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Abstract Baxley is one of the important cereal crops in the world. Helminthosporium diseases ale considered as most destructive diseases which etta.ck this crop •. In this respect spot blotch became one of the main cause,ls of yield reduction of baIley in Egypt specie,1ly in warm,. wet weather in coestal regions. The causal organism was isola.ted from different localities in Egypt., identified end the pathogenicity wa.s det e.rmined.. The host range and viability of the pathogen were studied together with the activities of pectolytiC, cellulolytic and.oxidative enzymes for both the paghogen and extracts of baxley plants. The relationship between resistance and chemical components of baIley plants i.e. aminO acidS, sugars and phenolic c0mpounds and the toxic effect of culture filtrates of the fungus were evaluated. The susceptibility and resistance of different bal:ley variet ies to the disease was studied. The effect of different fungicides on linear growth of the pathogen in l~boratory and in the greenhouse end the field was studied also. Results obtained could be summarized as follows: (1) spot blotch of barley in Egypt during seasons 1979-81 indicated that the disease was found in - 154 - coastal legions, Delta. and the Middle Governora.tes of Upper Egypt. The highest percentages of infection were observed at Kefr El-Sheikh, Alexandria, De.m.iett a and deer eased gradually south-waI ds. (2) Twelve isola.t es of !!.el~inthosporj.-ill!! sat ivum were isolated from diseased leaves showing typica.l spot blotch sympt ems. The pathogenicity test revee.led thet the se i sola.t es vexied great 1y in t heir pathogenicity together with differences in morphologica.l characteristics and isolate No.4 was the most virulent isolate, whezeas, isolate No. 12 was the least virulent one. (3) Results of the host range of Hel~intho~ori~~ sativum indicated t hat the fungus has a wide host lange in EgypL, as it was found to infect Avena. futua, Cynodon dactyl~L .~~ Lotundus, Echinochloa colonum, ~chi~2.h.1:2J!’£!’1!§.&slli, Horde~ vulgare, Loliu@ temule~~, ~olium ~erena, Oryza sa.t iVJ!, Polypogen monspelienais, Set ax ia. viridi~, Sorghum v~lgar~, Triticum vulgare and ~ maize. (4) The severity of the fungus increased gradually and zeached the maximum after 1 month, then gxadually decreased by ageing t i~l the 18th month. - 155 - (5) The highest activities of polygalacturonase (PG), Cellulolytio (ex) and pectinmethylestrese (PME) enzymes were found in the fungal filtra.tes of isola.te No.4 (the most viru1ent)~whereas the lowest activities were in isolate No. 12 filtrate (the less virulent). (6) As regards the effect of fungicides on enzymes activities studies indicated that PG and ex activities were reduced with the increase in the concentration of the tested fungicides specially in case of l?lant avax and ba.yleton, whe reas , Wolfen-thiram and Dithane M22 had little effect on PG and ex enzymes activities. (7) polyphenoloxidase, Pero~ida.se, Catalase and Ascorbic acid oxidase activities were relativ&ly higher in the mycelial matrix than in the filtrate of each of the tested isolates. Also these activities were higher in the highly pathogenic isOlates (isolate No.4) than the least pathogenic one (isolate No. 12). These activities incYeased alsO by increasing the incubation periods in both mycelial matYix and fungal filtrate. (8) Adult plants showed high levels of polyphenol- !xidase activity as compared with the seedlings. - 156 - In this .respect infection with H. !!.ativJ!!!lcaused gr adual, Lncr ease in enzyme act ivity specially in the .resistant varieties specie.llY in the seedling stage. (9) A~ult plants and seedlings of resistant vaxieties exhibited higher levels of peroxidase a.ctivity e.s compared with the susceptible cnes. In this regar d the Lncr ease of per 0:: idase eC t i vi t y was slight in susceptible varieties and higher in resistant ones specially in adult plants. (10) Catalase activity was higher in seedling and adult leaves of the tested varieties specially in resistant ones. Also, infection with the pathogen exhibited higher catalase activity in the resistant cultivars than in susceptible ones. (11) Healthy leaves from seedlings and a.dult plants of the resistant varieties exhibited higher activity of ascorbic acid oxidase enzyme then that in the suscept i ble onea , Inoculat i on wi t h g. .~ti.Y”..’!m result ad an increase in aScor bic acid oxide.se enzyme activity speciallY in the leaves of resistant varieties than in that of susceptible ones and in adult plants than 1n seedling stage. - 157 - (12) Concerning phenol Lc compounds, reSI.11 t s indicated that total, free, conjugated and ortho-dihydroxyphenols were fCQlld in higher amounts in the resistant varieties than in susceptible ones. However, it was found clearly that phenolic compounds eccumulat ed fast er in resist ant var ieties then in susceptible ones as a result of infection end also by long incubation period spec ially aft ex 10 days fr om inOcLllat ion and in re$istent plants. (13) Total and reducing sugars contents were higher in leaves of susceptible varieties than in the resist ant ones. Adult plant s conta.ined higher amounts of total and reducing sugars then the seedlings. Inoculation with li. ~~~Jv~ caused pronounced decrease in both total and reducing sugars in seedlings or adult plants of susceptible vaxieties, whereas, inoculation induced an increase in the resistant ones. (14) Paper chIomatogrsphic analysis showed the presence of Maltose, Sucrose, Glucose, Ga~actose and Fr ac t 0 se in inoculat e4 and uninoc uLat ed leaves of all the tested varieties in both seedlings and adult plants. However, no ·clear correlation was found between resistance or susceptibi1ity of the tested barley varieties and any of the above-mentioned sugasSt (15) Concernj~g of total free amino acids, their content increased as a result of inoculation with Helm1~~hosporium sati~ in both resistant and susceptible vaxieties in the seedlings as well as in adult plents. In this regard, susceptible varieties contained