Mycorrhizal and non-mycorrhizal tomatos

Root architecture and root growth are important for exploration of soil for water and nutrients, as the acquisition of these resources drives plant growth. Several important concepts, however, govern the development of roots and their direct and indirect effects on plant growth:

• Roots are highly plastic, i.e., architecture and growth are highly responsive to environmental conditions, and therefore can optimize resource acquisition.
• Tradeoffs exist in root form and function. The costs of producing roots can yield benefits in terms of the acquisition of soil water and nutrients and ultimately, plant growth and fitness.
• Genetic analysis has revealed that root architectural traits are often multi-gene or quantitative traits.
• Roots affect attributes of plant communities and ecosystems, due to their effects on resource acquisition, growth, productivity, water budgets, and nutrient cycling.

Mycorrhizae are another avenue by which plants increase soil resource acquisition. For many plant species, the arbuscular mycorrhizal (AM) association is known to have the following effects:

• Fungi extend the network of fine root hairs and increase the uptake of nutrients.
• Plant photosynthate to the fungus is exchanged for increased nutrient supply.
• The symbiosis can be more or less mutualistic vs. parasitic, depending on environmental circumstances, e.g., nutrient availability.
• Mycorrhizae's major role is increasing plant access to phosphate, but uptake of other poorly soluble but essential nutrients such as Cu and Zn is also enhanced.
• The role of AM mycorrhiza in N nutrition is less well understood.

Several projects have been completed or are underway to study role of root architecture and arbuscular mycorrhizae for vegetable crops. In several of our studies, we use two genotypes of tomato plants: a mycorrhiza defective tomato mutant (rmc hereafter) or its mycorrhizal wildtype progenitor Lycopersicon esculentum Mill. cv. 76R (76R MYC+ hereafter). A few of our past and current projects include:

• Mycorrhizae and microbial communities in organic production
• Biofumigation, soil microbial communities, and plant nutrient uptake
• Arbuscular mycorrhizae in wild and cultivated lettuce
• Lettuce root architecture and extraction of soil moisture
• Roots, mycorrhizae, and soil respiration
• Mycorrhizae and elevated CO2

References

Jackson, L.E. 2004. Soil biology: root architecture and growth. Encyclopedia of Soils in the Environment. Elsevier Ltd. pp. 411-421.