Articles
Nitrogen storage and biennial bearing in apple
Article number
1432_7
Pages
51 – 58
Language
English
Abstract
Biennial bearing, or alternate bearing, occurs for some apple cultivars and is characterized by a heavy crop one year, the “on” year, accompanied by little to no crop the following year, the “off” year.
While environmental factors such as spring frosts and drought can initiate a biennial bearing cycle in fruit trees, genetics also play an important role, with certain cultivars having a greater likelihood of bearing biennially.
In apples, ‘Honeycrisp’ is prone to biennial bearing, even when environmental factors remain favorable for fruit production.
Regenerative buds can make up more than 90% of buds in an “on” year, while in the “off” year, maybe 20% or less of the buds are reproductive.
Nonstructural carbohydrates fulfill distinct roles within plants, influencing flower bud initiation and fruit bud formation.
Moreover, nitrogen reserves also have an important role in spring growth and flowering.
We sought to quantify nonstructural carbohydrate and nitrogen levels of various plant tissues in both “on” and “off” trees of ‘Honeycrisp’ and ‘Gala’. Nonstructural carbohydrates were higher in trees with a higher crop load in ‘Honeycrisp’, while nitrogen levels were lower in high-cropped trees.
In ‘Gala’, carbohydrate and nitrogen content was not different between crop loads.
In 2023, there was less separation for ‘Honeycrisp’. We theorize that abnormal events in 2022, when leaf senescence was disrupted and delayed going into winter, could have disrupted normal carbohydrate and nitrogen translocation patterns in the trees.
Crop load had more of an effect on carbohydrate and nitrogen levels for ‘Honeycrisp’ than ‘Gala’. Carbohydrate and nitrogen levels of trees impact biennial bearing, although the strength and influence of these relationships are currently unclear.
While environmental factors such as spring frosts and drought can initiate a biennial bearing cycle in fruit trees, genetics also play an important role, with certain cultivars having a greater likelihood of bearing biennially.
In apples, ‘Honeycrisp’ is prone to biennial bearing, even when environmental factors remain favorable for fruit production.
Regenerative buds can make up more than 90% of buds in an “on” year, while in the “off” year, maybe 20% or less of the buds are reproductive.
Nonstructural carbohydrates fulfill distinct roles within plants, influencing flower bud initiation and fruit bud formation.
Moreover, nitrogen reserves also have an important role in spring growth and flowering.
We sought to quantify nonstructural carbohydrate and nitrogen levels of various plant tissues in both “on” and “off” trees of ‘Honeycrisp’ and ‘Gala’. Nonstructural carbohydrates were higher in trees with a higher crop load in ‘Honeycrisp’, while nitrogen levels were lower in high-cropped trees.
In ‘Gala’, carbohydrate and nitrogen content was not different between crop loads.
In 2023, there was less separation for ‘Honeycrisp’. We theorize that abnormal events in 2022, when leaf senescence was disrupted and delayed going into winter, could have disrupted normal carbohydrate and nitrogen translocation patterns in the trees.
Crop load had more of an effect on carbohydrate and nitrogen levels for ‘Honeycrisp’ than ‘Gala’. Carbohydrate and nitrogen levels of trees impact biennial bearing, although the strength and influence of these relationships are currently unclear.
Authors
T. Campbell, L. Kalcsits
Keywords
nitrogen remobilization, carbohydrate translocation, crop load management, flower bud initiation
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