Through in vitro identification, 137 new germplasm inbred lines of cassava cultivar‘GR891’ were evaluated for resistance to root rot. Additionally, genetic diversity analysis, including variance coefficients and genetic diversity indices, was conducted on the main agronomic traits of 93 resistant germplasm lines. The results showed that among the 137 cassava germplasm lines, 56 lines exhibited high resistance (40.88%), 37 lines showed resistance (27.01%), 33 lines were moderately resistant (24.09%), 9 lines were susceptible (6.57%), and 2 lines were highly susceptible (1.46%). The variation coefficients of the ten main traits of the 93 resistant cassava lines ranged from14.46% to 77.63%, and the genetic diversity indices ranged from 0.60 to 2.04, indicating a rich genetic variation in the inbred line progeny of ‘GR891’. Correlation analysis revealed that three pairs of traits were extremely significantly correlated, and three pairs were significantly correlated. The fresh tuber weight per plant showed a highly significant positive correlation with stem diameter and fresh tuber number per plant, with correlation coefficients of 0.490 and 0.680, respectively. Principal component analysis indicated that the cumulative contribution rate of the three principal components reached 74.52%, with plant height, stem diameter, main stem height, fresh tuber number per plant, and fresh tuber weight being the main factors influencing the phenotypic variation in cassava. These findings provide a scientific basis for the exploration of resistant germplasm against cassava root rot and for the genetic analysis of resistance.