Abstract
Herbaceous perennial species are receiving increased attention for their potential to provide both edible products and ecosystem services in agricultural systems. Many legumes (Fabaceae Lindl.) are of special interest due to nitrogen fixation carried out by bacteria in their roots and their production of protein-rich, edible seeds. However, herbaceous perennial legumes have yet to enter widespread use as pulse crops, and the response of wild, herbaceous perennial species to artificial selection for increased seed yield remains under investigation. Here we compare cultivated and wild accessions of congeneric annual and herbaceous perennial legume species to investigate associations of lifespan and cultivation with early life stage traits including seed size, germination, and first year vegetative growth patterns, and to assess variation and covariation in these traits. We use “cultivated” to describe accessions with a history of human planting and use, which encompasses a continuum of domestication. Analyses focused on three annual and four perennial species of the economically important genus Phaseolus. We found a significant association of both lifespan and cultivation status with seed size (weight, two-dimensional lateral area, length), node number, and most biomass traits (with cultivation alone showing additional significant associations). Wild annual and perennial accessions primarily showed only slight differences in trait values. Relative to wild forms, both cultivated annual and cultivated perennial accessions exhibited greater seed size and larger overall vegetative size, with cultivated perennials showing greater mean trait differences relative to wild accessions than cultivated annuals. Germination proportion was significantly lower in cultivated relative to wild annual accessions, while no significant difference was observed between cultivated and wild perennial germination. Regardless of lifespan and cultivation status, seed size traits were positively correlated with most vegetative traits, and all biomass traits examined here were positively correlated. This study highlights some fundamental similarities and differences between annual and herbaceous perennial legumes and provides insights into how perennial legumes might respond to artificial selection compared to annual species.
Highlights
Life history theory traditionally categorizes plants as annuals, typified by fast growth and high reproductive effort, and perennials, typified by long-term survival and delayed reproduction (Cole, 1954; Harper, 1977)
We explore life history differences in members of the common bean genus Phaseolus by addressing the following questions: 1) How do wild annual and perennial Phaseolus species from multiple geographic origins allocate resources to seed production and vegetative growth? 2) What is the phenotypic signature of artificial selection in cultivated annual and perennial Phaseolus species? 3) What covariation exists between seed and adult vegetative growth traits, and is it consistent across lifespans and between cultivated and wild forms in Phaseolus? We address these questions by examining seed size, germination, and vegetative growth allocation among three annual and four perennial Phaseolus species (Figure 1)
We found that wild accessions of annual species showed nonsignificantly greater germination and vegetative trait values than wild perennial accessions, but did not show greater seed size traits (Figure 2)
Summary
Life history theory traditionally categorizes plants as annuals, typified by fast growth and high reproductive effort, and perennials, typified by long-term survival and delayed reproduction (Cole, 1954; Harper, 1977) Exceptions to this general trend occur; patterns of plant resource allocation exist along a gradient, with some perennial species showing fast growth and high reproductive output (e.g., Verboom et al, 2004; González-Paleo and Ravetta, 2015). Exploration of this life history diversity is important in plant breeding, as wild, herbaceous perennial species are increasingly considered as sources of novel genetic variation through crosses and as entirely new domesticates targeted for seed products. Current research focuses in part on the development of crops to support the ecological intensification of agriculture, which aims to achieve both high yields and ecosystem services, such as soil and water retention (Ryan et al, 2018)
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