Socio-economic importance, domestication trends and in situ conservation of wild Citrus species of Northeast India

Plant growth-promoting traits of culturable seed microbiome of citrus species from Purvanchal Himalaya

Despite Northeastern India being "Treasure House of Citrus Genetic Wealth," genetic erosion of citrus diversity poses severe concern with a corresponding loss in seed microbial diversity. The seed microbiome of citrus species unique to the Purvanchal Himalaya is seldom explored for their use in sustainable orchard management. Isolation and characterization of culturable seed microbiomes of eight citrus species, namely, Citrus reticulata Blanco, C. grandis (L.) Osbeck, C. latipes Tanaka, C. megaloxycarpa Lushaigton, C. jambhiri Lush, C. sinensis (L.) Osbeck, C. macroptera Montr, and C. indica Tanaka collected from NE India were carried out. The isolates were then screened for an array of plant growth-promoting (PGP) traits [indole acetic acid (IAA) production, N₂ fixation, phosphate and zinc complex dissolution, siderophores, and Hydrogen Cyanide (HCN) production]. The pure culture isolates of seed microbiomes were capable of dissolving insoluble Ca₃(PO₄)₂ (1.31-4.84 µg Pi ml^-1 h^-1), Zn₃(PO₄)₂ (2.44-3.16 µg Pi ml^-1 h^-1), AlPO₄ (1.74-3.61 µg Pi ml^-1 h^-1), and FePO₄ (1.54-4.61µg Pi ml^-1 h^-1), mineralized phytate (12.17-18.00 µg Pi ml^-1 h^-1) and produced IAA-like substances (4.8-187.29 µg ml^-1 h^-1). A few isolates of the seed microbiome were also able to fix nitrogen, secrete siderophore-like compounds and HCN, and dissolve ZnSO₄ and ZnO. The 16S ribosomal Ribonucleic Acid (rRNA)-based taxonomic findings revealed that Bacillus was the most dominant genus among the isolates across citrus species. Isolates CG2-1, CME6-1, CME6-4, CME6-5, CME6-9, CJ7-1, CMA10-1, CI11-3, and CI11-4 were identified as promising bioinoculants for development of microbial consortium having multifaceted PGP traits for nutritional benefits of nitrogen, phosphorus and zinc, and IAA hormonal benefits to citrus crops for better fitness in acid soils.

A review of citrus plants as functional foods and dietary supplements for human health, with an emphasis on meta-analyses, clinical trials, and their chemical composition

Fruits, flowers, leaves, essential oils, hydrosols, and juices of citrus spp. Are utilized to prepare various forms of food products. Along with their nutritional values, in the health industry, different parts of the plants of the citrus genus have been used as supplements or remedies to prevent or control diseases. This review focused on reported meta-analyses and clinical trials on the health benefits of citrus plants as functional foods. Also, chemical compounds of various citrus species were reviewed. The following information sources were used for data collection: Google Scholar, the Web of Science, Scopus, and PubMed. Various keywords, including "citrus AND chemical compounds," "citrus AND phytochemicals," "citrus species," "citrus AND meta-analysis," "nutritional and therapeutical values of citrus spp.," "clinical trials AND citrus," "clinical trials AND Rutaceae," "health benefits of citrus spp.," "citrus edible or non-edible applications," and scientific names of the citrus plants were utilized to collect data for the review. The scientific name and common name of all twenty-eight citrus species, along with any of the above keywords, were also searched in the mentioned databases. Scientific papers and data sources were sought to review and discuss the citrus plant's nutritional and therapeutic importance. Several meta-analyses and clinical trials have reported beneficial effects of citrus spices on a variety of cancer risks, cardiovascular risk factors, neurologic disorders, urinary tract conditions, and gastrointestinal tract conditions. They have shown anxiolytic, antimicrobial, and pain-alleviating effects. Some of them can be helpful in managing obesity and cardiovascular risk factors.

Realizing certainty in an uncertain future climate: modeling suitable areas for conserving wild Citrus species under different change scenarios in India

Citrus is an important horticultural crop of India and is often prone to diseases, particularly under increased temperature scenarios. For developing disease-resistant Citrus varieties, conservation of wild relatives is extremely important. However, our knowledge on temperature tolerance of these wild relatives of Citrus to varied climate change scenarios is extremely limited. Therefore, we determined the climatic niche of six wild relatives of cultivated Citrus species (C. indica Tanaka, C. karna Rafin., C. latipes (Swingle) Tanaka, C. macroptera Montrouz., C. medica L., and C. sinensis (L.) Osbeck.) and identified the geographical areas in India that would remain climatically stable in future through ecological niche modeling (ENM). Raster data on 19 bioclimatic variables with a resolution of 0.04° were used to generate niche models for each Citrus species that delineated their potential distribution areas. Future species distribution predictions for the year 2050 were made using the climate change scenarios from the most appropriate climate models, i.e., IPSL-CM5A-LR and NIMR-HADGEM2-AO with four Representative Concentration Pathways (RCPs). Ensemble of current and future projections was used to identify climatically stable areas for each species. Precipitation-related bioclimatic variables were the key climatic determinants for the modeled distribution pattern. The consensus of current and future projections suggests that most areas with stable climates for the species in the future would be available in the northeastern states of Arunachal Pradesh, Meghalaya, Mizoram, and Tripura. Efforts for in situ conservation and establishment of germplasm banks and citrus orchards may be encouraged in these identified areas.

