Factors that impact on the ability of biofumigants to suppress fungal pathogens and weeds of strawberry

This research aimed at identifying factors that improve the efficacy of biofumigants for soil disinfestation against strawberry (Fragaria×ananassa) pathogens and weeds. In laboratory bioassays, volatiles released from the macerated roots of a Brassica rapa/Brassica napus biofumigant crop were six times more effective at suppressing the growth of the strawberry pathogen Rhizoctonia fragariae than shoots. Furthermore, the toxicity of the volatiles from the biofumigant crop to R. fragariae increased as plant developmental stage progressed. These results related to the release of higher quantities and greater diversity of isothiocyanates (ITCs) from the roots of mature biofumigant plants than from their shoots. Separate bioassays showed that volatiles from the biofumigant crop suppressed the growth of six different soil-borne pathogens (Alternaria alternata, Colletotrichum dematium, Cylindrocarpon destructans, Fusarium oxysporum, Pythium ultimum, Phytophthora cactorum, and R. fragariae) of strawberry and seven Trifolium spp. (clover) weeds. The suppression of Trifolium spp. by biofumigant volatiles did not relate to their seed size, but might relate to their hard-seededness or genotype. In the field, rotary incorporation of the biofumigant crop did not produce detectable levels of ITCs in soil; reduce the survival of the strawberry pathogens, P. cactorum and C. destructans; or affect populations of culturable soil microflora. Yet, it suppressed the growth of emerging weeds by 40% and the growth of P. cactorum by 20%. We hypothesise that allelochemicals other than ITCs, such as nitriles, or other biological mechanisms might also play a role in biofumigation. A key to improving the efficacy of biofumigation in the field seems to lie in the development of application technologies that can macerate and incorporate biofumigants evenly in soils, in addition to incorporating biofumigants under optimal edaphic conditions for release of ITCs.     

Non-chemical agents provide tenable,eco-friendly alternatives for the management of the major diseases devastating Indian mustard (Brassica juncea) in India

India is a leading producer of oilseed Brassicas, contributing approximately 23 percent of the country's total oilseed production. In India, the Indian mustard [Brassica juncea (L.) Czern. & Coss.] crop is ravaged by various diseases, including Alternaria blight, white rust, downy mildew, Sclerotinia rot and powdery mildew, which can contribute to fluctuations in crop yields. A field experiment examining an integrated disease management system for Indian mustard (B. juncea) was conducted under the All India Coordinated Research Project on Rapeseed-Mustard (Indian Council of Agricultural Research or ICAR) during three crop seasons (2006–09) at 11 locations to assess treatments suitable for the management of crop disease. The data from the different locations and years regarding disease severity and incidence were pooled and analyzed. Seed treatments with freshly prepared Allium sativum bulb aqueous extract (1 percent w/v) resulted in significantly higher initial plant stands, across locations and years. Seed treatment with A. sativum bulb extract, followed by its use as a foliar spray, resulted in significantly reduced Alternaria leaf and pod blight severity, reduced white rust severity, fewer stag heads per plot, reduced downy mildew and Sclerotinia rot incidence, and reduced powdery mildew severity, across locations and years. The combination also provided significantly higher seed yields compared with the control across locations and years and was at par with treatment by chemical fungicides. The combination used in the present study was as effective as the combination of seed treatment with Trichoderma harzianum and foliar spraying with Pseudomonas fluorescens and T. harzianum. Economic returns were higher when using biorational treatments (A. sativum bulb extract, T. harzianum, P. fluorescens) compared with chemical fungicides. The combination of seed treatments with T. harzianum followed by its use as a foliar spray (17.22), and the similar combination of seed treatments and foliar spraying with the A. sativum bulb extract (17.18), resulted in a higher benefit to cost ratio. This eco-friendly technology can help oilseed Brassica growers in India safeguard the crops from major diseases and increase the stability and productivity of the Indian mustard crop.     

