Melon Genotypes Research Articles

Cucumis melo endornavirus: Genome organization, host range and co-divergence with the host

A high molecular weight dsRNA was isolated from a Cucumis melo L. plant (referred to as ‘CL01’) of an unknown cultivar and completely sequenced. Sequence analyses showed that dsRNA is associated with an endornavirus for which a name Cucumis melo endornavirus (CmEV) is proposed. The genome of CmEV-CL01 consists of 15,078 nt, contains a single, 4939 codons-long ORF and terminates with a stretch of 10 cytosine residues. Comparisons of the putative CmEV-encoded polyprotein with available references in protein databases revealed a unique genome organization characterized by the presence of the following domains: viral helicase Superfamily 1 (Hel-1), three glucosyltransferases (doublet of putative capsular polysaccharide synthesis proteins and a putative C_28_Glycosyltransferase), and an RNA-dependent RNA polymerase (RdRp). The presence of three glycome-related domains of different origin makes the genome organization of CmEV unique among endornaviruses. Phylogenetic analyses of viral RdRp domains showed that CmEV belongs to a specific lineage within the family Endornaviridae made exclusively of plant-infecting endornaviruses. An RT-PCR based survey demonstrated high incidence of CmEV among melon germplasm accession (>87% of tested samples). Analyses of partial genome sequences of CmEV isolates from 26 different melon genotypes suggest fine-tuned virus adaptation and co-divergence with the host. Finally, results of the present study revealed that CmEV is present in plants belonging to three different genera in the family Cucurbitaceae. Such diverse host range is unreported for known endornaviruses and suggests a long history of CmEV association with cucurbits predating their speciation.

Seeds morpho-colourimetric analysis as complementary method to molecular characterization of melon diversity

Melon has undergone an intense process of selection and crossbreeding, resulting in many landraces distributed all over Europe, Africa and Asia. Due to this huge variability, the systematic position of this taxon has been reviewed many times in the last two decades. The goal of this article is to compare the phenotypic characterization achieved by seed features with the molecular analysis on melon genotypes. A set of 124 accessions of Cucumis melo has been selected for molecular and morpho-colourimetric analyses plus an additional selection of accessions of Cucumis sativus, Citrullus lanatus and Citrullus colocynthis used to highlight seed morphology distances among genus and species. Genotyping was performed on the basis of 211 polymorphic SNPs and was executed using the iPLEX® Gold MassARRAY Sequenom technology. A total of 137 parameters were specifically designed to evaluate seed colour, size, shape and texture. Both molecular and seed morpho-colourimetrical analyses confirm the existence of two melon subspecies while an intermediate group has also been found. A non random allelic distribution in SNPs located in specific genomic regions suggests that some of these regions may account for a part of the observed variation in seed size. Six major groups of varieties can be discriminated on the basis on seed traits.

Genetic diversity of Iranian melon cultigens revealed by AFLP markers

Iran is a part of the secondary centre of origin of melons, and therefore, there is a wealth of genetic variation of these species in this country. The Amplified Fragment Length Polymorphism (AFLP) marker was applied to investigate the genetic variations among five major Iranian melon cultigens (Cucumis melo) and ‘Ananasi’ as a general well-known cultivar. Ten primer pairs were used on 90 individuals producing 318 polymorphic fragments, with an average of 31.8 fragments per primer combination. The polymorphism rates ranged from 80 to 100%. The genetic similarities among accessions were calculated according to Dice’s Similarity Index and used to construct a dendrogram based on the Unweighted Pair Group Method with Arithmetic Average (UPGMA). The genetic distance estimates based on AFLPs ranged from 0.29 to 0.63, with a mean of 47±0.3. Iranian melon genotypes and the ‘Ananasi’ cultivar were considered as two separate groups on the cluster analysis. The principal coordinate analysis showed a separate allocation of the melon cultivar groups. The results demonstrated a wide diversity of Iranian melon cultigens. The high number of alleles and the high expected genetic diversity detected with the AFLP marker indicated that the Iranian melon cultigens had distinctive characteristics and were an important genetic diversity pool, which made them a valuable source of breeding materials.

