Capsicum recalcitrance: physiological and molecular challenges of pepper tissue culture

The genetic richness of the Capsicum genus holds significant potential for breeding programs, but it hinders the integration of biotechnological approaches for genetic improvement. In vitro manipulation and regeneration of pepper species have been limited by the inherent recalcitrance barriers of the genus, which mainly manifest in the massive obtention of structures with multiple shoot apical meristem (SAM) deformations. Fifty years of pepper tissue culture have demonstrated that explant responsiveness to culture conditions is essentially governed by molecular and physiological factors, and it is highly genotype-dependent. The empirical approach of the research carried out in this field has allowed to substantially improve the in vitro response by modifying the surrounding environment. Currently, there are several reports of pepper regeneration through organogenesis, somatic embryogenesis, and androgenesis. However, these protocols are quite inefficient and little reproducible in other Capsicum genotypes. Literature about pepper tissue culture has extensively reviewed the plant regeneration success achieved, but little is known about the multifactorial nature of this persistent phenomenon. This article summarizes the progress made in understanding the recalcitrant nature of the Capsicum genus, highlighting the influence of the molecular and physiological processes involved in the in vitro response.