Peach brown rot incidence related to pathogen infection at different stages of fruit development in an organic peach production system

Brown rot, caused by Monilinia fructicola, is the most widespread disease for organic peach production systems in Brazil. The objective of this study was to determine the favorable periods for latent infection by M. fructicola in organic systems. The field experiment was carried out during 2006, 2007 and 2008 using the cultivar Aurora. After thinning fruits were bagged using white paraffin bags, and the treatments were performed by removing the bags and exposing the fruit for four days to the natural infection during each of seven fruit stages from pit hardening to harvest. Throughout the entire growing season, the conidial density and the weather variables were measured and related to the disease incidence using multiple regression analyses. At the fourth day after harvest in each season, the cumulative disease incidence was assessed, and it ranged from 40 to 98%. The incidence of brown rot on fruit that were exposed during the embryo growing stage was lower than that of unbagged fruit throughout the entire season in 2006 and 2008. The relative humidity and the conidia density were significantly correlated to disease incidence. Based on our results, M. fructicola can infect peaches during any stage of fruit development, and control of the disease must be revised to account for organic peach production systems.     

防治花生腐霉果腐病的化学药剂筛选

花生果腐病是一种重要的土传病害,一旦发生会造成荚果腐烂落果,重病田可致绝收。群结腐霉菌(Py thium myriotylum)是引起花生果腐病最主要的病原菌。为寻找防治花生果腐病的有效药剂,本研究对6种化学药剂进行室内筛选,实验结果表明,96.8%的咯菌腈对引起花生果腐病的群结腐霉有较好的抑菌效果,EC50为3.16×10-5 mg/L,较低浓度的药剂就可以达到很好的抑制效果。盆栽接种后,用6种杀菌剂进行灌根,待荚果成熟后对病害发病情况进行调查统计,结果表明96.8%咯菌腈是防治花生果腐病最有应用潜力的药剂品种。     

Effect of different soil tillage and organic fertilizers on winter triticale and spring barley stem base diseases

Multi-factor crop management field experiments were conducted in Vezaiciai, in southwestern Lithuania, from 2004 to 2006 to assess the influence of tillage and organic fertilizer management on stem base disease development. The treatments included 4-year crop rotations of continuous grass, winter triticale, winter oilseed rape and spring barley in combination with three tillage systems (shallow (8–10 cm) non-ploughing tillage, shallow (10–12 cm) tillage and deep (20–25 cm) ploughing). Eyespot prevailed both in winter triticale and spring barley crops. Winter triticale was more susceptible than spring barley. Shallow tillage decreased eyespot incidence and severity relative to deep tillage. Crop residue management exerted a weak but statistically significant effect on the disease development on triticale; in general, slightly higher numbers of affected stems were recorded in triticale plots where the straw from the previous crop had been removed prior to planting. However, complete straw removal from plots significantly decreased eyespot severity in comparison with crop residue or manure management treatments in spring barley. The highest number of affected triticale and barley plants was found in shallow (10–12 cm) tillage plots. The effects of residue management on minimising eyespot severity can be expected only after a delay of a few years.     

Potato late blight control and top desiccation when pesticides are applied with a controlled droplet and a conventional sprayer

Disease development was observed in field plots to which two different fungicides, each at two rates, were applied regularly with either a conventional or a controlled droplet sprayer. The type of fungicide did not affect disease severity, but more disease damage occurred in the controlled droplet sprayer plots than in conventional sprayer plots. Reduced rates of fungicide resulted in higher disease incidence ratings than recommended rates of fungicides by end of the spraying season. Lower marketable tuber yields and greater incidences of late blight tuber rot were related to foliar disease levels, the different sprayer types, and rates of applied fungicide. No significant differences in terms of potato top desiccation efficacy between the two sprayer types were obtained. In addition, total tuber yield and level of vascular discoloration were similar for both the controlled droplet and conventional sprayer.     

