Resistance to Xylella fastidiosa was evaluated in 264 hybrids of crosses between Murcott tangor (Citrus reticulata × Citrus sinensis) and Pera sweet orange (C. sinensis) under field conditions. Uninfected hybrids were grafted with buds collected from Pera sweet orange plants infected with X. fastidiosa, forming a plant with two scions (i.e., hybrid branches and Pera sweet orange branches). From these plants, we chose 10 genotypes with three biological replicates. We evaluated gene expression, bacterial multiplication, and citrus variegated chlorosis (CVC) symptom development in both scions. X. fastidiosa was not detected in most hybrid scions and none showed disease symptoms. In contrast, all Pera sweet orange scions were infected with X. fastidiosa and expressed symptoms of CVC. We quantified the expression of 12 defense-related genes by qPCR comparing resistant to susceptible scions. We suggest that some of these genes are involved in resistance of the hybrids to X. fastidiosa, since their expression was significantly higher in the resistant hybrid scions than in tolerant hybrids and scions originated from CVC symptomatic Pera sweet orange buds. However, we note that these data should be interpreted carefully, as the plant genotypes tested are related but necessarily distinct (hybrids of C. reticulata and C. sinensis, in relation to a C. sinensis control). A principal component analysis revealed a relationship between the expression of these genes and hybrid scions, and between scions that originated from infected buds and the presence of the bacteria and plant symptoms. Multiyear field trials are necessary to develop plant resistance to X. fastidiosa. While the experimental design used here had limitations, it allowed us to identify a set of genes potentially involved in Citrus sp. resistance to this pathogen. Future work on the role of these genes in plant defenses to X. fastidiosa infection is necessary to confirm their importance in the displayed resistance phenotype.
In Brazil new varieties of citrus were selected along the years, but none sensory analysis is usually made to verify the acceptance as one of the bottleneck for fresh citrus juice industry and before the commercial release. We have evaluated the response of consumers (n=62) for eight new hybrids of the crossing between sweet orange and mandarin in five sensory attributes and used analysis of variance Tukey's procedure (HSD) and internal preference mapping for the data processing. The results were compared in relation to their standard physical-chemical characteristics and with commercial varieties: Murcott tangor (Citrus sinensis (L.) Osbeck x Citrus reticulata Blanco), Pera sweet orange (Citrus sinensis (L.) Osbeck, Cravo mandarin (Citrus reticulata Blanco). Hybrids TM x LP 222 and TC x LP 5 are candidates to become variety and TM x LP 94 was chosen for new sensory analysis. Flavor featured as the most important parameter for orange juice and some hybrids with adequate physical-chemical parameters presented low acceptance, while others with inadequate parameters showed good acceptability, what suggests a new way to fruit selection.
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