Micropropagation of Little Bluestem (Schizachyrium scoparium L.)

Abstract

Native grasses are increasingly used in the landscape. Little bluestem (Schizachyrium scoparium L.), a perennial bunchgrass native to most of the United States, has ornamental traits, such as variation in leaf color, differences in growth morphology, and attractive seed heads. Traditionally, cultivars of little bluestem are propagated by division, which limits the production of new plants. Our objective in this study was to develop an improved micropropagation protocol for little bluestem that would produce true-to-type plants. In 2016, we cultured immature inflorescences of eight genotypes of little bluestem on Murashige and Skoog (MS) medium with four combinations of kinetin (1.0 or 2.0 mg·L−1) and 2,4-D (0.5 or 1.0 mg·L−1) under three levels of light (dark, semilight, full light) to initiate callus. Cultures were evaluated 30 days after initiation and those that had initiated callus were subcultured. Media for subculturing and rooting contained either 0.1 mg·L−1 or no 1-Naphthaleneacetic acid (NAA). Light level had no effect on callus initiation. Initiation media with 1.0 mg·L−1 kinetin and either level of 2,4-D induced callus at almost twice the rate of media with 2.0 mg·L−1 kinetin, and cultures initiated on those media also produced almost twice the number of rooted plants over all genotypes. Genotype affected the number of rooted plants produced. The addition of NAA to medium for subculturing and rooting did not increase the number of rooted plants. In 2017, we cultured immature inflorescences of four genotypes of little bluestem on MS medium with 0.5 mg·L−1 2,4-D and either 1.0 mg·L−1 kinetin or 6-benzylaminopurine (BAP) under full light. Cultures were evaluated 30 days after initiation. Cultures that had initiated callus were subcultured onto MS medium with the same growth regulators as the initiation medium but without 2,4-D. Cultures were cycled between subculture medium with growth regulator and subculture medium with no additional growth regulator until rooted. Cultures initiated and subcultured on medium with BAP initiated two to three times more callus than those on kinetin and produced twice as many rooted plants. Our recommendation for rapid micropropagation of little bluestem is to initiate cultures on MS medium with 1.0 mg·L−1 BAP and 0.5 mg·L−1 2,4-D. After callus initiation, cultures should be subcultured to medium with BAP but no 2,4-D, alternating with medium with no additional growth regulators, until rooted.