Effects of combined application of potassium phosphite and fungicide on stem and sheath disease control,yield, and quality of rice

Phosphite has been shown to suppress some diseases in different plant species but disease control in rice has not been investigated. In 2012/13 and 2013/14 potassium phosphite was sprayed at 1775 g ha⁻¹ and 3550 g ha⁻¹ in field plots of rice in Uruguay to determine if phosphite alone or in combination with label rates of a mixed strobilurin and triazole fungicide could be used to effectively control stem rot and aggregate sheath spot in irrigated rice. Six treatments consisting of different combinations of potassium phosphite alone or with a fungicide and an unsprayed control were assayed in one application at late-boot to early-heading. Phosphite alone in single and double rate slightly reduced severity and incidence of stem rot and produced a small yield increase over the unsprayed control. Fungicide at a 50% label rate with phosphite reduced stem rot severity and incidence to a similar level as the fungicide alone applied at the label rate. Disease severity was reduced by approximately 25% and incidence by 17–20% when compared with untreated control. Yield increase was 5% for both treatments over the unsprayed control. Fungicide combined with phosphite at single and double rates reduced stem rot severity by 40–45% and incidence by 34–38% when compared with untreated control, with yield increased by 10% over the unsprayed control and 5% over plots treated with a fungicide. These results indicate that a single application of potassium phosphite combined with fungicide can be used efficiently to manage of rice stem diseases.     

Field reactions of plum cultivars to the shot-hole disease in southern Italy

The reactions to shot-hole disease (Stigmina carpophila) of nine plum cultivars and seed-propagated myrobalan trees were evaluated during three years in three commercial orchards located at Nova Siri, Matera, Italy. In July 2006, May 2007, June 2007 and June 2008, shot-hole severity and twig defoliation were assessed. Pathogen pressure was higher in 2007 and 2008 than in 2006. In the three years of study, cultivar Golden Plumza was the most susceptible to the shot-hole measured by leaf severity, however it showed variable defoliation percentages in different years. The seed-propagated myrobalan trees were the most resistant, although they showed a slight degree of defoliation in 2007 and 2008. Intermediate reactions to the disease occurred in cultivars Angeleno, Autumn Giant, Fortune, Green Sun, October Sun, Santa Rosa, Sorriso di Primavera and T.C. Sun. A significant correlation between shot-hole leaf severity and twig defoliation was detected. To our knowledge, this is the first report on screening for resistance of plum cultivars to shot-hole disease.     

Maize genotype susceptibility to Rhizoctonia solani and its effect on sugar beet crop rotations

Root and crown rot is the major soil-borne fungal disease in sugar beet. In Europe, the disease is mainly caused by the anastomosis group (AG) 2-2IIIB of the basidiomycete Rhizoctonia solani (Kühn). No chemical fungicide to control the disease has been registered in Europe. Therefore, agronomic measures must be optimized to keep the disease severity below an economic damage threshold and to minimize white sugar yield losses. R. solani AG 2-2IIIB infects many other crops besides sugar beet, including maize, where it causes root rot. Sugar beet and maize are frequently grown in the same crop rotation. The proportion of cultivated maize in several European sugar beet growing areas is expected to rise due to a projected increase in demand for renewable resources over the next few years. Although the susceptibility to and tolerance of the disease varies among cultivars in both crops, little is known about the effects of cultivar susceptibility in the pre-crop on a subsequent susceptible crop. The cultivation of R. solani-resistant maize genotypes in rotation with resistant sugar beet might therefore be a useful tool in an integrated control strategy against R. solani, eliminating the need to restrict the desired crop rotation for phytosanitary reasons. A crop rotation experiment with artificially inoculated R. solani was conducted in the field to investigate the pre-crop effects of maize cultivars which differed in their susceptibility to R. solani on a susceptible sugar beet cultivar. We hypothesized that the maize genotype would influence the inoculum potential and performance of a susceptible sugar beet genotype grown after a maize pre-crop, and that this would correlate with the susceptibility of the maize genotype. The results demonstrate that the susceptibility of maize genotypes is consistent over a period of years and that cultivated maize genotypes influenced the inoculum potential measured as disease severity in sugar beet. However, disease severity in sugar beet did not correlate with the disease susceptibility of the genotype of the maize pre-crop. Possible reasons for this missing relationship might be differences in the quality of maize residues for the saprophytic survival of the pathogen or a genotype-specific alteration of the antagonistic microbial community. However, our findings showed that in the presence of maize- and sugar beet-pathogenic R. solani, the most favourable maize cultivar for a crop rotation cannot be determined solely on the basis of its resistance level against Rhizoctonia root rot.     

