Immature embryo rescue, culture and seedling development of acid citrus fruit derived from interploid hybridization

Abstract

Interploid sexual hybridizations were completed in 2001 and 2002 between seven lemon (Citrus limon(L.) Burm. f.) varieties, ‘Key’ lime (C. aurantifolia (Cristm.) Swing), Palestine sweet lime (C. imettioides Tan.), ‘Lakeland’ limequat (C. aurantifolia x Fortunella japonica (Thumb.) Swing.), and ‘Etrog’ citron (C. medica L.) as diploid progenitors and four allotetraploid somatic hybrids (‘Key’ lime + ‘Valencia’ orange, ‘Hamlin’ orange + ‘Femminello’ lemon, ‘Valencia’ orange + Rough lemon, and ‘Valencia’ orange+ ‘Femminello’ lemon) in efforts to generate improved seedless triploid acid fruit hybrids. Efficient recovery of triploid progeny from such crosses requires embryo rescue to avoid embryo abortion due to endosperm failure. Germination of rescued genetically diverse immature embryos was induced on two culture media (EME and Gamborg’s B5), with two sucrose concentrations (50 or 70 g l⁻¹). All media contained 0.5 g l⁻¹ malt extract and 4.50 μM GA₃. Germination of globular, heart and torpedo shaped embryos (defined as small embryos) was significantly (p < 0.05) affected by medium and genotype. Gamborg’s medium induced 82.89% germination. Of germinated embryos, 11–65% developed into normal plants with differences among crosses. Cotyledonary embryos (defined as immature embryos with fully developed cotyledons) germinated and developed into normal plants at higher rates than less-developed embryos. In efforts to improve the efficiency of plant recovery, small embryos from ‘Todo el año’ × HF and ‘Lisbon’ × HF crosses conducted during 2002 were rescued and cultured on three media (MS, Gamborg’s, and RMA) for comparison. Media did not significantly affect the proportion of normal plant recovery.