Evaluation of Genetic Relationships Among Melon Genotypes Based on Morphological Markers

Selection of suitable genotypes resistant to unfavorable environmental and soil conditions and diseases is important to increase yield of melon (Cucumis melo L.). This study was undertaken to evaluate melon genotypes and to examine phylogenetic relationships between genotypes. Nineteen melon types from Iran and Afghanistan were used. Thirty-five morphologic characteristics were evaluated based on the melon International Plant Genetic Resources Institute descriptors. Flesh thickness, fruit length, fruit diameter, and cavity length were positively correlated with fruit weight. Factor analysis was used to determine effective characteristics and numbers of main factors. For each factor a loading of ≥0.65 was considered significant. Effective characteristics were categorized into 9 main factors that contributed to 92.44% of overall variance. Fruit length, fruit ratio (L/W), cavity length, cavity ratio (L/W), flesh hardiness, soluble solids content, placenta color, and secondary skin color pattern were defined mainly by the first factor contributing 26.37% of total variance. Melon genotypes were clustered based on 9 factors and at a similarity distance of 20 and further divided into 6 groups. Group Cantalupensis and Inodorus genotypes were not separated. There was a high diversity in genotypes that could be used in breeding.

Overexpression of the CmACS-3 gene in melon causes abnormal pollen development

Sexual diversity expressed by the Curcurbitaceae family is a primary example of developmental plasticity in plants. Most melon genotypes are andromonoecious, where an initial phase of male flowers is followed by a mixture of bisexual and male flowers. Over-expression of the CmACS-3 gene in melon plants showed an increased number of flower buds, and increased femaleness as demonstrated by a larger number bisexual buds. Transformation of CmACS-3 in melons showed earlier development of and an increased number of bisexual buds that matured to anthesis but also increased the rate of development of the bisexual buds to maturity. Field studies showed that CmACS-3-overexpressing melons had earlier mature bisexual flowers, earlier fruit set, and an increased number of fruits set on closely spaced nodes on the main stem.

Diversity among Indigenous Germplasms of Melon (Cucumis meloL.) Through Seed Protein Profiling Pattern

Diversity among 25 melon landraces was carried out using SDS-PAGE of seed protein extracted in Tris-Hcl buffer (0.0625N). A total of 12 seed protein bands could be resolved across the 25 genotypes of melon and were distributed in four distinct zones namely A, B, C and D. These zones were sub-divided into A1, A2, A3, B1, B2, B3, B4, C1, C2, D1, D2 and D3 sub-zones. Variation in banding pattern was observed in all these zones, based on which and the similarity in the protein banding pattern, 25 genotypes of melon were classified into 13 different groups. Group-I comprised of more number of genotypes (a total of 5). In some cases it was observed that the genotypes having contrasting morphological traits (round vs oblong fruit shape) possess similar protein profile. Like in Group-I out of 5 genotypes, only one genotype (PMM-8) had oblong fruit shape and rest were having round fruit shape. On the basis of UPGMA analysis, 25 melon genotypes were categorized into two major clusters. Cluster one comprised of 21 genotypes while cluster two comprised of 4 genotypes.

The Physiological Parameters to Compare for Drought between Early Stage in Pot and Mature Stage in Field for Melons

Melon research was carried out in order to investigate the relationships of drought responses between young and mature plants. These relationships will be useful to shorten the drought breeding process and it will not be necessary to grow the melon plant until the mature stage. Therefore time, labor and money can be saved in the drought breeding programs. Twenty-nine days old plants grown in pot and 113 days old plants grown in field under the drought stress were compared for some physiological parameters. The number of melon genotypes was 29 for both the pot and field experiments. The parameters investigated were stomatal conductance, membrane injury, leaf water potential, leaf osmotic potential, leaf temperature, leaf Ca and K concentrations. The main results of the melon research were: 1) The data relative to control showed definitely higher relationships than the data in absolute under the drought, 2) The most important relationships between young and mature tomato plants that can be used to shorten screening/breeding process were stomatal conductance, leaf temperature, leaf osmotic potential, membrane injury, and leaf Ca concentration, respectively.

