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2 Journal of Applied Genetics

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Development of genetic maps of citrus varieties 'Murcott' tangor and 'Pera' sweet orange using fluorescent AFLP markers

100%

de O. A. C. , Bastinel M. , Cristofani-Yaly M. , Do Amaral A. M. , Machado M. A.

nr 3

219-231

The progeny of 87 BC₁ hybrids of 'Murcotť tangor and 'Péra' 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 ≤ 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 ('Murcotť map: 65 fAFLPs, average distance between them 29.5 cM, divided into 9 linkage groups (LGs), total size 1651.47 cM; 'Péra' map: 55 fAFLPs, average distance between them 31.9 cM, divided into 5 LGs, total size 1596.2 cM). The second 'Murcotť 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 'Murcotť tangor and 'Péra' sweet orange genetic maps in research on identification of citrus QRLs (quantitative resistance loci) to Xylella fastidiosa and QTLs (quantitative trait loci) related to the productivity and quality of the juice, respectively, is discussed.

Identification of QTLs associated with citrus resistance to Phytophthora gummosis

86%

Siviero A. , Cristofani M. , Furtado E. L. , Garcia A. A. F. , Coelho A. S. G. , Machado M. A.

nr 1

Citrus gummosis, caused by Phytophthora spp., is an important citrus disease in Brazil. Almost all citrus rootstock varieties are susceptible to it to some degree, whereas resistance is present in Poncirus trifoliata, a closely related species. The objective of this study was to detect QTLs linked to citrus Phytophthora gummosis resistance. Eighty individuals of the F₁ progeny, obtained by controlled crosses between Sunki mandarin Citrus sunki (susceptible) and Poncirus trifoliata cv. Rubidoux (resistant), were evaluated. Resistance to Phytophthora parasitica was evaluated by inoculating stems of young plants with a disc of fungal mycelia and measuring lesion lengths a month later. Two QTLs linked to gummosis resistance were detected in linkage groups 1 and 5 of the P. trifoliata map, and one QTL in linkage group 2 of the C. sunki map. The phenotypic variation explained by individual QTLs was 14% for C. sunki and ranged from 16 to 24% for P. trifoliata. The low character heritability (h² = 18.7%) and the detection of more than one QTL associated with citrus Phytophthora gummosis resistance showed that inheritance of the resistance is quantitative.