Melon Cultivars Research Articles

Fruit characters of Cucumis melo L.: ‘tacapa green black’, ‘melona’ and ‘meloni’

<p class="Abstract">Melon <span lang="IN">has high
 demand</span>, but most of the Indonesian farmers <span lang="IN">planted
 import seeds of melon</span> which has expensive price. Hence, Indonesia should produce high-quality melon seeds. This
 research used three melon cultivars (<i>Cucumis melo </i>L.): ‘Tacapa Green
 Black<span lang="IN"> (GB)</span>’, ‘Melona’, and ‘Meloni’ which are the
 result of breeding in Genetic and Breeding Laboratory, Faculty of Biology, Gadjah
 Mada University. The purpose of this study is to describe<span lang="IN"> fruit</span> morphological characters of these melon
 cultivar<span lang="IN">s</span>. ‘Tacapa <span lang="IN">GB’</span> is breeding result of Testcross<i> </i>♀ <span lang="IN">‘</span>Act3 434<span lang="IN">’</span> X F1 <span lang="IN">‘</span>PI 371795<span lang="IN">’</span>, ‘Melona’
 is segregation<span lang="IN"> from ‘Luna’</span> and ‘Meloni’ is
 breeding result of ♀ ‘SL-3’ X ♂ ‘PI 371795’. Seeds of ‘Tacapa <span lang="IN">GB’</span>, ‘Melona’
 and ‘Meloni’ was planted. <span lang="IN">While
 harvest</span>, these
 melons w<span lang="IN">ere</span> measured, observed, and documented to obtain the quantity and
 quality <span lang="IN">of fruit </span>characters. Data were analyzed and compared each other. The
 results showed ‘Tacapa <span lang="IN">GB’</span> has weight average of 3<span lang="IN">.</span>2 kg, brix of 7–9, fruit shape's is oval, fruit color is
 yellow-green, and rind color is dark green. ‘Melona' has weight average of 0<span lang="IN">.</span>8 kg, brix of 7–15, fruit color is orange, having lobes,
 and sweet. ‘Meloni' has an oval shape, fruit color is pale yellow, the weight
 of 1<span lang="IN">.</span>1 kg, brix of 8–16 and fragrant.<o:p></o:p></p>

The effect of ethepon treatment on the formation of flower in melon (Cucumis melo L.)

<p class="Abstract">Melon is a potential horticultural crop which the production is increased significantly each year in
 Indonesia. However, a melon plant that has been widely developed in Indonesia
 faced a problem due to the high tropical temperature that affected the fall of
 flower causing failure in fruit production. In addition, the variation of sex
 expression in melon flower is important for genetic analysis and breeding
 programs. Ethepon is one of plant chemical growth regulator that is known to
 change the sex expression of the plant by increasing the number of female
 flower in monoecious plant especially Cucurbitaceae. This research aimed to
 analyze the effect of ethepon treatment
 on the sex determination of melon flower. This study was conducted by 3 stages
 treatment of ethepon during March – July
 2014, namely when 2, 5, and 7 weeks after planting. Split-plot design has been
 used with the main plots were arranged in a completely randomized design by
 cultivating different melon cultivars i.e: Melodi Gama 1, Melodi Gama 3,
 Bartek, and PI 371795. The data were analyzed by F-test and Duncan Multiple
 Range Test (DMRT) with significance level at 5 % using software SAS 9.3. The
 result showed that ethepon treatment
 affected the formation of melon flower by increasing the number of female or
 hermaphrodite flower and decreasing the number of male flowers, especially in
 the concentration of 75 ppm and 100 ppm but with different responses by
 different cultivar. <o:p></o:p></p>

Tolerance of melon cultivars to irrigation water salinity

ABSTRACT The use of saline water for irrigation causes severe restriction to nutritional balance, growth and production in many crops due to the effect of salts on plant and soil. The objective of this study was to investigate the response of melon (Cucumis melo L.) cultivars to various levels of irrigation water salinity on yield and fruit quality. A field experiment was conducted in a split-plot randomized block design with four replicates. The factors were five levels of irrigation water salinity (0.54, 1.48, 2.02, 3.03 and 3.90 dS m-1) in the plots and five melon cultivars (C1 - Sancho - Pele de sapo; C2 - Medellín - Pele de sapo; C3 - Mandacaru - Canary; C4 - Néctar - Galia; C5 - Sedna - Cantaloupe) in the sub-plots. According to the results, among the five genotypes studied, Sancho was the most salt-tolerant genotype, followed by Mandacaru, Medellín, Sedna and Néctar. Since irrigation water salinity did not influence the mean fruit weight, the reduction in the number of fruits was the main cause of yield reduction of the melon crop under high salinity water. The contents of total soluble solids increased under high salinity level.

