ADVANCES IN CITRUS BREEDING, Breeding methods

ADVANCES IN CITRUS BREEDING

1. An Assignment on ADVANCES IN CITRUS BREEDING COURSE TITLE- ADVANCES IN BREEDING OF FRUIT CROPS COURSE NO.- FSC- 602 CREDIT HOURS- 3 (2+1) Submitted to Dr. Rajshree Shukla Krantikari Debridhur College of Horticulture and Research Station, Jagdalpur Submitted by Vidhya Sagar Mali Ph.D previous year Dept. of Fruit Science Mahatma Gandhi University of Horticulture and Forestry (C.G.)

2. Contents Introduction Centre of origin, Taxonomy and Classification Cytogenetics, Genetic resources, Floral biology and Objectives Attributes of Scion and Rootstocks Different approaches in citrus improvement Future aspects of citrus breeding References Mahatma Gandhi University of Horticulture and Forestry (C.G.)

3. Mahatma Gandhi University of Horticulture and Forestry (C.G.) 1 INTRODUCTION Botanical name Citrus spp. Family Rutaceae Chromosome no 2n= 18 Origin Native to tropical and sub-tropical regions of Southeast Asia Type of fruit Hesperidium Edible part Juicy placental hair Pollination Self pollination (Homogamy) Type of bearing habit Mix bearing Citrus

4. Mahatma Gandhi University of Horticulture and Forestry (C.G.) Centre of origin 2 S.No. Species Common name Centre of origin 1. Citrus medica L. Citron India 2. Citrus lemon L. Lemon Eastern Himalayan 3. Citrus aurantifolia swingle Kagzi lime India 4. Citrus jambhiri Lush. Rough lemon Northeast India 5. Citrus reticulata (L.) blanco Mandarin Cochin- China 6. Citrus sinensis osbeck Sweet orange Southern indo china 7. Citrus maxima Merr. Pummelo Polynesia and Malay Recent evidence supports that the Yunnan province in the Southern China may be the centre of origin as a diversity of species is found there. (Gmitter and Hu, 1990) There are three major centre of diversity in India North – East : Assam, Meghalaya, Garohills, Tripura ( Citrus indica ) South India : Gajanima, Kichli, Wild mandarin North – West region : HP, Jammu & Kashmir (Hilly areas) ; Lemon (Galgal)

5. Mahatma Gandhi University of Horticulture and Forestry (C.G.) TAXONOMY OF CITRUS 3 Kingdom Plantae Division Monholiophyta Class Dicotyledonae Sub class Polypetalae Order Geraniales (21 families) Family Rutaceae (7 sub families) Subfamily Aurantoidae ( 2 tribe ) Tribe Citrea Group C The citrus fruit tree ( 6 genera ) Genus Citrus Genus Citrus consists of three genera Citrus , Fortunella and Poncirus and two subgenera : Papeda and Eucitrus . Majority are diploid Basic chromosome number is : x = 9

6. Mahatma Gandhi University of Horticulture and Forestry (C.G.) CLASSIFICATION OF CITRUS SPECIES 4 ACID GROUP Acid lime Citrus aurantifolia Sweet lime Citrus limettoides Tahiti Or Persian lime * Citrus latifolia Rangpur lime Citrus limonia Lemon Citrus limon Rough lemon Citrus jambhiri Sweet lemon Citrus limetta Volkamer lemon Citrus volkameriana Kharna khatta Citrus kharna Citron * Citrus medica MANDARIN GROUP Santra/ Sweet orange Citrus reticulate Satsuma mandarin Citrus unshui Willow leaf mandarin Citrus deliciosa Cleopatra mandarin Citrus rashni King Citrus nobilis Tangerins Citrus tangerina Temple Citrus temple

