Effects of vegetation indices, auxin, and biostimulator treatments on the rooting of Rhododendron pulchrum cuttings

Resumo

The objective of our study was to develop a protocol enabling the use of vegetation indices to evaluate the rooting of Rhododendron pulchrum cuttings. Six root growth parameters were recorded after those cuttings were exposed to rooting media for 47 days. Among plants with different of soil-plant analysis development (SPAD) and normalized difference vegetation index (NDVI) values, those with higher values exhibited significantly higher values for the root number, root length, and root dry weight, suggesting that reflectance indices were useful in measuring the root growth parameters of R. pulchrum cuttings. Another aim of this work was to study the effects of a plant growth regulator (PGR) and biostimulant on rooting for cutting propagation. Treatments with indole-3-butyric acid (IBA) of 2000 mg×L^-1 alone and combined with 1-naphthaleneacetic acid (NAA; 2000 mg×L^-1), salicylic acid (SA; 10^-4 M), and thiamine (TA; 800 mg L^{- 1}) were applied to cuttings of R. pulchrum. The same observations on six different rooting parameters were recorded and analyzed after cuttings were exposed to rooting media for 99 days for the auxin test, and 62 days for the SA and TA tests. Compared to NAA, IBA enhanced root growth and development as determined by increases in all parameters, and therefore it was used thereafter. Successful results for the root number and root dry weight were achieved using cuttings of R. pulchrum with a combination of IBA and SA. In addition, the mix of IBA and TA resulted in higher root numbers. These combined treatments are recommended for establishing stem cuttings for raising R. pulchrum plants in the nursery.