Study of the susceptibility of some local melon cultivars to infestation with some sucking insects and their associated predators

Study of the susceptibility of some local melon cultivars to infestation with some sucking insects and their associated predators

Antioxidant activity of cell-wall components in netted melon flesh against ascorbic acid oxidation during fruit development

Melon (Cucumis melo) fruit is known to contain a high level of vitamin C, as do Valencia orange and Satsuma mandarin. Previously, we reported that cell-wall components of melon flesh demonstrated a marked effect in maintaining the UV absorbance of ascorbic acid (high antioxidant activity), compared with the flesh of 18 fruit species. In this study, changes in antioxidant activity against ascorbic acid oxidation were measured in water extract of alcohol-insoluble solids (AIS) of the flesh of three cultivars of melon ('Andesu', 'Gurandoru', and 'Life') during fruit development, between 10 and 51 days after anthesis (DAA). The antioxidant activity per unit weight was increased with fruit development in all cultivars, especially after 45 DAA. The flesh firmness and dry weight of AIS decreased with fruit development. As the main component of the water-soluble fraction is pectic substances, uronic acid and neutral sugar contents in the water-soluble fraction of AIS were determined. A marked increase in the neutral sugar content was observed, while the increase of uronic acid was comparatively low. In our previous study, the antioxidant activity, measured by the ascorbic acid oxidation method, was higher in low-methylated pectins than in high-methylated pectins. Antioxidant components in AIS of melon flesh are discussed.

Severity of gummy stem blight on melon in relation to cultivars, use of fungicides and growing season

ABSTRACT The authors aimed to evaluate the resistance to gummy stem blight and the agronomic traits of the melon crop in the Southern Region of the State of Tocantins, Brazil, in two growing seasons, submitted or not to treatment with fungicides. Two experiments were carried out: dry season (experiment I), and rainy season (experiment II), respectively, comprising the periods from July to October 2013 and from March to May 2014. Six melon cultivars were used in each season. In the dry season: Eldorado 300, Hibrix, Dourado Amarelo, Louro, Gaúcho Redondo and Canarian; and in the rainy season: Eldorado 300, Hibrix, HF-4439, Louro, Gaúcho Redondo and Canarian. Treatments consisted of each cultivar and split plot with (WA) or without fungicides application (NA). All cultivars were susceptible to disease, considering that Gaúcho Redondo was the least susceptible in the dry season. The fungicide application decreased disease severity in the dry season, however the productivity of the crop in treatments without fungicide application were not compromised, due to the late onset of the disease, and ranged from 19.2 t/ha for Eldorado 300 up to 41.9 t/ha for Canarian. The total soluble solids showed average values of 12°Brix, except for cultivar Gaúcho Redondo, which showed brix value lower than commercial standards. During the rainy season, fungicide application did not protect the plants, which did not complete the cycle, resulting in the absence of marketable fruit production. The climatic characteristics observed in the rainy season, with high humidity, leaf wetness and high temperatures are favorable for the development of gummy stem blight in melon plants. Thus, in Tocantins, the dry season is characterized as the best time of year for cultivation, between April and September.

