Effect of cultural practices and fungicides on Phytophthora fruit rot of watermelon in the Carolinas

Phytophthora fruit rot of watermelon, caused by Phytophthora capsici, is an important and emerging disease in Southeastern U.S.A. The effects of two cultural practices (raised bare ground and raised plastic mulched beds) used for growing watermelon and different fungicide treatments on development of Phytophthora fruit rot were evaluated. The experiments were conducted over three years (2005-2008) at research stations in North Carolina and South Carolina, U.S.A. Fungicides were applied at weekly intervals on the diploid cv. Mickey Lee for an average of five applications. Fruit rot incidence was recorded at the end of each experiment. Fruit rot incidence in the non-treated plots was 66% across two states and six trials. Overall, the levels of fruit rot on the raised bare ground and raised plastic mulched beds were not significantly different. Based on percent disease reduction relative to the non-treated check plots, the fungicide Captan was the most effective across years and locations (range = 23-70%, mean = 57%), followed by mandipropamid (25-65%, mean = 50%), fluopicolide (24-65%, mean = 43%) and cyazofamid (0-48%, mean = 31%). Mefenoxam, the current standard treatment reduced fruit rot by 8-28% (mean = 18%). The addition of copper hydroxide to the spray mix did not significantly enhance effectiveness of Captan or mandipropamid. The variability in fungicide efficacy observed in these experiments across locations and years demonstrates the importance of environmental conditions in disease development and management. Even when the most effective fungicides are used, heavy losses may occur when conditions are highly favorable for disease development. Ultimately, effective control of Phytophthora fruit rot of watermelon will require an integrated management strategy that includes well-drained fields, water management and crop rotation in addition to fungicides.     

Berberine as a natural compound inhibits the development of brown rot fungus Monilinia fructicola

Peach brown rot is a severe disease caused by ascomycete fungus Monilinia fructicola and is primarily controlled by chemical fungicides. However, the utilization of fungicides has caused many problems such as microbial resistance, environmental pollution, and fruit contamination. The growing concern for food safety requires alternative management methods that are safe to humans and benign to the environment. Here we report that the extract from Coptis chinensis (a Chinese herb named “Huang Lian”) demonstrates a strong inhibition to M. fructicola. The 50% effective concentration (EC₅₀) of C. chinensis extract to M. fructicola was only 0.91 mg/mL, while the EC₅₀s to other fungi such as Botrytis cinerea and Alternaria solani were 14.09 mg/mL and 27.35 mg/mL, respectively. These results indicate that the extract of C. chinensis has a specific inhibition to M. fructicola. Subsequent partitioning of the ingredients in C. chinensis extract revealed that berberine, the conventional anti-bacterial alkaloid, was the predominant ingredient that exerted robust inhibition against M. fructicola. The EC₅₀ and minimum inhibitory concentration (MIC) against M. fructicola were as low as 4.5 μg/mL and 46.9 μg/mL, respectively. Compared to berberine’s analogs in C. chinensis such as palmatine, berberine tannate and jatrorrhizine, berberine showed the strongest inhibition against M. fructicola. This finding provided insight into the structure–activity relationship between berberine and its analogs. Notably, not only can berberine prevent spore germination and hyphal growth, it also inhibits the activity of cutinase secreted by M. fructicola, implying the potential function of berberine in reducing the pathogenesis of M. fructicola. In addition, the strong in vivo inhibition of berberine against M. fructicola was observed with no visual cytotoxicity noted to peach fruits, even at berberine concentration of 400 μg/mL. Note that this was much higher than its MIC value (46.90 μg/mL). Overall berberine, as a natural compound, may be a promising candidate in control of brown rot.     

Identification and characterization of Colletotrichum fructicola causing black spots on young fruits related to bitter rot of pear (Pyrus bretschneideri Rehd.) in China

