Unmanned aerial systems (UAS)-based field high throughput phenotyping (HTP) as plant breeders’ toolbox: A comprehensive review

It is projected that food demand will exceed its supply in 2050 due to global population growth if the production rate remains the same. Replacement of natural vegetation by cropland is unsustainable as it could cause global warming worse. Increasing the rate of genetic gain through artificial selection, also known as plant breeding, is a sustainable approach. Phenotyping, a process of measuring plant characteristics (traits), is unavoidable in plant breeding regardless of which methods (molecular or conventional) being used. Traditional phenotyping of a complex trait has been a bottleneck due to its labor-intensive and time-consuming nature. In recent years, there has been a massive scientific investigation on utilizing an unmanned aerial system (UAS) for agricultural application, as well as high throughput phenotyping (HTP) platform. Although there have been existing literature reviews on UAS-based HTP, a review discussing the pipeline of implementing this tool and in what situations or applications plant breeders could utilize it as a tool is still limited. Consequently, this paper overviews (1) a potential bottleneck in plant breeding pipeline, (2) necessary equipment and regular pipeline for implementing UAS-based HTP, (3) various plant phenotyping tasks that could be accomplished by using UAS-based HTP, including a trait-direct measurement, predictive breeding, application of UAS-based HTP as a marker and, identification of quantitative trait loci (QTLs), (4) contributions of UAS-based HTP on improving the rate of genetic gain, and (5) an outline of the future direction of plant breeding in the high throughput era alongside with artificial intelligence. This comprehensive review would be beneficial to plant breeders, especially those who are considering adopting this technology to their programs.