Papaya Cultivars Research Articles

Occurrence and Impact of Papaya Ring Spot Virus in the Marathwada Region of Maharashtra, India

Papaya ring spot virus (PRSV) is a major challenge to global papaya cultivation, including in the Marathwada region of Maharashtra, India. This study aimed to survey the prevalence of PRSV disease across three agroclimatic zones of Marathwada during, 2022. Infected plants exhibited various symptoms on leaves such as vein clearing, chlorosis, mosaic, blistering, leaf curling, puckering and shoestring appearance. Other symptoms such as, ringspots on leaves, fruits and stems, oily streaks on petioles and stems, malformed fruits, stunted growth of plants. Depending on the stage of infection, diseased plants produced few or no fruits. The survey revealed that, an average PRSV incidence ranging from 0.03% to 100%. Further analysis examined the influence of PRSV incidence on papaya cultivar, crop age and agroclimatic zones. Results indicated that older plants were more susceptible to PRSV than younger ones. Among the cultivars studied, the Red Lady cultivar demonstrated high susceptibility to the virus. However, there were no significant differences in the percent disease index (PDI) across the agroclimatic zones. These findings highlight the need for targeted management strategies, including the development of resistant cultivars and region wise disease control measures, to reduce the impact of PRSV on papaya production.

Comparison of the Morphological Characteristics, Yield, and Quality Traits of Fruits of Two Papaya Cultivars Grown Under Protected Cultivation

This study aimed to investigate the morphological characteristics and performance of Formosa and Sunrise Solo papaya cultivars under protected cultivation in subtropical climate conditions as well as the relationships between the yield and factors affecting the yield. The Formosa cultivars had higher values in terms of plant height (519.4 cm), stem diameter (238.4 mm), first flowering height (138.2 cm), and duration from flowering to harvest (141 days) compared to the Sunrise Solo cultivars. The yield per plant was higher in the Formosa cultivars (52.5 kg/plant/year) than in the Sunrise Solo cultivars (27.4 kg/plant/year). The values of fruit peel color parameters were highest in the spring, the fruit flesh firmness was highest in the autumn, and the soluble solid content was higher in fruits harvested in the summer. Medium to high positive phenotypic correlations were found between the first flowering height and fruit set, fruit weight, yield, fruit width, fruit length, and fruit flesh firmness (0.371–0.595) and between the fruit set (number/plant) and fruit weight, yield, fruit width, fruit length, and fruit flesh firmness (0.388–0.819) (p ≤ 0.01). The papaya can be commercially cultivated under protected cultivation in extreme subtropical conditions, and the Formosa cultivars generally performed better than the Sunrise Solo cultivars across many parameters.

Genetic Variability and Evolutionary Dynamics of Papaya Ringspot Virus and Papaya Leaf Distortion Mosaic Virus Infecting Feral Papaya in Hainan Island.

Commercialized genetically modified (GM) papaya cultivars have protected papaya from the devastating disease caused by papaya ringspot virus (PRSV). However, papaya leaf distortion mosaic virus (PLDMV), which causes similar infection symptoms but is serologically distinct from PRSV, was found to be a competitive threat to the papaya industry. Our study surveyed the occurrence of PRSV and PLDMV, as well as the transgenic markers of the 35S promoter from cauliflower mosaic virus and the neomycin phosphotransferase II gene in feral papaya plants, which were found frequently growing outside of cultivated papaya fields on Hainan Island. In total, 123 feral papayas, comprising 62 (50.4%) GM plants and 61 (49.6%) non-GM ones, were sampled. Among them, 23 (18.7%) were positive for PRSV, 49 (39.8%) were positive for PLDMV (including five plants co-infected by PRSV and PLDMV), and 56 (45.5%) were free of either virus. In traditional papaya-growing regions, we detected fewer PRSV-infected plants (2 in 33, 6%) than in other regions (21 in 90, 23%). However, overall, whether plants were transgenic or not made no difference to PRSV incidence (P = 0.230), with 9 PRSV-infected plants among 62 GM papayas and 14 among 61 non-GM papayas. Phylogenetic and genetic differentiation analysis showed a clear correlation between PRSV and PLDMV populations and their geographic origins. Negative selection was estimated for the selected gene regions of both viruses. Notably, PLDMV has deviated from neutral evolution and experienced population expansion, exhibiting increased genetic diversity, and is becoming the predominant threat to papaya in Hainan.

