The BBCH-scale for citrus is a classification system used in biology to describe the phenological development of citrus plants using the BBCH-scale.
Biology is the natural science that studies life and living organisms, including their physical structure, chemical processes, molecular interactions, physiological mechanisms, development and evolution. Despite the complexity of the science, there are certain unifying concepts that consolidate it into a single, coherent field. Biology recognizes the cell as the basic unit of life, genes as the basic unit of heredity, and evolution as the engine that propels the creation and extinction of species. Living organisms are open systems that survive by transforming energy and decreasing their local entropy to maintain a stable and vital condition defined as homeostasis.
Phenology is the study of periodic plant and animal life cycle events and how these are influenced by seasonal and interannual variations in climate, as well as habitat factors. The word, coined by the Belgian botanist Charles Morren around 1849, is derived from the Greek φαίνω (phainō), "to show, to bring to light, make to appear" + λόγος (logos), amongst others "study, discourse, reasoning" and indicates that phenology has been principally concerned with the dates of first occurrence of biological events in their annual cycle. Examples include the date of emergence of leaves and flowers, the first flight of butterflies and the first appearance of migratory birds, the date of leaf colouring and fall in deciduous trees, the dates of egg-laying of birds and amphibia, or the timing of the developmental cycles of temperate-zone honey bee colonies. In the scientific literature on ecology, the term is used more generally to indicate the time frame for any seasonal biological phenomena, including the dates of last appearance.
Citrus is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, lemons, grapefruits, pomelos, and limes.
The phenological growth stages and BBCH-identification keys of citrus plants are:
| Growth stage | Code | Description |
|---|---|---|
| 0: Sprouting/Bud development | 00 | Dormancy: leaf and inflorescence buds undifferentiated, closed and covered by green scales |
| 01 | Beginning of bud swelling | |
| 03 | End of bud swelling: green scales slightly separated | |
| 07 | Beginning of bud burst | |
| 09 | Green leaf tips visible | |
| 1: Leaf development | 10 | First leaves separating: green scales slightly open, leaves emerging |
| 11 | First leaves visible [1] | |
| 15 | More leaves visible, not yet at full size | |
| 19 | First leaves fully expanded | |
| 3: Shoot development | 31 | Beginning of shoot growth: axes of developing shoots visible |
| 32 | Shoots about 20% of final length | |
| 39 | Shoots about 90% of final length | |
| 5: Inflorescence emergence | 51 | Inflorescence buds swelling: buds closed, light green scales visible |
| 53 | Bud burst: scales separated, floral tips visible | |
| 55 | Flowers visible, still closed (green bud), borne on single or multiflowered leafy or leafless inflorescences | |
| 56 | Flower petals elongating; sepals covering half corolla (white bud) | |
| 57 | Sepals open: petal tips visible; flowers with white or purplish petals, still closed | |
| 59 | Most flowers with petals forming a hollow ball | |
| 6: Flowering | 60 | First flowers open |
| 61 | Beginning of flowering: about 10% of flowers open | |
| 65 | Full flowering: 50% of flowers open; first petals falling | |
| 67 | Flowers fading: majority of petals fallen | |
| 69 | End of flowering: all petals fallen | |
| 7: Development of fruit | 71 | Fruit set; beginning of ovary growth; beginning of fruitlets abscission |
| 72 | Green fruit surrounded by sepal crown | |
| 73 | Some fruits slightly yellow: beginning of physiological fruit drop | |
| 74 | Fruits about 40% of final size. Dark green fruit: end of physiological fruit drop | |
| 79 | Fruits about 90% of final size | |
| 8: Maturity of fruit | 81 | Beginning of fruit colouring (colour-break) |
| 83 | Fruit ripe for picking; fruit has not yet developed variety-specific colour | |
| 85 | Advanced ripening; increase in intensity of variety-specific colour | |
| 89 | Fruit ripe for consumption; fruit has typical taste and firmness; beginning of senescence and fruit abscission | |
| 9: Senescence, beginning of dormancy | 91 | Shoot growth complete; foliage fully green |
| 93 | Beginning of senescence and abscission of old leaves | |
| 97 | Winter dormancy period | |