In recent years, Pyrus bretschneideri Rehd. var. ‘Suli’ has been damaged by a disease characterized by the presence of black spots on young fruit in China, which was always followed by severe bitter rot on matured fruits. The etiology of these symptoms and their relationship with the bitter rot was unknown. A colony was routinely isolated from young and matured ‘Suli’ pear fruits showing black spots and rot symptoms, respectively. This fungal colony was identified as Colletotrichum fructicola based on morphological characteristics and DNA sequence data of 7 regions. C. fructicola was confirmed to be capable of eliciting both black spots and bitter rot symptoms by completion of Koch's Postulates. The results suggested that the disease characterized by the presence of black spots on young fruits is indeed an early stage of the bitter rot observed on matured fruits of ‘Suli’ pear. Variety resistance analysis indicated an obvious resistance variation possessed by the pear varieties generally cultured in China, with black spots only occurring on some pear varieties. Our results also indicated that wounding can break the quiescent infections, enhance the infectivity of C. fructicola, and lead to more rapid rot of young and matured fruits. These results provided a clear clue that C. fructicola can invade some varieties of P. bretschneideri Rehd. directly without entry via wounds, but subsequently turned into quiescent infection and causing black spots on the fruit surface. The quiescent infection acts as a pathogenic factor responsible for bitter rot of matured fruits. The influence of temperature and pH conditions for growth and colony morphology of C. fructicola were also evaluated. The characterization of C. fructicola causing bitter rot of pear (P. bretschneideri) is expected to provide useful information for controlling this economically important disease.     

Management of peanut pod rot I: Disease dynamics and sampling

Peanut fields are monitored for pod rot, which is typically caused by Pythium spp. and Rhizoctonia solani, in order to determine need, and the type and timing of fungicide applications. Pod rot can lead to damaged peanut kernels and when damage exceeds 2.49%, substantial price reductions occur. Nine fields or tests were sampled weekly for pod rot during the 2009 through 2012 growing seasons. The sampling was conducted on fields treated uniformly with fungicides for pod rot or within large research plots with various fungicide treatments. Pythium myriotylum was the most frequently identified pathogen species, although Rhizoctonia spp. were also recovered from diseased pods at all sites. Pod rot incidence was related to percent damaged kernels at harvest in 3 of 5 sites. Collection of 304 samples (sample unit = 46 cm of row) in a field was required to estimate 1% pod rot accurately (CV = 20%). There was a linear relationship between average % pod rot in a field, and the percentage of sampling units (absence/presence) with pod rot at low disease incidences. Scouting for pod rot of peanuts to make in-season fungicide applications will be hampered by high sample number, destructive sampling of plants, frequent sampling (due to rapid increase of disease), and the poor relationship between disease during the season and kernel damage at harvest. Making one preventative application at 60–70 days after planting may be a better practice than timing the initial fungicide application based on sampling for disease.     

Control of brown rot on nectarines by tea polyphenol combined with tea saponin

Postharvest peach fruit are susceptible to fungal decay. To search for effective alternatives to currently used fungicides for disease control, the in vitro and in vivo antifungal activities of tea polyphenol (TP) and tea saponin (TS) individually or their combination were evaluated against Monilinia fructicola isolated from infected nectarine fruit in this study. The in vitro experiments showed that both TP and TS inhibited the mycelial growth in a dose-dependent manner and their combination exhibited an additive or synergistic antifungal interaction with the cotoxicity factor (CTF) exceeding −20. The in vivo experiments showed that they both effectively controlled brown rot on inoculated nectarine fruit and their combination (TP: TS, 1:2) significantly improved the controlling effect. Our results also revealed that TP and TS induced the activities of phenylalanine ammonia-lyase (PAL), peroxidase (POD), polyphenoloxidase (PPO), chitinase and β-1,3-glucanase in inoculated nectarine fruit and their combination strengthened the induction. These findings suggested that the combination of TP and TS could effectively control brown rot on postharvest fruit and that the mechanism of the control might be attributed to the induction of defensive enzyme activities.     

Quantification of yield loss due to coffee leaf scorch

Coffee leaf scorch caused by Xylella fastidiosa is widespread in major coffee-growing regions of Brazil. This study was done to quantify the yield loss caused by this disease. The severity data of the disease were collected during the 2006, 2007 and 2008 seasons at commercial plantations growing Coffea arabica ‘Catuaí’ in São Gotardo-MG in 250 plants of three blocks of 7000 coffee plants each. Fifty selected plants per block with different disease severities were determined. The linear regression showed a significant relationship (P < 0.01) between disease severity and bean yield and between disease severity and grain size in all years. The relationship between yield and the disease severity was significant (P < 0.01). For each 1% increase in the disease severity, there was a decrease of 1.22, 1.34 and 2.02 bags of bean yield/ha in 2006, 2007 and 2008, respectively, thus showing the importance of the disease in reducing coffee bean yields.     

