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  • Author or Editor: James D. McCreight x
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Melon (Cucumis melo L.) is a fresh vegetable and dessert fruit that may also be cooked or dried, processed for juice and flavoring, and the seeds of which are a source of high-quality cooking oil and high protein seed meal. Melon production throughout many parts of the world is now threatened by the crinivirus Cucurbit yellow stunting disorder virus (CYSDV) in tropical and subtropical areas favorable to its whitefly vector. CYSDV is transmitted by the sweetpotato whitefly, Bemisia tabaci Gennadius, biotypes A, B, and Q. CYSDV first appeared on melon in the 1980s in the United Arab Emirates and emerged on melon in the Yuma, AZ, and Imperial Valley, CA, regions and western Mexico during the Fall season of 2006 followed by Florida in 2007. PI 313970, C. melo var. acidulus Naudin, a salad-type melon from India, expressed high-level resistance to CYSDV in Yuma and Imperial Valley in Fall 2006, but it was not immune; the virus was detected in asymptomatic plants. Inheritance of resistance to CYSDV in PI 313970 was studied in three naturally infected, replicated field tests in Imperial Valley during the Fall seasons of 2007 and 2008 and the Spring season of 2009. Resistance in PI 313970 was recessive: all F1 PI 313970 (PI) × susceptible ‘Top Mark’ (TM) and BCTM individuals were susceptible, and the F2 and BCPI segregated 3:1 and 1:1 susceptible to resistance, respectively. Frequency distributions of CYSDV symptom severity ratings suggested a single recessive gene in PI 313970 for resistance to CYSDV. PI 313970 was, however, observed to be variable for resistance; a few plants in each test expressed distinct symptoms of CYSDV infection and its frequency distributions overlapped those of ‘Top Mark’. This variation may represent genetic variation selectable for uniform reaction to infection by CYSDV or phenotypic variation in the resistant reaction. The genetic relationship between the genes for resistance to CYSDV in PI 313970 (recessive) and TGR-1551 (dominant) is not known.

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In 1963, melon (Cucumis melo L.) plant introductions (PI) 124112 and PI 180280 were reported variable in response to inoculation with the T-1 or Freitag's isolates of watermelon mosaic virus. Most plants were symptomless, but some had small pinpoint necrotic lesions on cotyledons and leaves. The T-1 and Freitag's isolates of watermelon mosaic were later designated watermelon mosaic virus 1, and more recently renamed papaya ringspot virus watermelon strain (PRSV-W). When inoculated with California or Florida isolates of PRSV-W in 1993, WMR 29 a western U.S. shipping type melon derived from PI 180280 was symptomless (incompatible reaction) and SDS-immunodiffusion assays were negative. In contrast when inoculated with the same PRSV-W isolates, PI 124112 had incompatible reactions characterized by wilting, local lesions, systemic necrotic spots and necrosis and negative SDS-immunodiffusion assays.

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Segregating generations from crosses of cultivated lettuce (Lactuca sativa L.) with wild lettuce (L. saligna L.) are affected by sterility and abnormal growth. Resistance to lettuce infectious yellows virus (LIYV) was, therefore, studied in crosses of previously reported LIYV-resistant (PI 261653) with LIYV-susceptible (PI 490999, PI 491000 and PI 491001) L. saligna accessions. Simple Mendelian ratios for resistance (measured as numbers of symptomless and symptomatic plants, and as number of symptomatic leaves per plant) to LIYV were not evident. PI 491001 had the fewest symptomatic plants and the fewest symptomatic leaves per plant. The potential value of L. saligna for development of LIYV-resistant cultivated lettuce will be discussed.

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Cucurbit leaf crumple geminivirus (CuLCrV) is transmitted by sweet-potato whitefly (Bemisia tabaci) biotype B (SPWF-B) and occurs on cucurbits in Arizona, California, Texas, and Mexico. This virus is identical to Cucurbit leaf curl virus, and their symptoms are similar to Squash leaf curl virus on squash (Cucurbita sp.) and Melonleaf curl virus on melon (Cucumis melo L.). Melon has been reported to be either susceptible to CuLCrV, or to have the ability to recover from infection. Twenty-three melon cultigens were inoculated with CuLCrV in greenhouse tests using SPWF-B. Eighteen of the cultigens tested were highly susceptible to CuLCrV (≥60% infected plants) and generally exhibited pronounced CuLCrV symptoms: `Amarillo', `Edisto 47', `Esteem', `Fuyu 3', `Impac', `Moscatel Grande', `Negro', `Perlita', PI 234607, PI 236355, PI 414723, `PMR 5', `Seminole', `Sol Dorado', `Sol Real', `Top Mark', `Vedrantais', and WMR 29. Five cultigens were resistant to CuLCrV (<40% infected plants that exhibited restricted, mild symptoms): MR-1, PI 124111, PI 124112, PI 179901, and PI 313970. Symptoms abated with time in both groups although infected plants remained positive for the virus. Ten of the cultigens (`Edisto 47', `Fuyu 3', `Impac', MR-1, PI 124112, PI 313970, PI 414723, `PMR 5', `Top Mark', and WMR 29) were included in field tests in 2003 and 2004 that were naturally infected with CuLCrV. With the exception of PI 414723, the greenhouse and field data were consistent for reaction to CuLCrV.

