ISOLATION OF TOMATO STRAINS VARYING IN POTASSIUM ACQUISITION USING A SAND-ZEOLITE CULTURE SYSTEM

One hundred tomato strains, representing widely diverse geographic areas, were evaluated in a sand-zeolite culture medium for their response to both low (0.25 mM) and adequate (1.0 mM) K levels. Three types of strains differing in K acquisition were classified: (1) efficient strains characterized by their ability to acquire K under low-K stress and with dry matter accumulation comparable to the strains grown under adequate-K supply, (2) inefficient strains that grew well under adequate-K supply but with a low capacity to acquire K at low-K stress and correspondingly lesser dry weight production, and (3) slowly growing strains featured by low K content in tissue and low dry matter accumulation irrespective of external K levels. The efficient and slowly growing strains came mostly from South and Central America, where tomato originated and was domesticated. Strains from other regions, however, mostly showed inefficiency in K acquisition. Two distinct features associated with the efficiency of K acquisition were identified. One was the proliferation of root length and another was high net K-influx rates per unit root length under low-K stress. Our results suggested that mechanisms for efficient acquisition of nutrients were lost during the cultivation of plants, and centers of plant origin and domestication contain valuable genetic resources for improving plant efficiency in nutrient acquisition.