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Demethylation inhibitors (DMIs) are a class of single-site fungicides with high levels of protective and curative efficacy against Venturia inaequalis, the causal agent of apple scab. To determine the prevalence of resistance to the DMI fungicide myclobutanil, 3,987 single-lesion conidial V. inaequalis isolates from 141 commercial, research, and baseline orchard populations were examined throughout New England, the mid-Atlantic, and the Midwest from 2004 to 2013. Of these orchard populations, 63% had practical resistance, 13% had reduced sensitivity, and 24% were sensitive to myclobutanil. A sensitivity baseline for the recently introduced DMI fungicide difenoconazole was established to make comparisons with myclobutanil sensitivity in orchard populations. The mean effective concentration of difenoconazole at which mycelial growth was inhibited by 50% (EC50) was determined to be 0.002 µg ml-1 for 44 baseline isolates of V. inaequalis. From 2010 to 2013, 1,012 isolates of V. inaequalis from 37 of the 141 orchard populations above were screened for sensitivity to difenoconazole. In all, 1 orchard population had reduced sensitivity to difenoconazole, while the remaining 36 orchard populations were sensitive to the fungicide. In field experiments, difenoconazole demonstrated high levels of apple scab control on mature apple fruit, despite the fact that the population of V. inaequalis had practical resistance to difenoconazole. Although our results indicate widespread resistance to myclobutanil but not difenoconazole, due to the propensity for cross-sensitivity among DMI fungicides, growers with myclobutanil resistance should be cautious when using difenoconazole for disease management. [ABSTRACT FROM AUTHOR]

Fire blight incidence and spread of the shoot blight phase of the disease was studied in four apple cultivars in replicated blocks over 4 years (1994 to 1997). Cv. York was highly susceptible, followed by 'Fuji' and 'Golden Delicious,' which were moderately susceptible, and 'Liberty,' which was least susceptible. On York, the first appearance of shoot blight was within 48 h of its predicted appearance according to the Maryblyt model in 3 of the 4 years studied. Shoot blight epidemics in York in 1995 and 1996, and Fuji in 1995, were best described with a logistic model that showed apparent infection rates ranging from 0.05 to 0.20, indicating a low to moderately high rate of disease increase. The spatial positions (row and column) of all infected plants in each subplot were recorded on plot maps on each sampling date. The binomial and β-binomial distributions were fit to the data to test for spatial aggregation of disease incidence for each cultivar plot. Maximum likelihood estimation was possible for 92 (43.6%) of the 211 data sets subjected to this analysis. Of these, 35 data sets were better fit by the β-binomial distribution than the binomial distribution. The binary power law was used to characterize the relationship between the variance among quadrats within each plot to the variance expected for that plot given the observed level of disease incidence. The binary power law provided an excellent fit to the full data set and to nearly all of the subsets and, with b > 1, indicated that heterogeneity changed systematically with disease incidence. A covariance analysis was conducted to determine the effect of the factors 'year,' 'cultivar,' 'orchard plot,' and 'observation date' on the intercept and slope parameters of the binary power law. In general, plot followed by year had the greatest impact on parameter estimates and is an indication that location and seasonal factors impact heterogeneity of disease, although the specifics could not be ascertained from this study. Ordinary runs analysis was used to analyze the pattern of diseased trees within rows and detected significant nonrandom patterns of disease incidence in 63.5% of the orchard plots over the 4-year study. From these data sets, 68.7% had significantly fewer runs, particularly at disease incidences greater than 0.1. The fewer-than-expected runs at incidences greater than 0.10 provides strong evidence of localized spread. [ABSTRACT FROM AUTHOR]

The objectives of this study were to determine the seasonal production patterns of Leucostoma cinctum conidia in peach and cherry orchards and the effects of irrigation on dispersal of conidia. Conidia were trapped throughout the year and were present in highest numbers during spring and summer on both cherry and peach. The pathogen was dispersed 1.0 m by water drops that simulated irrigation drops that would impact cankers during over-the-canopy irrigation. Spore production and dispersal also resulted from the use of over-the-canopy and under-tree impact sprinklers. Although the two irrigation methods were not directly compared, the latter mode dispersed propagules of L. cinctum over horizontal distances of about 6 m, a distance sufficient to account for the movement of the pathogen between trees within and across orchard rows. It is concluded that disease management could be improved by alteration of horticultural and irrigation practices. [ABSTRACT FROM AUTHOR]

