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 responseto colonization by mycorrhizal fungi relates to its abilityto 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 wereexamined in detail. Plants were grown at four levels of addedphosphate or with mycorrhizal inoculum. Vegetative and reproductivegrowth, phosphorus uptake and root length density were measuredduring the course of plant development. Mycorrhizal symbiosissignificantly increased above-ground dry mass, root length,phosphorus content and yield under low phosphorus conditionsin ‘LA1709’, while it had less effect on these characteristicsin ‘large cherry’. When uninfected, however, ‘LA1709’grew and reproduced poorly unless high amounts of phosphoruswere added to the soil, while ‘large cherry’ grewwell under very low phosphorus conditions. This was because‘large cherry’ had significantly higher root lengthdensities than ‘LA1709’, enabling plants from thisgenotype to explore more soil volume and acquire greater amountsof phosphorus when grown without mycorrhizal fungi in low phosphorussoil. ‘Large cherry’ also had higher phosphorususe efficiency and allocated a greater proportion of phosphorusto reproduction when uninfected than ‘LA1709’. Itappears traits that affect a plant's ability to acquire andutilize phosphorus efficiently for growth and reproduction canalso affect its response to mycorrhizal colonization in tomato.Copyright1998 Annals of Botany Company. Tomato,Lycopersicon esculentum,mycorrhiza,Glomus etunicatum,phosphorus, reproduction, lifespan.