Dynamic Bandwidth Allocation (DBA) is a major research challenge in the migration of Passive Optical Networks (PON) systems towards Long Reach PON, especially when hybrid WDM/TDM is used (LR WDM/TDM PON). New solutions for Dynamic Bandwidth and Wavelength Assignment (DBWA) are sought to address two main critical issues of such PON systems: how to schedule the transmissions over multiple wavelengths and how to efficiently exploit the bandwidth in presence of long propagation delays of long reach scenarios. In this work, for the first time, we investigate the Multi-thread polling in a LR WDM/TDM PON. Then, we propose a new DBWA scheme, called EFT-partial-VF Multi-threaded, which effectively combines some of the features of, the Earliest Finish Time with Void Filling (EFT-VF) algorithm, with the Multi-thread algorithm. The two proposed solutions, namely the MT algorithm and the EFT-partial-VF Multi-threaded algorithm, provide significant improvement in terms of average delay, if compared with existing algorithms such as the EFT and the EFT-VF. Besides this, we extend the definition of polling cycle to hybrid WDM/TDM PON and we provide a method to calculate it.