Evaluation of in-furrow fungicide treatments to control rhizoctonia root rot of wheat

The efficacy of eight fungicides, placed in-furrow at sowing, to reduce rhizoctonia root rot and increase yields of wheat was examined in glasshouse and field experiments. Under glasshouse conditions three of the fungicides, coated on clay granules at a rate equivalent to 400 g a.i. ha⁻¹, reduced root rot of wheat grown in soil inoculated with Rhizoctonia solani. None of the chemicals stimulated growth of wheat in the absence of disease, but three retarded growth. Experiments at six sites with different soil types and rhizoctonia risk in north-west Victoria, Australia, showed that the fungicide-coated granules were generally ineffective at reducing both incidence and severity of rhizoctonia root rot of wheat. However, tebuconazole was effective at two sites and at one of these flutriafol, RH-7592, cyproconazole and diniconazole also reduced disease severity. Yields were increased by 51% with tebuconazole at one site, by 40% with diniconazole at another and by between 23 and 30% with RH-7592, diniconazole, flutriafol and flutolanil, at a third site.     

Fusarium proliferatum and Fusarium tricinctum as causal agents of pink rot of onion bulbs and the effect of soil solarization combined with compost amendment in controlling their infections in field

Laboratory tests and field trials were conducted in 2010 and 2011 in Salerno province, Southern Italy, to determine the causal agent(s) of pink rot of roots and bulbs of onion and the effects of soil solarization combined with municipal food waste compost amendment in reducing their infections on bulbs of onion. Three fungi were mainly isolated: Fusarium proliferatum and Fusarium tricinctum on bulbs and roots and Pyrenochaeta terrestris exclusively on roots. P. terrestris produce symptoms on roots, but it was not able to cause damage on unwounded bulbs. F. proliferatum and F. tricinctum were able to induce symptoms when inoculated separately and showed no synergistic effects on severity of symptoms on bulbs. They induced symptoms on roots at a lesser extent. Combined inoculations of P. terrestris with both Fusarium species on roots have not increased symptoms severity of pink rot of onion. This is the first report of F. tricinctum as agent of pink rot of onion bulbs. Two years field trials have been carried out from 2009 to 2011 to evaluate the efficacy of soil solarization, applied alone or in combination with municipal food waste compost amendment, for controlling pink rot of onion bulb caused by F. proliferatum and F. tricinctum. For this purpose, soil solarization, alone and combined with compost amendment, were compared with metham sodium and an untreated control. The results of both trials demonstrated that, in presence of pink rot of onion bulbs, compost amendments, applied after solarization, strongly reduced the efficacy of soil solarization from 68.7% to 16.3% in 2010 and from 76.9% to 4.6% in 2011. Organic amendments applied before soil solarization significantly reduced the efficacy of this technique only in 2011. Significant yield increases were detected at the end of both trials in plots treated with solarization alone, metham sodium and compost applied after solarization. The highest incidence of unmarketable infected plants recorded in plots solarized and then amended with compost was compensated by the increase of bulb size and plant weight. These results demonstrated as the benefits achieved with compost amendments in controlling pink rot of onion are not easily predictable and applicable on large scale.     

