Micro-texture regions (MTRs), characterized as the clusters of grains with similar crystallographic orientations in the polycrystalline microstructure, play a significant role in fatigue crack nucleation and life of structures of Ti alloys. This paper develops a parametrically upscaled constitutive and crack nucleation modeling (PUCM/PUCNM) platform for predicting structural-scale fatigue crack nucleation in α/β Ti-6Al-4V alloys, whose polycrystalline microstructures contain MTRs. The PUCM/PUCNM platform bridges micro and macro scales through thermodynamically-consistent incorporation of representative aggregated microstructural parameters (RAMPs) in macroscopic constitutive relations. A RAMP that captures both the MTR size and contrast in the overall texture is proposed to represent MTR intensity in the microstructure. A functional form is derived using the genetic programming-based symbolic regression. The PUCM/PUCNM tool is used to simulate an engine blade under dwell loading conditions. The results exhibit the reduction of nucleation life with a higher level of MTR intensity, despite the same overall textures.