Exogenous GABA application improves the NO 3 − -N absorption and assimilation in Ca(NO 3 ) 2 -treated muskmelon seedlings

Abstract The potential of exogenous γ-aminobutyric acid (GABA) application to improve the NO 3 − -N absorption and assimilation in Ca(NO 3 ) 2 -treated muskmelon seedlings was investigated in ‘Yipintianxia 208’, a salt-sensitive melon cultivar grown in a deep-flow hydroponic system. Plants were treated under control or 80 mM Ca(NO 3 ) 2 stress conditions with or without foliar spraying 50 mM GABA. We found that under Ca(NO 3 ) 2 stress, the activities of nitrate reductase (NR), glutamate synthetase (GS), and glutamate amino-transferase (GOGAT) in muskmelon seedlings were significantly reduced, while the activities of glutamate dehydrogenase (GDH), glutamate oxaloacetate transaminase (GOT), and glutamate pyruvate aminotransferase (GPT) were enhanced. These changes lead to a decrease in the content of NO 3 − -N and an increase in that of NH 4 + -N in muskmelon roots and leaves, which further severely inhibited the plant growth. Exogenous GABA application effectively improved the absorption of NO 3 − -N in muskmelon roots and leaves under Ca(NO 3 ) 2 stress and the NH 4 + -N assimilation by enhancing the activities of nitrogen assimilation enzymes (NR, GS, and GOGAT) in muskmelon seedlings. Exogenous GABA also reduced the NH 4 + release by limiting the GDH deamination, thus further alleviating the ammonia toxication induced by Ca(NO 3 ) 2 stress. Our results suggest that exogenous GABA applications can relieve the nitrogen metabolic disorders caused by Ca(NO 3 ) 2 stress and eventually promote plant growth. In addition, Exogenous GABA regulated the transaminase (GOT and GPT) activities, maintaining the balance of the amino acid metabolism. Furthermore, the accumulation of the functioning as a nitrogen source endogenous GABA was promoted, eventually improving the resistance of muskmelon seedlings to Ca(NO 3 ) 2 stress.

Scanning Electron Microscopy study of root tissue of muskmelon: Transferring Fusarium wilt resistance from snapmelon to muskmelon

The overall aim of this study was to investigate the level of Fusarium oxysporum f. sp. Melonis (F.o.m.) infection by studying the Scanning electron micrographs of transverse sections of parent inbred lines and developed F1 hybrid. The current study involved KP4HM-15 (Fusarium wilt resistant inbred line) in a crossing program with well adapted muskmelon cv. Punjab Sunehri (PS) to develop FW resistant hybrid possessing high yield and quality traits. Fom infects melon root and trails through the cortical and endodermal cells to reach xylem vessels by penetrating through pits. This is the first SEM appraisal of the whole tap root of field grown melon accessions, KP4HM-15, PS and PSxKP4HM-15 (MH-41) (F1 hybrid) aimed to discern the role of the root morphometric characters for imparting FW resistance. The trend for root epidermo-cortical thickness was KP4HM-15>PS>MH-41 while for the xylem diameter was MH-41> KP4HM-15>PS. The F1 hybrid exhibited FW resistance intermediate among the two parents i.e. absence or presence of less mycelia as compared to the susceptible parent (PS). However, the extent of infection was higher than the resistant parent KP4HM-15, which shows that partial resistance was transferred from KP4HM-15 to MH-41. This study accentuates the resistance gene mining and use of wild melon accessions to introgress FW resistance in commercial melon cultivars.

Further Evidence of Cucurbit Host Specificity among Acidovorax citrulli Groups Based on a Detached Melon Fruit Pathogenicity Assay.

Bacterial fruit blotch, caused by the gram-negative bacterium Acidovorax citrulli, is a serious economic threat to cucurbit crop production worldwide. A. citrulli strains can be divided into two genetically distinct groups, with group I strains infecting a range of cucurbit species and group II strains being predominantly associated with watermelon. Group I and II A. citrulli strains differ in their arsenal of type III secreted (T3S) effector proteins and we hypothesize that these effectors are critical for cucurbit host preference. However, the pathogenicity or virulence assays used for A. citrulli, including infiltration of seedling cotyledons and mature fruit rind tissues with cell suspensions and spray inoculation of seedlings, lack the sensitivity to consistently distinguish strains of the two groups. Here, we describe an immature, detached melon fruit assay based on 'Joaquin Gold' melon (Syngenta, Rogers Brand) that clearly indicates differences in host specificity between group I and II A. citrulli strains. Using this assay, four group I strains (M6, AAC213-52, AAC213-55, and XJL12) induced typical water-soaked lesions in melon fruit rind tissue 7 to 10 days after pinprick inoculation. In contrast, four group II strains (AAC00-1, AAC213-44, AAC213-47, and AAC213-48) did not induce water-soaked lesions on detached melon fruit rinds during the same period. These data suggest that group I A. citrulli strains have a specific capacity to infect immature Joaquin Gold melon fruit, whereas group II strains do not. Interestingly, this differential pathogenicity phenotype was not observed on foliar seedling tissues of the same melon cultivar, suggesting that host preference of A. citrulli strains is specific to immature fruit tissues. Using the immature melon fruit inoculation assay, a T3S system mutant of the group I A. citrulli strain, M6 (M6ΔhrcV), failed to induce water soaking. This indicates that T3S effectors are involved in A. citrulli cucurbit host preference, and that this assay is suitable for future studies of unique T3S effectors that distinguish group I and II strains.

