Horticultural Classification of Citrus Cultivars

Globally, citrus fruits are grown over an area of 11.42 million ha with 179.0 million tons production. China with 82.7 m tons production is the major producer of citrus fruits followed by Brazil (18.14 m tons) and India (10.53 m tons) (FAOSTAT, 2019). All commercially used scion and rootstock cultivars belong to the genus Citrus, except kumquats, Fortunella spp., and Poncirus trifoliata, which are used as rootstock only all over the world. Worldwide citrus cultivars divided into four, reasonably-well-defined horticultural groups: the Sweet oranges, the mandarins, the grapefruits and the pummelos and the common acid members. The true or ‘biological’ citrus, including species of Citrus (C. reticulata, C. maxima and C. medica), share certain characteristics, however, these are clearly differentiated according to the morpho- taxonomic traits. Hundreds of different citrus cultivars are available. Many varieties were chance finds from natural populations, and not the product of intentional breeding efforts. Other varieties in common use have originated from planned citrus hybridization and breeding efforts from worldwide. Most of the readers will be well acquainted with the cultivated types of Citrus scion and rootstocks. This chapter provides ripening season information for worldwide, farmers/gardeners have had success with citrus in many different regions of world where tropical/subtropical climatic conditions occur

Standardization of stage wise water requirement in drip irrigated Kinnow mandarin orchards under sub-tropical conditions

An experiment on drip irrigation scheduling based on pan evaporation replenishment was conducted in Kinnow orchard at Punjab Agricultural University, Ludhiana during 2010-2018. Year was divided into six stages (stage 1 to stage VI) including two months in each stage. First treatment included irrigation scheduling with 30 and 40% ER, treatment two with 40 and 60% ER, treatment three with 60 and 80% ER, alternatively during stages I to VI. However, fourth and fifth treatments had irrigation with 80% ER and 30% ER, respectively, in all the stages. Maximum daily open pan evaporation (9.15 mm) was recorded in May and minimum (1.19 mm) was recorded in January. The water requirement varied from 2.8 liters day-1 tree-1 in stage-I to 58.3 liters day-1 tree-1 in stage-III. Linear increase in vegetative and reproductive growth was observed with increase in irrigation water. Polynomial relationship studies indicated the increase in water quantity applied to Kinnow with increase in temperature subject to the prevailing relative humidity. Similarly, volumes of water applied increased with increased mean evaporation. The study concluded that drip irrigation scheduling with 60 to 80% ER alternatively, starting from January to December save significant amount of water, without affecting yield and quality of Kinnow under subtropical conditions

Biotechnological Interventions for Reducing the Juvenility in Perennials

During shoot apex development, the plants undergo a very complex transition phase of flowering for successful reproduction, seed/cone setting and fruit development. The conversion of vegetative shoot meristems to floral meristems depends upon numerous endogenous, exogenous factors and flowering genes for the development of floral parts. The perennial crops suffer from the limitation of the innate ability to keep some meristems in the vegetative state for the polycarpic growth habit leading to the long juvenile phase. Conventional breeding approaches viz. selection of early flowering parental lines, flower thinning and grafting are time-consuming requiring more time for the release of a new cultivar which is undesirable for rapid crop improvement. The best way to accelerate the perennial plant breeding improvement programs and to reduce the long juvenile phase is the induction of early flowering through the utilization of biotechnological approaches. The ability to allow the transmission of an early flowering gene to the progeny in a Mendelian fashion is the major advantage of biotechnological interventions. The introgression of early flowering traits from non-commercial germplasm or sexually compatible species to perennial species through the biotechnological aspects will act as a boon for crop improvement in future studies. The present review gives an overview of various flowering genes in perennial crops accompanying the implementation of biotechnological approaches including overexpression studies, RNA interference, Virus-induced flowering and CRISPR-Cas approaches that will help in reducing the period for induction of flowering in perennial crops

Cloning and Characterization of Limonoid Glucosyltransferase from Kinnow Mandarin (Citrus reticulata Blanco)