Salicylic acid alleviates cadmium-induced inhibition of growth and photosynthesis through upregulating antioxidant defense system in two melon cultivars (Cucumis melo L.).

Cadmium (Cd) is a widespread toxic heavy metal that usually causes deleterious effects on plant growth and development. Salicylic acid (SA), a naturally existing phenolic compound, is involved in specific responses to various environmental stresses. To explore the role of SA in the tolerance of melon (Cucumis melo L.) to Cd stress, the influence of SA application on the growth and physiological processes was compared in the two melon cultivars Hamilv (Cd-tolerant) and Xiulv (Cd-sensitive) under Cd stress. Under 400-μM Cd treatment, Hamilv showed a higher biomass accumulation, more chlorophyll (Chl), greater photosynthesis, and less oxidative damage compared to Xiulv. Foliar spraying of 0.1 mM SA dramatically alleviated Cd-induced growth inhibition in the two melon genotypes. Simultaneously, SA pretreatment attenuated the decrease in Chl content, photosynthetic capacity, and PSII photochemistry efficiency in Cd-stressed plants. Furthermore, exogenous SA significantly reduced superoxide anion production and lipid peroxidation, followed by increase in the activities of antioxidant enzyme superoxide dismutase, guaiacol peroxidase, catalase, and ascorbate peroxidase, and content of soluble protein and free proline in both the genotypes under Cd stress. The effect of SA was more conspicuous in Xiulv than Hamilv, reflected in the biomass, photosynthetic pigments, stomatal conductance, water use efficiency, and antioxidant enzymes. These results suggest that exogenous spray of SA can alleviate the adverse effects of Cd on the growth and photosynthesis of both the melon cultivars, mostly through promoting antioxidant defense capacity. It also indicates that SA-included protection against Cd damage is to a greater extent more pronounced in Cd-sensitive genotype than Cd-tolerant genotype.

Texture Analysis in Melon Landraces through Instrumental and Sensory Methods

The present article deals with the relation between fruit texture and human perception in a large group of non-climacteric melon genotypes, by measuring several mechanical properties and discussing their relationship with some sensory parameters. Juiciness resulted the main factor in melon consumer acceptance, but firmness, cohesiveness, fibrousness, springiness, and resilience also defined quality groups. Consumers (53.9%) preferred a fruit of medium firmness, outstanding juiciness, and medium-high fibrousness; 24.5% of consumers have chosen a less firm fruit than the majority, while 21.6% of consumers wanted a less fibrous melon. The combination of textural traits could be larger applied in future breeding programs.

Genetic diversity among Chinese Hami melon and its relationship with melon germplasm of diverse origins revealed by microsatellite markers

Thick-skinned melon called Hami melon is the most widely cultivated and exported type of melon in China, and mainly grown in Xinjiang province. Here the genetic variation of 64 melon genotypes including 43 Xinjiang Hami melon accessions was analyzed using 36 simple sequence repeat (SSR) markers yielding 145 alleles. The polymorphic information content of SSR markers ranged from 0.09 to 0.83 (average 0.45). Based on the SSR markers, the melon accessions were clustered into 2 major groups (thick and thin-skinned melons). In addition, the sub-cluster analysis based on SSR markers partitioned different botanical groups, even separating similar agronomic trait groups (Xinjiang landraces var. ameri and var. inodorus). SSR analysis showed that 4 SSR markers (CMBR150, CMCTT144, CMBR84 and CMBR12) produced polymorphic bands of different sizes between these two botanical groups. Those four molecular markers might be related to melon fruit maturing time. A considerably low level of genetic diversity was detected in Xinjiang melon accessions. Genetic distances indicated the relatively narrower genetic base but specific taxonomic status of Xinjiang landraces compared with foreign reference accessions.

