Mechanical properties of corn cobs were determined from quasi static radial compression force deformation curves. Cobs were cut axially to small pieces of approximately 2.5 cm length. Different races, including Sikkim Primitive maize, with varying knob number were tested for their relative contribution to the macro-structure components of the corn cob: to its apparent modulus of elasticity, crushing strength and modulus of toughness in relation to knob composition. The studies showed the variation of modulus of elasticity along its length. It is less in races with soft cob and low knob number. It has been found that Young's modulus has the higher value near the middle of the cob towards the butt for all the corn races except Palomero Toluqueno. Table 1 shows the average values of the properties. It was observed that the race Bolita has the highest, and Sikkim Primitive (T-26) the lowest value of modulus of elasticity. Palomero Toluqueno has the highest crushing strength and T-26 has the lowest. Pira has the highest modulus for toughness and Celaya has the lowest value.

Our experience on working with landraces of Northeastern Himalayan maize suggests that maize strains with soft and flexible cobs possess relatively low knob number. Hardness of the cob reflects introgression of teosinte into maize.

Table 1. Main effects of races on physical and mechanical properties of the cob.

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