Use of mango root DNA density to quantify differences in mango fine-root distribution

S.L. Bithell, L.T.T. Tran-Nguyen, M.N. Hearnden, A.C. McKay, D.M. Hartley
We utilised a mango root qPCR soil DNA-based method and evaluated the field capability of the method to quantify mango root DNA density (RDD) by comparing qPCR results to root dry matter (DM) for soil samples from two orchards (Darwin and Katherine) with 'Kensington Pride' rootstocks. We also investigated the sensitivity of the method and DNA yield by spiking samples with fine roots from each orchard. Sites were sampled by soil coring and soil samples dried before sieving (minimum aperture 2 mm) to remove roots. Soil samples containing fine-root fragments (including some spiked with mango roots) were analysed using the mango root qPCR assay. Sieving took a maximum of 15 min per sample (up to 1.5 kg soil). The roots removed by sieving were dried and weighed. The RDD values from the two orchards showed that the DNA concentrations differed between depths (0-10 and 10-20 cm); these differences were similar to the fine-root (root diameter ‹1.64 mm) DM results. However, comparison of RDD values against the DM concentration of fine roots used to spike samples showed that the surface (0-10 cm) samples had lower DNA yields than expected if all spiked fine-root material was live. These findings have implications; in particular, the qPCR method may be useful to identify differences in the proportion of live root material relative to fine-root mass. Furthermore, fine-root experimental capability will be improved by the ability to rapidly sieve samples and have qPCR analyses completed on soil samples, instead of the labour-intensive washing, sorting and scanning required for root quantification by traditional methods.
Bithell, S.L., Tran-Nguyen, L.T.T., Hearnden, M.N., McKay, A.C. and Hartley, D.M. (2017). Use of mango root DNA density to quantify differences in mango fine-root distribution. Acta Hortic. 1183, 35-42
DOI: 10.17660/ActaHortic.2017.1183.6
fine roots, root DNA concentration, root DNA density (RDD), root dry matter, root distribution

Acta Horticulturae