Zinc - rooting cofactor in rubber tree mini-cuttings

Abstract

The rubber tree (Hevea brasiliensis Müell. Arg.) is a species of significant economic interest in the natural rubber industry in Brazil and the world. This species presents recalcitrance to rooting, and its cuttings are difficult to propagate. This study aimed to evaluate the effect of the pre-conditioning of rubber tree mini-cuttings with zinc on the improvement of the adventitious rooting of rootstocks. Mini-cuttings were standardized with 45 mm length and submitted to preconditioning by immersion of the mini-cutting base in solutions containing 0.00; 0.04; 0.08; 0.16; 0.32 and 0.64 mg L-1 of Zn, for 24 hours. The experimental design was randomized blocks with six treatments and four replicates of 10 mini-cuttings. The rubber tree mini-cuttings were placed in a fitotron-type growth chamber, at 25 °C, with 12-hour photoperiod, 5,000 K intensity, and 95% of relative air humidity, for 60 days. The survival rate, number of buds, percentage of mini-cuttings that had leaf abscission, the percentage of mini-cuttings with callogenesis in the root meristem, the percentage of rooted mini-cuttings, the number of primary roots and root length were evaluated. The highest values of survival rate, the number of buds, the number of primary roots, the percentage of mini-cuttings with callogenesis in the root meristem, the percentage of rooted mini-cuttings and root length were observed with 0.16 to 0.26 Mg L-1 of Zn. The use of zinc in the mini-cuttings of rubber tree reduces linearly the percentage of mini-cuttings that had leaf abscission and the formation of callogenesis in the root meristem.
 
 The rubber tree (Hevea brasiliensis Müell. Arg.) is a species of a large economic interest in the natural rubber industry in Brazil and the world. This species presents recalcitrance to rooting, and its cuttings are difficult to propagate. This study aimed to evaluate the effect of the pre-conditioning of rubber tree mini-cuttings with zinc on the improvement of the adventitious rooting of rootstocks. Mini-cuttings were standardized with 45 mm length and submitted to preconditioning by immersion of the mini-cutting base in solutions containing 0; 0.04; 0.08; 0.16; 0.32 and 0.64 mg L-1 of Zn, for 24 hours. The experimental design was randomized blocks with six treatments and four replicates of 10 mini-cuttings. The rubber tree mini-cuttings were placed in a fitotron-type growth chamber at 25 °C, with 24-hour photoperiod, 5,000 K intensity and 95% relative humidity for 60 days. The survival rate, number of buds, percentage of mini-cuttings that had leaf abscission, the percentage of mini-cuttings with callus, the percentage of rooted mini-cuttings, the number of primary roots and root length were evaluated. The highest values of survival rate, the number of buds, the number of primary roots, the percentage of mini-cuttings with callus, the percentage of rooted mini-cuttings and root length were verified with 0.16 to 0.26 Mg L-1 of Zn. The use of zinc in the mini-cuttings of rubber tree reduces linearly the percentage of mini-cuttings that had leaf abscission and the formation of root calluses.

Histology and induction of rooting in rubber tree cuttings (Hevea brasiliensis (Willd. Ex A.Juss.) Müll.Arg.)

“…Starting in the 1970s, priority was given to in vitro methods that were booming at the time, but after years of investment, alternative techniques of rubber tree clones could not be propagated efficiently for commercial scale (Masson and Monteuuis, 2017). Although numerous researches have been conducted (Alves et al, 2019;Antwi-Wiredu et al, 2018;Cardoso, 1961;Lemos-Filho et al, 1994;Masson and Monteuuis, 2017;Medrado et al, 2000;Muzik, 1953;Muzik and Cruzado, 1958;Muzik and Cruzado,1956), few published studies have achieved rooting success, however, none of them used the combination of techniques tested in our study (Castro et al, 1987;Medrado et al, 1995;Mendes, 1959;Monteiro et al, 2015;Silva et al, 2020;Vallejos-Torres et al, 2021).…”

“…Despite being related to the degree of lignin in the tissue, these cells are not necessarily related to cell maturity, being possible to form in any period, not only in mature tissues (Apezzatoda-Gloria & Carmello-Guerreiro, 2003). Ontogenesis studies would be convenient to verify the cellular behavior during tissue maturation, in addition to verifying whether root formation occurs in regions near the interruptions of the sclerenchyma ring, or independently of it since there are several studies showing that rooting was granted without arising from mechanical techniques (Castro et al, 1987;Silva et al, 2020;Monteiro et al, 2015;Medrado et al, 1995;Mendes, 1959;Vallejos-Torres et al, 2021).…”