Twenty-three apple (Malus xdomestica) cultivars were tested in the field and laboratory for their relative susceptibility to the black rot pathogen, Botryosphaeria obtusa. Wounded fruit were inoculated in the field at 2 to 3 weeks preharvest with mycelium from 14- to 21-day-old cultures. In the laboratory, detached fruit were inoculated similarly. Fruit were rated for relative susceptibility to the fungus by determining disease severity of attached fruit in the field based on lesion growth (mm/degree-day) and detached fruit in laboratory inoculations of wounded fruit (mean lesion diameter after 4 days). Based on the laboratory and field data from two growing seasons, cultivars were classified into three relative susceptibility groups--most susceptible: Orin, Pristine, and Sunrise; moderately susceptible:Suncrisp, Ginger Gold, Senshu, Honeycrisp, PioneerMac, Fortune, NY75414, Arlet, 'GoldenSupreme, 'Shizuka, 'Cameo, 'Sansa, and 'Yataka; and least susceptible: Creston, Golden Delicious, Enterprise, Gala Supreme, Braeburn, GoldRush, and Fuji. Compared to previous cultivar rankings, the results of the present study indicate that no new apple cultivars from the first NE-183 planting show greater resistance to Botryosphaeria obtusa than current standard cultivars. [ABSTRACT FROM AUTHOR]

The objective of this study was to determine the effects of calcium salts on growth of Botryosphaeria dothidea and incidence of white rot. The relative virulence of five B. dothidea isolates was determined using the apple cultivars Fuji, Gala, Golden Delicious, Liberty, and York. Cultivar and isolate differences in lesion diameter were significant. Cultivar differences occurred between Fuji, which was most susceptible, and Gala, which was least susceptible. Isolates PA-1 and PA-2 were most virulent. Isolate PA-4 was used at conidia concentrations of 1 × 10[sup 4], 1 × 10[sup 5], 1 × 10[sup 6], and 1 × 10[sup 7] conidia per ml on Golden Delicious fruit to test the effects of four inoculum concentrations on fruit infection by B. dothidea. Incidence of infection on detached, nonwounded fruit increased as inoculum concentration increased. The effects of four calcium salts on infection of wounded fruit by conidia were examined in field and laboratory experiments. In the field experiments, lesion size was slightly reduced on fruit treated with either calcium hydroxide or calcium silicate after wounding and prior to inoculation with conidia of B. dothidea, whereas lesions that developed at wounds treated with calcium chloride or calcium propionate were similar to those of the control. In the laboratory experiments, in several instances supplementation with calcium salts resulted in increased lesion diameter relative to the control. Two of five isolates tested showed increased percent germination with all four calcium salts, and one isolate showed increased germination in the presence of two of the four calcium salts. Germ tube elongation was not affected by calcium salts for four out of five isolates tested. There was significant variation among isolates and calcium salts on the growth of B. dothidea in liquid culture. Calcium chloride and calcium hydroxide enhanced the growth of three isolates and had no effect on the other three isolates. Calcium propionate inhibited the growth of four isolates and had no effect on the other two isolates. Calcium silicate inhibited the growth of one isolate and had no effect on the other five isolates. [ABSTRACT FROM AUTHOR]

Compares conventional and alternative systems for the establishment of apple trees on a replicated, whole-orchard scale. Tree growth and pest incidence; Soil organic matter and fertility; Fertilizer use efficiency; Nitrate mobility; Apple leaf nutrient analyses from trees grown under alternative and conventional management systems.

Presents findings of a study which examined the link of increased resistance to Leucostoma personii with somaclonal variation in wound healing in field-grown peach. Techniques used in vitro culture of Prunus persica; Plant material used; Procedure followed in tissue culture; Result of laboratory study of peach trees.

Salinity could become a threat to hydroponically grown plants due to the differential ion uptake process by the crop itself and/or using low quality irrigation water containing non-essential ions such as sodium and chloride. This study was conducted to determine the interactive effects of salinity and foliar application of ascorbic acid (AsA) on the survival capacity of Chinese kale plants. Three-week-old plants at the 4-leaf stage were exposed to salinity by application of 0, 50 and 100 mM NaCl for 14 days. The activities of antioxidant enzymes, catalase (CAT), peroxidase (POX) and ascorbate peroxidase (APX) along with changes in the accumulation of proline, lipid peroxidation and chlorophyll content in leaves were estimated. Salinity induced obvious changes in the activities of antioxidant enzymes, lipid peroxidation, proline accumulation and chlorophyll content in the leaf tissues. Exogenous application of AsA (5 and 10 mM) to stressed plants resulted in a significant increase (P< 0.05) in APX activity and reduction in the activities of antioxidant enzymes (CAT and POX) as well as a decrease in the contents of stress-induced proline and malondialdehyde (MDA). Higher chlorophyll content was also recorded in stressed plants using AsA. The inherent capability of AsA to scavenge free radicals may have assisted the plant using the lower oxidative damages. The results of this study showed that AsA treatment would reduce the deleterious effects of salt-induced oxidative stress and improve plant tolerance to salt stress. [ABSTRACT FROM AUTHOR]