Population parameters of Tetranychus turkestani (Acari: Prostigmata: Tetranychidae) on fourteen melon genotypes

The antixenosis effects of Galia, CMD-158, CMC-132, CMI-157, CMI-167, CMI-175, Ananasi, Yellow Canary, Samsoori, Honey Dew, Bargney, CM-170, Khaghani and Garmsari, and the life table parameters of T. turkestani on CMC-132, CMI-167, Ananasi, Samsoori, Honey Dew and Bargney, were examined at 28 ± 1°C, 65 ± 10 % RH and a photoperiod of 16:8 L:D. In free-choice assay, the lowest preferences by adults were observed on CMI-167, Samsoori and Ananasi opposed to Honey Dew and Bargney were preferred the highest by adults of T. turkestani . The longest developmental times for both sexes were observed on CMC-132 and Ananasi, while the shortest developmental times were obtained on Honey Dew, Samsoori for females. The lowest total fecundity was observed on CMC-132 whereas the maximum was on Honey Dew. In addition, the highest value of intrinsic rate of increase ( r m ), net reproductive rate ( R 0 ), finite rate of increase ( l ) of T. turkestani were observed on the Honey Dew. The Weibull and Enkegaard models were used to fit survivorship ( l x ) and age specific fecundity ( m x ) data, respectively. The comparison and cluster analysis of biological parameters of T. turkestani on different melon genotypes demonstrated that CMC-132, Ananasi and CMI-167 were the most resistant genotypes to this pest.

Kuraklık Stresi Uygulanan Kavun Genotiplerinde Bazı Fizyolojik Değişimler Üzerine Araştırmalar

In this research, responses of melon genotypes (Midyat, Semame, Ananas, Yuva) that have determined salt tolerance levels were evaluated for leaf area, relative humidity, stomatal conductance, leaf water potential and leaf temperature under drought stress conditions. For this aim, in this study, three different watering levels (S0, S1 and S2) were used. (S0: control-plant-available water, 40% is consumed for irrigation, S1: plant-available water, 90% is consumed for irrigation, S2: during the period of 3-4 leaves of plants completely cut off from the irrigation). In the study, which is generally tolerant melon genotypes (Midyat and Semame) close to the development of the control plants showed the face of drought stress, in turn, are sensitive to salt melon genotypes (Yuva and Ananas) were affected by the drought stress significantly. Midyat and Semame genotypes leaf area under stress conditions, the relative humidity, the content, stomatal conductance, leaf temperature and leaf water potential values significantly, while retaining the same in terms of parameters of Yuva and Ananas genotypes markedly decreased compared with control plants. Tolerance to drought stress in determining the result of the study of leaf area, leaf temperature, stomatal conductance and concluded that one of the effective parameters.

Aroma and sensory quality of honeydew melon fruits (Cucumis melo L. subsp. melo var. inodorus H. Jacq.) in relation to different rootstocks

