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Soybean rust, Phakopsora pachyrhizi, has been considered a threat to the production of the U.S. soybean, Glycine max. During the past decade, this disease gradually spread to Africa, South America, and recently to the United States. Previous soybean rust risk assessments with an assumption of availability of spores early in a season showed that weather conditions (dew and temperature) during a growing season, in general, are suitable for disease development in U.S. soybean-growing regions. Predicting the time of rust appearance in a field is critical to determining the destructive potential of rusts, including soybean rust. In this study, comparative epidemiology was used to assess likely rust incipient time in four locations within the U.S. Soybean Belt from south to north: Baton Rouge, LA; Charlotte, NC; Indianapolis, IN; and Minneapolis, MN. Temperature effects on the infection cycle of five rusts occurring in the Midwest were evaluated using a general disease model. The likely incipient times were examined with the modeling results. Among the rusts studied, early-appearing rusts had suitable conditions for development earlier in a season. However, a lag period of several weeks to more than 3 months was found from the time when conditions are suitable for a rust to develop or when hosts are available to the time when the rust was detected in fields. Length of the lag period differed among the rust species examined. If nature of long-distance dispersal is not significantly different among the rusts, implications of our study to the expected seasonal soybean rust incipience in fields lead to two possible scenarios: (i) average appearance time of soybean rust across the Soybean Belt should be somewhere between appearance times of common corn rust and southern corn rust, and (ii) with late appearance of the disease, late-planted soybean in the south has greater risk. [ABSTRACT FROM AUTHOR]

The nematicidal activities of ammonium hydroxide, chitin and cottonseed meal applied to soil were enhanced by nitrapyrin, a nitrification inhibitor, in pot experiments. In a field trial, root galling index of tomato plants grown in the soil treated with 250 kg NH[sub 4]OH-N/ha in combination with nitrapyrin was lower than that of tomato plants grown without nitrapyrin 40 days after planting; however, there was no difference between these treatments in tomato yields and root galling indices at the end of the experiment (128 days). Nitrapyrin inhibited the nitrification of the ammonium added to the soil or released from cottonseed meal for up to 28 days, and kept ammonium concentrations and soil pH values higher for longer periods compared with those in soils treated without nitrapyrin. It is suggested that higher ammonia (NH[sub 3]) concentrations due to high soil pH and ammonium concentrations in the soil for longer periods caused the enhancement of nematicidal activities by nitrapyrin. The use of ammonia-releasing compounds in combination with a nitrification inhibitor may make nematode control more feasible by reducing the amount of amendments applied. [ABSTRACT FROM AUTHOR]

The nematicidal activities of ammonia-releasing and ammonium compounds were tested against the root-knot nematode Meloidogyne javanica in pot, microplot and field experiments. Among ten compounds tested, NH[sub 4]OH, (NH[sub 4])[sub 2]HPO[sub 4] and NH[sub 4]HCO[sub 3] showed greatest nematicidal activity at concentrations of 300 mg N/kg of NH[sub 4] or NH[sub 2] in pots. NH[sub 4]OH was found to be the most nematicidal of these compounds. Enclosure of pots containing NH[sub 4]OH-treated soils in plastic bags reduced the concentration of NH[sub 4]OH needed to kill the nematodes from 200 mg N/kg in open pots to only 75 mg N/kg. In a microplot experiment, treatment of nematode-infested soil with NH[sub 4]OH at 70 mg N/kg reduced the root-galling index to 0. In one field experiment, the nematicidal efficacy of NH[sub 4]OH on tomato plants at doses of 1000 and 2000 kg N/ha was equivalent to those of Telopic C35[sup ®] or metham sodium in combination with cadusafos. In another field experiment, NH[sub 4]OH at 500 and 1000 kg N/ha increased tomato yield and at 1000 kg N/ha reduced the galling index, compared with untreated controls. The results suggest that NH[sub 4]OH may serve as a nematicide in alkaline sandy soils. [ABSTRACT FROM AUTHOR]

