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Abstract -101- Summary The relationship between the two soil b~ne fungi fW!!ar~~ oxysP.9Y}DJlf. sp. fab.- Yu and :rang, and Cephalosporium acremonium Corda as wilt pathogens to broad bean ( Vicia Ieba L.), and grain sorghum (Sorghum b1color Moench), respectively was studied. The results -could be summarized as fo1lows:- I - Broad bean: 1) The healthy and diseased roots, hypocot1l, and ep1- cotyl at different ages grown in tubes and pots were histologically studied. 2) In regard to diseased plants ( in dishes), penetration of the root, hypocotyl and base of epicotyl occurred directly through the epidermal cells,in between two epidermal cells, in addition, penetration also occurred through the ~ot hairs. 3) After penetration ( in tubes) hyphae developed intercellularly and intracellularly witbin tbe cortex of the root until reacbing the x11 •• vessela, which were seen plugged. In older agee, cortical • -102- cells began to collapse, and the percentage of plugged xylem vessels increased in the successive older ages. There was a decrease in diameters af cortex, vascular cylinder, and pith , and in number and diameter of xylem v •••• ls in diseased roots than in healthY ones due to retardation of the secondary growth in tbe,forller. 4) In pota, the collapse of cells successivel1 increased according to the age of the root, and finally, there was a general collapse ,and xylem vessels and adjacent oells were plugged. In contrast to the diseased root grown ,in tube, percentage of plugged xylem vessels of the diseased ropt grown in pots decreased in the successive older ages. 5) The effect of the pathogen wa’ prominent on roots grown in tubes than on those grown in pot •• 6) D,iseased lateral roots in tub •• or pots •• re ••• - ller, a’ expected, than the healtbY on•• , glob~ lar bodies were seen in the cortical cella of the former. 7) Hypocotyl of diseased plant was _ller in di.etel’ than in the healthy on., xyl ••••••• 1. nuab.r and -103- diameter were also smaller and their plugging was pronounced. The outer layers of the cortex were collapsed. 8) In diseaoed epicotyls of plants grown in tubes, hyph~e were not detected , but the effect of the pathogen waS greater than in the root system, there was a severe collapse in the cortex, and a great decrease in number and diameter of xylem vessels which were almost plugged. 9) In epicotyJs of older ages grown in pots, tbe collapse of cells increased, and the percentage of plugging decreased due to the increase in secondary xy~em vessels which was retarded in diseased plants ~han in the healthy ones. II- -Gr-a-in--s-or-gh-u-m-: 10) The diseased radiole root grown in tube resembled the healthy one in structure , penetrat10n occurred in between two 81>1d81’11al c8118 by a hypha with nallen tip, 1:1 _--r-------------------------------------: -104- 11) At older ages, hyphae aggregated in the cortez of the root. then penetrated the endoder.mis causing darken~ng of its cells, and extended to the YaSC~ ular cylinder especially the xy1 •• v•••• ls• No plugging of xylem vessels -.& observea. At th. age of 12 days , the root b.gan to deteriorate. 12) .In the mesocotyl of diseased plant- grown in tube • the disease deYeloped atml1ar17 to that in the root, except the preseence at a dark material 1p the intercellular space. ot tbe oortex, and plugging of xyl- vessels was pronounoed. 13) In colt!Pptile and leat blades, there were longitudinal streaks due to the (lark.ning ot the •••- eular bundles, and bJpbae were .eeD b.twe.n the eoleoptile and the outer leaf and among the inner. |