ARS | Publication request: Reproductive growth dynamics in Medicago: Understanding seed and pod resource allocation to improve crop yield

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 20, 2009
Publication Date: July 16, 2009
Citation: Grusak, M.A. 2009. Reproductive growth dynamics in Medicago: Understanding seed and pod resource allocation to improve crop yield [abstract]. 2009 Model Legume Congress. p. 44.

Technical Abstract: Reproductive yield in legume species is determined in part by the partitioning of available photoassimilates and other nutrients from the vegetative plant to the growing seeds. However, legume seeds develop within a pod, and the tissues of the pod wall also require the input of resources from the maternal plant; thus, there is the potential for resource competition between seeds and pod walls. Understanding the molecular regulation of this competition, both within fruit and at the whole-plant level, could help us develop strategies to manipulate reproductive resource allocation in important agronomic legumes. Furthermore, in many agronomic legumes, seed yield (i.e., crop yield) can be determined in part by the available space with which the seeds can grow within the pod. Thus, pod size can influence final seed size, and not surprisingly, crop yield has been enhanced in certain legume species by selecting for a large pod phenotype. While the biophysical constraints of the enveloping pod walls can be appreciated, our understanding of how space limitations affect the broader issues of seed growth phenomena (i.e., import and storage) or source leaf processes (i.e., assimilation and export) has yet to be fully realized. In Medicago truncatula, we have focused on four aspects of pod morphology that we believe have the potential to contribute to our global understanding of seed and crop yield phenomena in legumes. Firstly, analysis of diverse germplasm has shown that overall pod size is positively correlated with seed size; secondly, the pods of M. truncatula are coiled, and in many genotypes the coil diameter is diminished towards the apex, such that seed size also decreases towards the apex; thirdly, the walls of M. truncatula pods are hard and thick, thereby potentially constraining the growth of seeds in terms of their thickness; and fourthly, the allocation of dry matter between pod wall and seeds varies dramatically across M. truncatula accessions, as well as across diverse Medicago species. We will present developmental data on seed and pod growth, including growth dynamics by seed position within the pod, as well as overall allocation percentage differences between diverse Medicago accessions. These results will be discussed with respect to overall crop yield phenomena and the potential for seed-to-seed differences in gene expression within developing pods. Furthermore, we will present data to suggest that comparative studies between M. truncatula and the other members of this genus could provide useful insight into the regulation of reproductive allocation in legumes.