7. Mahatma Gandhi University of Horticulture and Forestry (C.G.) 5 ORANGE GROUP Sweet orange Citrus sinensis Sour orange Citrus aurantium Myrtle-leaf orange Citrus myrtifolia Japanese summer grapefruit Citrus natsudaidai PUMMELO & GRAPE FRUIT GROUP Pummel or shaddock * Citrus grandis or maxima Grapefruit Citrus paradise Kumquat Fortunella spp. PAPEDA GROUP Ichang papeda Citrus inchengensis Yuzu of Japan Citrus jumos Khasi papeda Citrus latipes Melanesian papeda Citrus macroptera Mauritius papeda Citrus hitrix Alemow Citrus macrophylla OTHER SPECIES GROUP Kitchili Citrus maderaspatana Calamondrin Citrus madurensis Indian wild orange Citrus indica Gajanimma Citrus pennivesiculata

8. Mahatma Gandhi University of Horticulture and Forestry (C.G.) CYTOGENETICS OF CITRUS 6 Virtually all cultivated form of Citrus , Fortunella and Poncirus are diploid and the diploid number of chromosomes in these genera is 18. Citrus and related genera have 18 chromosome in diploid somatic cells (Frost, 1925; Nakamura, 1929). GENETIC RESOURCES INSTITUTES Accessions CSIR- north east institute of science and technology, Jorhat, Assam 132 Regional station Meghalaya namely : East Khasi, hills, eastern west Khasi hills, Nongpoh and west Jaintia hills 33 Nagpur 614 Ludhiana 17 Sriganganagar 37 Tinsukia 139 Tirupati 117

9. 7 Mahatma Gandhi University of Horticulture and Forestry (C.G.) BLOSSOM BIOLOGY BLOOMING PERIOD : Flowering in India usually occurs mainly from February to April in the most if the citrus species. INFLORESCENCE : Inflorescence in different citrus species is of cymose type. FLOWERS : Staminate and hermaphrodite. ANTHESIS : The flowers open during the morning time . Anthesis occurs between 9 AM and 12 noon in citrus. DEHISCENCE : Dehiscence of anthers in citrus takes place at different times, in some before anthesis and some after anthesis. Usman et al. 2001

10. To breed varieties suitable for export. To develop varieties having less tendency of granulation. To develop varieties suitable for different agro-climatic condition. Producing early maturity citrus fruits with high yield and fruit quality. To develop rootstocks having resistance against biotic and abiotic stresses. OBJECTIVES Mahatma Gandhi University of Horticulture and Forestry (C.G.) FLOWERING, FRUIT SET AND MATURITY OF CITRUS Region Flowering time Fruit set Ripening North India March April- May January (Mandarins) Nov-Jan (Sweet Oranges) South India Dec- April Sept-Dec Sept-Dec March- April Sept-Oct Central India March- April Sept-Oct June Oct- Feb Aug-Oct (Sweet Oranges) Feb-March * Lemon and lime throughout the year. 8

11. PROBLEMS IN CITRUS BREEDING Self incompatibility and cross incompatibility is a common phenomenon which occurs widely in citrus. Most of the varieties of grape fruit are found to be self incompatible besides some varieties of lemon, sweet orange and mandarin exhibits self incompatibility of gametophytic type governed by oppositional alleles. 1. Self incompatibility 2. Long juvenility It is a major barrier in the progress of citrus breeding in India. 3. Time Citrus being perennial in nature takes more time for bearing. However this period can be reduced to a maximum of half by top working the seedling on an old tree. 4. Polyembryony Citrus being perennial in nature takes more time for bearing. However this period can be reduced to a maximum of half by top working the seedling on an old tree. Mahatma Gandhi University of Horticulture and Forestry (C.G.) 5. Sterility High level of sterility often leads to production of seedless fruits which is serious hindrance to develop varieties. 9 Singh et al., 2023