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Cucurbit leaf crumple virus (CuLCrV) is a geminivirus transmitted by Bemisia tabaci (Gennadius) biotype B (SPW-B) and common in melons (Cucumis melo L.) planted from July through September in the desert southwestern United States. Symptoms include chlorotic leaf spots, leaf curling and crumpling, and interveinal yellowing, and plants may be stunted. Melon breeding line MR-1, and six plant introductions (PIs; PI 124111, PI 124112, PI 179901, PI 234607, PI 313970, and PI 414723) exhibited partial resistance to CuLCrV in naturally infected field tests and controlled inoculation greenhouse tests. PI 236355 was completely resistant in two greenhouse tests. Partially resistant plants exhibited chlorotic spots, or mild expression of other typical CuLCrV symptoms; all such plants were positive for presence of virus using polymerase chain reaction analysis with a CuLCrV-specific primer pair from the BC1 region. Genetic resistance to CuLCrV in melon was recessive. Field and greenhouse data from F1, F2, and backcrosses of the F1 to ‘Top Mark’ and PI 313970 demonstrated a single, recessive gene for resistance to CuLCrV. Progenies from crosses of four partially resistant cultigens with ‘Top Mark’ were susceptible. Resistance in PI 313970 appeared to be allelic, with resistance in the other six cultigens based on F1 data. The name cucurbit leaf crumple virus and symbol culcrv are proposed for this gene.

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Abstract

Greenflesh Honeydew (GFHD) musk-melon (Cucumis melo L.) is an erratic performer in the varied environments of Arizona, California (Imperial Valley and San Joaquin Valley), and Texas. The vines are susceptible to powdery mildew caused by Sphaero-theca fuliginea (Schlecht. ex. Fr.) Poll, and the cucurbit mosaic viruses including papaya ringspot virus (watermelon mosaic virus, see ref. 3), watermelon mosaic virus 2, and zucchini yellow mosaic virus. Common quality defects of the fruit include traces of net, nonuniform shapes and sizes, low soluble solids, thin flesh, the cavity becoming watery prior to best edibility, and poor flavor. This report describes PMR Honeydew, a recently released powdery mildew resistant honeydew breeding line.

Open Access

Cucurbit yellow stunting disorder virus (CYSDV) is a devastating viral disease of melon that can cause significant yield and quality losses. This disease has recently emerged as a major concern in the southwest United States and major melon-growing regions across the world. Coinfection of melon by Cucurbit chlorotic yellows virus (CCYV) was recognized in Imperial Valley and neighboring production areas of California and Arizona in 2018, but its importance remains largely unknown. Identifying and deploying CYSDV resistance from elite germplasm is an economical and effective way to manage the disease. A F2:3 population was developed from a cross of susceptible ‘Top Mark’ with CYSDV-resistant PI 313970, which was shown to possess a single recessive gene for resistance to CYSDV. The F2:3 population was phenotyped in the field in response to natural, mixed infections by the two viruses, CYSDV and CCYV in the Fall melon seasons of 2018 and 2019. Phenotypic data (foliar yellowing) from both years were not useful for mapping CYSDV resistance quantitative trait loci (QTL), as PI 313970 and CYSDV-resistant F2:3 plants exhibited yellowing symptoms from CCYV coinfection. QTL analysis of the relative titer of CYSDV calculated from reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) data identified one locus on chromosome 3 at the physical location of S5-28,571,859 bp that explained 20% of virus titer variation in 2018 but was undetected in 2019. A locus on chromosome 5 between S5-20,880,639 to S5-22,217,535 bp explained 16% and 35% of the variation in CYSDV titer in 2018 and 2019, respectively. One or both of the markers were present in six of 10 putative melon CYSDV resistance sources. Markers flanking the 2019 QTL were developed and can be used in marker-assisted breeding of CYSDV-resistant melons.

Open Access

Races 1 and 2 of Podosphaera xanthii (syn. Sphaerotheca fuliginea) were defined in Imperial Valley, Calif. 1938 when P. xanthii overcame genetic resistance in `PMR 45'. Race 3 was first observed in the U.S. in 1976 in Texas; 15 additional races of P. xanthii have been reported in the literature since 1996. Races 1 and 2 have been common in Arizona and California based upon the effectiveness of the powdery mildew resistance genes in commercially available melon cultivars grown in these states. Field data from 11 commonly used melon P. xanthii race differentials in 2001 and 2002 indicated the presence of race 1 in the Imperial Valley and San Joaquin Valley of California, and Yuma, Arizona. In spring 2003, the powdery mildew race situation changed. The first evidence was the occurrence of a severe and widespread infection of powdery mildew in a commercial cantaloupe field. The 11 powdery mildew race differentials were susceptible to powdery mildew in a nearby replicated field test. PI 313970, a melon from India, was resistant to this apparent new race of powdery mildew.

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