An efficient RGB-UAV-based platform for field almond tree phenotyping: 3-D architecture and flowering traits

Francisca López-Granados,María Lovera,Ana I. de Castro,Jorge Torres-Sánchez,Octavio Arquero,Francisco M. Jiménez-Brenes

doi:10.1186/s13007-019-0547-0

Abstract

BackgroundAlmond is an emerging crop due to the health benefits of almond consumption including nutritional, anti-inflammatory, and hypocholesterolaemia properties. Traditional almond producers were concentrated in California, Australia, and Mediterranean countries. However, almond is currently present in more than 50 countries due to breeding programs have modernized almond orchards by developing new varieties with improved traits related to late flowering (to reduce the risk of damage caused by late frosts) and tree architecture. Almond tree architecture and flowering are acquired and evaluated through intensive field labour for breeders. Flowering detection has traditionally been a very challenging objective. To our knowledge, there is no published information about monitoring of the tree flowering dynamics of a crop at the field scale by using color information from photogrammetric 3D point clouds and OBIA. As an alternative, a procedure based on the generation of colored photogrammetric point clouds using a low cost (RGB) camera on-board an unmanned aerial vehicle (UAV), and an semi-automatic object based image analysis (OBIA) algorithm was created for monitoring the flower density and flowering period of every almond tree in the framework of two almond phenotypic trials with different planting dates.ResultsOur method was useful for detecting the phenotypic variability of every almond variety by mapping and quantifying every tree height and volume as well as the flowering dynamics and flower density. There was a high level of agreement among the tree height, flower density, and blooming calendar derived from our procedure on both fields with the ones created from on-ground measured data. Some of the almond varieties showed a significant linear fit between its crown volume and their yield.ConclusionsOur findings could help breeders and researchers to reduce the gap between phenomics and genomics by generating accurate almond tree information in an efficient, non-destructive, and inexpensive way. The method described is also useful for data mining to select the most promising accessions, making it possible to assess specific multi-criteria ranking varieties, which are one of the main tools for breeders.

Highlights

Almond is an emerging crop due to the health benefits of almond consumption including nutritional, anti-inflammatory, and hypocholesterolaemia properties
Four out of the six common varieties in both fields (Fd, Gu, La, Tu) showed similar flowering tends, i.e., maximal flower densities in the unmanned aerial vehicle (UAV) imagery taken on the 8th and 9th of March
Two almond phenotyping trials with trees of different ages were evaluated throughout a complete growing cycle using an approach based on two steps: (i) the generation of photogrammetric point clouds from images acquired with a low-cost camera on-board a UAV; and (ii) analysis of the point clouds using a fully automatic object based image analysis (OBIA) algorithm

Summary

Introduction

Almond is an emerging crop due to the health benefits of almond consumption including nutritional, anti-inflammatory, and hypocholesterolaemia properties. There is no published information about monitoring of the tree flowering dynamics of a crop at the field scale by using color information from photogrammetric 3D point clouds and OBIA. A procedure based on the generation of colored photogrammetric point clouds using a low cost (RGB) camera on-board an unmanned aerial vehicle (UAV), and an semi-automatic object based image analysis (OBIA) algorithm was created for monitoring the flower density and flowering period of every almond tree in the framework of two almond phenotypic trials with different planting dates. Almond (Prunus dulcis (Mill.) D.A. Webb) is an emerging and valuable crop due to the health benefits of almond consumption, including nutritional, anti-inflammatory, and hypo-cholesterolemia properties [1], and to the wide range of applications of almond by-products, e.g., almond shells are burned as fuel, and almond hulls are used as livestock feed [2], which increases almond’s potential profitability. Almond is a useful alternative crop because its agricultural machinery can be shared by both kinds of orchards, since their harvest and cultural practices are carried out on different dates (olive is harvested in winter and almond in late summer)

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Conclusion