Equivalent Stress Comparisons Among Tomato Strains Differentially Tolerant to Phosphorus Deficiency

Abstract

Abstract Physiological and morphological features of tomato ( Lycopersicon esculentum Mill.) strains differentially adapted to phosphorus (P) deficiency differed depending on whether the strains had been grown under a single level of low P in screening experiments or under specific levels of P that reduced growth of each of the strains to about 50% of maximum, i.e., at “equivalent stress”. These differences indicated that stress compensation contributed significantly to the physiological and morphological phenotypes of strains under the specific P level used for screening for low-P tolerance. Consequently, the true extent of genetic differences for these traits was not directly measurable. Differences between strains for root:shoot ratios, internal-P-use ratios, and kinetic parameters of P uptake still were observed at equivalent stress. Thus, the genetic bases of these differences seem secure. The P concentration in lower leaves of tolerant strains was lower than in intolerant strains, and the maximum rates of 32 P by uptake excised roots were increased in the tolerant strains.