12. INHERITANCE CHARACTERS OF CITRUS Characters Inheritance References Leaf Character Two principal genes Soost and Cameron 1975 Anthocyanin pigment in leaf Dominant gene controlling this reddish colour Taxopene 1962 Anthocyanin pigment in Fruit More than one recessive genes are involved Spigel- roy1988 Tristeza virus Single allele Mestre, 1997 Texture Polygenic control Yamamoto, 1990 Polyembryony More than one single gene Maheshwari and Rangaswamy, 1958 Seedless A recessive gene Spigel- roy1982 Nucellar embryony One or two dominant gene Soost and Cameron 1975 Mahatma Gandhi University of Horticulture and Forestry (C.G.) 10

13. 11 Mahatma Gandhi University of Horticulture and Forestry (C.G.) DESIRABLE ATTRIBUTES OF THE SCION CULTIVARS Desirable fruit size, shape, exterior appearance, tight skinned with pleasant flavor. Vigour and longevity of the tree with sufficient amount and regularity of the crop. Reduced tree size without the reduction of yield per unit canopy volume to facilitate easy handling of plants. Seedless or less seeded fruits. Season of ripening (early/late), storage life and adaptability to specific environments. Feasibility to mechanical harvesting. Compatibility with important rootstocks .

14. Mahatma Gandhi University of Horticulture and Forestry (C.G.) 12 DESIRABLE ATTRIBUTES OF THE ROOTSTOCKS CULTIVARS Reduction of tree size without affecting the yield or scion health. Compatibility with the important scion cultivars. Resistance to citrus and burrowing nematodes . Resistance to root rot diseases caused by Phytophthora, which seem to take a heavy toll of seedlings in the nursery and grown up trees in the field. Tolerance to excess salts , drought, cold and water logging. Rapid growth and lack of branching, so that it can be handled easily in the nursery.

15. 13 Mahatma Gandhi University of Horticulture and Forestry (C.G.) DIFFERENT APPROACHES IN CITRUS IMPROVEMENT 1. Conventional breeding methods 2. Modern breeding methods Selection Hybridization Polyploidy Mutation Breeding Introduction Biotechnological approaches Marker assisted breeding Ahmed et al., 2020

16. Mahatma Gandhi University of Horticulture and Forestry (C.G.) Mandarin – Santra from Aurangabad . Mandarin – Kinnow, Cleoptera, Clementine- USA Sweet orange - Washington Navel, Valencia, Jaffa, Blood Red Malta, Tangerines. Grape Fruit - Marsh seedless, Duncan, Foster, Thompson- USA Lemon- Lisbon, Eureka, Villafrance – USA The introduction of ‘Kinnow’ mandarin (King x Willow leaf) in 1947 showed great promise in North India. It was introduced in South India in 1958 and Punjab in 1959 and has performed extremely well in Punjab. 1. INTRODUCTION 14

17. 15 Mahatma Gandhi University of Horticulture and Forestry (C.G.) Exploitation of natural variability existing in a variety has resulted in the isolation of some promising clones in Citrus.   1. ‘ PKM 1 lime is a clonal selection from seedling progenies of kadayam Type of Tirunelveli district of Tamil Nadu.   2. ‘Yuvaraj Blood Red’ is a seedless and early maturing clonal selection from ‘Blood Red’ orange .   3. ‘ Pramalini’ and ‘Vikram’ , the two kagzi lime varieties were developed through clonal selection at Marathwada University.   4. ‘ Chakradhar’ is a thornless and seedless selection from Kagzi lime. 2. SELECTION

18. Crop Variety Salient features Sweet orange Pusa Round Early maturity (15th October under north India, Average fruit weight (242.18g), Juice content (48.47%) Lemon Pusa Lemon-1 Improved selection for commercial cultivation in NCT of Delhi and NC Region. Produced uniform size fruit in both summer and winter season. Early maturing than Kagzi Kalan (ready for harvest 15 -20 days earlier). Produces seedless fruit in solid block orcharding. Recently developed varieties through seedling selection Mahatma Gandhi University of Horticulture and Forestry (C.G.) http://Iari.res.in 16

