Breeding, genetic and genomic of citrus for disease resistance

Abstract

Although the citriculture is one of the most important economic activities in Brazil, it is based on a small number of varieties. This fact has contributed for the vulnerability of the culture regarding the phytosanitary problems. A higher number of varieties/genotypes with potential for commercial growing, either for the industry or fresh market, has been one of the main objectives of citrus breeding programs. The genetic breeding of citrus has improved, in the last decades, due to the possibility of an association between biotechnological tools and classical methods of breeding. The use of molecular markers for early selection of zygotic seedlings from controlled crosses resulted in the possibility of selection of a high number of new combination and, as a consequence, the establishment of a great number of hybrids in field experiments. The faster new tools are incorporated in the program, the faster is possibility to reach new genotypes that can be tested as a new variety. Good traits should be kept or incorporate, whereas bad traits have to be excluded or minimized in the new genotype. Scion and rootstock can not be considered separately, and graft compatibility, fruit quality and productivity are essential traits to be evaluated in the last stages of the program. The mapping of QTLs has favored breeding programs of several perennial species and in citrus it was possible to map several characteristics with qualitative and quantitative inheritance. The existence of linkage maps and QTLs already mapped, the development of EST and BAC library and the sequencing of the Citrus complete genome altogether make very demanding and urgent the exploration of such data to launch a wider genetic study of citrus. The rising of information on genome of several organisms has opened new approaches looking for integration between breeding, genetic and genome. Genome assisted selection (GAS) involves more than gene or complete genome sequencing and is becoming an import support in breeding programs of annual and perennial species. An huge information amount can be derivate from genome analysis. The use and benefit of such informations will depend on the genetic basis of the breeding program.

Genome wide selection in Citrus breeding

“…When referring to Citrus breeding, it is important to note that the citrus plant itself consists of two parts, the canopy and the rootstock, which are often from two different species and require targeted studies to improve their individual quality and interaction. Phenotypic selection is generally applied, but this is costly and time consuming, especially when the desired traits are expressed at later stages (Machado et al, 2011).…”

Karakterisasi Morfologi dan Isoenzim Aksesi Pamelo [Citrus maxima (Burm.) Merr.] Berbiji dan Tidak Berbiji

“…Selain itu keragaman genetik antarindividu dalam populasi dan antarkultivar pada jeruk secara alami dapat terjadi melalui hibridisasi, adaptasi terhadap lingkungan, dan mutasi. Beberapa kultivar jeruk manis yang ada saat ini berasal dari bibit yang mengalami mutasi somatik, sebagai contoh Baianincha berasal dari Baia yang merupakan mutasi somatik dari jeruk manis Seleta (Machado et al 2011). sembilan aksesi berbiji dan potensial tidak berbiji dan kelompok II terdiri atas empat aksesi tidak berbiji dan satu aksesi berbiji (Gambar 6).…”

Laranjeiras mediterrâneas de meia-estação em condições de sequeiro em clima subtropical no Brasil

“…Embora haja grande diversidade de citrinos em bancos de germoplasma (Machado et al, 2011), apenas um número pequeno desses recursos genéticos está disponível para uso em pomares comerciais. São cultivados em maior escala apenas quatro cultivares de laranjeiras doces em São Paulo: 'Hamlin', com frutos de maturação precoce; 'Pera', de maturação na meia -estação; e 'Natal' e 'Valência', ambas tardias .…”