Transcription factor CpWRKY50 enhances anthracnose resistance by promoting jasmonic acid signaling in papaya.

Colletotrichum brevisporum is an important fungal pathogen that causes anthracnose and has led to serious postharvest losses of papaya (Carica papaya L.) fruit in recent years. WRKY transcription factors (TFs) play vital roles in regulating plant resistance to pathogens, but their functions in papaya anthracnose resistance need further exploration. In this study, we identified a WRKY TF, CpWRKY50, which belongs to the WRKY IIc subfamily. During infection with C. brevisporum, expression of CpWRKY50 in anthracnose-resistant papaya cultivars was significantly higher than that in susceptible cultivars. CpWRKY50 was induced by methyl jasmonate, and CpWRKY50 localized in the nucleus. In yeast, full-length CpWRKY50 had transactivation activity, but CpWRKY50 variants truncated at the N or C termini did not. CpWRKY50 positively regulated papaya resistance to C. brevisporum, as demonstrated by transient overexpression of CpWRKY50 in papaya and heterologous expression of CpWRKY50 in tomato. Moreover, endogenous jasmonic acid (JA) and JA-isoleucine levels in the fruits of transgenic tomato OE lines were higher than in wild type both before and after inoculation with C. brevisporum, indicating that increased CpWRKY50 expression promotes JA accumulation. Furthermore, our results revealed CpWRKY50 directly binds to W-box motifs (TTGACC) in the promoters of two JA signaling-related genes, CpMYC2 and pathogenesis-related 4 CpPR4, thereby activating their expression. Our data support that CpWRKY50 positively regulates anthracnose resistance in papaya by promoting JA signaling. These results broaden our understanding of papaya disease resistance mechanisms and will facilitate the genetic improvement of papaya through molecular breeding.

Phenolic and Metabolic Profiles, Antioxidant Activities, Glycemic Control, and Anti-Inflammatory Activity of Three Thai Papaya Cultivar Leaves.

This study thoroughly examined the proximate composition, bioactive composition, and in vitro biological activities of three different cultivars of papaya leaf extracts (PLEs) as potential functional ingredients and nutraceuticals. The dark green leaves of three papaya cultivars, Khaek Dam (KD), Holland (H), and Thai Local (L), were used in this study. The protein content of the leaves ranged from 25.96 to 32.18%, the fat content ranged from 7.34 to 11.66%, the carbohydrate content ranged from 5.80 to 17.91%, the moisture content ranged from 6.02 to 6.49%, the ash content ranged from 11.23 to 12.40%, and the fiber content ranged from 23.24 to 38.48%. The L cultivar possessed significantly higher protein and carbohydrate contents, whereas the H cultivar had the highest ash content (p < 0.05). The total phenolic content (TPC) ranged from 113.94 to 173.69 mg GAE/g extract, with the KD cultivar having the highest TPC (p < 0.05). Several metabolic compounds such as phenolic compounds (particularly kaempferol, isorhamnetin, quercetin, ferulic acid, isoferulic acid, salicylic acid, sinapic acid, syringic acid, and vanillin), terpenoids (such as eucalyptol), glycosides, and indole were identified. The PLE from the KD cultivar had the highest levels of DPPH• inhibition, metal chelation, reducing power, and antidiabetic activity (p < 0.05), suggesting superior biological activity. All three PLEs reduced the proliferation of RAW 264.7 cells in a dose-dependent manner with low nitric oxide formation. These results indicate that the papaya leaf, particularly from the KD cultivar, could be a promising source of functional food ingredients.