19. Recently developed varieties through clonal selection Mahatma Gandhi University of Horticulture and Forestry (C.G.) Crop Variety Salient features Pummelo Arka Chandra Clonal variant of pummelo accession 18, prolific bearer , fruit weight ranged from 0.8-1kg, spheroid fruit shape and has white pulp, TSS (11-12°B), acidity (0.89%) and sweet. Arka Anantha Clonal variant of pummelo accession 25, prolific bearer. Fruit weight ranged from 0.8-1kg, spheroid fruit shape and has pink pulp, TSS (11-12°B), acidity (0.90%) and sweet. Pummelo- CHESP Selection of seedlings of pink flesh cultivar, total soluble solids-10-12º brix, acidity – 0.38  percent, e ach fruit contains 75-80 seeds, pulp recovery 55-60%. Yield - 250 to 350 kg per tree per year. ICAR-IIHR Annual report 2020 17

20. Variety Salient features Pusa sharad (Sweet Orange) Resistant to greening disease and free from granulation. (2021) Pusa Abhinav (Lemon) Pusa Abhinav is a promising clonal selection having medium vigorous trees, Moderately susceptible to citrus canker. (2021) Pusa Udit ( Lemon) Improved clonal selection having Medium sized fruits (40.0 g), round to ovule shape, smooth fruit surface, (2021) Mahatma Gandhi University of Horticulture and Forestry (C.G.) Seedless selection Variety Salient features Ruby Seedless Valencia seedless selection of Biogold’s Ruby Valencia, is a red-fleshed Valencia that matures from May to August in California. http://Iari.res.in https://www.freshplaza.com 18

21. 19 Mahatma Gandhi University of Horticulture and Forestry (C.G.) Citrus breeding involves selection and hybridization by controlled by crossing over of two genetically distinct parents to obtain desired variety. Scion breeding/Cultivar breeding Selection of breeding of high combining ability complementary and heritability of desired characters. Zygotic seedlings are planted and evaluated. Desired and best performing progenies are budded on commercial rootstocks and evaluated. E.g.- Kinnow mandarin – (King X Willow leaf) ( Honey, Sunburst, Fallago ) 3. HYBRIDIZATION

22. Mahatma Gandhi University of Horticulture and Forestry (C.G.) New sweet citrus scion hybrids SCSH-11-15/12 Sweet citrus scion hybrids (Pummelo x sweet orange), fruit weight (380-535 g) , higher juice content (45.33%), lower acidity content (0.86 to 1.12%). IARI Annual Report 2020 Somatic Hybridization Flhorag 1 : Highly tolerant to iron deficiency 20

23. 21 Mahatma Gandhi University of Horticulture and Forestry (C.G.) INTERGENERIC AND INTRAGENERIC HYBRIDS INTERGENERIC:- Though intergeneric hybrids are rare in fruit plants, much success has been obtained in Citrus. Hybrids of Poncirus Citrange:- A group having the parentage of trifoliate orange ( Poncirus trifoliata )and sweet orange ( C.sinensis ), the hybrids showed intermediate characters of the parents. The leaves are mainly trifoliate but unifoliate evergreen leaves are also observed in some plants. The fruits are juicy and flavoured. Some of the cultivars are Troyer, Carrizo, Morton, Etonia, Rusk, Coleman, etc. Hybrids of Fortunella   Orangequat - C.reticulata cv .Satsuma X F.japonica X F.margarita cv .Meiwa.

24. Mahatma Gandhi University of Horticulture and Forestry (C.G.) INTRAGENERIC HYBRIDS Tangor Mandrin x Sweet orange ( Citrus reticulata X Citrus sinensis ) e.g. Temple, Clementine, Monreal mostly monoembryonic. Tangelo Mandarin x grapefruit, ( C.reticulata x C.paradisi ) e.g. Orlando, Sampson, Minneola, Seminole, etc. Lemonima Citrus limon x Citrus aurantifolia Lemmonnage Citrus limon x C.reticulata INTERGENERIC HYBRIDS Citrange Poncirus trifoliate x Citrus sinensis Citrangequat Poncirus trifoliate x Fortunella margarita ( Kumquat) Cicitrange Citrange x Poncirus trifoliate Citrandarin Poncirus trifoliata x C.reticulata Citermon Poncirus spp. x C. aurantium Citumquat Poncirus spp. x C. Japonicum x F. margarita (Kumquat) Citrangedin ( Poncirus trifoliate x Citrus sinensis ) x Citrus mitis Citrumelo Poncirus trifoliate x Citrus paradisi (Grape fruit) 22

