Late wilt, a severe vascular disease of maize caused by the fungus Harpophora maydis, is characterized by relatively rapid wilting of maize plants before tasseling and until shortly before maturity. In Israel, the disease has become a major problem in recent years. The pathogen is currently controlled using cultivars of maize having reduced sensitivity. In an earlier work, we modified a molecular method for use as a diagnostic tool to evaluate disease progression in field-infested plants and showed that several fungicides suppressed H. maydis in vitro. Here, we examine the effect of different fungicides on disease progression in a contaminated maize field in the spring and summer of 2009 and 2010. The field was watered using a drip irrigation line for each row and the fungicides were injected directly into the drip line. One of the four fungicides tested, azoxystrobin, was highly effective compared with the control, inhibited the development of wilt symptoms and recovered cob yield by 100%. Although this is the first success in preventing disease symptoms in infested fields in Israel, the azoxystrobin treatment did not reduce the amounts of pathogen DNA in host tissues or delay its spread. Attempts to reduce concentrations of this fungicide or to apply it by spraying were less effective than the triple full dosage treatment. The presence of the pathogen in the host tissues of the successfully treated plants and its ability to undergo pathogenic variations are increasing the risk of pathogen resistance and the urgent need to develop new ways of controlling late wilt. 相似文献
Antibacterial and antiparasitic agents and a cysteine protease inhibitor (E‐64) were tested against Tetrahymena infection, a serious problem in guppy production worldwide. Chemicals were tested in vitro by a colorimetric assay for Tetrahymena survival. The most effective were niclosamide, albendazole and chloroquine, with 23%, 35% and 60% survival, respectively, following 2‐h exposure to 100 ppm. Longer incubation periods resulted in greater reductions in survival. Niclosamide was further studied in vivo at different dosages, administered orally to Tetrahymena‐infected guppies. Mortality rates were significantly lower in all treatment groups; in trial I, 30% and 33% mortality in 5 and 40 mg kg?1 niclosamide‐fed fish vs. 59% mortality in controls; in trial II, 35%, 13% and 10% in 50, 100 and 200 mg kg?1 niclosamide‐fed fish vs. 64% in controls. The effect of the cysteine protease inhibitor E64 was tested in tissue culture, by measuring histolytic activity of the parasite (Tet‐NI) on a guppy‐fin cell line, based on cell depletion. Tet‐NI feeding activity was significantly reduced following pretreatment with E‐64 relative to non‐treated Tet‐NI. E‐64‐pretreated Tet‐NI was injected i.p. into guppies: recorded mortality rates were significantly lower (35%) than that in non‐treated Tet‐NI (60%), suggesting inhibition of the parasite’s cysteine protease as a possible therapeutic approach. 相似文献
Abnormal development of the swimbladder is described in angelfish, Pterophyllum scalare (Lichtenstein 1823), a popular freshwater ornamental fish widely cultured in a range of strains and varieties.
Non-inflated swimbladders in some individuals became apparent when larvae reached an age of 2 weeks. Affected fish were incapable of maintaining their position in the water body and sank to the tank bottom, resting on their flanks. Swimming bouts involved arduous tail movements in an attempt to maintain their position in the water body. Affected fish had slender trunks and partly folded backward dorsal and ventral fins. Histologically, affected fish had a solid cluster of hypertrophic gas gland cells and a hyperplastic rete mirabile instead of a gas-inflated swimbladder. Although it was not determined whether atmospheric air is obligatory for initial inflation of the swimbladder in larvae of this species, the evidence presented suggests that access to the water surface for this purpose in angelfish may not be obligatory. Dilated swimbladders were observed in 1-day-old larvae that were still attached to the hatching stick or had dropped to the tank bottom, with no contact to the water surface. Larvae that had been collected from the water surface displayed similarly dilated swimbladders.