Characterization of gynodioecious Pune selection lines of papaya

Among major global threats to papaya cultivation, papaya ringspot virus (PRSV) is the most challenging one. In the absence of any PRSV resistant commercial papaya cultivar, PRSV management is restricted to minimizing yield losses. ICAR-Indian Agricultural Research Institute, Regional Station, Pune has developed PRSV tolerant dioecious papaya lines, Pune Selection (PS)-1, PS-2, PS-3 and PS-5. Being dioecious these lines have limited acceptability among farmers. Gynodioecious population from these lines were developed and characterized. They are numbered PS-1-1, PS-2-1, PS-3-1 and PS-5-1. These lines were characterized against prevailing commercial gynodioecious cultivar, Red Lady, for five generations. The average plant height of PS-2-1 and PS-5-1 (183 cm) was more than Red Lady (158 cm), however, stem girth of all lines was lesser than Red Lady. The fruiting height of all lines was less than Red Lady (87 cm). Length of the fruiting column of all lines was more than Red Lady (37 cm), except in PS-1-1. Fruit yield of all lines was more than Red Lady (16 kg/plant). Intensity of PRSV infection in Red Lady (48%) was considerably more than all lines. These lines can be used for developing PRSV tolerant gynodioecious papaya variety.

Differential expression of microRNAs in response to Papaya ringspot virus infection in differentially responding genotypes of papaya (Carica papaya L.) and its wild relative.

Papaya ringspot virus (PRSV) is one of the most devastating viruses of papaya that has significantly hampered papaya production across the globe. Although PRSV resistance is known in some of its wild relatives, such as Vasconcellea cauliflora and in some of the improved papaya genotypes, the molecular basis of this resistance mechanism has not been studied and understood. Plant microRNAs are an important class of small RNAs that regulate the gene expression in several plant species against the invading plant pathogens. These miRNAs are known to manifest the expression of genes involved in resistance against plant pathogens, through modulation of the plant's biochemistry and physiology. In this study we made an attempt to study the overall expression pattern of small RNAs and more specifically the miRNAs in different papaya genotypes from India, that exhibit varying levels of tolerance or resistance to PRSV. Our study found that the expression of some of the miRNAs was differentially regulated in these papaya genotypes and they had entirely different miRNA expression profile in healthy and PRSV infected symptomatic plants. This data may help in improvement of papaya cultivars for resistance against PRSV through new breeding initiatives or biotechnological approaches such as genome editing.

Exploring genetic diversity in inbred papaya lines for fruit quality in advanced stage of improvement

Despite the relevance of the global scenario regarding the papaya (Carica papaya L.) trade, there is still a limited number of papaya cultivars with different fruit patterns. Therefore, it is essential to explore the genetic variability at all levels of the germplasm used in the development of new papaya cultivars to meet its marketing goal. Thus, this study measured and explored the potential of genetic variability based on related to fruit quality traits, of a population of papaya lines in the F5 generation through several statistical analyzes. For this, 97 inbred lines obtained using the Single Seed Descent method, resulting from a cross between the JS-12 and Sekati genotypes, both with Formosa fruit pattern, were evaluated. Results indicated there was genetic variability in the fruit quality. The traits that most contributed to the variability were related to the fruit shape. The diverse population of 97 inbred papaya lines in the F5 generation showed promise for producing commercial-sized fruits in Formosa, Intermediate, and Solo patterns. Additionally, the selection of inbred papaya lines based on fruit shape using morpho-anatomical traits does not compromise physical and chemical parameters related to fruit quality.

Effect of Maleic Hydrazide and Waxing on Quality and Shelf-Life of Papaya (Carica papaya L.) Fruits

The effect of post-harvest treatment of Maleic hydrazide (MH)with and without waxing on the quality and shelf-life of ‘Baladi’ and‘Ekostika I’ papaya fruits at 18 ± 1 oC and 85% – 90% relative humiditywas evaluated. Maleic hydrazide at 250 and 500 ppm significantlydelayed fruit ripening by two and three days in both papaya cultivars,respectively, compared with untreated fruits. The higher theconcentration, the more was the delay in fruit ripening. The results alsoshowed that waxing in addition to MH resulted in a delay of two moredays in fruit ripening than treatment with MH alone. The effect of MHand waxing treatments in delaying papaya fruits ripening was manifestedin retarded respiratory climacteric, reduced weight loss and delayed fruitsoftening and increase in total soluble solids and ascorbic acid content

Evaluation of F1 papaya cultivars in Thailand and their marketing potential

Evaluation of F₁ papaya cultivars in Thailand and their marketing potential

Bitterness of Papaya Milk Is Related to Protein and Free Amino Acid Contents, with Phenylalanine and Tyrosine/Tryptophan Levels Being the Most Important

