Reliable callus-induced plantlet regeneration from leaf explants of Lagerstroemia speciosa and genetic fidelity assessment through ISSR markers
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AbstractCrapemyrtle (Lagerstroemia sp.) is the top-selling flowering tree in the U.S. However, threats from arthropod pests, including the recently emerged crapemyrtle bark scale (CMBS; Acanthococcus lagerstroemiae), severely jeopardize the aesthetic and production attributes of crapemyrtle. A tropical species, L. speciosa (L.) Pers. (Queen's Crapemyrtle) exhibits partial resistance to CMBS and other pests, but conventional breeding to incorporate the characteristics of L. speciosa into existing hybrids remains challenging. Recognizing the potential of tissue culture in facilitating molecular breeding, but also the possibility of undesirable somaclonal variations from in-vitro organogenesis, we utilized leaf explants of L. speciosa to develop a callus-induced regeneration protocol and assessed genetic fidelity of regenerated plantlets using inter-simple sequence repeat (ISSR) markers. Using woody plant medium (WPM) supplemented with 0.2 mg/L 2,4-D and 1.0 mg/L 6-BA achieved 97.9% callus induction. Shifting the growth regulators to 10.0 mg/L 6-BA and 0.5 mg/L NAA resulted in 32.4% of callus explants differentiating into adventitious buds. Finally, nodal segment proliferation (94.6%) and new shoot growth was maximized by using WPM supplemented with 1.0 mg/L 6-BA and 0.02 mg/L NAA. Explants rooted 100% using half-strength WPM supplemented with 0.2 mg/L IBA, and acclimatization survival was 98.3%. The ISSR primer analysis revealed 98.7% monomorphic markers, confirming the genetic integrity of the regenerated plantlets. We describe a reliable callus-induced regeneration system for L. speciosa, which will facilitate future molecular breeding and biotechnology to enhance cold hardiness, pest resistance, and other desired traits in this important genus.
