Abstract
AbstractBreeding programs for wheat (Triticum aestivum L.) and other crops require one or more generations of seed increase before replicated trials can be sown to assess yield. Extensive phenotyping at this stage is challenging because of the small sizes of plots and large numbers of lines under evaluation, and therefore, breeders typically rely on visual selection to promote lines to yield evaluation. Aerial high‐throughput phenotyping (HTP) enables the rapid acquisition of traits that may be useful for selection among early generation lines. With the objective of assessing the potential for aerial measurements recorded on seed increase plots to improve indirect selection for grain yield (GY), two sets of 1,008 early generation bread wheat breeding lines were sown both as replicated yield trials (YTs) and as small, unreplicated plots (SPs) at the International Maize and Wheat Improvement Center during two breeding cycles. Normalized difference vegetation indices (NDVI) collected with an unmanned aerial vehicle (UAV) in the SPs were observed to be heritable and moderately correlated with GY assessed in YTs. Furthermore, NDVI was more predictive of GY than univariate genomic selection (GS), with still higher overall predictive abilities from multitrait approaches. A related experiment showed that selection based on NDVI would have outperformed visual selection, though this approach would have driven a directional response in phenology because of confounding between phenology, NDVI, and GY. A restricted selection index was proposed to address this issue. These results provide a promising outlook for the use of aerial HTP to improve selection at the early generation, seed‐limited stages of breeding programs.
Highlights
For small grains as well as many other crops such as soybean and rice, limited seed yield per plant after deriving fixed lines can delay replicated yield testing until sufficient quantities of seed are accumulated through one or more generations of seed increase
The aerial Vegetation indices (VIs) traits were found to be more heritable than grain yield (GY) in both the yield trials (YT) and small plots (SP), and minimal differences were observed with respect to heritability among the multiple time-points on which the HTP traits were recorded
This is the first report aiming to assess the heritability of aerial VI traits measured on small, unreplicated plots and estimate the extent to which they are predictive of GY in replicated yield trials
Summary
For small grains as well as many other crops such as soybean and rice, limited seed yield per plant after deriving fixed lines can delay replicated yield testing until sufficient quantities of seed are accumulated through one or more generations of seed increase. The generation at which this occurs depends on the crop and breeding scheme followed, though in theory this may begin as early as the F3 with yield testing at the F4. Breeding lines at this stage are typically subject to visual selection, largely for phenology and disease resistance, as more extensive phenotyping is limited by time and costs. Selection at the early generation seed-limited stage of a breeding program relies on the assumption that the phenotype of a breeding line when sown in a small, unreplicated plot is predictive of its eventual performance in a larger replicated yield trial The ability to accurately cull breeding lines with low potential in the early generation seed-limited stage is highly desirable because it reduces subsequent expenditure on costly yield testing (Brennan, 1988).
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