Resistance to tomato leaf curl New Delhi virus in melon is controlled by a major QTL located in chromosome 11.

Identification of three genomic regions and underlying candidate genes controlling the high level of resistance to ToLCNDV derived from a wild melon. SNP markers appropriated for MAS management of resistance. Tomato leaf curl New Delhi virus (ToLCNDV) is a bipartite begomovirus that severely affects melon crop (Cucumis melo) in the main production areas of Spain since 2012. In this work, we evaluated the degree of resistance of four accessions (two belonging to the subsp. agrestis var. momordica and two to the wild agrestis group) and their corresponding hybrids with a susceptible commercial melon belonging to the subsp. melo (Piel de Sapo, PS). The analysis using quantitative PCR (qPCR) allowed us to select one wild agrestis genotype (WM-7) with a high level of resistance and use it to construct segregating populations (F 2 and backcrosses). These populations were phenotyped for symptom severity and virus content using qPCR, and genotyped with different sets of SNP markers. Phenotyping and genotyping results in the F 2 and BC1s populations derived from the WM-7×PS cross were used for QTL analysis. Three genomic regions controlling resistance to ToLCNDV were found, one major locus in chromosome 11 and two additional regions in chromosomes 12 and 2. The highest level of resistance (no or mild symptoms and very low viral titer) was obtained with the homozygous WM-7WM-7 genotype at the major QTL in chromosome 11, even with PSPS genotypes at the other two loci. The resistance derived from WM-7 is useful to develop new melon cultivars and the linked SNPs selected in this paper will be highly useful in marker-assisted breeding for ToLCNDV resistance in melon.

Changes of polyamines and CBFs expressions of two Hami melon (Cucumis melo L.) cultivars during low temperature storage

Hami melon (Cucumis melo L. var. inodorus Jacq) is susceptible to chilling injury (CI) during low temperature storage, which causes changes in physiological mechanisms and gene expression. In this study, cold tolerance of two Hami melon cultivars, namely Xinmi No. 3 and Xinmi No. 11 was evaluated. We assessed changes of membrane permeability, the content of polyamines (PAs), and the expression of C-repeat/dehydration-responsive element (CRT/DRE)-binding factors (CBFs) in different section of fruit of each cultivar stored at 3°C under 75–80% relative humidity. The results showed that Xinmi No. 11 was more cold tolerant than Xinmi No. 3, the content of PAs and the expression of CmCBFs in the cold-tolerant cultivar were significantly higher than in the cold-sensitive cultivar during storage at 3°C. CI was observed in the peel tissue, but not in the pulp tissue. The content of PAs and the expression of CmCBFs in the peel tissue were significantly higher than in the pulp tissue. The membrane permeability, putrescine (Put), spermine(Spm), and the expression of CmCBF1 and CmCBF3 in the peel tissue of Hami melon fruit increased with the degree of CI. Our results provide novel evidence about the positive correlation between the content of PAs, the expression of CmCBF1 and CmCBF3 and cold tolerance. The CI had major impact on Put, Spm and membrane permeability. The assessed parameters could provide sensitive indicators reflecting cultivar cold tolerance of Hami melon fruit under chilling stress.

