Proc. of Second World Avocado Congress 1992 p. 576

Preliminary Results In Vitro Selection for Tolerance to Chloride Excess in Avocado

Hector Gonzalez-Rosas and Gabriela Ramirez-Reyes

Centre de Fruticultura, Colegio de Postgraduados, Chapingo, Edo. Mexico 56230, Mexico

 

Jose Luis Rodriguez-Ontiveros and Samuel Salazar-García

Campo Experimental Santiago Ixcuintla, INIFAP, Apdo. Post. 139, Tepic, Nay. 63000, Mexico

Abstract. Avocado is one of the more sensitive fruit trees to high concentrations of chlorides and sometimes does not tolerate soil conductivity above 2 mmhos. This results in a reduction in production of up to 10%. With the use of in vitro embryo selection and taking advantage of the naturally existing genetic variation, it has been possible to identify valuable genotypes in a relatively short time. The purpose of the work was to determine if the method of in vitro culture of mature avocado embryos could be an acceptable option for the evaluation and selection of individuals tolerant to excess chlorides.

Mature embryos of creole avocado (races Mexicana and Antillana) were planted in a basic Murashige and Skoog medium, supplemented with NaCI, CaCI₂ , and a mixture of both salts, added at concentrations from 0.1 to 1.0% at 0.1% intervals. Data were taken to quantify germination under each treatment after 365 days incubation. On surviving plants, Y_p, Y_w, and Y_p were determined for stems and roots. Embryos of the race Mexicana performed as follows. Stems of plantlets developed on low concentrations (0.1% to 0.3%) of NaCI showed a drastic reduction in Y_w and Y_p upon passing from 0.1% to 0.3% salt causing a slight increase in Y_p which seems to indicate some osmotic adjustment. In the root, Y_w and Y_p increased upon passing from 0.1% to 0.3% concentration of CaCI₂. Only on 0.4% and 0.8% were plantlets obtained. In these, stems showed inconsistent ψ_w in contrast with Y_p. From 0.6% salt and greater, the reduction was still larger and Y_p increased indicating some osmotic adjustment in response to high levels of salt. Embryos of the race Antillana in NaCI developed into plantlets on 0.1% to 0.5% salt except at 0.3% where no plantlets were obtained. In all cases, stems did not show any trends with respect to Y_p, Y_w, or Y_p. For roots, 0.7% salt gave some response, and Y_w was reduced with concentrations of NaCl₂ decreased drastically at 0.5% concentration and Y_p increased. With respect to CaCI₂ , plantlets were obtained on all six concentrations. In stems, Y_w was reduced as the level of salt increased; Y_p in both stems and roots decreased with increased salt concentration. It can be concluded that it is possible to consider in vitro embryo culture as a viable and fast method for selection of salt tolerance in avocado.