Effects of irrigation deprivation and ground cover (Trifolium repens) in the tree row on brown rot incidence in peach

Brown rot can lead to considerable fruit losses in peach orchards and cultural practices likely to contend this major disease have to be promoted. In order to limit peach brown rot incidence in a three-year-old mid-season maturing peach orchard of the cultivar ’Ruby Bright’, four combinations of irrigation and soil management treatments were assessed: conventional (Conv) irrigation (I) and soil management (S) (ConvI+ConvS); modified (Mod) irrigation and soil management (ModI+ConvS); conventional irrigation and modified soil management (ConvI+ModS); and modified irrigation and soil management (ModI+ModS). Conventional irrigation and soil management in the tree row consisted of irrigation scheduling using tensiometer readings and herbicide use, respectively. Modified irrigation and soil management in the tree row consisted of water deprivation during stage III of fruit development and ground cover with white clover, respectively. For four consecutive years (2010–2013), in the conditions of the Middle Rhone Valley in France, the lowest and highest brown rot incidence were detected under (ModI+ModS) and (ConvI+ConvS), respectively, whereas brown rot incidence under (ModI+ConvS) and (ConvI+ModS) was intermediate. This lower brown rot incidence under the modified treatments occurred from one to two weeks before fruit maturity and was still observed for several days in post-harvest storage. Ground cover with white clover was shown to limit water availability in the soil after heavy rainfall compared to bare soil, probably limiting peach growth variations, well-known as a possible source of detrimental microcracks at the fruit surface. This suggests that under our conditions appropriate cultural practices, water deprivation and a clover crop cover in the tree row possibly decrease peach disease sensitivity, which might lead to the reduced use of pesticide sprays to control brown rot in the orchard.     

Control of brown rot of stone fruits by brief heated water immersion treatments

The effectiveness of brief (30 or 60 s) immersion in water at 24, 50, 55, 60, 65, or 70 °C was evaluated for the control of brown rot, caused by Monilinia fructicola, on California-grown peaches, nectarines, and plums. Inoculated fruits were treated and either stored at 20 °C for 5 days or at 0 °C and 95% RH for 30 days followed by 5 days at 20 °C to simulate commercial marketing conditions. Immersion in water at 55 °C for 60 s or at 60 °C for 30 or 60 s significantly reduced both decay incidence and severity among the remaining wounds that developed the disease. Water temperatures of 65 °C or higher were phytotoxic and caused moderate to severe surface injuries. Immersion in water at 60 °C for 60 s was effective for plums and it reduced the incidence of brown rot from more than 80% among control fruit to less than 2%. In nectarines, this treatment reduced decay incidence from 100 to less than 5% on fruit stored at 20 °C and from 73 to 28% on cold-stored fruit. Therefore, brief immersion in heated water can be an effective approach to manage postharvest brown rot of stone fruits, especially for the organic fruit industry.     

Injury to apples and peaches at harvest from feeding by Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) nymphs early and late in the season

Halyomorpha halys (Stål) (Hemiptera: Pentatomidae) is an invasive species that has become an important orchard pest in the Mid-Atlantic region of the US. Adults and nymphs feed on tree fruit. Feeding injury from adults has been characterized but the injury from nymphs has not been examined systematically. Since the four plant-feeding instars of H. halys (second through fifth) differ substantially in size, it is plausible that the effects of their feeding on fruit injury and injury expression may differ among them. We compared feeding injury at harvest from young nymphs (second plus third instars), older nymphs (fourth plus fifth instars), and adults that were caged on ‘Smoothee Golden’ apples and ‘Redhaven’ peaches in early June (peach and apple), late July (peach), and late August (apple). Individual apples and peaches were caged at fruit set and assigned to the following treatments (n = 28/treatment): 1) control (no H. halys), 2) young nymphs or 3) adults early in the season, and 4) young nymphs, 5) older nymphs or 6) adults later in the season. Fruit in each treatment were exposed to 3–4 young nymphs, two older nymphs or 1–2 adults placed in the cages for 96 h and evaluated for external and internal feeding injury within 36 h after harvest. No injury was recorded from unexposed peaches or apples. The percentage of injured fruit and number of injuries per fruit varied significantly among the exposed treatments. Early season feeding by young nymphs yielded the least injury to peaches and apples. In apples, the highest percentage of injured fruit and number of injuries per fruit were caused by late season feeding by adults. In peaches, early season adult feeding produced the highest percentage of injured fruit and injuries per fruit. More internal than external injury was recorded on peach and no such difference was observed on apple. The implications of these findings on H. halys management in fruit orchards are discussed.     