Papaya milk, a mixture of papaya pulp and dairy milk, is one of the most popular beverages in Taiwan. However, the enzymes present in papaya can cause accumulation of hydrophobic amino acids, resulting in a bitter taste of papaya milk. Thus, it is important to select papaya cultivars without the potential to form the bitter taste, but it is difficult to select these papaya cultivars using a sensory test. The purpose of this research was to investigate the relationship between the intensity of the bitterness with the contents of proteins and free amino acids. The results indicated that neither milk nor papaya alone tastes bitter. Heating the milk or the papaya before mixing and mixing only papaya latex with milk confirmed that an enzyme in papaya causes the bitter taste in papaya milk. The intensity of bitterness positively correlated with the contents of total soluble protein, free amino acids and the phenylalanine and tyrosine/tryptophan contents. Analyses using different papaya accessions in different seasons showed that tyrosine/tryptophan (r = 0.613***) and phenylalanine (r = 0.612***) correlate more strongly with bitterness intensity than the total soluble protein (r = 0.258*) or free amino acids (r = 0.38**). In this drink, milk provides the substrates to form the bitter substances, but the enzymes in the papaya are needed for the reaction to occur. The levels of the amino acids phenylalanine and tyrosine/tryptophan showed the highest correlation with the intensity of bitterness.

Efficient Induction of Papaya Embryogenic Callus and Plant Regeneration

Papaya ( Carica papaya &nbsp;L.) has high medicinal and production value, and it is of great significance to carry out efficient induction and plant regeneration of embryogenic&nbsp;callus of papaya for its industrial development. In this study, Zhongbai, the main papaya cultivar from Hainan was used as explants to explore the effects of different hormones and their additive combinations on embryogenic callus induction and plant regeneration. The results showed that the most suitable medium for papaya callus induction was K5: 1/2 MS+5 mg/L 2, 4-D+0.5 mg/L KT+3% sucrose+3.6 g/L phypagel.&nbsp;The most suitable medium for papaya embryogenic callus induction was M13: 1/2 MS+5 mg/L 2,4-D+0.6 mg/ L-proline+3% sucrose+3.6 g/L phypagel. And the most suitable medium for papaya bud differentiation was Ci: 1/2 MS+0.2 mg/L 6-BA, 0.2 mg/L NAA+3% sucrose+3.6 g/L phypagel. The best method for rooting of papaya was treatment with 100 mg/L rooting powder and soil plantation. This &lsquo;two-steps&rsquo; embryogenic callus induction system we created can significantly shorten the growth cycle of embryogenic callus. Furthermore, the system has a certain broad spectrum in different varieties of papaya, this study provides a solid foundation for further improving the efficiency of genetic transformation of papaya.

Comparative transcriptomics and genomic analyses reveal differential gene expression related to Colletotrichum brevisporum resistance in papaya (Carica papaya L.).

Colletotrichum brevisporum is an important causal pathogen of anthracnose that seriously affects the fruit quality and yield of papaya (Carica papaya L.). Although many genes and biological processes involved in anthracnose resistance have been reported in other species, the molecular mechanisms involved in the response or resistance to anthracnose in post-harvest papaya fruits remain unclear. In this study, we compared transcriptome changes in the post-harvest fruits of the anthracnose-susceptible papaya cultivar Y61 and the anthracnose-resistant cultivar G20 following C. brevisporum inoculation. More differentially expressed genes (DEGs) and differentially expressed long non-coding RNAs (DElnRNAs) were identified in G20 than in Y61, especially at 24h post-inoculation (hpi), suggesting a prompt activation of defense responses in G20 in the first 24h after C. brevisporum inoculation. These DEGs were mainly enriched in plant-pathogen interaction, phenylpropanoid biosynthesis/metabolism, and peroxisome and flavonoid biosynthesis pathways in both cultivars. However, in the first 24 hpi, the number of DEGs related to anthracnose resistance was greater in G20 than in Y61, and changes in their expression levels were faster in G20 than in Y61. We also identified a candidate anthracnose-resistant gene cluster, which consisted of 12 genes, 11 in G20 and Y61, in response to C. brevisporum inoculation. Moreover, 529 resistance gene analogs were identified in papaya genome, most of which responded to C. brevisporum inoculation and were genetically different between papaya cultivars and wild-type populations. The total expression dose of the resistance gene analogs may help papaya resist C. brevisporum infection. This study revealed the mechanisms underlying different anthracnose resistance between the anthracnose-resistant and anthracnose-susceptible cultivars based on gene expression, and identified some potential anthracnose resistance-related candidate genes/major regulatory factors. Our findings provided potential targets for developing novel genetic strategies to overcome anthracnose in papaya.

