Mycorrhizal response of two tomato genotypes relates to their ability to acquire and utilize phosphorus

The purpose of this study was to determine how a plant's response to coloni zation by mycorrhizal fungi relates to its ability to acquire and utilize p hosphorus for growth and reproduction. Two tomato genotypes previously foun d to be either responsive ('LA1709') or unresponsive ('large cherry') to my corrhizal colonization during early vegetative growth were examined in deta il. Plants were grown at four levels of added phosphate or with mycorrhizal inoculum. Vegetative and reproductive growth, phosphorus uptake and root l ength density were measured during the course of plant development. Mycorrh izal symbiosis significantly increased above-ground dry mass, root length, phosphorus content and yield under low phosphorus conditions in 'LA1709', w hile it had less effect on these characteristics in 'large cherry'. When un infected, however,'LA1709' grew and reproduced poorly unless high amounts o f phosphorus were added to the soil, while 'large cherry' grew well under v ery low phosphorus conditions. This was because 'large cherry' had signific antly higher root length densities than 'LA1709', enabling plants from this genotype to explore more soil volume and acquire greater amounts of phosph orus when grown without mycorrhizal fungi in low phosphorus soil. 'Large ch erry' also had higher phosphorus use efficiency and allocated a greater pro portion of phosphorus to reproduction when uninfected than 'LA1709'. It app ears traits that affect a plant's ability to acquire and utilize phosphorus efficiently for growth and reproduction can also affect its response to my corrhizal colonization in tomato. (C) 1998 Annals of Botany Company.