Tolerance of Tomato Strains to Phosphorus Deficiency in Root Culture

Abstract

Abstract Root culture was adapted for screening a diverse collection of tomato (Lycopersicon esculentum Mill.) strains for tolerance to low supplies of P. Fifty-one tomato strains were screened in 10 consecutive experiments for root fresh weight (RFW) production with high non-growth-limiting (25 μm) and low growth-limiting (7 μm) concentrations of P in a sterile, liquid medium. Twenty strains showing the most and least restricted root growth at low P in the initial 10 experiments were grown simultaneously in three final screening experiments. Restrictions in RFW at low P averaged 51% for four strains, consequently classed as low-P “intolerant”, and averaged 27% for three strains, consequently considered low-P “tolerant”. At high P, RFW of tolerant strains averaged 17% less than RFW of intolerant strains. At low P, RFW of tolerant strains averaged 23% greater than RFW of intolerant strains. The greater RFW production of intolerant strains at high P was due to higher internal P use ratios (IPUR = mg root dry weight (RDW) per mg P adsorbed). Differences in growth at low P were due primarily to differences in P uptake. However, the relative contributions of P use and P uptake efficiencies to low-P tolerance were different among strains. Root hairs of tolerant strains at low P were longer and covered a greater proportion of the root length than root hairs of intolerant strains. The pH of the culture medium of one tolerant strain was significantly lower than the medium pHs of the other strains.