A simple plant regeneration-ability assay in a range of Lycopersicon species

Abstract

Plant growth regulator-dependent (PGR-dependent) in vitro shoot organogenesis has been extensively studied in tomato (Lycopersicon esculentum), whereas PGR-independent adventitious shoot organogenesis received marginal attention in L. esculentum and no consideration at all in other Lycopersicon species. In the present study, induction of PGR-independent adventitious shoots was by decapitation of the apex and removal of preexisting shoot meristems of the seedling, and seedling culture on a medium with no PGR supplements. The existence of PGR-independent regeneration-ability was verified in L. esculentum genotypes (high pigment photomorphogenic mutants and wild-type counterparts) and was uncover amongst L. cheesmanii, L. chilense, L. chmielewskii, L. hirsutum, L. parviflorum, L.␣peruvianum and L. pimpinellifolium. Compared to species other than L. esculentum, high pigment photomorphogenic mutants displayed the weakest PGR-independent regeneration-ability. Our results imply that decapitated seedlings cultured on a medium without PGRs can serve as a convenient assay system for genotypic variation in self-controlled, PGR-independent, shoot regeneration-ability in a wide range of Lycopersicon species. Using transverse thin slices of the hypocotyl placed onto a medium supplemented with 0.2 μM zeatin reboside and 0.04 μM IAA, we assessed PGR-mediated shoot regeneration in L. esculentum genotypes. In a given genotype, more plants per seedling were established by PGR-mediated than by PGR-independent regeneration. However, with both modes of organogenesis, only a fraction of shoot buds eventually grew into normal plants, while others developed into abnormal regenerants having no stem. Percentage of stem-deficiency, in a given genotype, was higher in PGR-treated cultures, which indicates that PGRs amplify the formation frequency of imperfect adventitious apical shoot meristems. Unlike L. esculentum, adventitious shoot buds of other Lycopersicon species, induced by wounding seedlings that were not treated with PGRs, rarely formed regenerants lacking a stem.