Anatomic Leaf Structure of 'Sunrise Solo' and 'Golden THB' Papaya Plants

Papaya (Carica papaya L.) stands out as a strong economic driver, being one of the fruit trees that most contribute to the total volume of brazilian production. The description of leaf characteristics allows to understand structures that act in resistance to pathogens, relationships with water resources and photosynthetic of plants, in addition to contributing to genetic improvement programs. However, there are few studies that attempt to describe the leaf anatomy of the different papaya cultivars. Thus, this study aims to describe the main leaf structure of papaya cultivars Sunrise Solo and Golden THB. The leaves were collected in the municipalities of São Mateus and Aracruz, located in the north of the State of Espírito Santo, using transversal and paradermic sections and the usual techniques of plant histology. Both cultivars presented uni-stratified epidermis, followed by palisade chlorophyll parenchyma and lacunous with collateral vascular system. Calcium oxalate druses were more observed in the Sunrise Soil cultivar. The differences between cultivars were in the number of layers of mesophyll tissues.

Developing a robust in vivo hairy root system for assessing transgene expression and genome editing efficiency in papaya

Papaya is one of the most important fruits in tropical and subtropical countries. However, genetic improvement has had limited success to date due to time-consuming and complex transformation and regeneration technologies, as well as a lack of reproducible and efficient transient gene expression assays. Here, we report the development of a highly efficient Rhizobium rhizogenes-based in vivo hairy root system for evaluating transgene expression and activity including CRISPR/Cas gene editing reagents in the Vietnamese papaya cultivar Linhan. To optimize the papaya transformation parameters, we introduced the R. rhizogenes strain K599 into papaya hypocotyls at 1-, 5- and 10-mm below the cotyledon nodes by a needle using 5-, 7- and 10-day old seedlings and then monitored the frequency of hairy root formation at 18 days post infection. We found that the age of the seedlings and the distance of the infection site from the cotyledon node were inversely correlated with the efficacy of hairy root induction, being 5-day-old plants and 1-mm distance the best parameters. The etablished protocol was then employed to investigate transformation frequency using the gus reporter gene. Of the tested hairy roots, 47.22% were positive for GUS staining, which indicates a high level of transgene transfer and stability. Finally, we introduced a dual guide RNA CRISPR/Cas9 cassette targeting eukaryotic translation initiation factor isoform 4E (eIF(iso)4E) gene into papaya by R. rhizogenes and then screened for gene editing events by heteroduplex analysis and Sanger sequencing. Our analysis revealed that 50% of induced roots contained the expected mutations in the eIF(iso)4E gene, which makes our system ideal for testing transgene activity prior making stable transgenic papaya lines.

The Bio-Insecticidal Activity of Papaya (Carica papaya L.) Leaves Extract against Spodoptera litura Fabr. (Lepidoptera: Noctuidae) Larval Growth

Background: Papaya leaves produce several metabolites that may be toxic to an insect pest. In East Java, it is easy to find two cultivars in the yard, plantation, and moors, such as Thailand and local papaya. However, information about their utilization as bio-pesticides remains limited. This study aimed to investigate the relationship between those papaya cultivars and the effect of their extracts on Spodoptera litura larvae. Methods: The Thailand papaya cultivar (TPC) and Indonesian papaya cultivar (IPC) leaves were obtained from the medium and lowlands and were macerated with methanol until obtained a papaya leaves extract (PLE). The S. litura larvae on the instar phase 2 (n= 630) were used for treatment. The Ricinus communis leaves were sprayed with PLE concentrations of 0, 10, 20, 30, 40 and 50% and fed to S. litura larvae. Result: Based on the secondary metabolites, the papaya cultivars form two clusters associated with its origin. The 40 and 50% concentrations of PLE significantly affect the mortality and head-capsule width of S. litura indicated with broken pupae and failure to transform to imago. This result signifies the potential of papaya leaves extract as bioinsecticide for S. litura larvae.

