Genes encoding lysozyme (T4L) from T4 bacteriophage and attacin E (attE) from Hyalophora cecropia were used, either singly or in combination, to construct plant binary vectors, pLDB15, p35SAMVT4, and pPin2Att35SAMVT4, respectively, for Agrobacterium-mediated transformation of `Galaxy' apple, to enhance resistance to Erwinia amylovora. In these plasmids, the T4L gene was controlled by the cauliflower mosaic virus 35S promoter with duplicated upstream domain and the untranslated leader sequence of alfalfa mosaic virus RNA 4, and the attE gene was controlled by the potato proteinase inhibitor II (Pin2) promoter. All transgenic lines were screened by polymerase chain reaction (PCR) for T4L and attE genes, and a double-antibody sandwich enzyme-linked immunosorbent assay for neomycin phosphotransferase II. Amplification of T4L and attE genes was observed in reverse transcriptase-PCR, indicating that these genes were transcribed in all tested transgenic lines containing each gene. The attacin protein was detected in all attE transgenic lines. The expression of attE under the Pin2 promoter was constitutive but higher levels of expression were observed after mechanical wounding. Some T4L or attE transgenic lines had significant disease reduction compared to nontransgenic `Galaxy'. However, transgenic lines containing both attE and T4L genes were not significantly more resistant than nontransgenic `Galaxy', indicating that there was no in planta synergy between attE and T4L with respect to resistance to E. amylovora.
Kisung Ko, John L. Norelli, Jean-Paul Reynoird, Herb S. Aldwinckle, and Susan K. Brown
Nicole L. Russo, Terence L. Robinson, Gennaro Fazio, and Herb S. Aldwinckle
In 2002, apple rootstock trials using three scion cultivars were established at Geneva, NY, to evaluate 64 apple (Malus ×domestica Borkh.) rootstocks for horticultural performance and fire blight resistance. Field trials compared several elite Geneva® apple rootstocks, which were bred for tolerance to fire blight and Phytophthora root rot, to both commercial standards and elite rootstock clones from around the world. Three rootstocks performed well with all scion cultivars: ‘B.9’, ‘Geneva® 935’, and ‘Geneva® 41’. All three rootstocks were similar in size to ‘M.9’ clones but with elevated yield efficiency and superior resistance to fire blight. ‘Geneva® 11’ also performed very well with ‘Golden Delicious’ and ‘Honeycrisp’ with regard to yield efficiency and disease resistance. Resistant rootstocks greatly enhanced the survival of young trees, particularly with the susceptible scion cultivars ‘Gala’ and ‘Honeycrisp’. Results demonstrate the ability of new rootstock clones to perform better than current commercial standards, reducing financial risk to producers while promoting orchard health with enhanced disease resistance.
Robert C. Lamb, Herb S. Aldwinckle, and David E. Terry
‘Freedom’ is a productive, large, red apple, Malus domestica Borkh. that is very resistant to apple scab [Venturia inaequalis (Cke) Wint.], moderately resistant to apple powdery mildew [Podosphaera leucotricha (E. & E.) Salm], resistant to cedar apple rust (Gymnosporangium juniperi-virginianae Schw.), and to fire blight [Erwinia amylovora (Burrill) Winslow et al.]. It has been grown for 23 years without any disease-controlling sprays, and no losses have occurred in New York State. This apple was tested under the number NY 58553-1.
Randolph G. Gardner, James N. Cummins, and Herb S. Aldwinckle
Reactions of 122 apple clones, representing 26 pure and hybrid species of Malus, to Erwinia amylovora (Burrill) Winslow et al. were evaluated in the greenhouse, orchard, and field nursery. Vigorously growing shoots, 7 to 9 weeks old, were tip inoculated by injecting a 24-hour broth culture of a highly pathogenic isolate of E. amylovora. Lesion development, measured 5 to 7 weeks after inoculation, was expressed as a percentage of the current season’s shoot length killed by fire blight. Inter- and intraspecific variation in resistance, similar to that reported for Pyrus, was observed. The highest level of resistance, typified by a small necrotic lesion 2-3 mm in diameter around the inoculation point, occurred in small-fruited selections derived from Asiatic species. Few selections of the cultivated apple, Malus pumila Mill., were resistant. Fire blight ratings were assigned the clones based on their potentials as parents for breeding apple rootstocks.
