04469naa a2200205 a 450000100080000000500110000800800410001910000150006024501030007526000090017852037860018765000220397365000140399565300110400970000180402070000170403870000220405570000220407777301640409916554012009-01-15       2008    bl uuuu     u00u1 u    #d1 aFRANCO, D.  aCitrus variegated chlorosis damage assessment in six sweet orange cultivars in São Paulo, Brazil.  c2008  aThe citrus variegated chlorosis (CVC) is a bacterial disease very important in Brazilian citrus industry (Rossetti et al., 1997). It is caused by Xylella fastidiosa and affects the plant vegetative growth and fruit yield (Rossetti & De Negri, 1990 and Laranjeira & Pompeu Júnior, 2002). For disease control, the use of resistant or tolerant cultivars is highly recommended. Therefore, studies that evaluate these cultivars are very important (Laranjeira, 2006). From 1990 through 2007, 503 sweet orange cultivars were challenged against X. fasdiosa (Yamamoto et al., 2005a,b; Souza et al., 2005) and only one of them showed no symptoms (Stuchi et al., 2007). In this work we assess the CVC progression, severity and damage in six sweet orange [Citrus sinensis (L.) Osbeck] cultivars ('Sanguínea', 'Olivelands', 'Vaccaro Blood', 'Folha Murcha', 'São Miguel' and 'Finike'). Experimental works were carried out at the Citrus Experimental Station, Bebedouro, and São Paulo State, Brazil. The experimental design was randomized blocks, arranged in split-plots in time. One different rootstock was used for each block: 'Sunki' mandarin [Citrus sunki (Hayata) hort. ex Tanaka], 'Rangpur' lime (Citrus limonia Osbeck), and 'Cleópatra' mandarin (Citrus reshni hort. ex Tanaka) and 'Swingle' citrumelo [Citrus paradisi Macf x Poncirus trifoliata (L.) Raf]. The experimental unit was comprised of eighteen trees. Damage assessment was visually performed once a year using a 4-note scale, with all plants evaluated. The disease index was calculated by the number of evaluated trees and their ratings, for two years (2006 and 2007). CVC effects on plant development, yield and fruit quality of the six sweet orange cultivars were also evaluated by disease severity. Healthy plants and plants with more than 50% of the canopy with visual CVC symptoms were selected for this purpose in 2007 (eight years after planting). For this evaluation, experimental design was randomized blocks in a 6 x 2 factorial scheme (six cultivars and two infection levels), with four replicates and three trees per plot. Harvested fruits were classified into two size categories: adequate for juice extraction (diameter = 50 mm) and inadequate (&lt 50 mm). All fruits were analyzed for physical and chemical properties. Data was submitted to analysis of variance using the Fischer's Test, and the means were compared by the Tukey Test (P &lt 0.05). 'Folha Murcha' sweet orange had the lowest disease index, while 'São Miguel' and 'Vaccaro Blood' cultivars had the highest disease index and number of leaf symptoms. The canopy height of 'Finike', 'Folha Murcha' and 'Olivelands' sweet oranges was not reduced by CVC, suggesting greater disease tolerance. Fruit yield of affected trees was decreased in 32.71% for all cultivars. Fruit weight, height and diameter were always higher for healthy trees. Sweet orange cultivars presented different fruit soluble solids (SS), titratable acidity (TA) and ratio (SS/TA). Fruit chemical properties of 'Sanguínea', 'Vaccaro Blood' and 'Olivelands' sweet oranges were less affected by the disease. Sweet oranges showed some degrees of tolerance in studies by Laranjeira & Pompeu Júnior, 2002 and in the present work we observed a similar trend. The HLB symptoms are severe on sweet oranges but little is known about different levels of resistance within different varieties and germplasm accessions. Selection of plants is an efficient approach for genetic improvement and has been used since ancient times, especially in perennial crops such as citrus. Finding any 341 degree of tolerance against HLB within the sweet orange group would be significant improvement considering the actual mitigation effort to combat the disease. (Financial support: Fapesp 2004/16077-3).  aDoença de Planta  aVariedade  aCitros1 aSTUCHI, E. S.1 aSILVA, S. R.1 aMARTINS, A. B. G.1 aLARANJEIRA, F. F.  tIn: INTERNATIONAL RESEARCH CONFERENCE ON HUANGLONGBING, 2008, Orlando, Florida. Proceedings of the meeting... Orlando: Florida Citrus Mutual, 2008. p. 340-341.