are, i.e ,Nahda, SalJieni, Agamiml, Yabani 15, Giza 14, Giza 159, Giza 1’70, Giza 171, Giza 172 and IR 8. 10- No stable races were found from.the first asexual generation to the last one ’(after 36 months)~ HoweverSOme races showedstability during the 24 generations as IGl and IFlthen cllangedto other races, also their virulence changed as race cllanged. However,someraces changed but their virulence was not changed such ~ race I026 (with disease index 14) which cllanged to race I027 with the same disease iIJdex (14). 11- Bacterial and fungal spp were isolated from leaf surfaces of both susceptiblo or resistalllLrice varieties ..lfueir numbersincreased with the increase of age of the plant and also on the resistant varieties more than. sueceptible ones~ 12- ~o bacterial spp. showedant~onistic reaction against E. aryza.e. These isolates wereidenti:fied as: Bacillus cerious var~ lD,ycoidss and the aecond sp, have two isolates which were identified as Bacillus sUbtilis • .B1ocer1ne,antibiotic, was isolated and identified frolll culture filtrate of Bacillus cerious var m,ycoidAlS and Myoosubtiline from culture filtrate of the two isolates of 12. subtililll. ’fhese compoundswere effective in decreasing the infection of rice plants with E~oryzae especially Bioceren. Also the crude filtrate of the obovementioned Bacilli Walileffective in controlling E~oryzae eapecially that of 12~cereus v ; lll,ycoidlS_ 13- Total free amino acids showedsignificant differences at the seedling stage between susceptible and resistant varieties. Higher amounts were noticed in susceptible varieties. Yabani 15 found in leaf of healthy resistant Araby variety. However these amounts increased greatly in the infected plants whethe~’ susceptible or resistant than healthy ones. Proline was fouhd in higher amounts in infeoted Giza 180 resistant rice variety while therionine. arginine and glutanine were found in higher amounts in both in fected Giza 180 (R) and Nahda (3) rice varieties. In this respect leucine + isoleucine and aspara- . tic acids were found in hi~;Aer amounts in infected Yabani 15 (3’ varie ty. 14- At tillering stage althou~l total free amino acids was equal for the two susceptD~le varieties, Yabani 15 and Nahda but general decrease in all amino acids except therionine + glutamine was noticed in both susceptible anllresistant varieties. Higher amounts of alanine, serine and glycine werb present in infected Nahda (3) rice variety. However the lowest.amounts of total amino acids were found in healthy Araby (R) variety. Although proline amount, were reduced in all varieties but it was noticed in higher amounts in infected Giza 180 (R) rice variety. 15- At the adult stage of growth general increase in all the amounts of total amino acids was noticed in both infected susceptible and resistant varieties except incase of alonine in Nahda(S), Giza l80(R) and Araby (R) rice varieties. AlSO, proline amounts increased in Giza 180 infected plants only and do,creased in all the other treatnents. As far leucine + isoleucine their amounts increased except that oftherionine + glutamine in case of Nahda healthy. ’plints. However,it could be noticed that the total amounts of free amino acids were higher in infected plants than in heal thy ones and the highest amounts were noticed in Yabani 15 susceptible variety. l6~ In four tested varieties, Araby and Giza 180 re ’lstant rice varieties and Nahdaand Yabani 15 susceptible ones, , total sugars increased by ageing of the plants whether infected or not. However, the total sugar’contents were higher in infected plants than heaJtby one. specially the SLlSCep tible ones at tillering and adult stages of growth. 11- Reducing sugars were generally higher in infected rice plants than heal thy ones speciaUy at tillering stage. However,a general decrease in the reducing sugar contents Wasnotioed by the increase in plant age in all tested varieties. 18~ Healthy su.soeptible rice varie ties showhigher amounts of suorose than the resistant ones. Infected susceptible varie ties contain higher amounts of sucrose than resistant ones. Howeversucrose contents decreased at tillering and adult stages in all tested varieties. Also 1:he same trend was noticed as regards glucose and galactose exce~t that.their amounts decreased in case of Araby (R) variety in infeoted plants than in uninfeoted ones at the seedling and adult stages only. 19- Fruotose is found inhigner peroentages in infected plants and in susceptible varieties than ~ninfected plants as well as resistant varieties in different stages of plant growth. There was signifioant difference in fr~otose amounts between infected and uninfeoted plants in oase of Giza 180 (R) rioe varie ty at the adu.lt..ztage~ 20- The oontents of mannose were higher in susceptiLle variety either infected or not than the resistant one specially at the seedling stage. This inorease was noticed in Yabani 15 (3) variety and at the tillering stage mile no ’signifioant differenoes were noticed in the adult stage. 