Luciana González-Paleo

Thinopyrum intermedium (c.n. intermediate wheatgrass), marketed under the trade name Kernza, is a promising species for perennial grain production based on seed size, ease of threshing, resistance to shattering, and grain quality. Although numerous generations of breeding for seed yield have been completed, the impact of selection on non-target traits is unknown. Here, we evaluated structural and functional changes brought about by selection for seed yield over a sequence of nine selection cycles (C0 to C9). In two experiments under semi-controlled environmental conditions, we compared gas exchange (A, E, gs, and A/Ci curves), leaf and root morphology, and the structure of seedlings from 10 generations. We found that the selection for yield throughout cycles indirectly changed the leaf structure (leaf size, leaf thickness, and leaf anatomy) and physiology (carbon acquisition and transpiration per unit area), with later cycles showing larger leaves with higher rates of CO₂ assimilation and transpiration. Changes in root structure followed similar trends: selection resulted in longer, more branched, and finer roots. These changes in non-target traits are linked to resource-use strategies and to ecosystem services provided by Kernza. Understanding how the domestication of perennial grains impacts non-target traits will aid in the design of integrated breeding programs for Kernza and other perennial grain crops.

Improvements in seed yield during domestication and breeding are frequently achieved moving plants from the conservative syndrome of the plant economic spectrum towards the more acquisitive side, changing how plants acquire, allocate, use and store C and nutrients in relation to their wild relatives. The aims were to evaluate if domestication changed the N allocation, the internal plant N recycling (N resorption efficiency and proficiency, and N storage) and N‐use‐efficiency, in the perennial new crop Silphium integrifolium. We compared in a field experiment repeated in two locations (Kansas and Patagonia), a Wild (W) and two improved accessions, with high‐ (HYI) and low‐seed yield improved (LYI) accessions. HYI accessions produced more than twice the biomass and acquired twofold more N than LYI and Wild accessions. Changes in proportional N allocation were similar in both improved accessions (HYI and LYI) and locations: higher allocation to leaves and lower to the crown at pre‐anthesis (growth‐storage trade‐off) and higher allocation to seeds and lower to the crown at maturity (reproduction‐storage trade‐off). HYI and LYI allocated 50% more N to seeds in average, reducing a 31% the N allocated to the crown in relation to the Wild. Nitrogen use efficiency (NUE) and mean residence time (MRT) of N were reduced in both improved accessions. In HYI, the lower MRT was related to the lower storage of N in the crown and N removal through seed production, and in LYI was the result of the N lost through leaf senescence. HYI produced litter with lower N concentration (more proficient) that the wild accession. These could decrease the net N mineralization rate and soil N availability at long term. HYI plants should require higher external N inputs to the soil to sustain their N uptake requirements. LYI and Wild accessions, had lower resorption efficiency, but N recycled was allocated to the crown for future remobilization and uses (better internal cycling). The leaf litter type of these accessions with higher N content should sustain faster N‐cycles rates and N release to the soil. If the focus is on the ecosystem services, HYI accessions could help achieve a reduction in nitrate leaching by maximizing N uptake, N resorption and N removal through seed (i.e. nitrate catch crop), and also produce crop residues that slow down biogeochemical cycling and soil nutrient retention.

The perennial sunflower Silphium integrifolium Michx. (Asteraceae), also known as silflower, is a prospective dual-purpose forage plus grain crop. Pre-flowering biomass harvest for animal feed and the subsequent delay in plant growth and anthesis has the potential to benefit seed yield and/or offset yield loss from native pests, such as the native North American Eucosma giganteana (Lepidopera: Tortricidae). The aim of this study was to develop a cropping technology for silflower to (A) balance forage and grain production and (B) minimize seed loss. Silflower produced high-quality forage, but biomass harvest in early spring reduced same-season seed production by 45%. Despite significantly delaying flowering, forage harvest alone did not effectively reduce Eucosma colonization, although treating plants with the insecticide permethrin did reduce colonization. Our results do not support the proposal that S. integrifolium could be profitably harvested for both high quality forage and as an oilseed grain within the same season. Nevertheless, our findings suggest the possibility of developing a strategy of alternating between forage or seed production, depending on their differential economic values. The choice between harvesting biomass vs. seed could be made much later in the season for this perennial crop than the choice of planting an annual forage vs. annual grain crop.

Domestication of desert‐adapted perennials has been proposed as an alternative to increase cropping intensity in low input environments. However, selection for high yield in perennial crops provokes indirect changes in plant resource use. These changes might alter how nitrogen is acquired, allocated, used and stored, thus affecting plant longevity and yield stability. Using the perennial forb Physaria as a model, we compared the pattern of N allocation, use and conservation of high‐yield accessions (Y), and stable yield accessions (S), with their wild counterpart (W). We found a negative relationship between seed yield and N conservation capacity and their associated traits. The shift of strategy provoked by high yield selection implies changes in N allocation and a decrease in nitrogen use efficiency and conservation capacity at plant‐ and leaf‐level. S accessions also increase allocation to seeds, although they kept the N use and conservation traits of their wild counterparts, remaining in an intermediate position between the Y and W accessions profiles. The shift of strategy provoked by high yield selection implies a decrease in nitrogen use efficiency and conservation capacity that may be behind the loss of longevity and yield on subsequent years. Wild and stable accessions were more conservative and show traits that promote nitrogen conservation. These are key traits that should not be lost during the selection process if breeders want to achieve the adequate ideotype of perennial crop for arid systems.

Silflower (Silphium integrifolium Michx.) is in the early stages of domestication as a perennial version of oilseed sunflower, its close relative. Grain crops with deep perennial root systems will provide farmers with new alternatives for managing soil moisture and limiting or remediating soil erosion, fertilizer leaching, and loss of soil biota. Several cycles of selection for increased seed production potential following initial germplasm evaluation in 2002 have provided opportunities to document the botany and ecology of this relatively obscure species, to compare agronomic practices for improving its propagation and management, and to evaluate the differences between semi-domesticated and wild accessions that have accrued over this time through intentional and unintentional genetic processes. Key findings include: domestication has increased aboveground biomass at seedling and adult stages; seed yield has increased more, achieving modest improvement in harvest index. Harvest index decreases with nitrogen fertilization. Silflower acquires nitrogen and water from greater depth than typical crops. In agricultural silflower stands within its native range, we found that Puccinia silphii (rust) and Eucosma giganteana (moth) populations build up to unacceptable levels, but we also found genetic variation for traits contributing to resistance or tolerance. Breeding or management for reduced height and vegetative plasticity should be top priorities for future silflower research outside its native range.