Biotechnology Aids Orchard Management
Commercial production of tree fruits such as apple is labor-intensive. Mechanization of some or all of the manual tasks, such as tree pruning, fruit thinning, and fruit harvesting, has been a long time coming in orchard management. Although a number of platforms or machines have been developed, most of them remain to be improved to better serve the intended tasks.
One of the major challenges in mechanization of these routine manual tasks in orchard management is the irregularity of tree canopy, which is dynamic, complex, tall and wide, and highly variable depending on scion cultivars as well as rootstocks. In general, shorter tree statures with a narrower and more uniform canopy are friendlier to both humans and machines. Such tree form is also considered to be ideal for optimal light distribution, fruit size and fruit quality.
Are there any ways other than manual training to make the tree canopy friendly for mechanization of those labor-intensive routines in orchard management? A short answer is ‘Yes’ from a plant biotechnical viewpoint. Below I will briefly describe, using apples as an example, why biotechnology can play a key role in making the tree canopy more friendly for mechanization.
Natural Growth Variations
Like others, apple trees grow many lateral branches with an angle ranging from 30 to 60 degrees from the vertical axis, which form the canopy. Such tree growth habit is most common and called ‘standard’ in apple tree morphological studies. Nearly all commercial apple cultivars, such as ‘Red Delicious,’ ‘Empire,’ ‘Fuji,’ ‘Gala,’ ‘Golden Delicious,’ ‘Granny Smith,’ ‘McIntosh,’ and others are of ‘standard’ tree growth habit.
In addition to ‘standard,’ there are ‘columnar’ and ‘weeping’ growth habits in apple. Columnar growth habit was originally discovered from a sport (mutation) of ‘McIntosh,’ called ‘Wijcik McIntosh.’ Compared with ‘McIntosh,’ ‘Wijcik McIntosh’ has fewer branches that grow vertically, shorter internodes, and more spurs on the lateral shoots. Columnar trees mostly bear fruits on spurs that are branched on old wood, thus need little pruning. Due to these desirable characteristics of ‘Wijcik McIntosh,’ it has been used in apple breeding programs to develop columnar apple cultivars, which have a simple canopy suitable for high density orchards. There are many columnar apple cultivars available, such as ‘Irish Spire,’ ‘Telamon,’ and ‘Tuscan,’ but none of them are grown on a large commercial scale.
Weeping growth habit can be found in crabapples, such as ‘Red Jade’ and ‘Cheal’s Weeping,’ but it has not been used in commercial apple production thus far.
Understand Branch Growth
Extensive genetic studies have demonstrated that columnar growth habit is controlled by a single gene, dubbed Co. In the case of weeping, however, only a few dated reports are available. To date, the genetic control of weeping growth habit remains unknown.
Recently, National Science Foundation (NSF) Plant Genome Research Program has funded an in-depth collaborative research project led by Cornell University and USDA-ARS Appalachian Fruit Research Station in Kearneysville, WV (Assistant Professor Kenong Xu, Plant Molecular Biologist Chris Dardick and Research Engineer Amy Tabb). One of the ultimate goals of this project is to make apple and peach tree canopies friendlier for orchard operations by machines.
To accomplish the project research goals, genes control columnar and weeping growth habits will be identified to gain genetic and molecular insights into tree branch angles.
In addition, trees of standard, columnar and weeping growth habits will be investigated in detail to elucidate the underlying gene networks responsible for their differences in branch number, angle, size and shape. To better evaluate how trees grow in orchard and greenhouse conditions, Tabb has developed a robotic system for 3D tree architecture phenotyping. Achieving the project goals will lead to identification of a list of critical genes that control how apple and peach branches grow.
Precision Genome Editing
As described previously in my column in the September 2015 issue, the development of the CRISPR (Clustered regularly-interspaced short palindromic repeats) system represents a major breakthrough in biotechnology, especially in precision genome editing.
Once the genes that control tree branch growth behavior are identified, these genes not only can be used to assist the selection in conventional breeding programs, but also can be targeted by the CRISPR system to precisely edit them so that apple cultivars with a machine-friendly canopy will be developed, addressing one of the major challenges in mechanization of the manual tasks in orchard management.
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