The effect of Monosporascus cannonballus infection and fruit load on water balance in melon was studied under field conditions in naturally infested soil. Plant water uptake started to decrease shortly before plant wilting and death. Xylem hydraulic conductance of excised infected roots, measured at the onset of wilting, was five to seven times lower than that of healthy plants. An extensive rise in tylose formation was observed in xylem vessels and most vessels were plugged. Plant collapse and death usually occurred during the fruit maturation period. Fruit removal from infected plants prevented wilting, but did not prevent tylose formation and the associated increase in the root resistance to water flow. Continued removal of fruits increased the root plant dry weight ratio in both infected and non-infected plants, 3.5- and 5.8-fold, respectively. Infected plants, showing reversible wilt symptoms and from which fruits were removed, regained leaf turgor and remained alive. Fruit removal caused an immediate and sharp drop in leaf stomatal conductance in both healthy and infected melon plants. The largest reduction was observed after complete fruit removal, compared to plants with one or four to five fruits. Fruit removal also reduced the rate of leaf CO2 assimilation and leaf internal CO2 concentration. Removal of 70–85% of the leaf surface in infected plants did not alter disease progress, relative to control infected plants. The presence of fruits in M. cannonballus -infected plants apparently subjects the plants to progressive water stress till they die. Fruit removal reduced leaf stomatal conductance and increased root growth, thus enabling the plants to survive the constraint to water uptake and translocation imposed by the pathogen, through root destruction, tylose formation and root function. [Copyright &y& Elsevier]

Symptoms typical of a phytoplasma infection were observed on a large number of Limonium hybrids in Israel in October 2000. Phytoplasma infection was confirmed by electron microscopy and polymerase chain reaction analysis. To identify the agent of pathogen spread surveys were made of candidate leafhoppers vectors in Limonium hybrid crops: one known phytoplasma vector (Orosius orientalis (Matsumura)) was present in very large numbers, ≈-10-fold greater than any other species; three other known vectors were present in low to moderate numbers (Circulifer haematoceps complex (Mulsant et Rey), C. tenellus complex (Baker) and Exitianus capicola Stål); individual specimens of other vectors were occasionally found. Field collected specimens of these four species were shown to vector phytoplasma to healthy Limonium hybrid seedlings; this is the first time E. capicola has been shown to be a phytoplasma vector. A laboratory colony of O. orientalis was additionally shown to be able to acquire the phytoplasma from infected Limonium hybrids and subsequently vector it to healthy seedlings. [ABSTRACT FROM AUTHOR]

Sixty-four isolates of Colletotrichum gloeosporioides were isolated from infected Limonium spp. cultivated in 12 different locations in Israel. All isolates were identified as belonging to the C. gloeosporioides complex by species-specific primers. Of these isolates, 46 were resistant to benomyl at 10 μg/ml and 18 were sensitive to this concentration of fungicide. Based on arbitrarily primed polymerase chain reaction of all isolates and internal transcribed spacer-1 sequence analyses of 12 selected isolates, the benomyl-resistant and -sensitive populations belong to two distinct genotypes. Sequence analyses of the β-tubulin genes, TUB1 and TUB2, of five sensitive and five resistant representative isolates of C. gloeosporioides from Limonium spp. revealed that the benomyl-resistant isolates had an alanine substitute instead of a glutamic acid at position 198 in TUB2. All data suggest that the resistant and sensitive genotypes are two independent and separate populations. Because all Limonium plant propagation material is imported from various geographic regions worldwide, and benomyl is not applied to this crop or for the control of Colletotrichum spp. in Israel, it is presumed that plants are bearing quiescent infections from the points of origin prior to arrival. [ABSTRACT FROM AUTHOR]

Black mould, caused by Aspergillus niger, is the main fungal disease affecting date fruits. Symptoms develop inside the fruit, at the inner space between the pulp and the seed. This study focuses on the aetiology of black mould disease in Medjoul fruit. We followed symptom appearance naturally and after artificial A. niger inoculation at different development and maturity stages. Symptoms developed in only a short period during early fruit ripening. However, fruits were commonly colonized at earlier stages of development. Artificial inoculation of flowers and setting fruitlets increased the level of fruit colonization, while fungicide spraying at these stages decreased colonization. Several weeks following flower inoculation by A. niger, mycelium could be detected on degenerating stigmas and carpels as well as between the fruit and the calyx. Following inoculation with an A. niger strain expressing green fluorescent protein (A. nigerGFP), the pathogen was detected on stigmas of setting fruitlets but not within the stigmatic tissue or the transmitting tract of the carpel. The A. nigerGFP strain was detected during fruit development below the base of the large fruitlets and above the calyx surrounding the vascular bundle leading into the fruit. The results suggest that A. niger can infect and colonize flowers and setting fruitlets, grows on the degenerating carpels, and remains latent at a protected site at the base of the fruit until ripening. It then induces the typical black mould symptoms. The significance of these results for developing means to cope with the disease is discussed. [ABSTRACT FROM AUTHOR]