Efficacy of fumigant treatments and inoculum placement on control of Macrophomina phaseolina in strawberry beds

Soil disinfestation is one of the main concerns of strawberry growers. The phased-out of methyl bromide (MeBr) and the lack of equally effective fumigants has increased the difficulty in controlling soilborne pathogens such as Macrophomina phaseolina, causal agent of charcoal rot. Soil fumigant treatments were tested in Dover, Florida during the 2012–13, 2013–14 and 2014–15 seasons. The treatments included MeBr as a standard and common alternatives such as chloropicrin (PIC), 1,3-dichloropropene (1,3D), dimethyl disulfide (DMDS), potassium N-methyldithiocarbamate (Kpam) and sodium methyldithiocarbamate (Vapam). The efficacy of different fumigation rates and application methods was also investigated. Treatment effects were evaluated using sclerotia of M. phaseolina buried in bags 7.6 and 20.3 cm deep in the center of the bed, or 7.6 cm deep on the side of the bed (7.6 s). Additionally, strawberry crowns infected with M. phaseolina were buried 7.6 cm deep in the center of the bed during the 2012–13 and 2013–14 growing seasons. At the end of the 2013–14 and 2014–15 growing seasons, plant mortality and charcoal rot incidence (%) were also determined. Except for 1,3-dichloropropene:chloropicrin 39/60, most treatments were effective in reducing the colony forming units (CFUs) of M. phaseolina in buried bags or crowns buried at the center of the bed and reduced percent of charcoal rot incidence each season. Most treatments applied by shank produced similar reductions in inoculum levels at the center and sides of the bed, whereas drip treatments effectively reduced inoculum in bags buried at both depths in the center of the bed, but not at the side of the bed. Thus, one of the main problems of the current fumigants is poor distribution in the soil beds and strawberry growers should consider application methods that will achieve a more uniform distribution of the fumigants.     

Growing Brassica juncea as a cover crop, then incorporating its residues provide complementary control of Rhizoctonia root rot of sugar beet

Biofumigation is increasingly viewed as a potentially useful technique for controlling soil-borne crop pathogens, but its efficacy has not systematically been demonstrated at field scale. We investigated the differences in efficacy observed in the field, by analysing the mechanisms by which a Brassica cover crop can act as a biofumigant crop in the prevention of soil-borne disease development. We hypothesised that the biofumigant crop might have a negative effect on soil-borne pathogens whilst growing, and that the pulverisation of this crop and the incorporation of its residues into the soil may enhance this effect. We tested this hypothesis by carrying out three field experiments in 2006, 2007 and 2008 in which Brassica juncea (brown mustard) was managed in different ways within a sugar beet–winter wheat rotation and analysing effects on sugar beet root rot caused by Rhizoctonia solani. Three treatments were studied: mustard pulled out at flowering (MP), mustard crushed at flowering and incorporated into the soil (MC) and bare soil (BS) as a control. We assessed the effect of each treatment on root rot incidence and severity at harvest. Over the 3 years of the experiment, disease incidence was significantly higher on BS plots than on the other plots and was significantly higher on MP plots than on MC plots. MC treatment gave a significantly lower mean conditional severity (severity calculated for diseased beets only) than the BS and MP treatments. Mustard residue incorporation was consistently effective at decreasing disease incidence from year to year (43, 44 and 47% efficacy, as determined by comparison with the disease incidence on BS plots, in 2006, 2007 and 2008, respectively), but the efficacy of growing mustard was variable (36, 16 and 39% efficacy in 2006, 2007 and 2008, respectively). These findings provide insight into the mechanisms by which biofumigant crops may affect soil-borne diseases. These findings have implications for the possible use of biofumigant crops as a biological method for controlling soil-borne diseases at the field scale.     