Exploring an East Asian melon (Cucumis melo L.) collection for parthenocarpic ability

In melon (Cucumis melo L.), the amount of fertile pollen decreases at low temperature during winter and early spring and thereby restricts fertilization. A promising way to overcome this problem is to develop parthenocarpic cultivars. Parthenocarpic cucumber and squash, but not melon cultivars are available. In this study, we explored 172 accessions from an East Asian melon collection and identified accessions that exhibited strong parthenocarpic ability throughout the year. Crosses between parthenocarpic accessions and a non-parthenocarpic cultivar, and among parthenocarpic accessions indicated that parthenocarpy may be inherited in a recessive manner and is likely controlled by the same gene or genes in these accessions. The parthenocarpic indices, such as the size and number of parthenocarpic fruits, differed among the cultivation periods, indicating the importance of environmental factors for parthenocarpic fruit development. We conclude that it is possible to breed new cultivars with stable parthenocarpic ability throughout the year by using the identified accessions.

Papaya ringspot virus Populations From East Timorese and Northern Australian Cucurbit Crops: Biological and Molecular Properties, and Absence of Genetic Connectivity.

To examine possible genetic connectivity between crop viruses found in Southeast Asia and Australia, Papaya ringspot virus biotype W (PRSV-W) isolates from cucurbits growing in East Timor and northern Australia were studied. East Timorese samples from cucumber (Cucumis sativus) or pumpkin (Cucurbita moschata and C. maxima) were sent to Australia on FTA cards. These samples and others of pumpkin, rockmelon, honeydew melon (Cucumis melo), or watermelon (Citrullus lanatus) growing in one location each in northwest, north, or northeast Australia were subjected to high throughput sequencing (HTS). When the 17 complete PRSV genomic sequences obtained by HTS were compared with 32 others from GenBank, the five from East Timor were in a different major phylogroup from the 12 Australian sequences. Moreover, the East Timorese and Australian sequences each formed their own minor phylogroups named VI and I, respectively. A Taiwanese sequence was closest to the East Timorese (89.6% nt dentity), and Mexican and Brazilian sequences were the closest to the Australian (92.3% nt identity). When coat protein gene (CP) sequences from the 17 new genomic sequences were compared with 126 others from GenBank, three Australian isolates sequenced more than 20 years ago grouped with the new Australian sequences, while the closest sequence to the East Timorese was from Thailand (93.1% nt identity). Recombination analysis revealed 13 recombination events among the 49 complete genomes. Two isolates from East Timor (TM50, TM32) and eight from GenBank were recombinants, but all 12 Australian isolates were non-recombinants. No evidence of genome connectivity between Australian and Southeast Asian PRSV populations was obtained. The strand-specific RNA library approach used optimized data collection for virus genome assembly. When an Australian PRSV isolate was inoculated to plants of zucchini (Cucurbita pepo), watermelon, rockmelon, and honeydew melon, they all developed systemic foliage symptoms characteristic of PRSV-W, but symptom severity varied among melon cultivars.

Development of a muskmelon cultivar with improved resistance to gummy stem blight and desired agronomic traits using gene pyramiding

Gummy stem blight (GSB), caused by Didymella bryoniae (Auersw.) Rehm., is a severe disease affecting Cucurbitaceae crops including melons. The resistance of current melon varieties that carry a single Gsb resistance gene is insufficient to protect against the abundant variation of the D. bryoniae isolates. Pyramiding multiple Gsb resistance genes into melon cultivars is an effective way to develop a broad resistance spectrum and to increase the duration of GSB resistance. In this study, two resistance genes (Gsb-4 and Gsb-6) from two resistant accessions, PI482398 and PI420145, were pyramided into one variety using marker-assisted selection (MAS). The donor parent 4598 that contained Gsb-4 and Gsb-6 was hybridized with muskmelon Baipicui to produce BC<sub>1</sub>F<sub>1</sub> and BC<sub>2</sub>F<sub>1</sub>. Phenotyping and MAS enabled identification and pyramiding of two Gsb genes in individuals of F<sub>1,</sub> BC<sub>1</sub>F<sub>1</sub> and BC<sub>2</sub>F<sub>1</sub>. Field cultivation showed that individuals carrying both Gsb-4 and Gsb-6 had improved resistance to GSB and improved fruit quality. The results indicated that MAS-based pyramiding is an effective strategy for breeding melon cultivars with increased resistance to GSB.

Mapping Resistance to Alternaria cucumerina in Cucumis melo.