河北省小麦冠腐病田间发生消长动态监测

为了明确小麦-玉米连作种植模式下小麦冠腐病的发生危害规律及防治时期,采用田间定点、定期调查的方法,对该病害的田间消长动态进行了监测。结果表明,在2015-2016和2016-2017两个小麦生长季中,3个监测点小麦冠腐病的病株率和病情指数随小麦生育期推移呈上升趋势,春季小麦返青以后冠腐病的发生逐渐加重,拔节-灌浆期小麦冠腐病的发生快速增长。年度间小麦冠腐病的发生程度逐年加重,与2014-2015生长季灌浆期、2015-2016年相比,2016-2017年沧县监测点病株率变化不大,病害的病情指数增长1.0;宁晋监测点病株率增长1.8%~12.2%,病情指数增长0.9~4.3;景县监测点病株率增长21.3%~33.6%,病情指数增长13.5~14.6。在各监测点,随着年度间病害发生程度的加重,引起冠腐病的病原菌镰刀菌的分离频率也随之增加。     

Effects of cultivar resistance and single fungicide application on rice sheath blight, yield, and quality

The increased number of sheath blight (Rhizoctonia solani)-resistant rice (Oryza sativa) cultivars available will allow producers to use less fungicide and avoid significant reductions in grain and milling yields. Among cultivars currently in cultivation in the southern United States, sheath blight resistance levels range from very susceptible to moderately resistant. A study was conducted to determine the response of cultivars, with different levels of susceptibility, to sheath blight inoculations and fungicide application and to determine the impact of sheath blight disease development on rice yield and quality. Sheath blight epidemics in field plots were initiated by inoculation at the panicle differentiation growth stage in 2006 and 2007. Azoxystrobin at 0.17 kg a.i. ha⁻¹ was applied at mid-boot. Inoculation significantly increased sheath blight severity and incidence and caused yield losses of 8% in moderately resistant cv. Jupiter to 40% in very susceptible cv. Trenasse. Milling yields were affected to a lesser extent. Fungicide treatments reduced sheath blight incidence and severity, regardless of cultivar except in Jupiter. Single azoxystrobin applications were effective in minimizing yield loss due to sheath blight in all cultivars.     

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.     

Potato Early Dying and Yield Responses to Compost,Green Manures,Seed Meal and Chemical Treatments

Verticillium dahliae Kleb. is a soilborne fungal pathogen of many crops. In potato, it is the major causal agent of Early Dying. In Manitoba, potato fields planted with cv. Russet Burbank are infested with highly pathogenic V. dahliae isolates, which can produce up to 90 % disease severity. The objective of the study was to evaluate selected compost, green manure, and seed-meal treatments, in comparison with the soil fumigant Vapam, for their ability to reduce propagule density of V. dahliae in soil and decrease disease, and to enhance potato yield. Select green manure crops (oriental and white mustard, Canada milk vetch, sorghum-sudangrass, rye, alfalfa, oat/pea mixture), organic amendments (composted cattle manure and mustard seed-meal), and Vapam, and crop sequences that contribute to the suppression of Verticillium, or the improvement of potato yield were used in a 3-year field study initiated in 2006. Survival in soil of microsclerotia was evaluated as a measure of treatments’ success in potentially reducing Early Dying. Compost and seed-meal treatments, compared to an untreated control, reduced incidence to 30 and 40 %, respectively, but only seed-meal reduced V. dahliae propagule density. Overall, green manures over 1 or 2-years were ineffective in reducing propagule density or improving potato yield. Vapam was partially effective in reducing the propagule density only at the beginning of the potato season, but it did not reduce disease incidence compared to the control. Compost and seed-meal are promising as alternative control of V. dahliae. Only compost reduced disease and increased potato yield, which was associated with improved nutrient availability (phosphorus and sulfate) in soil.     