高温高湿地区套袋处理对火龙果果实品质的影响

为探讨适用于高温高湿地区的火龙果果袋,以红皮红肉型‘桂红龙2号’火龙果为材料,测定5种不同类型果袋套袋后袋内温湿度日变化及对火龙果果实品质、果实病害以及采后果实失水率等的影响。结果表明,套袋后袋内温度升高速度更快,白天袋内温度均显著高于对照;套袋使果皮变薄,增加可食率,促进了果皮鳞片转红,以牛皮纸袋为最高;套袋显著增加了果皮与果肉的色素含量;显著增加了果实可溶性固形物含量,不同程度的提高了葡萄糖和果糖的含量;但套袋也提高了果实苹果酸及柠檬酸的含量。套袋总体上降低了采后水分散失的程度,白色纸袋和无纺布袋有利于降低采后病害发生率,延长货架期。除黑色尼龙网袋以外,套袋均提高了果实煤烟病的发病率。综上,在广西南宁周边高温高湿地区,可使用黑色尼龙网袋,有利于防止鸟啄和虫害,或使用白色纸袋和无纺布袋,有利于延长货架寿命,但采收后要注意煤烟斑的清洗。     

Management of fusarium basal rot (Fusarium oxysporum f. sp. cepae) on shallot through fungicidal bulb treatment

Fusarium basal rot caused by Fusarium oxysporum f.sp. cepae is an economic disease of shallot. Field experiments were conducted at Debre Zeit during 2006 and 2007 cropping seasons to determine effective fungicides and their method of application for the management of fusarium basal rot of shallot. The field was naturally infested with F. oxysporum f. sp. cepae and treatments were arranged in randomized complete block design in four replications. Five fungicides, Mirage 50 WP, Folicur 25 EC, Seed plus 30 WS, Penncozeb 80 WP and Ridomil Gold 68 WG were evaluated as seed bulb dressing and bulb dip treatments against basal rot in the field and storage. Bulb dressing with Mirage, and dip treatment in Seed plus reduced the disease incidence by 40% and 43%, respectively over control. These fungicides also resulted in a significant reduction in severity, basal rot affected cull bulbs on shallot. Bulb rot during three months of storage on concrete ground floor and on wire mesh shelves was also reduced by seed bulb treatment over control. The highest increase in yield was obtained from bulb dressing with Mirage (42%) and Seed plus (45%) and from bulb dip treatment in Seed plus (44%) over control. Fusarium basal rot caused 45% loss in yield and 12-30% of bulb loss in the storage. The study showed that basal rot of shallot can be managed effectively by seed bulb dressing or dip treatment in Mirage or Seed plus.     

Management of silver scurf (Helminthosporium solani) with fungicide seed treatments and storage practices

Thiabendazole insensitive strains ofHelminthosporium solani, the causal agent of silver scurf, make controlling the disease with seed treatment difficult. Potato tuber seed treatments and environmental storage management practices were investigated as means to minimize silver scurf. Fungicide seed treatments were evaluated for control ofH. solani; disease was evaluated during the growing season, at harvest, and after 5 months of storage. Silver scurf was observed on progeny tubers eleven weeks after planting. Fungicides that reduced silver scurf incidence and severity on the seed resulted in reduced incidence and severity of the disease in the progeny tubers at harvest and significantly lower disease ratings after storage. Only small increases in disease incidence (0-8%) were seen after storage. Thiophanate-methyl with mancozeb, Captan with mancozeb, and fludioxonil were among the most effective in reducing the incidence and severity of silver scurf on seed and in progeny tubers (Incidence on progeny tubers at harvest for these three treatments were 3%, 9%, and 8% respectively). Thiophanatemethyl alone was not effective for control of silver scurf (48% incidence compared to 43% incidence for the untreated control). Environmental conditions in storage affected disease development. Reduced humidity (85%) during the curing period (0–3 weeks after harvest) significantly reduced (11%) the surface area of tubers infected with silver scurf. Free moisture on the tuber surfaces during storage significantly increased (15%) tuber surface area infection.H. solani was shown to survive in soil and on some potato storage building materials for up to 9 months. The silver scurf disease of potatoes can be suppressed using effective seed treatment and storage management.     