25. 23 Mahatma Gandhi University of Horticulture and Forestry (C.G.) INTERSPECIFIC HYBRIDS Hybrids Parental species Limonage Citrus limon x Citrus sinensis Limonimes Citrus limon x Citrus aurantifolia Limandarins Citrus limon x C.reticulata Tangelo C.reticulata x C.paradisi Tangor Citrus reticulata x Citrus sinensis HYBRIDS OF FORTUNELLA Hybrids Parental species Procimequat Fortunella japonicum x Citrus aurantifolia Limequat C.reticulata x Fortunella japonicum x Fortunella margarita Orangequat C.reticulata x Fortunella japonicum x Fortunella margarita x Meiwa

26. 24 Mahatma Gandhi University of Horticulture and Forestry (C.G.) 4. MUTATION BREEDING Crop Original variety Mutant cultivar Nature of mutation Navel orange Bahia Baraninha Limb sport   Washington Navelina, Navelate Marrs Lenge, Autumn Gold, Powell Summer, Weller Red. Limb sport Mandarin Owari Clausclina Bud sport   Pongan Pongan 86-1 Bud sport Grapefruit Walters(White fleshed) Foster(Pink fleshed) Limb sport   Foster(Pink fleshed) Hudson(Deep red flesh) Bud sport   Hudson(Deep red flesh) Star Ruby ( Deepest red peel) Limb sport       Thompson (Light pink flesh & peel) Redblush (deep red flesh) Limb sport     Henderson Flame Bud sport Pummelo A Local cv.( C.maxima ) Wuheputaoyou Bud sport

27. New high yielding seedless citrus variety It is a natural mutant variety developed from the Division of fruits and Horticultural Technology, ICAR Indian Agricultural Research Institute, New Delhi in 2020. Pusa Arun: New seedless and highly juicy pummelo variety Dubey et al., IARI 2020 Mahatma Gandhi University of Horticulture and Forestry (C.G.) 25

28. Variety Salient features PAU- Kinnow- 1 Low seeded PAU- Kinnow-2 Low seeded Varietal development through mutagenesis in citrus 26 Mahatma Gandhi University of Horticulture and Forestry (C.G.)

29. 27 Mahatma Gandhi University of Horticulture and Forestry (C.G.) 5. POLYPLOIDY BREEDING Most of the species and varieties of Citrus are diploid but occurrence of polyploidy has been reported in many cultivar. The Hongkong wild Kumquats, Fortunella hindsii may have been the first reported tetraploid. Polyploidy manipulation by crossing of tetraploids with diploids yielded some valuable triploid varieties like ‘Orablanco’ and ‘Melogold’. Most of the species and varieties of Citrus are diploid but occurrence of polyploidy has been reported in many cultivar.

30. 28 Mahatma Gandhi University of Horticulture and Forestry (C.G.) 6. MICROPROPAGATION SHOOT TIP/ AUXILLARY BUD CULTURE: For multiplication of superior clones of almost all cultivated species, hybrids, rootstocks etc. Utilized for propagation weak polyembryonic commercial cultivars. These are healthy, uniform, virus free true to type plants. EMBRYO RESCUE In, Citrus Nucellar embryony is the major hindrance for getting embryo. That’s why embryo rescue is important for getting embryo of hybrid in early stage of development which is a major breeding priority. RFLP analysis of low and high copy number, nuclear DNA can be used to distinguish zygotic from nucellar in vitro seedling.

