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 colonization by mycorrhizal fungi relates to its ability to acquire and utilize phosphorus for growth and reproduction. Two tomato genotypes previously found to be either responsive ('LA1709') or unresponsive ('large cherry') to mycorrhizal colonization during early vegetative growth were examined in detail. Plants were grown at four levels of added phosphate or with mycorrhizal inoculum. Vegetative and reproductive growth, phosphorus uptake and root length density were measured during the course of plant development. Mycorrhizal symbiosis significantly increased above-ground dry mass, root length, phosphorus content and yield under low phosphorus conditions in 'LA1709', while it had less effect on these characteristics in 'large cherry'. When uninfected, however,'LA1709' grew and reproduced poorly unless high amounts of phosphorus were added to the soil, while 'large cherry' grew well under very low phosphorus conditions. This was because 'large cherry' had significantly higher root length densities than 'LA1709', enabling plants from this genotype to explore more soil volume and acquire greater amounts of phosphorus when grown without mycorrhizal fungi in low phosphorus soil. 'Large cherry' also had higher phosphorus use efficiency and allocated a greater proportion of phosphorus to reproduction when uninfected than 'LA1709'. It appears traits that affect a plant's ability to acquire and utilize phosphorus efficiently for growth and reproduction can also affect its response to mycorrhizal colonization in tomato. (C) 1998 Annals of Botany Company.