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Establishment of a papaya (Carica papaya L.) Micropropagation protocol in a temporary twin vessel immersion system

Abstract:

Papaya production is affected by sexual variability in the seed. Conventional methods of propagation involve the maintenance of large land scale crops to supply the consumer's demand. Micropropagation techniques using temporary immersion of twin vessels (TIS) bioreactors are an alternative for papaya production. The objective of the study is to establish a disinfection protocol for the introduction of axillary buds and to evaluate different immersion times and inoculum density in the TIS to obtain a higher multiplication rate. Disinfection of the plant material was performed with 70% ethanol for 1 minute, 2% sodium hypochlorite for 5, 6 and 8 min, and sterile water washes. Percentage of contamination and oxidation was evaluated for 21 days. The introduction stage, Murashige & Skoog (MS) medium was used with 1 mg.L-1of gibberellic acid and 2 mg.L-1of kinetin. Similarly for the multiplication stage, MS medium was supplemented with 0.5 mg.L-1of benzyl adenine, 0.5 mg.L-1of indoleacetic acid, and 0.3 mg.L-1of gibberellic acid. The multiplication rate, number of leaves, height, and diameter of the stem was evaluated for 21 days. The plant material was transferred to the TIS to evaluate the immersion time (1 and 2 min) and density of the inoculum (4 and 8) in 200 mL of liquid multiplication medium, with an immersion frequency of 6 h, photoperiod of 12 h of lighting per day and 28°C. In the disinfection stage, 100% survival was achieved without oxidation using 2% sodium hypochlorite for 6 and 8 min. Survival rate was 96.4% and 83.33% for the introduction and multiplication stage in semi-solid medium, respectively. For the latter, 1.88 ± 0.02 leaves were observed, 1.12 ± 0.04 cm in height, diameter of 0.43 ± 0.01 cm, and a multiplication rate of 1.20 ± 0.02. In the TIS, 6.03 ± 0.04 leaves were observed, 1.65 ± 0.10 cm in height, diameter 0.73 ± 0.02, and a multiplication rate of 5.05 ± 0.06 using 2 min of immersion every 6 h with an inoculum density of eight. Research established that high multiplication was obtained by increasing immersion of plant material in liquid culture medium. This study will contribute to the strengthening of the productive sector, offering seedlings with the suitable sex (hermaphrodite), and high genetic and phytosanitary quality.