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The effects of the 'Cleopatra' mandarin and 'Swingle' citrumelo rootstocks and time of harvest on the quality of cold-stored (13°C and 90% R.H.) 'Ruby Red' and 'Star Ruby' grapefruit grown under the tropical conditions prevalent in Ceará state, Brazil, were evaluated. Fruit quality was assessed by mass loss and peel color, the percentage of juice, soluble solids, titratable acidity, pH, maturity index, and ascorbic acid content. The results suggested that 'Ruby Red' and 'Star Ruby' grapefruit presented similar amounts of soluble solids, pH, titratable acidity and ascorbic acid levels at harvest, and the trends over the course of storage followed similar patterns for both cultivars, regardless of rootstock. The influence of scion-rootstock combination on the studied variables was dependent on the time of harvest. The peel color of 'Ruby Red' grafted on 'Swingle' citrumelo is more vivid and redder when harvested in October than when harvested in August. 'Ruby Red' and 'Star Ruby' grapefruit harvested in October are sweeter, less acidic, juicier, and richer in ascorbic acid than those harvested in August. 'Cleopatra' mandarin rootstock might favor ascorbic acid levels at harvest, but the fruit may lose more weight during storage. [ABSTRACT FROM AUTHOR]

Abstract: Asiatic citrus canker, caused by the bacterial species Xanthomonas axonopodis pv. citri (Xac A), has had a detrimental impact on citrus production in various regions of the world. It has been suggested, based on reported field observations and other anecdotal evidence, that some citrus relatives, e.g. kumquats, have higher levels of tolerance to Xac A compared to commercial varieties. However, this has not been confirmed with rigorous scientific evidence. In this study, the growth rate of Xac A in challenged kumquat leaves was significantly hindered after 4 days of infection compared to that in susceptible grapefruit leaves. Cell death was observed in kumquat leaves however, typical symptoms of a hypersensitive response (HR) were not apparent until 3–4 days post-inoculation. Abscission of the leaves occured 5–7 days after infection, depending on the age of the leaf. The HR was accompanied by differential gene expression: two suppression subtractive cDNA libraries were constructed using Nagami kumquat mRNA to identify genes that were differentially expressed due to infection. A number of cDNA clones were randomly selected for sequencing. Homologues to components such as transcription factors, receptors and defense genes known to be involved in plant–pathogen interactions in general and plant cell death were identified. [Copyright &y& Elsevier]