Abstract: This paper provides an introduction to catastrophe theory and defines the principal conditions required for its application. The basic properties of bimodality, discontinuity, hysteresis, and divergence are defined and illustrated using the simplest structures of the theory. In this raper, catastrophe theory is applied in the interspecies ecosystem of aphid and broadbean. With only a minimun of general descriptive information about the aphid system, a qualitative catastrophe theory model is hypothesized. This model is rich in its ability to provide predictions and insight about the global behavior of the system.

Key words: Zn-inefficient rice cultivar, Zn-efficient rice cultivar, HCO₃^-, Root growth and nutrient absorption