Abstract

GANDARA-LEDEZMA, V. et al. Desinfección de foliolos de nogal pecanero adulto, e inducción de callogénesis in vitro. Polibotánica [online]. 2023, n.55, pp.121-144.  Epub May 26, 2023. ISSN 1405-2768.  https://doi.org/10.18387/polibotanica.55.9.

Until now, there is no protocol for the micropropagation of pecan trees (Carya illinoinensis) from explants of adult trees. Persistent microbial contamination and browning of tissues have impeded the success of previously proposed methods. Specifically, the adult tree leaf explant constitutes an unexplored starting point for the regeneration of C. illinoinensis. Therefore, the objective of this study was to determine a disinfection method and in vitro culture conditions that induce greater callus production in adult pecan tree leaf explants. Five disinfection methods were tested: (1) 70% ethanol for 50 s, 1.8-2.7% sodium hypochlorite with 2 drops/L of Tween 80 for 50 s, (2) 70% ethanol for 2 min, 1.8-2.7% sodium hypochlorite with 2 drops/L of Tween 80 for 2 min, (3) 70% ethanol for 2 min, 1.8-2.7% sodium hypochlorite with 2 drops/L of Tween 80 for 2 min, 1 g/L of carbendazim with 2 drops/L of Tween 80 for 20 min, (4) 70% ethanol for 2 min, 1.8-2.7% sodium hypochlorite with 2 drops/L of Tween 80 for 2 min, 8.8 g/L of carbendazim with 2 drops /L of Tween 80 for 20 min, and (5) 70% ethanol for 2 min, 1.8-2.7% sodium hypochlorite with 2 drops/L of Tween 80 for 2 min, 1 g/L of prochloraz with 2 drops/L of Tween 80 for 20 min. In addition, 6 different culture media were tested where the carbon source (sucrose, glucose and maltose), the inclusion of an antioxidant (AgNO3 and activated carbon), and the concentration of MS salts (maximum or one third of the maximum concentration) were varied. The explants were incubated for 50 days; a portion of the explants was incubated in the dark and the other under a photoperiod of 16 h. Likewise, some explants were inoculated in abaxial orientation, and others in abaxial orientation. The level of browning, the percentage of explants with callus, the fresh and dry weight of the calluses, and the percentage of explants contaminated by microorganisms were evaluated. The lowest percentage of contaminated explants was observed in the disinfection treatment that included immersion in prochloraz, and prochloraz was the only fungicide that allowed callogenesis in 100% of the treated explants. The darkening in the explants did not increase when the concentration of MS salts tripled. Glucose significantly reduced browning, but also significantly decreased the percentage of explants with callus, compared to that observed when using sucrose or maltose. The adaxial orientation promoted a higher percentage of explants with callus, with a fresh and dry weight, as well as a higher moisture percentage. The photoperiod prevented callus production, while incubation in the dark allowed more than 80% of the explants to produce callus in each treatment. The medium without antioxidant and the medium with 5 mg/L of silver nitrate gave similar browning results, while 1 g/L of activated carbon left the explants unviable. The present work proposes a method for the aseptic establishment and in vitro culture conditions for callus initiation in leaflets of adult pecan tree, with reproducible results.

Keywords : Carya illinoinensis; procloraz; carbendazim; callus; calli.

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