2758 Journal of Applied Sciences Research, 8(5): 2758-2765, 2012 ISSN 1819-544X This is a refereed journal and all articles are professionally screened and reviewed ORIGINAL ARTICLES Corresponding Author: El Said S. Hegazi, Pomology Department, Faculty of Agriculture, Cairo University, Giza, Egypt. Resistance of Some Olive Cultivars to Verticillium Wilt El Said S. Hegazi, Ayman A. Hegazi and Abdou M. Abd Allatif Pomology Department, Faculty of Agriculture, Cairo University, Giza, Egypt ABSTRACT The current study was conducted on twelve olive cvs. to investigate the resistance to Verticillium wilt a disease caused by Verticillium dahlia. One-year-old olive transplants were inoculated at green house with NET- 5 isolate of V. dahliae during the period of October 2011 to March 2012. Resistance was evaluated by assessing symptom severity using (0 – 5) rating scale and the percentage of dead plants. Cultivars were classified into a defined category. Chlorosis was the most common disease symptoms appeared on the infected olive transplants, the chlorosis severity was determined in all the studied cultivars. Dolce cv. recorded the highest percentage of defoliation, while Picual cv. recorded the lowest percentage. The percentage of disease incidence recorded the highest percentage (83.33%) in Dolce cv, while Cairo 7 recorded the lowest percentage (27.78). Disease severity ranged from (2.50 to 0.48). Dolce cv. recorded the highest disease severity (2.50) followed by Eggizi and Coratina cvs. (1.43 and 1.07, respectively), while Frantoio and Cairo 7 cvs. recorded the lowest values (0.48 and 0.56, respectively). The percentage of dead plants ranged from (0 to 12.50%). Dolce cv. recorded the highest percentage of dead plants (12.50%) followed by Eggizi cv. (10.00%), while Frantoio, Arbequina, Verdal and Cairo 7 recorded the lowest. Key words: Olive- Verticillium wilt - V. dahliae – Disease resistance. Introduction Incidence of verticillium wilt disease in olive trees is caused by Verticillium dalhiae Kleb. is a widespread disease, wherever this crop is grown (Sesli et al., 2010). Verticillium wilt disease considered as a serious problem in the majority of olive growing areas (Pagg and Brady, 2002). At present, control is based essentially on preventive methods such as the use of pathogen-free plants and soil when planting new olive orchards. Chemicals are not effective (Biris and Thanassoulopoulos, 1980). Early in (1971) Hartmann et al., in field studies to evaluate the degree of Verticillium wilt resistance in some olive rootstocks, they reported that trees grafting on Oblonga cv. remained free of symptoms, while 20 to 100 % of trees grafted on other rootstocks had the highest percentage of dead plants recorded for plants grafted on Olea ferruginea, while the lowest percentage was recorded for Oblonga (0%) and Sevillano (20%). Studies showed that the olive cvs. Frantoio, Coratina, Frangivento, Oblonga and Kalamon have interesting resistance properties (Wilhelm and Taylor, 1965; Hartmann et al., 1971; Schnathorst and Sibbett, 1971; Cirulli and Montemur-ro, 1976; Tjamos et al., 1991; Lopez-Escudero et al., 2004), while Ascolana, Cellina, Leccino, Manzanillo, Chemlali, Konservolia, Mission and Picual cvs. are susceptible (Wilhelm and Taylor, 1965; Cirulli and Montemurro, 1976; Tjamos., 1981; Wilhelm, 1981; Lopez-Escudero et al., 2004). According to Lopez-Escudero et al., (2004) disease symptoms depending on the degree of resistance, chlorosis was associated with the cultivars showing certain level of resistance, while defoliation occurred in the susceptible cultivars such as Picual and Cobrancosa cvs. Also, it has been determined susceptibility of some economically important olive cvs. and clones to V. dahliae. The severity of the disease has varied between 35.40 and 100% in the tested cultivars. The best results have been obtained from Gemlik cv. with the values of 35.40 - 36.25% (Erten and Yildiz, 2011). According to Cirulli et al., (2008) Frantoio cv. showed the least external symptoms (0.4). whlie, Coratina and Leccino cvs. showed the highest values of external symptoms Sesli et al., (2010) reported that a sudden wilt was observed in the susceptible cultivars, the percentage of dead plants ranged from 100% in Manzanillo, Edremit and Domat cvs. to 20% in Gernlik 2. According to Lopez-Escudero et al., (2004) percentage of dead plants differed according to cultivars and the pathogen isolates. The defoliating isolate of V. dahliae caused 70-100% dead plants in 13 of the 23 examined cultivars; the percentage of dead plants (PDP) reached 100% in olive cvs. Hendeno, Picudo, Manzanillo Sevilla and Arbequina, while Oblonga recorded 14.4%. On the other hand, the non defoliating