The anatomical and biochemical basis of resistance of Vigna vexillata (Benth) (Ace. TVNu 72) to Monica testulalis were investigated. An uncharacteristic network of fibrous structures was observed on the petal surface of TVNu 72 but not on those of the susceptible control, IT82D-716. Stems of TVNu 72 and IT82D-716 have thick and closely packed collenchyma cells. Both varieties have been identified as possessing resistance to stem feeding; however, IT82D-716 is susceptible to flower and pod damage. The distance between pod wall epicarp and mesocarp was significantly (P ≺ 0.05) smaller in IT82D-716, but cell and tissue arrangement were similar for both varieties.

Total sugar content in the pod wall and seed of TVNu 72 was higher (P ≺ 0.05) than in IT82D-716. Phenol content was lower (P ≺ 0.05) in the pod wall of TVNu 72 but the reverse was true for fresh and dry seeds. This suggests that neither phenol nor total sugar are involved in the resistance of TVNu 72 to M. testulalis. However, it seems that thick and compact collenchyma cells in the stems and Fibrous tissues on the petal surface contribute to the resistance in TVNu 72. The results are discussed in line with previous reports which indicate that trichomes are the principal factors in the resistance of TVNu 72 to M. testulalis.