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  • Author or Editor: R. Provvidenti x
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A high level of resistance to zucchini yellow mosaic virus (ZYMV) was found in four landraces of Citrullus lanatus (Thunb.) MatSum. & Nakai (PI 482322, PI 482299, PI 482261, and PI 482308) originally collected in Zimbabwe. This resistance is specific to the Florida strain of the virus (ZYMV-FL), which prevails in the United States. Inheritance studies were conducted by using a single-plant selection (PP261-I) of PI 48226I and the ZYMV-susceptible watermelon cultivar New Hampshire Midget. In F1, F2, and reciprocal backcross populations, resistance was conferred by a single recessive gene to which the symbol zym is assigned. There was no linkage between zym and one of the three homodimer bands of the isozyme phosphoglucoisomerase (Pgi-2b), which was found in PP261-1, and in other ZYMV-FL resistant plants.

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Bean common mosaic necrosis virus (BCMNV) includes four African strains, BCMNV-NL3, -NL-5, -NL8, and -TN1, previously considered to be members of the bean common mosaic virus (BCMV) group. Many bean cultivars resistant to BCMNV-NL8 were found to be susceptible to the other strains of the virus. `California Light Red Kidney' (CLRK) and `Carbon', resistant to BCMNV-NL8, were crossed with the susceptible cultivars Sanilac or Black Turtle 2 (BT-2). In plants of F1, F2, and reciprocal backcross populations involving CLRK × `Sanilac' or BT-2 × `Carbon', the resistance to BCMVN-NL8 was determined to be conferred by a single dominant factor. The same factor was detected in BCMNV-NL8-resistant `Great Northern 1140' and `IVT-7214, when crossed with the susceptible cultivar Stringless Refugee or BT-2.

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Passionfruit woodiness virus (PWV) can infect bean (Phaseolus vulgaris L.), causing a light and dark green foliar mosaic, veinbanding, downward curling, and plant stunting. The intensity of these symptoms can vary with the strain of the virus and cultivar, but they resemble those caused by bean common mosaic virus. In genetic populations derived from crosses and backcrosses involving cultivars that are resistant (`Black Turtle 1', `Clipper', and `RedKote') or susceptible (`Black Turtle 2', `California Light Red Kidney', and `Pioneer'), a single dominant gene conferred resistance to an Australian strain PWV-K. To this gene, the symbol Pwv (Passionfruit woodiness virus) is tentatively assigned. In plants derived from rooted cuttings of backcross populations, the same factor also conditioned resistance to three other Australian strains, PWV-Mild, PWV-51, and PWV-Tip Blight.

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Abstract

In controlled tests, 110 cultivars (77.5%) of common bean (Phaseolus vulgaris L.) responded to broad bean wilt virus (BBWV) with a localized infection (resistant), while 32 cultivars (22.5%) reacted with local and systemic infection (susceptible). The majority of susceptible cultivars were of the yellow-podded (wax bean) and red kidney types. In F1, F2, and backcross populations of the BBWV-resistant cultivar Sanilac with the BBWV-susceptible ‘California Light Red Kidney’ (‘CLRK’) resistance to systemic infection was conferred by a single dominant gene, to which the symbol Bbw is assigned. BBWV was not transmitted in 471 ‘CLRK’ seeds derived from severely infected plants.

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Seedlings of watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] are commonly affected by a partial chlorophyll deficiency that is activated by low temperatures (<20C), causing foliar symptoms and growth retardation. Cotyledons appear whitish-green, whereas the first leaves display a mosaic-like variegation consisting of scattered white flecks and patches. While this disorder is common in commercial watermelon cultivars, some land races from Zimbabwe appeared to be unaffected. From cross and backcross populations of the cold-sensitive cultivar New Hampshire Midget with the cold-resistant line PP261-1 (from PI 482261), the leaf variegation was determined to be conferred by a single recessive gene. The symbol slv (seedling leaf variegation) is assigned to this factor. The dominant allele at this same locus can be exploited for the development of new “cold-resistant” cultivars and F1 hybrids, thus providing economic gain due to earlier planting.

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A single plant selection of the cucumber (Cucumis sativus L.) cultivar Taichung Mou Gua (TMG-1) from China was the source of resistance to zucchini yellow mosaic virus (ZYMV) in crosses with the domestic cultivars Marketer and Marketmore 76. In F1, F2, and reciprocal backcross populations, resistance to ZYMV-CT (Connecticut strain) was demonstrated to be conferred by a single recessive gene to which the symbol zym was assigned.

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Abstract

In greenhouse and field tests, 46 accessions of Chinese cabbage (Brassica campestris L. ssp. pekinensis (Lour.) Olsson), recently introduced from Japan and the People's Republic of China (PRC), were evaluated for resistance to 3 major strains of turnip mosaic virus (TuMV-Cl, TuMV-C2, and TuMV-C3) and one of cauliflower mosaic virus (CaMV-1). Immunity and/or resistance to the TuMV strains was found among Chinese plant introductions (PI), whereas in Japanese cultivars sources of immunity or resistance were confined to the strains TuMV-C1 and TuMV-C2. None of the 46 cultivars was resistant to CaMV-1. PI 391560(1), PI 418957, PI 418959, and PI 419069 from the PRC were immune or resistant to each of the 3 strains of TuMV, representing valuable germplasm material for intra- and interspecific gene transfer. In early fall of 1979, an isolate of TuMV was recovered from a systemically infected plant of PI 391560(1). Although uncommon, resistance to this newly recognized strain (TuMV-C4) was found in plants of PI 418957. Strain specificity must be considered in developing TuMV-resistant cultivars, since their performance will depend upon the presence and distribution of the virus strains in a given locality.

Open Access

Resistance to white lupin mosaic virus (WLMV), a recently characterized member of the potyvirus group, was found in pea (Pisum sativum L.) plant introductions from Ethiopia (PI 193835) and India (PI 347485). In cross and backcross populations between plants of resistant PI 193835 with those of susceptible `Bonneville' and PP-492-5, this resistance was demonstrated to be governed by a single recessive gene. This gene was distinct from other genes previously found in PI 193835 and PP-492-5 (from PI 347492, India) conferring resistance to clover yellow vein virus (CYVV) and three strains of pea seedborne mosaic virus (PSbMV). Indirect evidence suggests that this newly recognized viral resistance gene, wlv, is a member of a cluster of closely linked genes located on chromosome 6. This gene cluster includes sbm-1, sbm-3, and sbm-4, which govern resistance to three PSbMV pathotypes, and cyv-2, which governs resistance to CYVV.

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Abstract

Five hundred ninety accessions of Citrullus lanatus, obtained from 42 countries, were exposed to natural infection with Sphaerotheca fuliginea (Schlecht) Poll. Only one line, P.I. 269677 from Belize, was highly susceptible. The fungus attacked all aerial parts of plants of this line, including fruits. All other lines, including those from areas of the world where powdery mildew of watermelon commonly occurs, were resistant or tolerant to the race of the fungus prevailing in NY.

Open Access

In a yellow summer squash (Cucurbita pepo L.) experimental line developed by Seminis Vegetable Seeds, the coat protein gene of an American strain of squash mosaic virus (SqMV-M88), conferred resistance to Arizona, California, New Jersey, and New York strains belonging to the two pathotypes of the virus. An analysis of genetic populations derived from crosses and reciprocal backcrosses of a homozygous SqMV-resistant line A127-1-2 with the susceptible cultivar Butterbar revealed that the high level of resistance mimics the response of a single recessive gene.

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