Infection with Alternaria cucumerina causes Alternaria leaf blight (ALB), a disease characterized by lesion formation on leaves, leading to substantial yield and quality losses in Cucumis melo (melon). Although fungicides are effective against ALB, reduction in the frequency of application would be economically and environmentally beneficial. Resistant melon lines have been identified but the genetic basis of this resistance has not been determined. A saturated melon genetic map was constructed with markers developed through genotyping by sequencing of a recombinant inbred line population (F6 to F10; n = 82) derived from single-seed descent of a F2 population from a cross between the ALB-resistant parent MR-1 and the ALB-susceptible parent Ananas Yokneum. The population was evaluated for A. cucumerina resistance with an augmented block greenhouse study using inoculation with the wounded-leaf method. Multiple quantitative trait loci (QTL) mapping identified two QTL that explained 33.9% of variation in lesion area. Several candidate genes within range of these QTL were identified using the C. melo v3.5 genome. Markers linked to these QTL will be used to accelerate efforts to breed melon cultivars resistant to ALB.

Analysis of genetic variability of commercial melon cultivars using SSR molecular markers.

Taking into account the scenario of melon production (Cucumis melo L.) in Brazil, it is notable the importance of the culture in the fruit market. The preference of the national market is concentrated in the fruits of the yellow type. Therefore, it is possible that the genetic base of the commercial cultivars is relatively narrow due to the loss of important genes in the breeding process, and it is possible to introgress external genes for increasing recombination possibilities that generate sources of resistance to the main diseases and superior genotypes. This study evaluated the genetic variability of 87 melon accessions composed of 72 commercial cultivars belonging to the Inodorus and Cantaloupensis groups and 15 plant introductions (PIs). Forty-four polymorphic SSR primers were used to amplify a total of 202 alleles. The expected heterozygosity presented an average of 0.519 and the PIC index of 0.458, being moderately informative. The dendrogram generated for the 72 cultivars grouped the genotypes into 2 main groups, and there was no association with the classification of groups of the genotypes in the grouping. The number of SSR markers was sufficient to predict wide genetic variability among the cultivars studied, with the similarity between 0.35 and 0.98. The dendrogram presented for the 72 cultivars and the 15 PI genotypes was not associated with the classification of the genotypes in the grouping, and the 15 PIs were well dispersed with similarity indexes that resemble the two groups studied. A set of 25 primers was identified that were useful in distinguishing the 72 cultivars. These primers can be used in later research with the cultivars, as well as in crop protection situations, being an important tool in the useful and rapid distinction of genotypes, and in commercial disputes regarding the certification of the main melon cultivars used in the country.

Occurrence of viruses infecting melon in Xinjiang of China and molecular characterization of Watermelon mosaic virus isolates

Cucurbit viruses have been associated with important economic losses in Xinjiang of China. Therefore, a comprehensive survey and sample collection was performed during the 2013 and 2014 growing seasons from the major melon-growing locations in Xinjiang which is the largest area for melon production in China. Samples were analyzed using reverse transcription-polymerase chain reaction (RT-PCR) to detect Watermelon mosaic virus (WMV), Zucchini yellow mosaic virus (ZYMV), Cucumber mosaic virus (CMV), Papaya ringspot virus (PRSV), Squash mosaic virus (SqMV), Tomato ringspot virus (ToRSV), Moroccan watermelon mosaic virus (MWMV), Tomato spotted wilt virus (TSWV), Watermelon silver mottle virus (WSMoV), Cucumber green mottle mosaic virus (CGMMV), and Zucchini yellow fleck virus (ZYFV). We collected 492 melon samples with virus-like symptoms. Out of these, 94.5 % of the samples were infected by at least one of these viruses. WMV was the most prevalent virus detected. WMV, CMV, and ZYMV were detected in 77.0 %, 60.0 %, and 41.1 % of infected samples, respectively, and the infection rate of these three viruses changed significantly among melon cultivars. Other viruses analysed were not detected in any sample tested. The number of multiple infections was high (average 57.2 %), with the most common double infection WMV + CMV (17.8 %), closely followed by WMV + ZYMV (14.4 %). Statistical analysis of the potential association among viruses showed that there was a strong association between several viruses for multiple infections. An analysis of WMV genetic diversity suggested that all isolates obtained in this study clustered into group A and that purifying selection was restricting variability in the population.

