Browsing by Author "Bedelu Theodros"

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    Characterization of two Nematodedestroying Fungi from Etillopia
    (1999-06) Bedelu Theodros; Abate Dawit (PhD)
    Under laboratory conditions, ART-l (LDso= 290 conidia/ml) was more efficient in destroying nematodes than ART-2 (LDso= 725 conidia/OIl), Investigation on the growth of MeloidogYlle incognita-infected tomatoes in the greenhouse showed that yield loss was highest in tomatoes treated with only k[, incognita (69.7%). Tomatoes treated with conidia of ART-lor ART·2 had lower losses: 44.5% for ART-l treated & 44% for ART-2 treated tomatoes. ART-2 required 3X the number of conidia of ART-l (180000 conidia/pot) to attain a nematode suppression effect similar to ART-I. Out of 3 solid media compared for their effects on the lateral growths of the isolates at room temperature, oatmeal agar (OA) gave the greatest colony diameters (6.3 cm for ART-l & 7.8 cm for ART-2). Maximal spore yields were also observed on this medium: ART·l, 4960 conidia/ml & ART-2, 31400 conidia/m!. A comparison of lateral growth, on medium A (MA), under different incubation temperatures (room temperature, 28°C, 32°C, & 37°C) showed that greatest colony diameters were attained at 28°C: 5 em & 5.7 cm for ART-l & ART-2 respectively. Broth of MA was found to be suitable for optimal mycelial biomass yield for both isolates (631 mg/IOO ml, ART·l; 755 mg/lOO ml, ART-2). However, ART-I, a slow grower on all solid media tested, gave a higher yit:;ld than ART~::! when grown in c~lej.n ID}ocr:tl :.;:tits·m€rll~~·! (G~S~l) broth (363 mg/lOO ml cr. 273 mg/IOO ml). Optimal mycelial biomass yield in MA broth was found to be in the pH range 4-5 for ART-2 (509·669 mgt 100 ml) & in the range 7·8 for ART-l (487-535 mg/IOO mI). ART·l & ART-2 produced extracellular proteases in CMS-2 broth. The proteases from both fungi had a temperature optimum of 50"C, & were optimally active in the alkaline range (7.5·8, ART-l & 7.5·9, ART- 2). ART-l produced more proteases (19 U/ml/hr) than ART-2 (14 U/ml/hr). ART-l proteases were more efficient in degrading nematodes than those of ART -2 by virtue of being produced in a larger quantity, suggesting that the difference in the nematode-destroying capabilities of ART-l & ART·2 was the result of the difference in the amount of proteases produced.