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Germán V. Sandoya, Krishna Subbarao, and Ryan Hayes

-desert winter-production-adapted cvs. Table 4. The ratio of the foliar symptom severity over market maturity of 34 iceberg cultivars evaluated at three time points in replicated field experiments in Salinas, CA, in 2013 and 2014. Resistance and horticultural

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Maryna Serdani, Robert A. Spotts, Jill M. Calabro, Joseph D. Postman, and Annie P. Qu

Powdery mildew (PM) occurs worldwide and is prevalent on susceptible cultivars wherever pears are grown, causing economic losses due to russeted fruit and an increased need for fungicides. A core subset of the Pyrus germplasm collection at the USDA National Clonal Germplasm Repository in Corvallis, Ore., was evaluated for resistance to Podosphaera leucotricha, the causal agent of PM, using greenhouse and field inoculations of potted trees. The core collection consists of about 200 cultivars and species selections, representing most of the genetic diversity of pears and includes 31 Asian cultivars (ASN), 122 European cultivars (EUR), 9 EUR × ASN hybrids and 46 pear species selections. Three trees of each core accession were grafted on seedling rootstocks. In 2001–02, trees were artificially inoculated in a greenhouse, grown under conditions conducive for PM, and evaluated for symptoms. The same trees were subsequently evaluated for PM symptoms from natural field infections during 2003 and 2004. In the greenhouse, 95% of EUR and 38% of ASN were infected with PM. Average PM incidence (percent of leaves infected) in the greenhouse (8% for ASN and 30% for EUR) was much higher than incidence in the field (2% for ASN and 5% for EUR) during 2003. Symptoms were also more severe in the greenhouse, with 46% of ASN and 83% of EUR with PM symptoms having a mean PM incidence of >10%. In the field, 42% and 22% of EUR and 23% and 13% of ASN were infected with P. leucotricha in 2003 and 2004, respectively. Field infection was very low during both years, with percentage leaves infected in ASN and species selections significantly different from EUR. In the field, 6% of ASN with PM symptoms had a mean PM incidence >10% during both years, while 15% and 2% of EUR accessions with PM symptoms had a mean PM incidence >10% in 2003 and 2004 respectively. These results should be very useful to pear breeding programs to develop improved PM resistant cultivars in the future, by using accessions with consistent low PM ratings.

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Annelle W.B. Holder, Winston Elibox, and Pathmanathan Umaharan

on the pathogenic variation of A . anthurii . The causal agent of BLS enters the vascular system of anthurium leaves via natural openings (stomata and hydathodes) or wounds ( Prior et al., 1985 ). Early foliar symptoms are small, angular, greasy

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Ute Albrecht and Kim D. Bowman

chlorosis or twig dieback. Border trees of the genotype ‘Hirado’ pummelo displayed conspicuous foliar symptoms (blotchy mottle and leaf chlorosis) throughout the canopy and were PCR-positive at all collection times beginning Sept. 2007. Table 1. Disease

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Sasmita Mishra, Scott Heckathorn, Jonathan Frantz, Futong Yu, and John Gray

identified previously. The goal of this research was to determine if net photosynthesis decreases with B deficiency before visible foliar symptoms, and if higher nonphotoinhibitory light levels enhance soluble carbohydrate status and therefore mitigate B

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James L. Gibson, Brian E. Whipker, Dharmalingam S. Pitchay, Paul V. Nelson, and C. Ray Campbell

Elemental deficiencies of N, P, K, Ca, Mg, S, Fe, Mn, Cu, Zn, and B were induced in `Osaka White' ornamental cabbage (Brassica oleracea var. acephala L.) plants. Seedlings were planted in 4.7-L plastic containers and fertilized with a complete modified Hoagland's solution or this solution minus the element that was to be investigated. Plants were harvested for tissue analysis as well as dry weight when initial foliar symptoms were expressed and later under advanced deficiency symptoms. Root architecture was also recorded for the plants treated with the solutions. The containers were replicated three times for each of the two harvests and were randomized in a complete-block design. Deficiency symptoms for all treatments were observed within five weeks. The most dramatic expression of foliar symptoms occurred with N (a purplish tinge on underside of lower foliage leading to necrotic margins on the mature leaves), P (elongated internodes and a purplish tinge on underside of mature leaves), K (compact internodes with chlorotic lower foliage leading to necrotic patches on the leaf margins and blade), Fe (bright yellow upper foliage leading to a bleach white appearance), Ca (complete meristem necrosis with lower foliage becoming chlorotic then necrotic), and B (deformed young leaves and fully expanded leaves becoming thick, leathery, and brittle). The dry weight of plants treated with solutions not containing N, P, Ca, Fe, or B was significantly lower when compared to the control. Foliar tissue concentration data will assist plant tissue analysis laboratories in establishing foliar symptom standards for grower samples.