The research evaluates the influence of some selected rootstocks on the C. melo L. subsp. melo var. inodorus H. Jacq. (honeydew melon) cv. Incas fruit quality. Four Cucurbita maxima×Cucurbita moschata hybrids (namely Polifemo, AS10, RS841 and P360) and two genotypes of melon (Energia and Sting), selected for their disease resistance, were tested as rootstocks under greenhouse conditions. Physical properties, chemical data, volatile constituents and sensory descriptors were used for quality determination. All the used rootstocks exhibited a good affinity with the scion, with Polifemo and RS841 showing a productivity higher (about 15%) and a significant increase in fruit weight (about 10%) than the control. As regards the titratable acidity (TA) and the total soluble solids (TSS), similar values resulted among the samples, except for the higher levels of TA in Incas/AS10 and Incas/Sting and the higher of TSS in Incas/AS10. As regards the volatile compounds, the content of key aroma, aldehydes containing a straight nine-carbon chain, such (Z)-3-nonen-1-ol and (Z)-6-nonenal resulted lower in most of the grafted samples (20–60% and 8–45% less than the control, respectively). In relation to the key aroma compounds, the melons grafted on Energia, RS841, P360 and Polifemo rootstocks resulted more similar to the control. 14 sensory descriptors were defined for the appearance, aroma, taste, texture traits, flavor and overall. Energia grafting combination presented the sensory descriptor intensities more close to the ungrafted Incas samples. In conclusion, the quality of the grafted inodorus melon fruits was modified in a different way according to the grafting combinations; RS841 and Polifemo can be successfully used as rootstocks for the inodorus melon since they increased disease resistance and productivity without determining relevant changes on fruity quality.

Diversity among melon (Cucumis melo L.) landraces from the Indo-Gangetic plains of India and their genetic relationship with USA melon cultivars

We report here the first broad genetic characterization of farmer-developed landraces of melon (Cucumis melo L.) from the Indo-Gangetic plains of India, an area overlooked in previous melon genetic diversity analyses of Indian melon germplasm. Eighty-eight landraces from three melon Groups in two subspecies (C. melo subsp. agrestis Momordica Group, and C. melo subsp. melo Cantalupensis Group and Reticulatus Group) were collected from the four agro-ecological regions (six sub-regions) of two northern states of the Indo-Gangetic plains of India, Uttar Pradesh and Uttarakhand. Significant differences were found among the landraces and eight USA Reticulatus Group reference cultivars for 18 plant and fruit traits: no. of primary branches per plant, days to marketable maturity, sex expression, fruit shape, flesh colour, netting, no. of fruit per plant, fruit weight, shelf life, total soluble solids (°Bx), ascorbic acid (mg/100 g), titratable acidity (%), fruit length and diameter, seed cavity length and diameter, flesh thickness, and resistance to Cucumber mosaic virus. The three melon groups differed significantly for 10 of the plant and fruit traits. Cantalupensis Group and Reticulatus Group accessions were andromonoecious, and the Momordica Group was monoecious. Neighbour-joining (NJ) tree and factorial correspondence analysis (FCA) of simple sequence repeat loci also revealed a high level of genetic variability in this germplasm. The 96 melon genotypes clustered into five groups in the NJ tree analysis: the 16 Indian Reticulatus Group accessions and eight USA reference cultivars formed a distinct group; and the 60 Cantalupensis Group accessions clustered in four other groups with the 12 Momordica Group accessions in a distinct subgroup of one of the Cantalupensis groups. The FCA plot largely confirmed the NJ tree with three distinct groups, one for each melon group. The close affinity of the Indian and USA Reticulatus melons was not unexpected, but it is not clear whether it was inherent in the group and maintained as Reticulatus melons moved from India through Central Asia and Europe to North America, or the result of recent intercrossing of Indian landraces with the USA-derived cultivars and selection for a broad range of Reticulatus type melons.

Reação fenotípica de plantas de abóbora e melão à infecção por isolados simples de ZYMV e misto de ZYMV+SQMV