The Inheritance Pattern of Key Desirable Agronomic and Fruit Quality Traits in Elite Red Papaya Genotypes

Knowledge of the heritability, genetic advance, and stability of key traits, such as the height to the first fruit, trunk circumference, number of marketable fruit, wasted fruit, fruit weight, fruit width, fruit length, flesh thickness, cavity width, cavity length, and soluble solid contents, is required. These were determined in ten advanced generation red papaya recombinant inbred lines (RIL; F5 generation). The F5 RIL were grown in four field sites, two each within two distinct agroecological climates: the Tablelands and Coastal regions. At each site, biological replicates (trees) of each RIL and the industry-standard red papaya cultivar, RB1, were grown. Agronomic traits and fruit-specific traits were assessed at five and 10 months, respectively, after seedling transplantation to the field. Height to first fruit, trunk circumference, fruit weight, and soluble solid contents were highly heritable and stable at all field sites (h2b.s, 0.7–0.9) with genetic gains of almost 18% observed for height to first fruit and fruit weight. Across all sites, the trunks of the F5 lines were 37% wider, the trees set fruit 47% closer to the ground and had 20% more marketable fruit with 33% smaller fruit cavity widths, and their fruit was 11% heavier and 12% sweeter than RB1.

Carica papaya L.: A Tropical Fruit with Benefits beyond the Tropics

Carica papaya L. (family: Caricaceae), also known as ‘papaya,’ is a tropical American fruit tree. Due to the bioactive components (carpaines, BITC, benzyl glucosinolates, latex, papain, zeaxanthin, choline, etc.) in its seeds, leaves, and fruits, it is revered for its excellent antioxidant, digestive, and nutraceutical benefits. Papayas are high in vitamins A, B, C, E, and K, folate, pantothenic acid, zeaxanthin, lycopene, lutein, magnesium, copper, calcium, and potassium. Being rich in fiber, antioxidants, and vitamin C, it lowers the cholesterol in the arteries; prevents arthritis; reduces aging, cancer, macular degradation, risk of cardiovascular diseases, and stress; increases platelet count; controls dengue fever; facilitates digestion, and lowers body weight. Papaya leaf extract, with many in vitro and case studies in combination therapies with modern medicine, especially for cancers and many other viral diseases, has been found to be an efficient cure. Humans have cultivated papaya cultivars for millions of years because of their significant commercial, medicinal, and agronomic value. Several reports have been published on the genetic modification of papaya for resistance to abiotic (herbicide, Al toxicity, etc.) and biotic stressors (PRSV, mites, Phytophthora, etc.), delaying ripening, and improving shelf life. However, most of these traits have not been introduced globally to all commercial papaya varieties. Unraveling the genetics of papaya has shed light on various domestication impacts, evolutionary patterns, and sex determination in fruit tree crops. It also serves as a potential step toward developing new cultivars to fight climate-oriented stress. Furthermore, extensive research on the stability of the ‘transgene’ across generations, and the ‘yield-penalty’ caused by the transgene, is required. Thus, meticulous crop improvement research on commercial papaya cultivars is necessary for long-term food and health security. This review article encompasses information on the traditional and modern medicinal uses, nutritional properties, phytochemistry, diseases and etiology, post-harvest measures, genomics, biotechnological strategies (for papaya improvement), and value-added products of papaya for food and health security.

First Report of Tobacco Mosaic Virus Infecting Papaya in China.