higher levels of total free amino acids than the resist ant ones in both Eeedling end adult plant stages. However, e.dult plants contained higher amounts of amino acids than seedlings. (16) Qualitative analysis indicated the presence of seventeen amino a.cids namely Cystine, Lycine. Histidine, Arginine, Aspazatic acid, Glycine, Serine, Glutamic, Therionine, Alanine, Proline, Tyrosine, Methionine, Valine, phenylalanine, Leucine and Iso-leucine in seedlings as well as adult plents of resistant and susceptible varieties. (17) The amounts of total amine acids inczeased as 8 xesult of infection in both the susceptible and zesistent varieties as compared with the uninoculated contrcl. (18) ’rhe quantities of carta.in amino acids as Lycine, Histidine and Arginine were higher in the susceptible vazieties then resistant ones, wheree.s the contrast we.s noticed as regards Tyrosine end phenylalanine. On the other hend, Proline appeeIed with higher concentrations in the susceptible vezieties than the resistant ones in both seedlings and adult stages and its concentrations were higher in healthy plants as compared with inocule.t ed ones. (19) In response to inoculation with Ii· s§;.liV:~.mTylcsine and Phenylalanine quantities increased in the resistant vaIieties and decreased in the susceptible ones. In this respect, Methionine and Valine increased as a result of infection in resistant varieties in the seedlings. The highest amoants of Lyeine, Histidine and Arginine were obtained in the infected susceptible varieties. As for, the other amino acids no general trend was noticed in either resistant 01 susceptible varieties. (20) The elude culture filtrate of two isolates of H-. sativum (one virulent and the other avirulent) .--,-.””.......--._’---- induced inhibitory effect on the percentage of seed germineti(n, lengths of cole~ptile and roots on ell - leU •• the testlj-d varieties.. HpweveI, the high concent- Iation of crude culture filtrate W8.S the most effective in this I espect. This effect decreased proporticne.llY with the dilution of crude filtrate. In this regard the most effective flitrete was take:n from 30 daYS eLd cultures end was that of the most virulent isolate No.4. (21) One to:x:_c fraction waS isola.ted in crystaline f cr m (rod cz:,stals), according to the method adopted by Lindberg (1971), and Turner (1971) and was identified as Helminthospcral. In this regard the virulent iselete No.4 produced 4.633 go/liter of eultuI€ medium of toxin; while the less virulent isola.te NO. 12 p:r:oduced 2.461 g./liter of cut t ure medium. The toxin gave simileI symptoms on seedlings and adult plants and effects as mentioned before. However, the phytoxic effect of the toxin decreased proportionallY by decresing its concentration. (22) Sczeening of 37 selected baxley varieties under greenhouse conditions in the seedlings, indicated that 16 vexieties weze highly resistant and 5 varieties were moderately susceptible, while !6 vazieties were susceptible. (n the other hand, under field conditions in adult stage results indicated that from 44 varieties, 19 were resistant, 4 modeIately susceptible, 13 susceptible and 8 were very susceptible. (23) As regards the correla.tion between the beha.vioUI of 45 v8xieties in both seedling and adult ,stages, it was fClxod that these vaIieties could be put in two gr~ups as follows: A- Thefrist group in which there was no effect of plant age on the vaxietel resistance or susceptibility as follows: 1. Seven vBxieties were resistent in both seedlings and adult stages. 2. Fourteen varieties were susceptible in both seedlings and adult plants. B- The second group in which there waS an important effect of plant age on the varietal resistance or susceptibility as folloWS: 1. Eleven varieties showed increasing resistance with age. 2. Six varieties were susceptible in the seedling stage end became resistant with age.3. Seven varieties showed increasing susceptibility with age. (24) Soreening fungicides !a vitro showed that the tested fungicides varied in their effect on fungal gIowtn. However, all the fungicides except Bevistin and Spergon almost stopped the linear growth of ~. ~~tivumat relatively low eoncentr a.tions of 100 ppm. This effect in •. creased with the increase in concentrations. The fungicides Wolfen thiram, Dexon, Plsntevax ~d Dithane M completely inhibited the fungal growth at the concentrations of 50, 200, 400 and 400 ppm respectively. (25) Using these fungicides as seed dressings under greenhOuse increased the percentage of seed germination, the number of ears per pot, the weight of grains in gm per pot and 100 grains weight. On the other hand, the severity of infection was xeduced as the fungicides were applied. However, wo].fsn *hiram, Dexon and Spergon were super ior in this respect while Vitavax and Brassteol followed the afolementioned fungicides in tneir effect, whereaS, Bavistin was almost uneffective. (26) Using these fungicides as foliage spraY under greenhOuse conditions (after artificial infection by splaying with a spore suspension at the concentration of 80,ouO - 100,000 conidia/ml. of Belminthoephorium sativum), the severity of infection was reduced while the weight of grains per pot and $be 100 gxains weight significantly increased Plantevax end Dithane M.45 (Mancozeb) were • supezior in this respect while Dlthane M22 (Mane~ and Bayleton followed them. (27) Using these fungicides as seed dressings under field conditions showed tha,t all the tested fungicides reduced the severity of infection and significantly increased the yield and weight of 1000 grains. In this respect, Wolten thiram, Dero.n and Vitavax were superior to the other tested fungir cides. Un the other ~aad, by using fungicides for oliage spray under field conditions after artiicial infection by spraYing spore suspension of elmlnthos Ottum Bativum, the severity of infection was reduced as the fungicides were applied whereas significant increase in the yield for each plot and the weight of 1000 grains was noticed. Dithane M45 end Plentavax were super io.r in this respect to the other tested fungicides. |