Com esse trabalho, objetivou-se verificar através da inoculação artificial, a reação fenotípica de plantas de abóbora cv. ‘Caserta’ a isolados de ZYMV e ZYMV+SqMV e também verificar a reação fenotípica em quatro genótipos de melão de um isolado misto (ZYMV+SqMV), ambos oriundos de regiões produtoras de melancia no Estado do Tocantins. O trabalho foi realizado em casa de vegetação com telados a prova de afídeo. O delineamentoexperimental utilizado foi o inteiramente casualizado com cinco plantas por parcela e três repetições. As plantas inoculadas foram observadas quanto ao aparecimento de sintomas aos 28, 33 e 38 dias após a primeira inoculação. Nas plantas de abóbora, inoculadas com o isolado simples, os sintomas predominantes exibidos foram mosaico e nervuras paralelas. Nas infecções mistas houve maior agressividade dos sintomas, evoluindo para deformações e estreitamentos foliares, além de bolhosidade, nervuras paralelas e esporão, comprometendo grande parte da área foliar das plantas avaliadas. Nos genótipos de melão, os sintomas observados foram mais agressivos nos genótipos Sunshine e Amarelo. No genótipo Eldorado observou-se apenas mosaico e no melão Valenciano não foram observados sintomas.

Selection of Melon Genotypes with Resistance to Fusarium Wilt and Monosporascus Root Rot for Rootstocks

Selection of Melon Genotypes with Resistance to Fusarium Wilt and Monosporascus Root Rot for Rootstocks

A Newly Developed Real-Time PCR Assay for Detection and Quantification of Fusarium oxysporum and Its Use in Compatible and Incompatible Interactions with Grafted Melon Genotypes

A reliable and species-specific real-time quantitative polymerase chain reaction (qPCR) assay was developed for detection of the complex soilborne anamorphic fungus Fusarium oxysporum. The new primer pair, designed on the translation elongation factor 1-α gene with an amplicon of 142 bp, was highly specific to F. oxysporum without cross reactions with other Fusarium spp. The protocol was applied to grafted melon plants for the detection and quantification of F. oxysporum f. sp. melonis, a devastating pathogen of this cucurbit. Grafting technologies are widely used in melon to confer resistance against new virulent races of F. oxysporum f. sp. melonis, while maintaining the properties of valuable commercial varieties. However, the effects on the vascular pathogen colonization have not been fully investigated. Analyses were performed on 'Charentais-T' (susceptible) and 'Nad-1' (resistant) melon cultivars, both used either as rootstock and scion, and inoculated with F. oxysporum f. sp. melonis race 1 and race 1,2. Pathogen development was compared using qPCR and isolations from stem tissues. Early asymptomatic melon infections were detected with a quantification limit of 1 pg of fungal DNA. The qPCR protocol clearly showed that fungal development was highly affected by host-pathogen interaction (compatible or incompatible) and time (days postinoculation). The principal significant effect (P ≤ 0.01) on fungal development was due to the melon genotype used as rootstock, and this effect had a significant interaction with time and F. oxysporum f. sp. melonis race. In particular, the amount of race 1,2 DNA was significantly higher compared with that estimated for race 1 in the incompatible interaction at 18 days postinoculation. The two fungal races were always present in both the rootstock and scion of grafted plants in either the compatible or incompatible interaction.

Correlation and Path Coefficient Analyses in Sweet Melon (Cucumis melo Var. Aegyptiacus L.) Under Irrigated and Drought Conditions

Genotypic correlation and path analyses were carried out for growth, yield and fruit quality traits in 13 sweet melon genotypes collected from different places in Egypt. Seeds of these melon populations were sown under irrigated and drought stress conditions. The analysis of variance for the studied traits showed that the differences among genotypes were highly significant for all studied traits under irrigation and drought stress. Under irrigated conditions, total yield per plant was positively and significantly correlated with fruit weight, flesh fruit thickness and fruit length. Positive direct effects were exhibited for fruit weight, number of fruits per plant and stem length on total yield per plant, while maximum positive indirect effects on total yield per plant were exhibited by fruit length and flesh fruit thickness through fruit weight. In case of drought stress conditions, total yield per plant had the highest positive and significant correlation with fruit weight followed by flesh fruit thickness, fruit length and stem length. Fruit weight had the greatest positive direct effect on total yield per plant followed by number of fruits per plant, fruit length and total soluble solid content. Flesh fruit thickness and fruit length had high positive indirect effect on total yield per plant via fruit weight. The results obtained from correlation and path analyses showed that the efficiency in the selection for total yield per plant in sweet melon should increased through the selection of fruit weight under irrigated conditions and fruit weight and fruit length under drought conditions.