Mandarina sorte Kinnow (Citrus reticulata Blanco) popularna je biljka iz roda citrusa u sjeverozapadnoj Indiji, koja se najviše uzgaja u državi Punjab. Međutim, limonoid aglikoni poput limonina uzrokuju gorak okus, što predstavlja najveći problem u industrijskoj proizvodnji soka od agruma. Iz tkiva mandarine sorte Kinnow izoliran je gen limonoid glukoziltransferaza (LGT) što kodira enzim za odgorčavanje, te je ispitan metabolizam razgradnje limonoida u agrumima. Nakon što je gen identificiran i karakteriziran, njegova cjelokupna sekvencija (1533 bp) deponirana je u bazu Nacionalnog centra za biotehnološke informacije (NCBI). Glukozil transferaza iz vrste Citrus reticulata (CrLGT) nalazi se na zasebnoj grani najveće podgrupe i filogenetski se razlikuje od onih u ostalih sorata mandarina, kao što je C. unshiu, te je jedinstvena po mnogim svojstvima. Ekspresija gena CrLGT na razini transkripcije ispitana je pomoću semikvantitativne metode u različitim tkivima biljke, kao što su mladi list, flavedo, albedo, opna i sjeme, tijekom rane (90 dana nakon cvatnje), srednje rane (150-210 dana nakon cvatnje) i kasne (240 dana nakon cvatnje) faze razvoja ploda, te je potvrđeno da je gen imao najveću ekspresiju u flavedu. Zaključeno je da izolirani gen LGT utječe na metaboličku razgradnju limonoida u agrumima. Pojačana ekspresija ovog gena može ublažiti gorčinu soka od agruma i povećati akumulaciju specifičnih glukozida koji imaju antikancerogena svojstva.Kinnow mandarin (Citrus reticulata Blanco) is a popular citrus crop of northwestern India and it occupies maximum fruit area in Punjab. However, citrus juice processing industry is still suffering from delayed bitterness problem caused mainly by limonoid aglycones such as limonin. In order to study citrus limonoid metabolism, limonoid glucosyltransferase (LGT) gene, which encodes a natural debittering enzyme, was isolated from the fruit tissues of Kinnow mandarin. After confirmation and characterization, its full-length gene sequence (1533 bp) was submitted to National Centre for Biotechnology Information. Citrus reticulata limonoid glucosyltransferase (CrLGT) occupies a position on an independent branch in the largest subgroup and is phylogenetically different from those in other mandarin species like C. unshiu, showing its uniqueness in several features. The transcript expression of CrLGT, evaluated in different tissues such as young leaf, flavedo, albedo, sac covering and seed of Kinnow mandarin during early (90 days after flowering (DAF)), mid (150-210 DAF) and late (240 DAF) fruit developmental stages using semi-quantitative method, showed the highest expression in flavedo. Thus, it was concluded that the isolated LGT gene has an effect on limonoid metabolic engineering in citrus. Overexpression of this gene can reduce the delayed bitterness problem in citrus juice and enhance the accumulation of specific glucosides that have anticancer effects

Comprehensive genome-wide identification and transferability of chromosome-specific highly variable microsatellite markers from citrus species

Abstract Citrus species among the most important and widely consumed fruit in the world due to Vitamin C, essential oil glands, and flavonoids. Highly variable simple sequence repeats (SSR) markers are one of the most informative and versatile molecular markers used in perennial tree genetic research. SSR survey of Citrus sinensis and Citrus maxima were identified perfect SSRs spanning nine chromosomes. Furthermore, we categorized all SSR motifs into three major classes based on their tract lengths. We designed and validated a class I SSRs in the C. sinensis and C. maxima genome through electronic polymerase chain reaction (ePCR) and found 83.89% in C. sinensis and 78.52% in C. maxima SSRs producing a single amplicon. Then, we selected extremely variable SSRs (> 40 nt) from the ePCR-verified class I SSRs and in silico validated across seven draft genomes of citrus, which provided us a subset of 84.74% in C. sinensis and 77.53% in C. maxima highly polymorphic SSRs. Out of these, 129 primers were validated on 24 citrus genotypes through wet-lab experiment. We found 127 (98.45%) polymorphic HvSSRs on 24 genotypes. The utility of the developed HvSSRs was demonstrated by analysing genetic diversity of 181 citrus genotypes using 17 HvSSRs spanning nine citrus chromosomes and were divided into 11 main groups through 17 HvSSRs. These chromosome-specific SSRs will serve as a powerful genomic tool used for future QTL mapping, molecular breeding, investigation of population genetic diversity, comparative mapping, and evolutionary studies among citrus and other relative genera/species