Abstract

Citrus fruits are grown in tropical, sub-tropical and Mediterranean climates worldwide. Citrus varieties are currently grafted over selected rootstocks that influence their performance increasing fruit quality, disease resistance and tolerance to abiotic stresses. Although breeding programs have made important advances, increasing rootstock salinity tolerance has been a major problem for conventional breeding. Our research focus was to improve salinity tolerance in citrus rootstocks through genetic transformation of in vitro growing plantlets. Proposed strategy is the over expression of the CBF3 transcription factor from Arabidopsis (AtCBF3), in four citrus rootstocks. The AtCBF3 is a master gene that has been used to induce drought, salinity and freeze tolerance in different plants. We have developed a transformation and rooting in vitro system, followed by an ex vitro propagation and acclimation protocol for transgenic rootstock lines. Up to date we have obtained 44 citrus rootstock transgenic lines. Propagation has been done by cuttings, consisting of a node with one bud, under greenhouse conditions. After collecting, cuttings were immersed in auxin solution and then disposed in hermetic clear boxes containing a mixture of sand, peat and perlite. Boxes were gradually aerated for plant hardening. Over 90% of the cuttings succeed developing adventitious roots and new shoots. Several copies of each transgenic line are being produced to carry out stress assays under greenhouse conditions. Transgenic lines have shown better performance than wild type un-transformed plantlets in preliminary salinity assays.