Effect of Brassicaceae seed meals with different glucosinolate profiles on Rhizoctonia root rot in wheat

The soil-borne pathogen Rhizoctonia solani AG 8 causes major yield losses in wheat (Triticum aestivum. L) production worldwide. Plant tissues of Brassicaceae species contain glucosinolates that are hydrolyzed in the presence of the enzyme myrosinase into products with pesticidal properties. Growth chamber studies were conducted to determine the effect of the Brassicaceae seed meals (SMs) from Brassica juncea, Brassica napus and Sinapis alba on the suppression of the R. solani AG 8 infection of winter wheat. Pasteurized sandy soils were amended with intact and denatured SMs of rape seed and mustard at a rate of 0.5% by soil weight. Regardless of the glucosinolate type and content, all intact and denatured Brassicaceae significantly reduced the infection of winter wheat seedlings by R. solani AG 8 compared to the un-amended control. However, soils amended with S. alba SMs had the lowest severity of Rhizoctonia root rot relative to other amended soils. Phytotoxicity arising from the use of Brassicaceae SMs was observed particularly in soils amended with high glucosinolate-containing SMs. These studies demonstrate that Brassicaceae SMs can be used to manage disease caused by R. solani AG-8. However, future studies will need to focus on strategies for diminishing the crop growth-reducing effects associated with Brassicaceae SM amendment to fully maximize these fungicidal benefits.     

Effects of crop rotation of soybean with corn on severity of sudden death syndrome and population densities of Heterodera glycines in naturally infested soil

Sudden death syndrome, caused by Fusarium virguliforme, and the soybean cyst nematode, Heterodera glycines, combined cause the highest yield losses in soybean. The objective of this study was to determine the effectiveness of corn rotated annually with soybean on reducing severity of sudden death syndrome (SDS) and if such crop rotation is beneficial to soybean root health and thus improves disease management strategies. Experiments were conducted from 2003 to 2006 through two cycles of a corn–soybean rotation on two commercial fields in Indiana. With one exception, the rotation of soybean with corn did not provide yield benefits compared to monoculture of soybean. Severity of foliar and root symptoms of SDS in rotation plots were never less than in soybean monoculture plots. At one location, soybean monoculture resulted in suppression of SDS compared to the corn–soybean rotation, while H. glycines reproduced freely. At the other location, monoculture of soybean resulted in suppressiveness against H. glycines, while SDS was limited in all treatments. The data suggest that soil suppressiveness can independently impact the pathogens that are important in SDS development. Because H. glycines can increase SDS symptoms, its suppression may also reduce severity of SDS. Current production systems consisting of yearly rotation of soybean with corn are highly vulnerable to the development of severe soil-borne disease complexes. The simple year-to-year rotation of corn and soybean is not considered sustainable. While monoculture of soybean resulted in some disease suppression in these trials, reliance on monoculture may be detrimental due to other environmental considerations beyond the scope of these trials. Including other crops may be beneficial in improving the sustainability of soybean and corn production systems.     

Insecticidal control of cereal aphids and its impact on the epidemiology of the barley yellow dwarf luteoviruses

Imidacloprid is a seed-applied nitroguanidine insecticide that has both contact and long-lasting systemic properties. Its direct effects on cereal aphid populations and indirect effects on barley yellow dwarf luteovirus (BYDV) incidence were examined in laboratory and field studies. Adult longevity and fecundity of three aphid species caged on various aged, imidacloprid-treated oat or wheat plants was reduced, although the quantitative efficacy of the compound differed among aphid species. The transmission efficiency of BYDV by aphids to imidacloprid-treated plants was lower, relative to nontreated plants, when plants were 10 days old, but similar to nontreated when plants were 24 days old. In three years of field trials using winter wheat and two years using spring oat, aphid populations were reduced significantly in imidacloprid-treated plots relative to nontreated plots. Although the number of alighting alate aphids did not differ significantly between imidacloprid-treated or nontreated plots, the number of apterous aphids remained significantly lower in the treated plots for the majority of the growing season. BYDV epidemics did not develop in spring oat in either of the two years. BYDV epidemics did develop in the fall in the emerging winter wheat crop. Rhopalosiphum maidis was the predominant aphid migrating into the 1991–1992 crop. The incidence of the BYDV-RMV serotype was three times higher in nontreated plots than in imidacloprid-treated plots. In the 1992–1993 and 1994–1995 seasons, R. maidis and R. padi were the predominant aphids migrating into the crop, although R. padi was the predominant colonizing aphid. The incidence of BYDV-RMV was similar in imidacloprid treated and nontreated plots in 1992–1993, but the incidence of the BYDV-PAV serotype was significantly less in the treated plots. In 1994–1995, the incidence of both BYDV-PAV and BYDV-RMV was higher in the nontreated plots than in the imidacloprid-treated plots. Imidacloprid offers several advantages both in terms of its long-lasting systemic activity and its mode of applicaiton. As a seed treatment, the amount of material applied is minimized, there is little waste and the environmental impacts are reduced. The effectiveness of the compound at reducing the fecundity or reproductive rate of several aphid species may be advantageous in controlling secondary spread of viruses. However, the contact properties of the compound, important in repelling aphids or preventing phloem feeding, may be short-lived, thus reducing its effectiveness in preventing primary spread of the virus into the crop, especially under high aphid and inoculum pressure.     