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Phillip Griffiths*

Cucumber mosaic virus (CMV) is an aphid-transmitted virus that infects snap bean growing regions in New York State and Wisconsin. The core collection of common bean accessions (Phaseolus vulgaris), the complete collection of scarlet runner bean accessions (Phaseolus coccineus) and snap/dry bean cultivars were screened for resistance to CMV. Although variation in foliar symptom expression was observed, no resistance was observed in 93 snap bean and16 dry bean cultivars tested, and only one of the 406 accessions from the core collection (PI 309881) was symptomless. PI 309881 did not have common bean characteristics, and was later identified as a tepary bean (Phaseolus acutifolius) accession based on morphology and PCR-RFLP of chloroplast DNA. Screening of 260 P. coccineus accessions was inaccurate when a visual rating of foliar symptoms was used. It was necessary to determine infection using ELISA and test plant screening with grey zuccini. Using this approach it was determined that 80 P. coccineus accessions were susceptible to CMV; however, the remaining accessions provided possible sources for transfer of CMV resistance to snap bean. Crosses of P. coccineus accessions were made to breeding line 5-593 and backcrossed to 5-593 and snap bean cultivar `Hystyle'. PI 309881 was crossed with ICA Pijao in order to develop interspecific hybrids. Populations were developed from the interspecific crosses/backcrosses and evaluated for CMV resistance using ELISA and visual ratings of foliar symptoms.

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James L. Gibson, Jude Groninger, Sharon Wombles, and Kathryn Campbell

Elemental deficiencies of N, P, K, Ca, Mg, S, Fe, Mn, Cu, Zn, or B were induced in plants of Pentas lanceolata `Butterfly Red'. Rooted stem cuttings were planted in 4.87-L plastic containers and fertilized with a complete modified Hoagland's solution or this solution minus the element that was to be investigated. Plants were harvested to measure dry weights when initial foliar symptoms were expressed and later under advanced deficiency symptoms. Deficiency symptoms for all treatments were observed within 7 weeks. The most dramatic expression of foliar symptoms occurred with N (medium green young leaves with interveinal chlorosis on base and tip), S (spindle-like young and recently mature leaves), Cu (purple-brown roots and young leaves with downward pointed leaf tips), and B (multiple youngest leaves arising from shoot tip). At the initial stage, all nutrient-deficient plants had similar dry weights, when compared to the control. Dry weights of plants treated with solutions not containing P were significantly lower when compared to the control under an advanced deficiency. In order to help prevent the development of deficiencies, minimal critical tissue levels have to be determined for adaptation by the greenhouse industry for nutritional monitoring.

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M.E. Scott and T.E. Michaels

Effective genetic resistance to common bacterial blight [Xanthomonas campestris pv. phaseoli (Smith) Dye] is not present in common bean (Phaseolus vulgaris L.) cultivars grown in Ontario. Foliar symptoms and seed yield of white pea bean breeding lines from a P. vulgaris/P. acutifolius interspecific cross in the presence and absence of common blight were evaluated. In inoculated plots, seven of the 20 breeding lines did not differ significantly in severity of foliar symptoms from the most resistant controls, XAN 159 and XAN 161. The most susceptible lines tended to have the highest yield when grown under disease-free conditions (r = 0.61 and 0.49 at two locations). However, the susceptible lines showed an average yield loss of 25% when disease-free and inoculated plots were compared, while resistant lines had little or no yield loss. The most severely infected lines tended to have the greatest loss in yield (r = 0.72 and 0.53 at two locations). A resistant breeding line from this study is available as OAC 88-1.

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James L. Gibson, Jude Groninger, Sharon Wombles, and Kathryn Campbell

Elemental deficiencies of N, P, K, Ca, Mg, S, Fe, Mn, Cu, Zn, or B were induced in plants of Allamanda nerifolia. Rooted stem cuttings were planted in 4.87-L plastic containers and fertilized with a complete modified Hoagland's solution or this solution minus the element that was to be investigated. Plants were harvested to measure dry weights when initial foliar symptoms were expressed and later under advanced deficiency symptoms. Deficiency symptoms for all treatments were observed within 6 weeks. The most dramatic expression of foliar symptoms occurred with N (yellow-green young leaves with necrotic tips), K (downward bending medium-green mature leaves with splotchy chlorosis), S (greenish-yellow young and youngest leaves), and Zn (young leaves with interveinal chlorosis from base to tip). At the initial stage, all nutrient-deficient plants had similar dry weights, when compared to the control. Dry weights of plants treated with solutions not containing N or P were significantly lower when compared to the control under an advanced deficiency. To help prevent the development of deficiencies, minimal critical tissue levels have to be determined for adaptation by the greenhouse industry for nutritional monitoring.