Intact-plant screening for tolerance of nutrient-deficiency stress

Summary

Critical factors in the selection of appropriate screening procedures to detect different phenotypic responses to nutrient-deficiency stress are discussed. Various morphological, anatomical, and physiological plant factors responsible for adaptations to nutrient deficiency, particularly low-P stress, are reviewed. Also, the relative effectiveness of various screening culture techniques for detecting phenotypic efficiencies based on specific plant features are considered.

The relative ineffectiveness of liquid culture media in detecting plant factors critical in P acquisition from low-P natural environments is recognized, and a culture medium that is effective under these conditions is described. P adsorbed onto alumina, after mixing with coarse sand, serves as a P source in nutrient cultures. Buffered P concentrations approximating soil solution concentrations are maintained in this system, and P availability at the root surface seems diffusion-limited. With this system, significant differences in the growth of tomato strains under P stress were detected.

The desirability of screening phenotypes at the same degree of depression from maximum yield (equivalent deficiency stress) is discussed. The need for evaluations at equivalent stress is associated with the capacities of plants in general to respond to deficiency stress with morphological and physiological changes that may not be under genetic control, for example an increase in root:shoot ratio. Additional capacity to adjust the same plant factors often are characteristic of specific phenotypes. The relative growth of the same tomato strains under equivalent and non-equivalent P-deficiency stress is compared. Significant strain differences were observed under both conditions. However, the relative responses among strains for several efficiency parameters were very different under the two types of stress.