Biological control of wheat stripe rust by an endophytic Bacillus subtilis strain E1R-j in greenhouse and field trials

Endophytic Bacillus subtilis strain E1R-j, isolated from wheat roots, inhibits a wide range of microorganisms. In this study, we determined its inhibitory effect on urediniospore germination of Puccinia striiformis f. sp. tritici (Pst), the causal agent of wheat stripe rust and biocontrol effect on the rust development using bacterial cell suspension (BCS) and fermentation liquid with and without bacterial cells (FLBC and FL). Urediniospore germination was significantly inhibited by all three formulations in vitro. The maximum inhibition rate was 84.1% treated with the 10-fold dilution of original formulation of FLBC. Microscopic observation revealed that the bacterial treatments caused urediniospores and germ tubes ruptured, which resulted in protoplasm release and dysfunction of fungal structures. Urediniospore germination was also significantly inhibited by spraying E1R-j on leaf surface before inoculation. Formulations FLBC and FL were both better than formulation BCS. In a condition-controlled greenhouse, application of FLBC and FL 24 and 0 h before Pst inoculation displayed a protective mode in reducing disease severity, and the control efficacy was between 54.0% and 87.7%. For formulation BCS, only the application of 24 h before Pst inoculation significantly reduced rust severity with control efficacy 51.8%. The incidence of diseased leaves in the treatments of FLBC and FL were significantly reduced compared to the non-treated plots in the field experiments conducted in the season 2007–2008. The control efficacy was 51% and 43% for the two treatments, respectively. This study is helpful for further developing a biocontrol approach for managing stripe rust.     

Calcium and potassium fertilization of potatoes grown in North Florida. II. Effect on the bacterial soft rot potential in the tubers

In studies on a sandy soil in Florida over a 3-yr period (1984–86), applications of Ca (CaSO₄) inconsistently affected the bacterial soft rot potential of potato tubers (Solanum tuberosum). The potential was estimated from the severity of the disease (percent surface area decayed) in tubers that had been immersed in an aqueous cell suspension ofErwinia carotovora subsp.carotovora and then incubated 4 days in a mist chamber at 24 C. With freshly harvested tubers (tested within 5 days after harvest), disease severity averaged 49, 11, and 4% over all treatments in 1984, 1985, and 1986, respectively, which was roughly proportional to rainfall on the crop,e.g., 37, 18, and 15 cm, respectively. Disease severity decreased, did not change, and increased with increased Ca rate (0, 450, and 900 kg.ha^-1) in 1984, 1985, and 1986, respectively. In each season, severity was affected by interactions involving the Ca treatments. Most interactions involved cultivar. The efficacy of Ca applications to potatoes grown in low Ca soils for enhancement of tuber resistance to bacterial soft rot may be limited by factors associated with environment or cultivar that are not completely understood.