Reproductive parameters and life expectancy of Tetranychus urticae (Acari: Tetranychidae) on 12 genotypes of melon and cucumber in laboratory condition

The effect of two host plant species including eight genotypes of melon (Cucumis melo L.) and four genotypes of cucumber (Cucumis sativus L.) was studied on reproductive parameters: life expectancy and mortality of Tetranychus urticae (Koch) at 25 ± 1 °C, 60 ± 5% rh and a photoperiod of 16L:8D hours. The results indicated that the highest value of the gross fecundity rate of T. urticae was 96.72 ± 16.70 (eggs/female) on Mir sultan and the lowest value was 14.33 ± 0.88 on Ananasi. The maximum value of gross fertility rate (41.55 ± 4.79) was recorded on Sultan, while the minimum value (1.38 ± 0.08) was recorded on Ananasi. The net fecundity rate was varied from 0.47 ± 0.09 on Ananasi to 23.53 ± 3.96 eggs/female on Sultan. The net fertility rate was 12.96 ± 2.18 on Sultan and 0.04 ± 0.009 on Ananasi, which was the maximum and minimum values, respectively. The range of gross hatch rate on different melon and cucumber genotypes was 9.67% on Ananasi to 72.46% on Super sultan. The cohort reared on Super sultan had the highest mean eggs per day and those on Shah abadi had the lowest mean eggs per day. In addition, the mite demonstrated the maximum value of mean fertile eggs per day with the amount of 1.66 ± 0.19 eggs/female when fed on Sultan, and Ananasi demonstrated the minimum value (0.09 ± 0.005). The life expectancy of one-day-old adults of T. urticae was estimated to be 16 days on Garmak Isfahan and 26.62 days on Mir sultan which is the maximum and minimum values, respectively. Furthermore, the highest mortality percentage of immature stages of T. urticae was recorded on Ananasi and the lowest was recorded on Super sultan. Comparison of the data collected in this study revealed that the mites had considerably better performance on cucumber genotypes than melon genotypes, so we can assume that cucumber is the preferable host species for T. urticae. The use of preferable and resistant host plants is helpful in crop rotation and it will be one of the beneficial strategies to integrated pest management programmes.

Reference gene selection for gene expression analysis in melon infected by Fusarium oxysporum f.sp. melonis

Eleven candidate reference genes were evaluated in stem tissues of two melon (Cucumis melo L) genotypes infected with Fusarium oxysporum f.sp. melonis (FOM) race 1, to investigate the most stable internal control gene to use in gene expression study in melon under biotic stress. The candidate reference genes, utilized in the qRT-PCR, were selected among the most common reference genes reported in melon literature as well as on melon sequences found in available databases. The expression stability of the reference genes selected, was tested by using the geNorm and NormFinder statistical algorithms. Irrespective of the plant response to FOM infection, there was substantial agreement in gene ranks of both software. The ribosomal protein L2 gene had the high transcript stability while the elongation factor, cyclophilin7 and 18S rRNA were the least stable. The best three reference genes, ribosomal protein L2, actin* and cyclophilin were used to normalize the expression data of the glutathione S-transferase in the resistant and susceptible plants. Differences in the expression data emerged for both genotypes and were more evident in the resistant one. The ribosomal protein L2 showed similar normalized expression values in both genotypes and thus it could be indicated as unique internal control for gene expression analysis in melon under FOM infection. This work represents the first in-depth study on reference genes validation in melon under biotic stress condition. The identification of such genes would improve the accuracy and reliability of gene expression studies and speed up candidate disease resistant gene analysis in melon.