Quinone-outside-inhibitor (Qol) fungicides are a safe and effective means of managing apple scab caused by Venturia inaequalis. To determine the prevalence of both quantitative (partial) and qualitative (complete) Qol resistance in V. inaequalis in the northeastern United States, we sampled single-lesion conidial isolates (n = 4,481 ) from 120 commercial and research orchards from 2004 to 2011 with a range of exposure to Qol fungicides from none to several applications a year. In all, 67% of these orchard populations of V. inaequalis were sensitive to Qol fungicides, 28% exhibited Qol practical resistance, and 5% were not sensitive Qol fungicides but had not become practically resistant. Isolates with qualitative Qol resistance, conferred by the G143A cytochrome b gene mutation, were found in 13 of the 34 Qol-resistant orchard populations. To evaluate the stability of the G143A mutation, 27 isolates were selected from different orchard populations to represent the scope of regional populations. These isolates were subcultured continuously in the presence or absence of the Qol fungicide trifloxystrobin. All isolates that initially possessed qualitative resistance maintained the resistant genotype (Gl43A) for six transfers over 6 months in both the absence and presence of trifloxystrobin. Given the observed Qol resistance in orchard populations of V. inaequalis and the stability of the G143A mutation in individual isolates, apple scab management paradigms must encompass strategies to limit selection of Qol resistance in the sensitive orchard populations remaining in the region. [ABSTRACT FROM AUTHOR]

'Fuji' apple fruit were collected in Shaanxi Province, China, and 186 fungal isolates were obtained from the fruit core region. Fungi were isolated from fruit with symptomless core regions, as well as from the core regions of fruit showing browning, typical moldy core, or core rot. Based on phylogenetic and morphological analysis, all fungi were identified to species. Pathogenicity was determined by cutting apple fruit into halves and daubing spore suspensions containing 1 × 104 up to 1 × 108 spores/ml on the carpel in the core region. Pathogenicity varied significantly among genera, with Alternaría and Cladosporium spp. causing core browning at lower spore concentrations and moldy core at higher spore concentrations. Combinations of pathogens initi-ated more browning and moldy core than the pathogens applied alone. Epicoccum and Phoma spp. predominated in dry core rot, whereas primarily Trichothecium but also Fusarium and Pénicillium spp. caused wet core rot. Core browning was introduced as a new type of core symptom, along with moldy core, dry core rot, and wet core rot. Alter-naría alternata, A. tenuissima, A. arborescens, Cladosporium clado-sporioides, and C. tenuissimum were the main pathogens causing core browning and moldy core. [ABSTRACT FROM AUTHOR]

Phytophthora stem and root rot, caused by Phytophthora sojae, is one of the most destructive diseases of soybean [Glycine max (L.) Merr.], and the incidence of this disease has been increasing in several soybeanproducing areas around the world. This presents serious limitations for soybean production, with yield losses from 4 to 100%. The most effective method to reduce damage would be to grow Phytophthora-resistant soybean cultivars, and two types of host resistance have been described. Race-specific resistance conditioned by single dominant Rps ("resistance to Phytophthora sojae") genes and quantitatively inherited partial resistance conferred by multiple genes could both provide protection from the pathogen. Molecular markers linked to Rps genes or quantitative trait loci (QTLs) underlying partial resistance have been identified on several molecular linkage groups corresponding to chromosomes. These markers can be used to screen for Phytophthoraresistant plants rapidly and efficiently, and to combine multiple resistance genes in the same background. This paper reviews what is currently known about pathogenic races of P. sojae in the USA and Japan, selection of sources of Rps genes or minor genes providing partial resistance, and the current state and future scope of breeding Phytophthora-resistant soybean cultivars. [ABSTRACT FROM AUTHOR]

The article discusses the economic damage and genetic diversity of sooty blotch and flyspeck (SBFS) fungi, which colonizes the surface wax layer of cultivated tree and vine crops such as apples, pears, and oranges. It states that the fruiting bodies, hyphae, and survival structures of SBFS cause the appearance of blemishes that can downgrade the fruit quality. Moreover, it classifies the two taxonomic species of SBFS fungi which are Gloeodes pomigena and Zygophiala jamaicensis.