An Feng

Involvement of rootstocks and their hydraulic conductance in the drought resistance of grafted rubber trees

Improving drought resistance of rubber trees has become a pressing issue with the extension of rubber plantations and the prevalence of seasonal drought. Root system is vital to water and nutrients uptake of all plants, therefore, rootstocks could play decisive roles in drought resistance of grafted rubber trees on a specific scion clone. To investigate the responses of different clone rootstocks and their grafted trees to water stress and find applicable methods for selecting drought resistant rootstocks, seven related parameters and root hydraulic properties of both seeds originated and grafted saplings of PB86, PR107, RRIM600 and GT1 were measured to assess their drought resistance. It was shown that the rootstock drought resistance and root hydraulic conductance may improve the drought resistance of the grafted rubber trees. Among the four clone rootstocks, GT1, which demonstrated more resistant to drought and higher root hydraulic conductance, was comparatively resistant to drought both for the seed propagation seedlings and grafted saplings. In addition, studies on the grafted saplings with different root hydraulic conductance further validated the possibility of selecting drought resistant rootstocks on the basis of rootstock hydraulic conductance using a high-pressure flow meter. Key words : Rubber tree (Hevea brasiliensis), rootstock, hydraulic conductance, drought resistance, highpressure flow meter.

Application of SmartRoot system for determining morphological parameters of fine roots of Hevea brasiliensis

Aims Our objective was to examine the possibility of using SmartRoot, free software based on ImageJ, for the measurement of fine root length, surface area, volume and diameter of Hevea brasiliensis. Methods Photos were taken at heights of 15 and 40 cm from the fine root samples before the samples were sub- jected to comparison for accuracy of measurement of fine root length, surface area, volume and diameter of H. brasiliensis. The same images were analyzed manually and semi-automatically as well. Then the results obtained from SmartRoot were compared with those from WinRhizo, an expensive, popular, professional software for root analysis. Important findings The average normal root mean square errors (NRMSE) between 15 and 40 cm height for fine root length, surface area, volume and diameter were 2.87%, 15.73%, 32.38% and 16.88%, respectively. In addi- tion, the NRMSE between manual and semi-automatic analysis for the same morphological parameters were 3.06%, 21.00%, 40.96% and 11.64%, respectively. Furthermore the NRMSE between SmartRoot and WinRhizo on fine root length, surface area, volume and diameter were 5.31%, 9.37%, 9.61% and 5.77%, respectively, signify- ing a high consistency between the two software systems. The results indicated that it is feasible to employ the SmartRoot system for determination of fine-root morphological parameters of H. brasiliensis due to its satisfac- tory accuracy, reliability, easy operation and time-saving advantages. For better accuracy, photos are recom- mended to be taken at the height of 15 cm and analyzed with the semi-automatic method.