31. 29 Mahatma Gandhi University of Horticulture and Forestry (C.G.) SHOOT TIP GRAFTING It has been standardized in mandarins and sweet orange which produce true to type, virus free precocious planting materials. PROTOPLAST FUSION AND GENETIC TRANSFORMATION Development of triploid scions and rootstocks with resistance to biotic and abiotic factors. Genetic transformation studies and use of coat protein gene could produce tolerant varieties for citrus decline. SOMATIC HYBRIDIZATION It is an allotetraploid Somatic hybrid produced by protoplast fusion developed at the Plant Improvement Team in Lake Alfred, Florida, USA. Fusion of Changsha mandarin ( Citrus reticulata ) and trifoliate orange 50-7 ( Poncirus trifoliata ). It is used for tree size control, cold hardy, shown a positive reaction to the Huanglongbing disease. UFR-6 ( CITRUS) Grosser et al., 2015

32. Breeding approaches for rootstock Improvement Rootstock Parentage Release Year US SuperSour-2 P. trifoliata ‘Benecke’ × ( C. aurantium ‘Chinotto’ × Citrusichangensis 2018 US SuperSour-3 C. reticulata ‘Sunki’ × US-802 ( Citrus maxima × P. trifoliata) 2018 US SuperSour-4 C. maxima ‘Hirado’ × C. reticulata ‘Cleopatra’ 2023 US SuperSour-5 C. maxima ‘Mato’ × C. reticulata ‘Shekwasha’ 2023 Developed from Rootstock hybrid Parentage Important traits IIHR, Bengaluru CRH-12 Rangpur lime x Trifoliate orange Highly resistant to Phytophthora, citrus nematode & moderately tolerant to salinity, tolerant to drought CRH-57 Rough lemon x Trifoliate orange resistant to Phytophthora, citrus nematode , tolerant to salinity and drought CRH-47 Cleopatra Mandarin x Trifoliate orange Moderately tolerant to salinity Mahatma Gandhi University of Horticulture and Forestry (C.G.) 30

33. Mahatma Gandhi University of Horticulture and Forestry (C.G.) CRISPR/Cas9 S.no Species Trait References 1 2. Grape fruit Sweet orange Canker disease resistance Canker disease resistance Jia et al ., 2017 Wang e t al ., 2019 Clustered regularly interspaced short palindromic repeat 31

34. Mahatma Gandhi University of Horticulture and Forestry (C.G.) Fast-track breeding system to introduce CTV resistance of trifoliate orange Precocious flowering and fruiting of the BC 2 progenies a, b, c and precocious flowering of the BC 3 progenies around 3 weeks after seed planting d . The normal flower e was generated in the BC3progenies with transgenes and fertile pollen f that was obtained from the flower Endo et al ., 2020 32

35. Mahatma Gandhi University of Horticulture and Forestry (C.G.) Fast Track Breeding Fast Track utilizes genetic engineering strategies for inducing early flowering that produces generation cycles of one year or less. Introgression of resistance genes from wild species by hybridization with early flowering transgenic line. Selection of early flowering seedlings carrying the trait of interest (resistance gene) using molecular markers for further back crossing. Repeated back crossing until the linkage drag is minimized and desired parental traits are combined in a seedling population. Technology has the potential to integrate into existing breeding programs and addresses its limitations and vulnerabilities. Hypothesis was first time proposed in Poplar. Fast Track fruit tree breeding are currently being applied to other perennial tree fruits such as plum and citrus (Rodriguez et al., 2014). 33

36. 34 Mahatma Gandhi University of Horticulture and Forestry (C.G.) FUTURE ASPECTS Genetic improvement and evaluation of genetic resources for development of improved cultivars in tropical fruits. Assessment on impact of climatic variation on phenology, and incidence of insect pests and diseases of tropical fruits. Evaluation of sustainable and input use efficient technologies under different agro climatic conditions. Bio-intensive and eco-friendly management of major insect-pests and diseases in tropical fruits. Production of healthy planting material in tropical fruits. Effective dissemination of technology developed by AICRP in collaboration with KVKs. CONCLUDING REMARKS Citrus breeding is a long-term process but new molecular approaches to breeding are reducing breeding time. A traditional breeding and biotechnology can play fundamental role in fruit crop improvement. Greater efforts are required to make improvement upon the traditional varieties. Genetic engineering can make a substantial contribution to improved nutrition in crops.

