What is the Difference Between Orthodox and Recalcitrant Seeds

The key difference between Orthodox and recalcitrant seeds is that orthodox seeds survive during drying and freezing in ex situ conservation, while recalcitrant seeds do not survive during drying and freezing in ex situ conservation.

Moisture is the amount of water content in seeds. The seed moisture is expressed as a percentage. A small change in seed moisture content has a large effect on the storage of the seeds. In order to reasonably predict the possible storage life of each accession, the moisture content of seeds should be determined. The terms orthodox and recalcitrant seeds came into usage in 1973. E.H Roberts classified seeds for the first time based on physiological behaviour such as seeds moisture content into two categories: orthodox and recalcitrant seeds. Currently, seeds are divided into three groups based on seed moisture content: orthodox, intermediate and recalcitrant.

CONTENTS

1. Overview and Key Difference
2. What are Orthodox Seeds
3. What are Recalcitrant Seeds
4. Similarities – Orthodox and Recalcitrant Seeds
5. Orthodox vs Recalcitrant Seeds in Tabular Form
6. Summary

What are Orthodox Seeds?

Orthodox seeds are the seeds that survive during drying and freezing in ex situ conservation. According to details of the U.S Department of Agriculture, there is a variation in the ability of orthodox seeds to withstand drying and freezing. It was identified that some seeds are more sensitive than others. Typically, orthodox seeds are long-lived seeds. Orthodox seeds can successfully have dry to moisture contents as low as 5% without any injury. They are also able to tolerate freezing. Therefore, they are also known as desiccation-tolerant seeds. Moreover, orthodox seeds have a prolonged life with low moisture content and freezing temperatures. Therefore, ex situ conservation of orthodox seeds is not problematic.

Figure 01: Orthodox Seeds

Examples of orthodox seeds are seeds of most annual crops, biennial crops and agroforestry species. These crops have normal small seeds. Furthermore, orthodox seed plants include Capsicum annum, Citrus aurantifolia, Phoenix dactylifera, Hamelia patens, Lantana camera, Pisidium guajava, Anacardium occidentale, etc. The seeds of most legumes and grains are also included in this group. The life span of orthodox seeds is around 100 years to 2000 years.

What are Recalcitrant Seeds?

Recalcitrant seeds are the seeds that will not survive during drying and freezing in ex situ conservation. They cannot be stored for long periods like orthodox seeds because they do lose their viability. Typically, recalcitrant seeds are very large in size. These seeds cannot survive drying below 20-30% relative moisture content without any injury. They are also known as desiccation sensitive seeds. The storing of recalcitrant seeds is problematic in ex situ conservation.  This is because their high moisture content encourages microbial growth and results in rapid seed deterioration. Secondly, storing recalcitrant seeds at freezing temperatures causes ice crystal formation that disrupts cell membranes. Therefore, plants that produce recalcitrant seeds must be stored in the growing phase rather than seeds.

Figure 02: Recalcitrant Seeds

Recalcitrant species belong to trees and shrubs. Some examples of plants that produce recalcitrant seeds are avocado, cacao, coconut, jackfruit, lychee, mango, rubber, tea, plants used in traditional medicine, some horticultural tress, etc. Furthermore, the longevity of recalcitrant seeds is remarkably short, from few weeks to months.

What are the Similarities Between Orthodox and Recalcitrant Seeds?

• Orthodox and recalcitrant seeds are types of seeds based on seed moisture content.
• Both terms were coined by Eric Roberts.
• These terms came into usage in 1973.
• These seeds types are used in modern agriculture practices.

What is the Difference Between Orthodox and Recalcitrant Seeds?

Orthodox seeds are the seeds that will survive during drying and freezing in ex situ conservation. In contrast, recalcitrant seeds are the seeds that will not survive during drying and freezing in ex situ conservation. So, this is the key difference between orthodox and recalcitrant seeds. Furthermore, orthodox seeds can successfully dry to moisture contents as low as 5% without any injury, while recalcitrant seeds cannot dry to moisture contents below 20-30% without any injury.

The following side by side comparison table details the differences between orthodox and recalcitrant seeds.

Summary – Orthodox vs Recalcitrant Seeds

E.H Roberts, in 1973, coined the terms orthodox and recalcitrant seeds. He classified seeds for the first time based on physiological behaviour such as seeds moisture content. The key difference between Orthodox and recalcitrant seeds is that orthodox seeds survive during drying and freezing in ex situ conservation, while recalcitrant seeds do not survive during drying and freezing in ex situ conservation.

Reference:

1. “Orthodox Seed.” An Overview | ScienceDirect Topics.
2. “Recalcitrant Seed.” An Overview | ScienceDirect Topics.

Image Courtesy:

1. “Orthodox seeds” By Gmihail at Serbian Wikipedia – Own work (CC BY-SA 3.0 rs) via Commons Wikimedia
2. “Recalcitrant seed” By Gmihail at Serbian Wikipedia – Own work (CC BY-SA 3.0 rs) via Commons Wikimedia

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