Citrus Production: Citrus (Citrus sp. L.)

1. Introduction:

• Citrus: Citrus sp. L.
• Chromosome No. 2n = 18
• Family: Rutaceae
• Crop is native to South East Asia and Indo China
• Citrus are branched evergreen trees
• Leaves are leathery in texture
• Spines arises from the axis of the leaves
• Fruits are hesperidium with five locules
• Inflorescence: Cymose type
• Staminate and hermaphrodite flowers
• Flowers are white in colour
• Lemon and Citron are purplish on outside
• Five sepals, five petals, numerous stamens
• Pollen viability 45 – 80 % depends upon season
• Long juvenile period
• Full bloom in spring
• Three flowering seasons in citrus:

Season

2. Cultivated species of Citrus:

• Citrus sinensis: Orange
• Citrus reticulate: Mandarin
• Citrus paradise: Grape fruit
• Citrus limon burm: Lemon
• Citrus aurantifolia: Lime
• Citrus maxima: Pummelo
• Citrus medica: Citron

3. Objectives of Scion Improvement:

• Seedlessness
• High productivity
• Sensory fruit quality (Loose peel, Pigments)
• Fruit quality (TSS/acid ratio, Juice content, flavor and colour)
• Season of ripening
• Resistance to adverse climatic and soil conditions

4. Objectives of Rootstock Improvement:

• Compatibility with important scion cultivars with wider adaptability
• Higher number of seeds per fruit and polyembryony
• Tolerant to salinity, drought, cold and water lodging
• Reduction of tree size in scion cultivars
• Quality contribution to scion
• Resistance to biotic factors

5. Genus: Citrus (WT Swingle, 1948)

A) Sub – genus: Eucitrus

• Citrus medica: Citron
• Citrus limon: Lemon
• Citrus aurentifolia: Acid / Sour lime
• Citrus auratinum: Sour / Bitter Orange
• Citrus sinensis: Sweet Orange
• Citrus reticulate: Mandarin
• Citrus grandis: Pummelo
• Citrus paradise: Grape Fruit
• Citrus indica: Indian wild orange
• Citrus tachibana: Tachibana Orange

B) Sub – genus: Eucitrus

• Citrus ichangensis
• Citrus latipes
• Citrus micrantha
• Citrus celebica
• Citrus microptera
• Citrus hystrix

Most citrus species are diploid.

One natural triploid is Tahiti lime (Citrus latifolia)

Genome size: 360 Mbp

6. Inheritance of Characters:

• Leaf characters: Two major genes
• Anthocyanin pigment in leaf: Dominant gene controlling reddish colour
• Anthocyanin pigment in fruit: More than one recessive gene
• Tristeza virus: Single allele
• Fruit texture: Polygenic control
• Polyembryony: More than one single gene
• Nucellar embryony: One or two dominant gene

7. Breeding Bottlenecks:

• Male or female sterility
• Self / Cross compatibility
• Long juvenile period
• Nucellar embryony
• Breeding Outline:

• Breeding Methods:
• Introduction
• Selection
• Hybridization
• Mutation Breeding
• Polyploidy Breeding
• In-vitro Plant Regeneration
• Somaclonal Variations
• Micro Grafting
• Shoot Tip Culture
• Somatic Hybridization
• Anther Culture
• Embryo Rescue
• Mapping and Marker Assisted Selection
• Gene Transformation
• Gene Editing
• Genome Sequencing
• Resistance to biotic and abiotic stress