37. Mahatma Gandhi University of Horticulture and Forestry (C.G.) CCRI NAGPUR VISION 2050 Genetic resource and crop improvement Functional genomics and phenomics based gene identification for specific trait and gene pyramiding to have cultivar of multiple resistance on one hand and identifying gene for some negative traits like genes leading rootstock vulnerability to Phytophthora , drought tolerance, nutrient deficiency etc. characterization and cataloguing of citrus germplasm using microsatellite molecular markers. Marker-aided-selection of citrus germplasm for useful traits e.g. less seeded, suitable for processing, tolerance to drought, floods, salinity and diseases. Rootstock improvement through protoplast fusion. Anti-oxidant and neutraceutical profiling of citrus germplasm could be new objectives in citrus breeding programme. Contd…

38. Clonal selection for better yield and quality and ploidy manipulation for seedlessness. Evaluation and barcoding of citrus germplasm. Hybridization for scion and rootstock improvement. An engineered rootstock capable of withstanding both biotic as well as abiotic stress, besides fitting well into high density planting will improve factor productivity of citrus orchards. Identification of germplasm tolerant to water stress (drought and flood). Mahatma Gandhi University of Horticulture and Forestry (C.G.)

39. Anonymous (2020 Annual report of IIHR, Bangalore). Anonymous (2020 Annual report of IARI ). Dinesh M. R. , 2015, Fruit Breeding, New India Publishing Agency, New Delhi 110034. Khan I ,2007, Citrus genetics, breeding and biotechnology, CAB international Oxfordshire OX10 8DE,UK. Ladaniya S. Milind, 2008, Citrus fruit biology ,technology and evaluation, Academic press. Rajput C B S, Haribabu Sri R ,1985,Citriculture, Kalyani publishers, New Delhi 110002. Salonia F.,Ciacciulli a.,Poles L.,Pappalarado H.D., Mafia S and Licciardello New Plant Breeding Techniques in Citrus for the Improvement of Important Agronomic Traits 2020. Front Plant Sci. 11: 1234. Santhi VP, Nireshkumar N, Vasugi C, Parthiban S, and Masilamani P. Role of rootstocks to mitigate biotic & abiotic stresses in tropical and subtropical fruit crops,2020. A review Role of rootstocks to mitigate biotic and abiotic stresses in tropical and subtropical fruit crops: A review International Journal of Chemical Studies . 8(5): 499-510. REFERENCES Mahatma Gandhi University of Horticulture and Forestry (C.G.)

40. Mahatma Gandhi University of Horticulture and Forestry (C.G.)

41. Mahatma Gandhi University of Horticulture and Forestry (C.G.) MOSAMBI JAFFA PINEAPPLE HAMLIN

42. Mahatma Gandhi University of Horticulture and Forestry (C.G.) VALENCIA BLOOD RED STAR RUBY MARSH SEEDLESS

43. Mahatma Gandhi University of Horticulture and Forestry (C.G.) RED BLUSH DUNCUN CITRUS SELECTION 900 CITRUS SELECTION 411

44. Mahatma Gandhi University of Horticulture and Forestry (C.G.) RED BLUSH CITRUS SELECION 950 RED PUMMELO 5-1-99-2 RED PUMMELO 5-1-99-5

45. Mahatma Gandhi University of Horticulture and Forestry (C.G.)

46. Mahatma Gandhi University of Horticulture and Forestry (C.G.) STAR RUBY RED BLUSH FOSTER FLAMINGO RED PUMMELO HANNA