Chitosan boehmite-alumina nanocomposite films and thyme oil vapour control brown rot in peaches (Prunus persica L.) during postharvest storage

Brown rot (Monilinia spp.) affects the shelf life, fruit quality and marketability of peaches (Prunus persica L.). Increasing consumer concern regarding food safety makes it necessary to search for natural environmentally friendly alternative products for postharvest disease control. In this investigation, polyethylene terephthalate (PET) punnets containing thyme oil (TO sachets) and sealed with chitosan/boehmite nanocomposite lidding films significantly reduced the incidence and severity of brown rot caused by Monilinia laxa in artificially inoculated peach fruits (cv. Kakawa) held at 25 °C for 5 days. Furthermore, PET punnets containing TO sachets and sealed with chitosan/boehmite nanocomposite lidding films significantly reduced the brown rot incidence to 10% in naturally infected fruits stored at 0.5 °C, 90% RH for 7 days and at the simulated market shelf conditions for 3 days at 15 °C, 75% RH. The chitosan/boehmite nanocomposite lidding films maintained the active components of thyme oil, thymol (56.43% RA), caryophyllen (9.47% RA) and β-linalool (37.6% RA) within the (head space volatiles) punnet. Panellists preferred fruits packed from commercial punnet containing thyme oil (sachets) and sealed with chitosan/boehmite nanocomposite lidding films due to overall appearance, taste, and natural peach flavour.     

Detection ofCorynebacterium sepedonicum in potato cultivars with different propensities to express ring rot symptoms

Various potato cultivars were grown in field plots from seed pieces inoculated withCoryneacterium sepedanicum by vacuum infiltration. Foliage symptoms were recorded during the growing season and tuber symptoms at harvest. Cultivars were ranked according to the frequency with which the progeny tubers expressed external bacterial ring rot symptoms. Those that yielded 50–100% symptomatic tubers were placed in symptom expression class (SEC) 1; those that produced 25–49%, 10–24%, and ≤9% symptomatic tubers were placed, respectively, in SEC 2,3, and 4. The incidence of latent ring rot infections in stems and tubers were similar among cultivars in the different SEC classes. Bacterial population densities, quantified by immunofluorescence, were as high as 10¹⁰ cells/g in stems from cultivars of all SEC classes. Mean populations in tubers ranged from 10⁶ – 10⁷ cells/g and did not differ significantly among cultivars.     

Potassium phosphite for control of downy mildew of soybean

Downy mildew of soybean, caused by Peronospora manshurica, is widely spread throughout Brazil. The objective of this study was to evaluate the use of potassium phosphite to control this disease. Field experiments were conducted during the growing season of 2006/2007 and 2007/2008 in the state of Parana in southern Brazil. The experimental design consisted of completely randomized blocks in a factorial arrangement (4 × 2) with four replications. Four rates of potassium phosphite (0, 375, 750 and 1500 g P₂O₅ + K₂O ha⁻¹) were applied at two growth stages, V6 (fifth trifoliolate leaf) and R2 (full flowering), followed by one or two applications of pyraclostrobin and epoxiconazole (66.5 + 25 g a.i. ha⁻¹) at R3 (pod development) or R2 and R5.1 (10% of pod filling), mainly for the control of Asian soybean rust (Phakopsora pachyrhizi) and powdery mildew (Microsphaera diffusa). Field experiments were conducted to quantify the severity of downy mildew on leaves, nutrient content in leaf tissue (N, P and K), leaf area index (LAI), yield and seed weight. The maximum severity of downy mildew was observed at a growth stage of R5.3 (50% of pods were ripe), with 14% and 46% of the leaf area affected in 2006/2007 and 2007/2008, respectively. Also it was detected some effect of phosphite on Asian rust control but it was mostly in the trial of 2007/08 when the epidemic was very low (9.7-21.8% of severity). There was a linear reduction in the severity of downy mildew and a significant improvement in the LAI with an increase in the rate of phosphite applied. During the 2006/2007 growing season, a significant yield improvement was observed due to the application of the highest rate of phosphite. Two fungicide applications following phosphite application significantly improved the control of Asian soybean rust and powdery mildew, yield and seed weight when compared to a single fungicide application.     

