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ABSTRACTThe yield and the composition of the peel essential oils (EO) of six new citrus hybrids obtained from the crosses between Murcott tangor—TM [Citrus reticulata Blanco x Citrus sinensis (L.) Osbeck] and Pera sweet orange—LP [C. Sinensis (L.) Osbeck] was evaluated for the first time. The EO yield of the citrus varied from 0.34% to 0.59%. The hybrids that presented higher EO yield per hectare were TMXLP44 (36 L ha−1) and TMXLP294 (21 L ha−1). The majority compound in all samples was the limonene (>80%). Linalool presented the second highest concentration in the samples, being the sample TMXLP294 the one that presented the highest content of this compound (>13%). The principal components analysis revealed that TMXLP44 is the sample that more differs from the parents, whereas TMXLP372 and TMXLP294 are more similar to their parents Murcott tangor and Pera sweet orange, respectively.

Reported in Brazil since the 1930’s, citrus leprosis, caused mainly by citrus leprosis virus C, has been a major concern for the national sweet orange production. In recent years, the disease has spread to several other countries and it is now considered a worldwide threat. The occurrence of the disease has been studied almost exclusively in sweet oranges because other citrus genotypes are of secondary relevance in Brazil and in some other American countries where it occurs. Here we report 12 resistant citrus genotypes among 160 accessions evaluated. After 90 days of the infestation with viruliferous mites, asymptomatic genotypes were observed in sour orange, lemon, grapefruit, mandarins, tangelo, and tangor groups. The results revealed promising genotypes resistant to the disease, which can be incorporated in citrus breeding programs aiming to obtain varietal resistance, and confirmed the susceptibility of many citrus genotypes to CiLV-C. This assay ratify the already reported uneven level of susceptibility within the citrus group.

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Abstract: The progeny of 87 BC1 hybrids of ‘Murcott’ tangor and ‘Pêra’ sweet orange, genotyped with fluorescent amplified fragment length polymorphism (fAFLP) markers, was used for the construction of genetic maps for both citrus varieties. Mapping strategies, considering the progeny as a result of backcrossing and cross-pollination, were exploited in Mapmaker 2.0 (LOD score ≥ 3.0 and 9 ≤ 0.40) and JoinMap 3.0 software (LOD score ≥ 3.0 and 9 ≤ 0.25), respectively. Genetic map distances (in cM) between the linked fAFLPs were estimated, in both packages, by the Kosambi’s function. Maps of both parents were constructed in Mapmaker with 121 of the 202 fAFLP markers showing 1:1 Mendelian segregation rates (’Murcott’ map: 65 fAFLPs, average distance between them 29.5 cM, divided into 9 linkage groups (LGs), total size 1651.47 cM; ’Pêra’ map: 55 fAFLPs, average distance between them 31.9 cM, divided into 5 LGs, total size 1596.2 cM). The second ’Murcott’ map, constructed through linkage analysis of 347 fAFLP markers with 3:1 or 1:1 segregation rates by using JoinMap, resulted in the linkage of 227 markers with an average distance of 4.25 cM among them, divided into 9 LGs of 845 cM. fAFLP loci showing distorted segregation and/or clustered were observed in different LGs of the maps generated by all the software. The use of the ’Murcott’ tangor and ’Pêra’ sweet orange genetic maps in research on identification of citrus QRLs (quantitative resistance loci) toXylella fastidiosa and QTLs (quantitative trait loci) related to the productivity and quality of the juice, respectively, is discussed.