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Bacterial spot of cucurbits, caused by Xanthomonas cucurbitae, is an emerging disease of cucurbits. This study was conducted to identify Cucurbita species that are resistant to X. cucurbitae. We developed a reliable method for inoculating cucurbit plants by spraying plants with X. cucurbitae suspensions containing carborundum. Symptoms of the disease developed within 7 days after inoculation. Subsequently, we evaluated the virulence of six isolates of X. cucurbitae in the greenhouse and observed that X. cucurbitae isolated from cucurbit fields in Illinois, Michigan, Kansas, Ohio, and Wisconsin were more virulent than the reference ATCC 23378 strain. Then, we screened 81 commercial cultivars of gourds, pumpkins, and squashes, as well as 300 Cucurbita spp. accessions, for their resistance to X. cucurbitae under greenhouse and field conditions. In the greenhouse study, all commercial cultivars and some of the accessions developed typical symptoms of bacterial spot disease, while some of the accessions developed fewer lesions. In the field studies, infection of leaves and fruits was caused by both natural inoculum and spray‐inoculation of plants with a suspension of the X. cucurbitae isolate from Illinois. Among 300 accessions tested, 9 and 21 accessions were classified as resistant and less resistant, respectively. Resistant and less resistant accessions belong to the species Cucurbita maxima, C. maxima subsp. maxima, C. maxima subsp. andreana, and C. okeechobeensis subsp. martinezii. This is the first report of potential resistance to bacterial spot of cucurbits. [ABSTRACT FROM AUTHOR]

Surveys were conducted during 2004 to 2006 to identify the viruses infecting pumpkin and squash in Illinois. In 2004, 16 jack-o-lantern pumpkin (Cucurbita pepo) samples and one squash (C. pepo) sample were collected from 11 counties. In 2005, 85 jack-o-lantern pumpkin, 12 processing pumpkin (Cucurbita moschata), 37 squash, and six gourd (C. pepo) samples were collected from 54 counties. In 2006, 85 jack-o-lantern pumpkin, 16 processing pumpkin, 51 squash, and 18 gourd samples were collected from 47 counties. Cucumber mosaic virus (CMV), Papaya ringspot virus (PRSV), Squash mosaic virus (SqMV), Tobacco ringspot virus (TRSV), Tomato ringspot virus (T0RSV), Watermelon mosaic virus (WMV), Zucchini yellow mosaic virus (ZYMV), and unknown potyviruses were detected in pumpkin, squash, and gourd fields during the surveys, using enzyme-linked immunosorbent assay (ELISA). Overall, 86, 11, 75, and 79% of jack-o-lantern pumpkin, processing pumpkin, squash, and gourds, respectively, were tested positive for virus infection during the survey. WMV was detected in 47, 46, and 52% of the samples in 2004, 2005, and 2006, respectively, and was the most prevalent virus throughout the state. SqMV was detected in more counties than any other virus because it was identified in 65 and 88% of the counties surveyed in 2005 and 2006, respectively. SqMV was detected in 6, 41, and 48% of the samples in 2004, 2005, and 2006, respectively. During the surveys, CMV was detected in 6, 4, and 3% of the samples; PRSV was detected in 6, 11, and 4% of the samples; and ZYMV was detected in 18, 4, and 4% of the samples tested in 2004, 2005, and 2006, respectively. TRSV was detected in 3% of the samples in 2005, for the first time on pumpkin in Illinois. Pathogenicity of the detected viruses was proved for CMV, PRSV, SqMV, WMV, and ZYMV on summer squash ('Fortune' and 'Grey Zucchini'), jack-o-lantern pumpkin ('Howden'), and processing pumpkin ('Dickinson'). All of the viruses were present alone and mixed in the samples tested. Earlier in the growing seasons (July and early August), single-virus infections were detected. Mixed infections were more common from the second week of August until the end of the growing season in October. Dual infection of WMV and SqMV was the most prevalent mixed virus infection detected in Illinois. Most viruses infecting pumpkin and squash showed similar symptoms. The most common symptoms observed in the commercial fields and in the greenhouse studies were light- and dark-green mosaic, veinbanding, veinclearing, puckering, and deformation of leaves of pumpkin, squash, and gourds. Severe symptoms included fernleaf and shoestring on leaves and color breaking and deformation of fruit. [ABSTRACT FROM AUTHOR]

This study was conducted to investigate pathogenic, morphologic, and genetic variations among Phytophthora capsici isolates from processing pumpkin (Cucurbita moschata) fields in Illinois. Random amplified polymorphic DNA (RAPD) markers were employed to assess genetic variation among 24 isolates of P capsici from 10 individual fields at six locations. Unweighted mean pair group analysis clustered isolates into six groups. The genetic distances ranged from 0.03 to 0.45. Inoculation of pumpkin seedlings in the greenhouse revealed that the isolates belonged to six distinct genetic groups differing significantly (P = 0.05) in virulence. Isolates tested exhibited four growth patterns in culture: cottony, rosaceous, petaloid, and stellate. P. capsici isolates. including an ATCC isolate (ATCC-15427), with cottony growth pattern did not grow at 36°C. The mean oospore diameter of A1 mating type isolates was greater than that of A2 mating type isolates. Nine of 24 isolates tested produced chlamydospores in V8-CaCO3 liquid medium. [ABSTRACT FROM AUTHOR]