virus (≤92% and 91% respectively) ( Brown et al., 2002 ). None of the six viruses has caused significant, widespread economic losses to melon production in these areas (T.A. Turini, unpublished). Genetic resistance has not been reported to any of these
James D. McCreight, Hsing-Yeh Liu and Thomas A. Turini
M.K. Ehlenfeldt, A.W. Stretch and A.D. Drape
A group of 1031 genotypes representing 245 different crosses from a joint U.S. Dept. of Agriculture-New Jersey Agricultural Experiment Station blueberry breeding program was evaluated for blueberry red ringspot virus (BBRRSV) symptoms after 8 years of field exposure. Among 41 parents represented by 10 or more progeny, significant differences were observed in offspring BBRRSV expression. The species Vaccinium lamarckii Camp. (4x) and V. amoenum Ait. (6x) and the cultivars Woodard (6x) and Earliblue (4x) seem to have high frequencies of alleles for BBRRSV resistance. Significant differences were also found among 21 different crosses. The most resistant cross was `Elizabeth' x `Earliblue', which had a 23% BBRRSV incidence. Progeny evaluation revealed that none of the parents involved produced families in which all plants were resistant; hence, resistance to this virus may be under polygenic control.
Phillip Joy, Rajasekaran Lada, Angus Ells and Brian Williams
The individually quick frozen “baby” carrot industry is growing. Crack development during freezing (CDF) has recently become a quality issue. There is little scientific information available on the causes of CDF. Studies were initiated to determine genetic resistance for CDF and to identify crack-resistant varieties. Ten varieties and breeding lines (Columbia, HMX-0331, Sugarsnax, Sweet Bites, Tasty Peel, Top Cut, Trinity, XCR-0124, XCR-9650, and XCR-9840) were grown under the same field conditions, harvested identically, and processed. Samples were removed after a quick freeze tunnel and tested immediately for membrane stability using electrical conductivity (EC/g) and a membrane injury index. Percentage cracked, the length, width, and depth of cracks were also measured. Another set of samples were placed in freezer storage at –10 °C for 8 weeks and tested again for the same parameters. EC/g and membrane injury indexes showed significant interactions between variety and length of storage time. Crack length, width, and depth were significantly higher in XCR-9650 and XCR-9840, while Trinity had the smallest dimensions. Crack depths after week 8 in freezer storage were also significantly higher (0.30 cm) than those at week 0 (0.21 cm). Finally, percent cracked was also dependent on the variety and length of storage time. Trinity had the lowest percentage of cracked pieces (16%), whereas XCR-9650 (70%) had the highest percentage of visible cracking. Freezer storage time also played a role in CDF, since cracked percent significantly increased by 4% over the 8 weeks. Our results clearly reveal that there are differences in CDF among varieties. Among all, Trinity had the highest resistance to cracking, comparable to all the varieties except XCR-9650 and XCR-9840.
Adelheid R. Kuehnle, Fure-Chyi Chen and Nellie Sugi
Bacterial diseases continue to plague ornamental crops, Genetic resistance offers one way to manage disease; combined with use of indexed propagules and sanitation, it can be a powerful control. Classical breeding offers some genetic solutions. Introgression, by genetic engineering, of antibacterial genes derived from the Cecropiamoth is a second breeding approach which appears promising in other horticultural crops. A case study for control of Xanthomonas, species of which severely limit geranium, anthurium, and other ornamental production, is given for anthurium. Transgenic anthurium plants expressing or containing antibacterial genes coding for the antibacterial peptides Attacin, P13 and T4 lysozymes, and the modified cecropins Shiva and SB37 were produced and challenged with bacteria. Juvenile and adult plants showed various degrees of tolerance to bacterial blight. The implications of this approach to bacterial disease control in various ornamental cropping systems will be discussed.
James D. McCreight and William M. Wintermantel
2010. Genetic resistance to CYSDV in PI 313970 does not confer immunity because the virus was detectable in all plants regardless of symptom expression using RT-PCR. Quantitative methods are being used for subsequent studies on replication and movement
Robert M. Pyne, Adolfina R. Koroch, Christian A. Wyenandt and James E. Simon
by fixing it at both loci and removing susceptibility alleles from the breeding population. This study provides evidence for a heritable form of downy mildew resistance that can be used to breed for genetic resistance in a commercial sweet basil
James D. McCreight
) and wild related species ( L. perennis , L . saligna , L. serriola , and L . virosa ) germplasm collection at Salinas, CA ( McGuire et al., 1993 ) revealed two potentially unique sources of genetic resistance to lettuce aphid. Materials and
Kristin A. Schneider and James D. Kelly
Root rot, caused by Fusarium solani f.sp. phaseoli, is a serious disease of bean for which successful control has been elusive. Genetic resistance to the pathogen is considered quantitative and is strongly influenced by environmental factors. To reduce environmental variation and facilitate selection in earlier generations, an accurate, consistent, and nondestructive greenhouse screen was developed for the evaluation of Fusarium root rot resistance in bean. We describe a protocol that involves the germination of seedlings in perlite, inoculation of roots and hypocotyls 10 days after planting and evaluation within 4 weeks. The accuracy of this greenhouse screen was confirmed by demonstrating significant correlations between greenhouse and field ratings. Two experiments that included 24 and 21 diverse bean genotypes, respectively, were performed in the greenhouse and the ratings were correlated with field ratings over two growing seasons. Correlation coefficients between the greenhouse and field ratings were significant and as high as 0.99. Numerous genotypes can be evaluated within a short time for relatively minimal costs and labor. Furthermore, once roots have been rated and dipped in fungicide, plants can be transplanted for production of seed. This simple, rapid, and inexpensive protocol reduces environmental variation inherent to field ratings, thereby more accurately representing physiological resistance while maintaining a close association with observed field ratings.
Tommy E. Thompson and L.J. Grauke
Thirty-six cultivars and 948 seedlings from 15 controlled crosses in the U.S. Dept. of Agriculture-Agricultural Research Service pecan [Carya illinoinensis (Wangenh.) K. Koch] breeding program at Brownwood, Texas, were rated for susceptibility to nut scab [Cladosporium caryigenum (Ell. et Lang.) Gottwald] to determine heritability of this trait. Differences between parents and progenies, and within progenies, were highly significant. Within most families, a complete range of resistance reactions were evident, from fully susceptible to fully resistant. Heritability of resistance was determined by regressing individual progeny values on female, male, and midparent values, with the midparent heritability estimate being the highest (0.54). This moderate level of additive gene action and the identification of superior parents in this study will contribute to the efficiency of breeding resistant cultivars.
Christian A. Wyenandt, James E. Simon, Margaret T. McGrath and Daniel L. Ward
chemical control options and genetic resistance, basil downy mildew has the potential to destroy basil production in the eastern United States and in all other areas where basil is being produced. Fig. 1. Chlorosis (yellowing) of sweet basil ‘Nufar