Papaya (Carica papaya. L) is widely cultivated in tropical and subtropical regions of China and has high nutritional and medicinal values. More than 11 species of papaya viruses have been recorded in the world, but the most destructive one for papaya production in China is papaya ringspot virus (PRSV) (Li, 2019). In order to control PRSV, a transgenic papaya cultivar, designated as 'Huanong No.1', carrying the nuclear inclusion b (Nib) cistron of PRSV Ys isolate, was successfully commercialized in 2006, and has shown a wide range of resistance to PRSV in China (Li et al. 2007). However, more than 10% of 'Huanong No.1' plants developed different virus-like symptoms on leaves, including mosaic, yellow mottle, and deformation in some plantations of Guangdong Province, China in 2020 (Suppl Figure 1a, b, and c). Based on observation of the symptomatic phenotypes, the field surveys indicated that the disease incidence ranged from 10% to 40%, resulting in significant loss of papaya fruit. The virus particles were purified from symptomatic papaya plants following Gooding and Hebert (1967) and rigid filamentous particles resembling tobacco mosaic virus (TMV) were observed by transmission electron microscopy. Purified virus samples were further utilized to mechanically inoculate healthy seedlings of papaya, Nicotiana glutinosa and N. tabacum K326. At 15 days after inoculation, the obvious symptoms of virus infection on different plants were observed. The diseased plants showed systemic mottling and mosaic in the papaya leaves (Suppl Figure 1d), necrotic spots on the leaves of N. glutinosa (Suppl Figure 1e), mosaic and mottling spots on leaves of N. tabacum K326 (Suppl Figure 1f). These symptoms produced on the hosts were exactly the same caused by TMV. In order to reconfirm the species of the infected virus, the total RNA was extracted from the single leaf of 30 diseased papaya plants using RNAiso Plus kit (Takara, Japan) and reverse transcription--polymerase chain reaction was performed using TMV coat protein cistron specific primers (TMV-CP-R: 5'-TCAAGTTGCAGGACCAGA-3' and TMV-CP-F 5'- ATGTCTTACAGTATCACTAC-3') as described previously (Srivastava et al. 2015). An expected 480-bp fragment was amplified from all of the samples. Sequence analysis revealed that the diseased papaya was infected with TMV, designated as Cpa-TMV. In order to understand the difference among TMV isolates on papaya and other host plants, the whole genomic sequence of TMV from papaya was obtained and analyzed. The total length of the genome of Cpa-TMV was 6395 bp, and the sequence was submitted to the NCBI database (GenBank no. OK149218). A neighbor-joining phylogenetic tree of 19 TMV isolates was constructed using MEGA X software. Phylogenetic analysis indicated that the 19 TMV isolates were divided into Clade I, II and III (Suppl Figure 2). Interestingly, Clade I was composed of 12 Chinese mainland isolates, which further was grouped into IA (Northern China) and IB (Southern China), while 6 isolates from other countries and 1 isolate (pet-TMV) from China Taiwan belong to Clade II and III. It is inferred that the TMV isolates from Chinese mainland are quite different from other countries and China Taiwan. This suggests that geographical differences between Northern and Southern China may lead to the gradual differentiation of TMV isolates and eventually induce those isolates to evolve into two subclades. To our knowledge, this is the first report of TMV infection on papaya under natural conditions. It is necessary to find effective methods to control TMV in transgenic papaya.

Effect of Arbuscular Mycorrhizal Fungi and Bio - Inoculants on Germination and Seedling Growth of Carica papaya L. Var. Gujarat Junagadh Papaya-1

Background: Glomus intraradices fungi and three bio-inoculants (Pseudomonas fluorescens, Trichoderma viride, and Trichoderma harzianum) are known to have certain beneficial effects on germination and seedling growth of several tropical fruit crops. A pot study was conducted to evaluate the effects of arbuscular mycorrhizal (AM) fungi and bio inoculants on seed germination and seedling growth of a papaya cultivar Gujarat Junagadh Papaya-1 at regional horticultural research station (RHRS), ASPEE College of Horticulture and Forestry (ACHF), Navsari Agricultural University, Navsari, Gujarat, India.&#x0D; Methods: The seeds of papaya were sown in the Monsoon season (June-Aug 2019) in polybags. The seeds of papaya were coated by AM fungi (G. intraradices), three bio inoculants, and their combinations. There were 9 treatments including control treatment.&#x0D; Results: An application of T. harzianum was found to be the most effective on seed germination and seedling growth by enhancing germination percentage (89%) along with early emergence (6 days) and consolidating all the growth parameters. T. harzanium was also effective on underground plant parts such as tap root length and diameter. The combination of all four bio-inoculants also gave significant results. Results from this study could be helpful for the West Indian fruit growers by enhancing the opportunities to use bioagents for sustaining their farming systems.