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Abstract SUMMARY The present invcsligation was planned 10 stndy Some faetors affecting leaf spols di<ease of Iaba bean CJlnsed by Ro.1ntis fllbae Sardo Slemphylillln botrYOSllIII Wall. and Alfcl’Ilaria altcrllata (Fr.) Keissler . The results could be summarized as follows: (1) Isolalion and palhogenieity tests indicate that BolrY1is fabae Sard., Slemphylium bofryosum Wall. and Allern3l’ia allernala (Fr.) Ke/ssl er are the main causals of Ieaf spots disease of Iaba bean lVicia faba I, Also, D. fabae was more virulent than Stem. hoh’yosum and Alt. alte”naL, and the combination of the three fungi was rnoro virulent than any of the three fungi alone. (2) DotTyfis fabae gave its best rate of growth on leaf exh”act oCCaba bean agar medium, while the lowest rate of gl”owth was on Brown’s medium whereas Slem. bolryosmn grew well on Czapelc’s medium and ils Iowest rata of gl”Owth was on Brown’s medium • Mt. allemala resembled Jl. fabae in ils gl”Owlh in the different medln , (3) Leaf cxudates of healthy Ieaves of Gize 402 and Equadolce cvs, which are morc susceptible to Il, fallae, cnhanced Spore germination and the rate oCgrowth of B. fabae in vilro as eompared with the ””,udales of Giza 3 and Giza 2 cvs, the less Susceptibles . (4) Faba bean cultivars diffel”Cd in their reaction to D. fabae . The tested eultivars were as follows: Giza 2 was mode ra le Suscepliblc, Giza 402 and Eqnadolce were susceptible and Giza 3 was moderate resistant. (5) TI,e growlh of II. fabae was completely hdJibited when Bavistin 50 and Topsin M70 were added 10 polala dexl rose agar medium at the rate 10 ppm of their 102 active ingredients whereas the fungicide Dithane M45 inhibited mycelial growth at 50 ppm. Also, thc growth of Stcm. botrvoSlllll was complctely inhibited with the concentration 200 ppm for the fungicides Plantvax 20 Ec, Bavistin 50 and Dithane M45 . \Vhcrcas, Dithano M 45 and Plantvax 20 Ec checked the growth of Alt. alteinata at 100 and 200 ppm. (6) Under greenhouse conditions all the tested fungicides Le Bavistin 50, Topsin 1\170, Plantvax 20 Ee and Dithann M 45 were effective in reducing the severity of leaf spots infection with n. labae . Dithane 1\145 with concentrations 375, 250 and 125 I 100 L resulted in the least infection with R. fabac after 60 days from inoculation on the two tested cultivars Giza 2 and Giza 402 • In this respect, Plantvax 20 Ee followed by Topsin 1\1 70 were more effective than llavistin 50 • Also, increasing the tested concentrations of all fungicides was in concomitant with the reduction in percentage of spotted a reas . (7) Plant length, No. of leaves, Fresh and dry weight of leaves were affected with inoculation with n. fabae and Giza 402 cv, was the most effected one. Also, the effcct of different fungicides ou plant length, No. of leaves and fresh and dry weight of leaves differed according to the sensitivity of cultivars to the concentration of fungicides and their effectiveness against B. fabae • (8) The heaHhy leaves of both cuhivars i.e Giza 402 and Giza 2 conteued nore tutal and reducing sugars than the diseased one • Spraying with fungicides exhibitcd all illCI’CHSCin tutal mid J’cdudng slIgm’s in healthy plan’s cOlllpat’cd with infectcd plants espccially in the susceptible cultlver Giza 402 • (9) Frec and total phenols were produced and accumulated at a faster rate in Giza 2 (moderate susceptible) than that of Giza 402 (susceptible) • As regards the conjugated phenols, an apposite trend in both tested cvs. was 1I0ticed • Spraying 103 with fungicides was not effective in increasing free and total phenols compared with healthy leaves while the contrast was noticed in case of diseased leaves except in case of Topsin 1\170 (150 g I 100 L) and Plantvax 20 Ec (100 mil 100 L) for Giza 2 and Dithane M 45 (250 I 100 L) and Topsin M 70 (50 g I 100 L) for Giza 402 • (10) Total free amino acids were higher in diseased leaves than in healthy ones. Also, the susceptible cultivar Giza 402 contained higher levels of total free amino acids than the moderate susceptible cv. Giza 2 • As regards, the effect of spraying with fungicidcs, total free amino acids was differed with the different treatments . (11) In grccnh ouse experiments, foliar nutrients Foliar and FoIiaI’x (modified) were the best in reducing disease severity. (12) Number of leaves and fresh and dry weight were lower in the plants that inoculated with I1. fahae compared with uninoculated ones. In this respect, spraying with foliar nutrients exhibited an increase in the mean number of leaves and dry weight for all nutrients whereas, the length of plants was not affected except in case of spraying with Foliar x (modified) for Giza 3 cv. only. (13) Spraying with foliar nutrients increased leaves content of total and reducing sugars compared with unsprayed plants. (14) Also, spraying with foliar nutrients showed an increase in total and free phenols especially in case of spraying with X-Garden for Giza 3, Foliatrin or Foliar x (modified) 1’01” Giza 402 and Foliatrin fur Equadolce cv. compared with unsprayed plants. (15) Spraying with Foliar x (modified) showed an Increase in the total free amino acids for Giza 2, Giza 3 and Giza 402 whereas spraying with any of the other nutrients exhibited a decrease ill them. (16) Healthy leaves content of N, P and K was higher than that inoculated 104 with H. fahae . Spraying with foliar nutrients exhibited an increase in the leaves content of nitrogen especially in case of spraying with Foliar x (modified) and Foliar x for Giza 2 and Equado1ce cvs, respectively . On the other hand, spraying with foliar nutrients did not give a significant increase in leaves content of P and K • (17) In field experiments, all fungicides under investigation decreased significantly infection with leaf spot diseases than untreated plants. Dithane M 45 at the rate of 2.5% was the best of aU ill case of Giza 402 ill the first season only and for Giza 3 cv in the two seasons. ”’hel”eas, Bavistin 50 at the rate of 0.1% was the best in case of Giza 2 in the flrst season and Giza 402 in the second season. Also, Topsin 1\1 70 at the rate of 0.1% was the best in the second season in case of Giza 2 and Giza 3 cvs.. These fungicides also raised the yield of plants and the weight of 100 seeds. (18) Severity of infection with leaf spot diseases increased with the increasing of sowing density. Less infection and good yield was obtained when sowing one seed per hill at the two sides of the ridge at distance of 25 cm between bills. (19) Also, in field experiments, addition of calcium superphosphate (P) and potassium sulphate (K) generally reduced the percentage of infection than untreated plants. Whereas, the addition of ammonium sulphate in the low level resulted in a decrease in the percentage of infection compared with the high level (NJ • The decrease in the disease severity coincided with an increase in the yield per plot and the weight of 100 seeds. |