Randolph G. Gardner, James N. Cummins, and Herb S. Aldwinckle
Seedling progenies from controlled crosses involving Malus sp. clones were tested for resistance to Erwinia amylovora (Burrill) Winslow et al. by shoot tip inoculation. In progenies from crosses between fire blight-susceptible M. pumila selections, over 90% of the seedlings were killed. In most progenies from crosses between resistant and susceptible selections, regardless of species source, few resistant seedlings occurred. Progenies from crosses between resistant parents generally had the most resistant seedlings, but segregated some highly susceptible offspring. Distribution patterns suggested quantitative control of resistance, with resistant parents heterozygous for resistance genes. In progenies from crosses of the highly resistant M. × robusta No. 5 (R5) and M. × sublobata PI 286613 (613) with susceptible parents, about 1/8 of the seedlings exhibited the fire blight reaction of the highly resistant parent. All progenies of 613 and R5, including those obtained by selfing and by crossing the two with each other, segregated some susceptible offspring. In a replicated nursery test involving seedlings of a 613 progeny, various fire blight resistance classes in the population were distinguished statistically. Resistance in 613 and R5 was interpreted as oligogenic (conditioned by few genes), with dominant, additive genes carried in the heterozygous condition.
James N. Cummins, Herb S. Aldwinckle, and Ross E. Byers
‘Novole’ is being introduced for its value as a parent in resistance breeding programs and for trial use as a vole-resistant root- and trunk-stock for the commercial apple orchard. ‘Novole’ transmits to progeny resistance to a number of environmental hazards, including pine vole and meadow vole.
Stan C. Hokanson, Phil L. Forsline, James R. McFerson, Warren F. Lamboy, Herb S. Aldwinckle, and Aimak D. Djangaliev
Malus sieversii, the main progenitor of domesticated apple, is native to areas in Central Asia. To better represent Malus wild germplasm in the USDA–ARS germplasm collections, maintained in Geneva, N.Y., a cooperative project was initiated with the Republic if Kazakhstan to collect and assess that country's wild populations of M. sieversii and to develop more secure in situ reserves to complement ex situ holdings in the United States and Kazakhstan. To date, four exploration trips to the region have included participants from the United States, Kazakhstan, Canada, New Zealand, and South Africa. Four Kazkh scientists have toured USDA–ARS sites, exchanged information, and collected germplasm in the United States greenhouse screens of 1600 have revealed potentially new sources of resistance to apple scab, cedar apple rust, and fire blight. An isozyme analysis of maternal half-sib families from four regions suggests the populations of M. sieversii collected represent a single panmictic population, with over 85% of total genetic variation due to differences among families. The most recent collections in 1995 were directed towards more ecologically diverse regions, including a site (Tarbagatai) at the most northern limit for M. sieversii equivalent to northern Minnesota in the United States. Some trees in this region produced fruit nearly 70 mm in diameter with excellent aroma, firmness, and color. This germplasm is being systematically characterized for horticultural traits, pest and disease resistance, and molecular markers.
Gayle M. Volk, Christopher M. Richards, Ann A. Reilley, Adam D. Henk, Philip L. Forsline, and Herb S. Aldwinckle
Seeds and scionwood of Malus sieversii Lebed. have been collected from wild populations of apple trees in Kazakhstan. Seedlings and grafted trees were planted in the orchards at the U.S. Dept. of Agriculture Plant Genetic Resources Unit in Geneva, N.Y. We developed core collections to capture the genetic and phenotypic diversity represented in the trees from each of two of the Kazakhstan collection sites. These core collections capture more than 90% of the genetic diversity of the original populations, as determined using seven unlinked simple sequence repeat markers and 19 quantitative traits. Since phenotypic evaluations of these materials have been completed, the 35 trees within each population will be used as parents in crosses so that the genetic diversity in the orchard populations can be captured as seed for long-term ex situ conservation. This strategy of storing seeds, rather than maintaining costly field collections, could be applied to other collections of wild plant materials in the National Plant Germplasm System.
William C. Johnson, Phil L. Forsline, Herb S. Aldwinckle, William C. Johnson, Phil L. Forsline, H. Todd Holleran, Terence L. Robinson, and John J. Norelli
In 1998, the USDA-ARS and Cornell Univ. instituted a cooperative agreement that mobilized the resources for a jointly managed apple rootstock breeding and evaluation program. The program is a successor to the Cornell rootstock breeding program, formerly managed by Emeritus Professor of Horticultural Sciences James N. Cummins. The agreement broadens the scope of the program from a focus on regional concerns to address the constraints of all the U.S. apple production areas. In the future, the breeding program will continue to develop precocious and productive disease-resistant rootstock varieties with a range of vigor from fully dwarfing to near standard size, but there will be a renewed emphasis on nursery propagability, lodging resistance, tolerance to extreme temperatures, resistance to the soil pathogens of the sub-temperate regions of the U.S., and tolerance to apple replant disorder. The program draws on the expertise available at the Geneva campus through cooperation with plant pathologists, horticulturists, geneticists, biotechnologists, and the curator of the national apple germplasm repository. More than 1000 genotypes of apple rootstocks are currently under evaluation, and four fire blight- (Erwinia amylovora) resistant cultivars have been recently released from the program. As a service to U.S. apple producers, rootstock cultivars from other breeding programs will also be evaluated for productivity, size control, and tolerance to a range of biotic and abiotic stress events. The project will serve as an information source on all commercially available apple rootstock genotypes for nurseries and growers.