03030naa a2200253 a 450000100080000000500110000800800410001910000180006024500600007826000090013852022730014765000100242065000220243065000160245265300110246870000170247970000250249670000150252170000200253670000220255670000190257870000190259777301600261616553982009-01-15       2008    bl uuuu     u00u1 u    #d1 aSTUCHI, E. S.  aNavelina ISA 315 sweet orangeba CVC tolerant cultivar.  c2008  aThe citrus variegated chlorosis (CVC), caused by Xylella fastidiosa subp. pauca, is a serious disease in Brazil. The use of resistant cultivars is highly recommended to allow a long-term coexistence with the disease. From 1990 through 2007, 503 sweet orange cultivars were challenged against X. fasdiosa (Yamamoto et al., 2005; Souza et al., 2005). The Navelina ISA 315 cultivar - a clone recovered by in vitro culture of undeveloped ovules - was introduced from Italy for CVC resistance studies, and showed to be infected by cachexia during indexing procedures. Plants were established in two field blocks in 2000 (block 1) and 2001 (block 2) with a total of three and eight trees. One and four plants were inoculated by approach grafting of CVC infected nursery trees, respectively. Inoculation was performed in the field nine to eleven months after planting. Nursery trees of the cultivar were inoculated with bacterial suspension in 2006 and 2007. Twenty sweet orange trees showing severe symptoms of CVC were topworked with Navelina ISA 315 with a total of 248 buds grafted in 2007. Isolation of the bacteria infecting the original field trees and the topworked ones was performed. From 2000 through 2007, the presence of typical symptoms of the disease in the trees was evaluated visually twice a year. PCR tests using specific primers for X. fastidiosa were conducted for all trees in the two blocks and for the nursery and the topworked ones. None of the trees challenged showed symptoms despite the positive PCR results and bacteria recovering from the topworked trees (Stuchi et al., 2007). In February 2008, 69/218 topworked branches showed symptoms. However, the eleven trees in field showed no leaf and fruit symptoms. The behavior of Navelina ISA 315 could be explained by a somaclonal variation induced the tolerance to CVC or by the influence of Cachexia on CVC symptoms expression and by some endophytic as Curtobacterium flaccumfaciens colonizing the cultivar and inhibit the development of X.fastidiosa as reported previously (Araújo et al., 2002; Lacava et al. (2004). The same rationale is being considered now against HLB and 553 sweet oranges available in two Brazilian germplasm collections will challenged in field and screenhouse conditions.  aClone  aDoença de Planta  aGermoplasma  aCitros1 aSILVA, S. R.1 aCOLETTA-FILHO, H. D.1 aFRANCO, D.1 aCARVALHO, S. A.1 aSEMPIONATO, O. R.1 aDONADIO, L. C.1 aALVES, K. C. S  tIn: INTERNATIONAL RESEARCH CONFERENCE ON HUANGLONGBING, 2008, Orlando, Florida. Proceedings of the meeting... Orlando: Florida Citrus Mutual, 2008. p. 337.