Screening new melon (Cucumis melo) cultivars from international seed companies for Australian markets

As Australian fruit and vegetable breeding programmes by public research institutions are progressively downsized or curtailed, new cultivars for production horticulture are increasingly being sourced from breeding programmes of overseas companies. Typically, such cultivars are purchased initially on the basis of their description and performance overseas, together with price. However, there is a significant risk that these could fail under Australian conditions and markets: for example, disease resistance claims may not hold up when exposed to different races of the causal organism in Australia; flavour and visual attributes may not suit Australian consumers; some cultivars may not prove as productive as found overseas; and unforeseen genetic weaknesses may become apparent. This paper reports results of irrigated field trials conducted in south-east Queensland over 2 years using melon (Cucumis melo) cultivars sourced from seed companies in Taiwan, Vietnam, China and USA. A preliminary screening trial in year 1 was used to shortlist a smaller number of cultivars for more detailed trials in year 2 to assess their potential productivity for commercial use and their novelty appeal for non-commercial markets.

Effects of salt and drought stresses on physiological and biochemical changes in callus tissues of melon cultivars

In our previous study, two salt- and drought-tolerant genotypes and two sensitive genotypes were selected according to the growth parameters measured. The aim of present study was to determine the activity of antioxidative stress enzymes in some salt- and drought-sensitive and salt- and drought-tolerant melon cultivars grown in in vitro culture under salt and drought stress conditions. Besides to determine out whether in vitro callus culture can be used as a screening method under salt and drought stresses in a melon screening study. In this study, the magnitude of cell wall damage (lipid peroxidation) was lower in the tolerant genotypes than in the sensitive ones. The amount of lipid peroxidation was higher in the salt-stressed seedlings than in those that were drought-stressed. In this study, antioxidant enzyme (superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase) activities were investigated in the callus tissues of four melon genotypes under salt and drought stress. The antioxidant enzyme activities showed differences among melon genotypes.

Mapping quantitative trait loci for fruit traits and powdery mildew resistance in melon (Cucumis melo).

BackgroundFruit characters affect consumer preferences and the market value of melons is determined by fruit quality. Most fruit quality-related traits are controlled by multiple genes, and are influenced by environmental factors. Furthermore, powdery mildew is another limiting factor in melon production. To develop new melon cultivars with disease resistance and high quality fruits using the molecular marker-assisted breeding strategy, identification of quantitative trait loci for fruit quality and disease resistance is required.ResultsThe F2 populations from the cross of TARI-08874 (Cucumis melo ssp. melo) and ‘Bai-li-gua’ (C. melo ssp. agrestis) were used to map the quantitative trait loci (QTLs) for fruit-related traits and powdery mildew resistance in two trials. All traits were significantly different (P < 0.05) between parents. The generated linkage map consisted of twelve major linkage groups (LGs), spanning 626.1 cM in total, with an average distance of 8.3 cM between flanking markers. Nineteen QTLs were detected for seven melon traits, among which ten QTLs were localized to the same positions as the corresponding QTLs described in other studies. Four of these QTLs were detected in both trials. The results of identified QTLs in this study suggested that fruit size in the tested populations were mainly determined by fruit diameter and flesh thickness. All of the major QTLs for fruit diameter and flesh thickness were identified on LG5 and LG11. Four QTLs identified responsible for netting width of fruit rind were co-localized with the QTLs for netting density, suggesting similar genetic mechanisms affecting these two traits. Additionally, only one major QTL for powdery mildew resistance was detected on LG2, and it was closely linked to a simple sequence repeat (SSR) marker CMBR120 which was identified in a previous study.ConclusionBecause the netting feature is a crucial factor for external appearance of fruits in Asia market, we focus on mining the genetic information of fruit netting. This is the first report of QTL mapping to netting width. Furthermore, new QTLs were identified for netting density (qND4, qND6, and qND7) and netting width (qNW2, qNW4, qNW6, and qNW7) successfully. In addition, novel QTLs for fruit diameter (qFD5), flesh thickness (qFT11) were also detected.