Somatic embryogenesis in anther-derived fast-growing callus as a long-term source for doubled-haploid production of coconut (Cocos nucifera l.)

Abstract

Cocos nucifera, one of the most important plantation crops is cross pollinated and has a diploid chromosome complement of 2n = 2x = 32. Doubled-haploid coconut plants are produced at low frequency through anther culture. Non-embryogenic fast-growing calli (FGC) are also produced in anther culture. The present study was undertaken to induce embryogenic calli from these FGC and to test their origin. The FGC were subjected to heat pretreatment at 38 °C for 3 and 6 days and cultured on three media with different plant growth regulator combinations in liquid, solid and liquid layered on solid (layered) culture, and with different sucrose concentrations. Highest callogenesis and weight increase in FGC was achieved after heat pretreatment of intact FGC cultured in solid Eeuwen’s Y3 medium supplemented with 100 µM 2,4-dichlorophenoxyacetic acid. Weight increase of FGC was negatively correlated with sucrose concentration. Incorporation of cytokinins facilitated the conversion of FGC to embryogenic callus. Histological studies revealed that these embryogenic calli consisted of a cambium-like zone, a characteristic feature of embryogenic calli. Flow cytometry confirmed that embryogenic calli derived from FGC originated from reduced microspores. Therefore, FGC are a good source of explant for the production of doubled-haploid plants of coconut over an extended period.