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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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Dominique-André Demers, Martine Dorais, and Athanasios P. Papadopoulos

. Ehret et al. (1993) observed that increasing the leaf-to-fruit ratio (reduced number of fruit on plants) increased the incidence and severity of fruit russeting in tomato. Bakker (1988) and Ehret et al. (1993) observed that the incidence of

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Eric Curry

Discussion Fruit russeting. In 2007, fruit russeting in the section of orchard used for this study was insufficient to establish treatment differences (data not shown). Because russeting across the region was less, this effect was likely related to climate

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Chun-hui Shi, Xiao-qing Wang, Xue-ying Zhang, Lian-ying Shen, Jun Luo, and Yu-xing Zhang

. Therefore, reducing fruit russeting is a top priority among producers. The suberification process is closely related to lignin and phenolic concentrations ( Bernards, 2002 ; Graça and Santos, 2007), and it has been reported that lignin, cellulose, and

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Steven McArtney, J.D. Obermiller, and A. Green

of P-Ca sprays for reducing shoot growth or gibberellin sprays for reducing fruit russet or cracking may be reduced if both materials are applied (Apogee; BASF Corp., Research Triangle Park, N.C.). Miller (1998) reported that concentrations of P

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Moritz Knoche and Eckhard Grimm

also induced microcracking of the apple fruit CM, which, in turn, is followed by formation of a periderm that becomes visible as fruit russeting ( Faust and Shear, 1972a ). The objective of this study was to establish the effect of surface moisture, i

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Esmaeil Fallahi, S. Krishna Mohan, and Brenda R. Simons

Effects of several growth regulators and mineral nutrient sprays on `Rome Beauty' apple (Malus domestica Borkh.) russetting under climatic conditions of southwest Idaho were studied in the 1990 and 1991 growing seasons. Zinc (Zn-50), Calcium as a 12% liquid nutrient (Stopit-6), and fungicide (Polyram) sprays slightly increased, while GA (Provide) decreased fruit russetting.

In 1991, GA and repeated Semperfresh (sucrose ester, carboxymethyl cellulose and mono and diglycerides) applications reduced russetting while Bayleton application increased russetting. Russetting varied from year to year. In 1991, a season of severe fruit russetting, trees which received a fungicide treatment for powdery mildew had generally higher incidence of fruit russetting regardless of treatments. It is believed that interaction between relative humidity, temperature, and systemic sprays used for powdery mildew control contribute to `Rome Beauty' russetting.

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Esmaeil Fallahi, Michael J. Kiester, Bahar Fallahi, and Shahla Mahdavi

, SDP is scaled from 1 (least fruit SDP, progressively to 6 = most SDP or starch hydrolysis). Percentages of fruit russet, water core, and sunburn at harvest were calculated by counting the total number of fruit with each of these incidences, divided by

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J.R. Schupp, H.A. Schupp, and M.H. Bates

A study was conducted in 1992 at Highmoor Farm, Monmouth, ME to test the effects of fish hydrolysate fertilizer on fruit set, fruit size and fruit quality of apple. Mature, semi-dwarf `Delicious' and `Golden Delicious' trees received 2.76g/1 N, supplied by either fish hydrolysate fertilizer or urea, or received no fertilizer (control). Fertilizers were applied via three foliar sprays applied at seven day intervals, beginning at petal fall. Fish hydralysate fertilizer reduced fruit set of `Delicious' and `Golden Delicious'. Foliar urea increased fruit set and yield of 'Golden Delicious'. Neither fertilizer affected mineral nutrient concentrations of leaves collected in July. Fish hydrolysate increased fruit russeting on both cultivars. Fish hydrolysate is not recommended as a foliar fertilizer for apples.

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Esmaeil Fallahi, Brenda R. Simons, and Max W. Williams

Effects of hydrogen cyanamide and Wilthin on blossom thinning and the consequences of thinning on fruit set, yield and fruit quality of `Rome Beauty' was studied. A full bloom application of hydrogen cyanamide at the rate of 0.25% (Dormex formulation) or 0.25% of Wilthin both followed by a fruit thinning by Sevin + NAA effectively thinned mature trees of `Rome Beauty' and had a similar effect on fruit set, yield and fruit quality. The effects of these two chemicals at these rates on several aspects of fruit set, yield and quality were similar to the effects of Elgetol. Hydrogen cyanamide, Elgetol and 0.25% Wilthin at full bloom resulted in a higher percentage of single fruit set, thus, less labor for hand thinning. Application of 0.37% Wilthin at 20% bloom or at full bloom resulted in larger fruit size, but induced fruit russetting. Soluble solids of fruit from trees with Elgetol, 0.37% Wilthin at 20% bloom or at full bloom were higher than fruit from other treatments. Hydrogen cyanamide at 0.50% resulted in a satisfactory level of blossom thinning in `Friar' plums.