Carotenoids,Phenolic Profile,Mineral Content and Antioxidant Properties in Flesh and Peel of <Emphasis Type="Italic">Prunus persica</Emphasis> Fruits during Two Maturation Stages

Carotenoids and phenolic profile, antioxidant activity as well as concentrations of selected macronutrients (K, N, Mg, Ca and Na) and micronutrients (Zn, Cu and Mn) in flesh and peel of peach fruit were recorded at two harvest dates. Predominant mineral was potassium, followed by calcium, magnesium and sodium. The concentration of most micronutrients was greater in the peel than in the flesh especially in early season. The concentration of most elements in flesh and peel decreased during fruit maturation. Total carotenoids content varied with respect to the cultivar. β-cryptoxanthin and β-carotene were the major carotenoids in both tissues and flesh contain the lowest amounts. Neochlorogenic acid, chlorogenic acid, catechin, epicatechin, gallic acid, rutin, quercetin-3-O-galactoside, cyanidin-3-O-glucoside, cyanidin-3-O-rutinoside, were detected in both peel and flesh, with chlorogenic acid and catechin being the predominant components. Peel extracts showed markedly higher antioxidant activities, when estimated by ABTS or DPPH assays, than the flesh counterparts, consistent with the observed higher phenolic content. Overall, total phenolics levels increased at full ripening stage in both peel and flesh. The results found herein provide important data on carotenoids, phenolic and macro- and micronutrient changes during fruit growth, and emphases peach fruit as a potential functional food.     

Effect of biocontrol agent Bacillus amyloliquefaciens and 1-methyl cyclopropene on the control of postharvest diseases and maintenance of fruit quality

Efficacy of biocontrol agent Bacillus amyloliquefaciens PPCB004 was evaluated on the control of anthracnose and phomopsis rot in ‘Solo’ papaya pre-treated with 1-methyl cyclopropene (100 μl) (1-MCP) during storage. This treatment was compared to the untreated control, commercial treatment (washing in chlorinated water), stand alone 1-MCP and PPCB004 treatment. Although fruit pre-treated with 1-MCP delayed the ripening (100% yellow) after cold storage by 9-10 d, it showed higher incidence and severity of anthracnose and phomopsis rot than the fruit subjected to commercial treatment. Application of PPCB004 after 1-MCP pre-treatment (1-MCP + PPCB004) reduced the anthracnose and phomopsis incidence and severity after cold storage (10 °C, 85% RH for 14 d) and ripening at 25 °C. The 1-MCP + PPCB004 treatment helped to retain the fruit firmness, overall quality and uniform yellow skin (100%) and flesh colour after ripening. The PPCB004 was effectively recovered from stand alone PPCB004 and 1-MCP + PPCB004 treated fruit after cold storage and ripening. The PPCB004 population showed an increase by 1 log units after ripening in 1-MCP + PPCB004 treated fruit. After ripening the recovery of PPCB004 population was higher (0.7 log units) in 1-MCP + PPCB004. The total recovery of fungal population on the fruit surface after ripening was lower in 1-MCP + PPCB004 and stand alone PPCB004 treated fruit. It can be concluded that application of B. amyloliquefaciens PPCB004 with 1-MCP pre-treated papaya (at 25-30% skin yellow stage) can significantly reduce disease incidence associated with 1-MCP treatment. This treatment has the potential for commercial application in the ‘organic’ papaya industry.     

Evaluations of shallot genotypes for resistance against fusarium basal rot (Fusarium oxysporum f. sp. cepae) disease

Fusarium basal rot (FBR) caused by Fusarium oxysporum f. sp. cepae (Foc) is one of the most significant production constraint to shallot. Field experiment was conducted in a naturally Foc infested soil at Debre Zeit Agricultural Research Center during 2006 and 2007 cropping seasons to evaluate the level of resistance of sixteen shallot genotypes against FBR disease. Treatments were arranged in randomized complete block design with four replications. The genotypes significantly varied in their susceptibility to FBR and yield. They were grouped into tolerant, moderately and highly susceptible types. Five genotypes (DZ-Sht-168-1A, DZ-Sht-157-1B, Huruta, Negelle and DZ-Sht-169-1b) were identified to be tolerant as they had reduced disease severity levels from 26.8 to 32.5% and increased mean yield by more than 5 t ha⁻¹ compared to highly susceptible genotypes (DZ-Sht-076-4, DZ-Sht-201-1C and DZ-Sht-054-3A). Among the tolerant genotypes, DZ-Sht-169-1b had greatly reduced bulb rot incidence by 48% in ground storage and 30% in wire mesh shelf as compared to highly susceptible genotype DZ-Sht-201-1C. The tolerant genotypes have high yielding characteristic, and farmers could adopt them for cultivation where FBR is a problem.