Melon plants grafted on Cucurbita rootstock may suffer from nutritional deficiencies due to reduced absorption and translocation of minerals to the foliage. Melon (Cucumis melo L.) cv. 6023 was grafted onto two interspecific Cucurbita rootstocks (Cucurbita maxima × Cucurbita moschata) 'TZ-148' and 'Gad'. Nongrafted melons were used as controls. Two fertilization field experiments were conducted in walk-in tunnels in the northern Arava valley of southern Israel. Two fertigation regimes were used: 1) standard and 2) enriched for magnesium (Mg; 150 mg·L-1), manganese (Mn; 7.5 mg·L-1), and zinc (Zn; 0.75 mg·L-1) to increase the concentrations of the lacking elements. The enriched fertigation significantly increased Mn, Zn, and Mg contents in the leaf tissue. Concentrations of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), sodium (Na), chloride (Cl), iron (Fe), and boron (B) were unaffected by the enriched fertilizer. There were no deficiency symptoms in grafted plants supplied with the enriched fertilizer. [ABSTRACT FROM AUTHOR]

Gray mold, caused by Botrytis cinerea, severely affects the base of the stems of lisianthus (Eustoma grandiflorum) plants as well as the cut stems left after flowers are harvested. This study examined infection of lisianthus plants by B. cinerea under laboratory and commercial greenhouse production conditions typical for Israel and evaluated cultural methods for manipulating disease development in commercial greenhouses. Although the lower nodes of lisianthus stems are typically infected, in this study, the inherent susceptibility of these nodes was less than that of nodes midway up the stem. Greater light intensity (4,860 lux) was associated with significantly more severe stem wounds than lower light intensities of 140 to 1,020 lux. Lower light intensity (140 lux) was associated with significantly more severe leaf infection. The development of gray mold along leaves toward the stem was slower at 26°C than at 18 to 20°C and was fastest at relative humidity (RH) levels close to saturation (>99%). B. cinerea infection developed in all stem wounds exposed to 65 to 99% RH and at temperatures of 12 to 29°C. Infection severity in stem wounds (measured as lesion length) on whole plants was significantly less at 26°C than at 18 or 22°C, and was significantly higher at 99% RH compared with 70 to 85 and 85 to 95% RH. Severity of gray mold was the greatest at 15 to 22°C and 85 to 99% RH. Under commercial greenhouse conditions, supplemental calcium (Ca(NO3)2) applied in fertigation or as a spray led to moderate yet significant reduction in disease severity. In addition, polyethylene soil cover and the use of buried drip irrigation instead of surface drip irrigation suppressed gray mold significantly on cut stems following harvest. Covering the soil with polyethylene also suppressed gray mold significantly as compared with the common practice of growing lisianthus in bare soil. [ABSTRACT FROM AUTHOR]

• Incompatible graft shows a demarcation line between scion and rootstock. • Incompatible graft shows accumulation of specific metabolites in the scion. • Incompatible graft has lower rootstock content of trans-zeatin type cytokinins. The effect of the rootstock on the acropetal and basipetal transport of photoassimilates and hormones was studied in the 'Kiran' (Ki) melon cultivar grafted onto pumpkin rootstocks with different degrees of compatibility. A complementary experiment was performed to compare the incompatible combination (as evidenced by plant collapse at the fruit ripening stage), designated Ki/r53, with self-grafted r53/r53 as a model compatible combination. Both experiments showed the accumulation of a number of amino acids, sugars, and sugar alcohols in the scion of the incompatible Ki/r53 grafts. Additionally, they showed a marked reduction of trans -zeatin-type cytokinins and an elevated content of cis -zeatin-type cytokinins in the rootstock, and the opposite pattern in the scion, hinting at the possible involvement of a hormonal signal for graft compatibility. There was no direct evidence of a blockage at the graft union, since hormone acropetal and basipetal trafficking was demonstrated for all combinations. Dye uptake experiments did not show xylem flow impairment. A possibly significant finding in the incompatible combination was the deposition of undifferentiated cells in the hollow space that replaces the pith region in melon and pumpkin. The link between the above findings and the collapse of the plants of the incompatible combination remains unclear. [ABSTRACT FROM AUTHOR]