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Beiquan Mou

06-833 in the field. Disease Resistance The breeding lines, along with nine commercial leaf lettuce cultivars, were planted in trials at the Spence Farm of the Agricultural Research Service of the USDA, Salinas, CA, in the past 4 years with the

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Vidyasagar R. Sathuvalli, Shawn A. Mehlenbacher and David C. Smith

; Sathuvalli et al., 2011a , 2011b ). The potential breakdown of single resistance genes is always a concern in disease resistance breeding. Molnar et al. (2010a , 2010b ) showed that an isolate from Michigan was able to infect ‘Gasaway’ and OSU 408.040 in

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Beiquan Mou and Edward J. Ryder

. Insect and disease resistance. The breeding line, along with commercial leaf lettuce cultivars, were planted in trials at the Spence Farm of the Agricultural Research Service of the USDA, Salinas, CA, on 28 June 2006, 19 June 2007, 10 June 2008, and 9

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Mark K. Ehlenfeldt, James J. Polashock, Allan W. Stretch and Matthew Kramer

Breeding and selection for plant disease resistance remains one of the most economically and environmentally sound approaches to improving crop quality and yield ( Lynch et al., 2003 ). As part of a long-term breeding program in blueberries, we

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Juan M. Osorno, Carlos G. Muñoz, James S. Beaver, Feiko H. Ferwerda, Mark J. Bassett, Phil N. Miklas, Teresa Olczyk and Bill Bussey

‘Mayflower’ navy bean Crop Sci. 29 1571 1572 Miklas, P.N. 2005 DNA markers (SCARS) linked with disease resistance traits in bean ( Phaseolus vulgaris L.) 2 Nov. 2006. <

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John M. Capik, Megan Muehlbauer, Ari Novy, Josh A. Honig and Thomas J. Molnar

“pyramiding” of two or more resistance genes into one cultivar as a possible means to develop plants expressing more durable forms of disease resistance. Recent work at Rutgers University, New Brunswick, NJ, has shown that pathogenic variation may exist in A

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Kathy Zuzek, David Zlesak, Vance Whitaker, Steve McNamara and Stan C. Hokanson

, several polyantha rose cultivars were acquired and evaluated for their performance in Minnesota. Although many had desirable ornamental features, their winter hardiness and disease resistance were not sufficient for Minnesota landscapes. In 1992, an

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Ed Stover, David G. Hall, Robert G. Shatters Jr. and Gloria A. Moore

Assessments of the resistance of citrus germplasm to huanglongbing (HLB) can be expedited by inoculating plants under laboratory or greenhouse settings with the HLB bacterium, Candidatus Liberibacter asiaticus (CLas). Consistent rapid screening is critical to efficiently assess disease resistance among plant materials; however, a number of factors may govern the efficacy of such inoculations. Despite the rapidity at which HLB can spread in a grove, it often takes 8 to 10 months for high levels of CLas and HLB symptoms to develop even in highly susceptible sweet orange. Therefore, two experiments were conducted to assess factors that might influence efficiency in screening for HLB resistance. In one experiment, three test citrus genotypes (‘Kuharske’, previously shown to be HLB resistant; rough lemon, previously shown to be HLB tolerant; and ‘Valencia’, HLB susceptible) were bud grafted using CLas-infected buds from four different source genotypes. All bud source genotypes had similar levels of CLas titer, but citron, rough lemon, and Volkamer lemon were hypothesized to be better bud inoculum sources as they are more tolerant of HLB than ‘Valencia’. Among the three test genotypes over all sources of infected buds, inoculations of ‘Kuharske’ resulted in lower CLas titers and fewer HLB symptoms than inoculations of rough lemon or ‘Valencia’. Inoculations of rough lemon resulted in higher CLas titers and more pronounced HLB symptoms when it was inoculated using infected buds from rough lemon or ‘Valencia’. Grafting ‘Valencia’ with infected buds from Volkamer lemon resulted in less disease than when ‘Valencia’ was grafted with infected citron, rough lemon, or ‘Valencia’ buds. Overall, these results suggest that the source of CLas-infected buds used to graft-inoculate some genotypes will influence disease development. Trunk cross-sectional area increase for the year following infection was 3× higher in ‘Kuharske’ and rough lemon, compared with ‘Valencia’. ‘Kuharske’ had very low levels of CLas (30 CLas/µg DNA), whereas ‘Valencia’ (43,000 CLas/µg DNA) and rough lemon (6700 CLas/ µg DNA) had relatively high levels. As an alternative to graft-inoculating plants with CLas-infected buds, plants can be subjected to infestations of CLas-infected Asian citrus psyllid (ACP) as occurs naturally. Of interest is if transmission rates of CLas and the development of HLB in a genotype are greater when the ACP have been feeding on the same host genotype. An experiment was therefore conducted to assess transmission of CLas by ACP reared on CLas-infected rough lemon to five different genotypes (‘Carrizo’, ‘Flame’ grapefruit, rough lemon, ‘Temple’, and ‘Valencia’). These assessments were made using a detached leaf assay recognized as a faster method of gauging transmission rates of CLas than using whole plants. Higher percentages of ACP died when they were transferred from infected rough lemon to healthy ‘Carrizo’, and lower percentages died when they were transferred to rough lemon or ‘Flame’. However, CLas transmission by infected ACP occurred to at least some leaves of each genotype in each of the five different assays, with 70% or more leaves of each genotype becoming infected in at least one assay. Over all assays, there was relatively little variation among genotypes in the percentage of leaves becoming CLas infected and in the titer of CLas developing in infected leaves. However, there were relatively large differences in transmission rates among individual assays unrelated to differences among test genotypes. Because of the rapidity of the detached leaf assay, efforts are merited to improve consistency of this inoculation method.

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Hävard Eikemo, May B. Brurberg and Jahn Davik

. El-Shiek, A. 2002 Utilizing wild Fragaria virginiana in strawberry cultivar development: Inheritance of photoperiod sensitivity, fruit size, gender, female fertility and disease resistance Euphytica 126 177 184

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Marivi Colle, Elizabeth N. Straley, Stephanie B. Makela, Sue A. Hammar and Rebecca Grumet

plants, it is possible that a mixed disease response could result from variability within the PI sample. Variability within cucurbit PI accessions for disease resistance responses has been observed frequently (e.g., Davis et al., 2007 ; Donahoo et al