A Global Perspective on the Population Structure and Reproductive System of Phyllosticta citricarpa

The citrus pathogen Phyllosticta citricarpa was first described 117 years ago in Australia; subsequently, from the summer rainfall citrus-growing regions in China, Africa, and South America; and, recently, the United States. Limited information is available on the pathogen's population structure, mode of reproduction, and introduction pathways, which were investigated by genotyping 383 isolates representing 12 populations from South Africa, the United States, Australia, China, and Brazil. Populations were genotyped using seven published and eight newly developed polymorphic simple-sequence repeat markers. The Chinese and Australian populations had the highest genetic diversities, whereas populations from Brazil, the United States, and South Africa exhibited characteristics of founder populations. The U.S. population was clonal. Based on principal coordinate and minimum spanning network analyses, the Chinese populations were distinct from the other populations. Population differentiation and clustering analyses revealed high connectivity and possibly linked introduction pathways between South Africa, Australia, and Brazil. With the exception of the clonal U.S. populations that only contained one mating type, all the other populations contained both mating types in a ratio that did not deviate significantly from 1:1. Although most populations exhibited sexual reproduction, linkage disequilibrium analyses indicated that asexual reproduction is important in the pathogen's life cycle.

Inferring Phylogenetic Relationships of Indian Citron (Citrus medica L.) based on rbcL and matK Sequences of Chloroplast DNA

Phylogenetic relationships of Indian Citron (Citrus medica L.) with other important Citrus species have been inferred through sequence analyses of rbcL and matK gene region of chloroplast DNA. The study was based on 23 accessions of Citrus genotypes representing 15 taxa of Indian Citrus, collected from wild, semi-wild, and domesticated stocks. The phylogeny was inferred using the maximum parsimony (MP) and neighbor-joining (NJ) methods. Both MP and NJ trees separated all the 23 accessions of Citrus into five distinct clusters. The chloroplast DNA (cpDNA) analysis based on rbcL and matK sequence data carried out in Indian taxa of Citrus was useful in differentiating all the true species and species/varieties of probable hybrid origin in distinct clusters or groups. Sequence analysis based on rbcL and matK gene provided unambiguous identification and disposition of true species like C. maxima, C. medica, C. reticulata, and related hybrids/cultivars. The separation of C. maxima, C. medica, and C. reticulata in distinct clusters or sub-clusters supports their distinctiveness as the basic species of edible Citrus. However, the cpDNA sequence analysis of rbcL and matK gene could not find any clear cut differentiation between subgenera Citrus and Papeda as proposed in Swingle's system of classification.

Genetic diversity and phylogenetic analysis of Citrus (L) from north-east India as revealed by meiosis, and molecular analysis of internal transcribed spacer region of rDNA

The north-eastern region of India is reported to be the center of origin and rich in diversity of Citrus (L.) species, where some wild and endangered species namely Citrus indica, Citrus macroptera, Citrus latipes, Citrus ichagensis and Citrus assamensis exist in their natural and undisturbed habitat. In order to have comprehensive information about the extent of genetic variability and the occurrence of cryptic genomic hybridity between and within various Citrus species, a combined approach involving morphological, cytogenetical and molecular approaches were adopted in the present study. Cytogenetic approaches are known to resolve taxonomic riddles in a more efficient manner, by clearly delineating taxa at species and sub species levels. Male meiotic studies revealed a gametic chromosome number of n = 9, without any evidence of numerical variations. Bivalents outnumbered all other types of associations in pollen mother cells (PMCs) analyzed at diplotene, diakinesis and metaphase I. Univalents were frequently encountered in nine species presently studied, though their presence appropriately did not influence the distributional pattern of the chromosomes at anaphases I and II. The molecular approaches for phylogenetic analysis based on sequence data related to ITS 1, ITS 2 and ITS 1 + 5.8 s + ITS 2 of rDNA using maximum parsimony method and Bayesian inference have thrown light on species inter-relationship and evolution of Citrus species confirming our cytogenetical interpretations. The three true basic species i.e. Citrus medica, Citrus maxima and Citrus reticulata with their unique status have been resolved into distinct clades with molecular approaches as well. C. indica which occupies a unique position in the phylogenetic ladder of the genus Citrus has been resolved as a distinct clade and almost behaving as an out-group. The presences of quadrivalents in C. indica also echo and support its unique position. From our study it is amply clear that C. reticulata also has close relation to C. ichagensis, as these species have clustered together, denoting their close genetic relationship. On the other hand, our studies did not demonstrate a clear differentiation between subgenera Citrus and Papeda at the rDNA level. The combined approach of cytogenetical and molecular analysis did complement our early karyological findings and helped in resolving many a taxonomic riddles.