21- The amounts of total phenols were higner in infected plants in all teBted varieties.’ Also their amounts were higher in resistant varieties than susceptible ones. It is olearly notioed that these amounts increased also by the inorease in plant age speoially in reBistant infeoted and uninfeoted plants • . 22- Resistant varieties contain higher amounts of free phenols than susoeptible ones specially •.t seedling and til1eming stages, whereas their amounts were almost similar exoept in oese Q~ Araby (R) infected plants. • 23- As for conjugated phenols their amounts were higher in all infected varieties than healthy ones speoially at tillering and adult stages. Also their amounts were higher in susceptible infected and lminfected plants than resistant varieties specially at seedling and adult stages, whereas the contrast was noticed at the tillering stage. 24- The highest amounts of 0 dihydroxyphenol were detected in infected and uninfected resistant varieties in all stages of the growth. As regards the tested susceptible varieties, the infected plants showed higher amounts of O. dihydroxyphenols than uninfected plants. It could be noticed also that it’s amounts decreased by ageing of the plants, speoially at the adult stage of growth. 25- Four organio acids, i.e. citric, malic, succinic and fUmarie acids were detected in rice varieties i.e. ~by and Giza 180, resistant varieties; Nahda and Yabani 15; susceptible -onea, 26- The infection with r. oryzae caused little decl~ase in citric aoid contents in seedling stage while in the tillering and adult stages it’s amounts increased oonsiderably speoially in resistant varieties. 27- The amounts of malic acid increased by infection except in case of Yebani 15 in seedling stage. These amount s decreased in infected plants in tillering stage except in case of Giza 180 resis tant varie ty. As for the adult stage malic acid amounts increased in infected plants except in Hahda susceptible rice variety. 28- The amounts of succinic and fumaric acids decreased in susceptible varieties due to infeotion, whereas contrast results were noticed as regards the resistant varieties in all stages of growth except Araby resistant variety in the tillering stage of growth. 29- The isolated races differed in there virulence and also in their contents of total free amino acids. Race I~7 w’hichhave the highest disease index (22) produced lC1Ner amounts of amino acids both in culture filtrate and mycelial mat, except asparatic, valine, phenylalanine and leuoine + isoleucine in culture filtrate whereas it produoed lower amounts of all amino acids in mycelial mat. In this respeot the secord race in virulence IB5 ahowed lower amounts of total free amino acids either in the filtrate or mycelial mat. The fifth race in virulence gave the highest amounts of amino acids whereas the least amol.uitswere obtained by race IB5 which ranks the second in it’s virulence, whereas the highest amounts j,a obtained by race I~21 which ranb the fourth in its virulence (16) both in the filtrate or mycelial mat. Thus it could be conoluded that there is no oorrelation between the virulenoe of the race and the amounts of free amino acids both in filtrate or myoelial mat• 30~ Also, results indicated that there is no correlation between the ra.ce virulence of l~or,y;zaeand the amounts ·of total and reducing sugars in both the culture filtrate or the mycelial mat, of each race. 31- As regards sucrose amounts, the h~hly pathogenic race - IA17(22) produced moderate amounts of it, while races IA(l21) (16), IB5(20) and IBi5 (15) differed in their virulence but produced low amounts of Blorose whereas race 1Fi(12) and IG2(10) the least virulent races pro’l(’ duced high amounts of sucrose. As before a reversble correlation ooeficient was obtained between ra.ces virulence and different sugar contents. 32- Nooorrelation was obtained between amino acids contents and. different contents of sugars and race virulence with Yabani 15 rice variety. :.n- The infection with the eight races ot l. or,y;zaeon Yabani 15; susceptible rioe variety, decreased the amounts of all organio acids, i.e. oitric, malio. auccini.o and tamaric aoids. Generaly no correlation was obtained between ra.ce virulence and all tested organic aoids. 34- Results showed clearly that there is no oorrelation between the race virulence end its ability of produc:U1g toxins. ,,5- Total, free and conjugatedphenols increased as a result of infection of the susceptible variety Iabani 15. As regards the interaction betweenrace virulence and phenolic compoundsa negative c~rrelation could b. noticed. |