The possible cause of swimbladder non-inflation in angelfish is presently under investigation. Although the aetiology remains unknown, we found some alterations in gene expression that were associated with swimbladder non-inflation. The underlying factors have yet to be determined, although genomic alterations, environmental conditions or induced mutation, which involves both factors, are suspected as contributory factors. 相似文献
Failure to inflate the swim bladder is regarded a major obstacle in the rearing of many fish species. We present a study of swim bladder non-inflation (SBN) in angelfish, Pterophyllum scalare. A normal developing primordial swim bladder was first discernable at the end of the first day post-hatch (p.h.) as a cluster of epithelial cells with a central lumen, surrounded by presumably mesenchymal cells. Initial inflation occurred on the fourth day p.h. Prior to inflation the swim bladder epithelium consisted of an outer squamous and inner columnar layer. Cells of the inner layer were filled at their basal region with an amorphous material, which disappeared upon inflation. A pneumatic duct was absent, and larvae presented no need to reach the water surface for inflation, suggesting that angelfish are pure physoclists. A model for the role of the amorphous material in normal initial inflation is proposed. Abnormal swim bladders were apparent from the fourth day p.h., and methylene blue (MB) at a concentration of 5 ppm significantly increased the prevalence of SBN. Histologically, abnormal swim bladders in larvae hatched in 5 ppm MB could not be distinguished from those in fish raised under routine conditions (0.5 ppm MB). We suggest that MB may have a teratogenic effect in angelfish. 相似文献
Triploidy as a result of thermal shock exposure of fertilized eggs decreases the growth rate ofOreochromis aureus as compared to their diploid controls, but this is due to the higher female ratio present in triploids (86%) and the lower
growth rate of females. When females and males are considered separately, the growth rate is not significantly different in
diploids and triploids. Since triploidy results in a malfunctioning steroidogenesis in females (mainly testosterone (T) and
17β-estradiol (E2)), but does not affect the growth rate, it is concluded that female gonadal steroids do not influence growth unless in pharmacological
concentrations. These low levels of gonadal steroids are generally accompanied by higher levels of gonadotropin (GtH), but
the difference is not always significant.
Despite their lower growth rate diploid females have higher plasma concentrations of growth hormone (GH) during several months
compared to the triploid females and diploid males. 3,5,3′-triiodo-L-thyronine (T3) levels, however, are comparable between diploid and triploid females (except for 1 month), but higher in diploid males in
4 of the 5 months studied. 11-ketotestosterone (11kT) is always higher in males. These results indicate that the higher growth
rate of males may be related to the high circulating levels of T3 and 11kT. 相似文献
Profiles of plasma growth hormone (GH) in male tilapia hybrid (Oreochromis niloticus x O. aureus) were measured and compared at different times of the year. The profiles did not appear to be repetitive, however, differences in their nature were observed at the different seasons; the most erratic profiles were seen in the height of the reproductive season (July), while the peaks were more subdued in the spring and disappeared in the autumn. Peaks in male fish were more prominent than in the females when measured in July. Perifused pituitary fragments from fish with a high GSI responded to salmon gonadotropin-releasing hormone (sGnRH) analog (10 nM-1 M), while those from fish with a low GSI barely responded to even the highest dose. Exposure of perifused pituitary fragments from sexually-regressed fish to carp growth hormone-releasing hormone (cGHRH; 0.1 M) or sGnRH (I M) stimulated GH release only after injection of the fish with methyl testosterone (MT; 3 injections of 0.4 mg kg 1). The same MT pretreatment did not alter the response to dopamine (DA; 1 or 10 M). GH pituitary content in MT-treated fish was lower than in control fish, which may be explained by the higher circulating GH levels in these fish, but does not account for the increased response to the releasing hormones. Castration abolished the response of cultured pituitary cells to sGnRH (I fM-100 nM) without altering either their basal rate of secretion or circulating GH levels. Addition of steroids to the culture medium (MT or estradiol at 10 nM for 2 days) enabled a GH response to sGnRH stimulation in cells from sexually regressed fish. Pituitary cells which had not been exposed to steroids failed to respond to sGnRH, although their response to forskolin or TPA was similar to that of steroid-exposed cells. It would appear, therefore, that at least one of the effects of the sex steroids on the response to GnRH is exerted proximally to the formation of cAMP, or PKC, presumably at the level of the receptor. An increase in the number of receptors to the GH-releasing hormones, following steroid exposure, would explain also the changing nature of the GH secretory profile in different stages of the reproductive season. 相似文献
Bacterial fruit blotch (BFB) of cucurbits, caused by Acidovorax avenae subsp. citrulli, is a serious threat to the watermelon and melon industries. To date, there are no commercial cultivars of cucurbit crops
resistant to the disease. Here we assessed the level of tolerance to bacterial fruit blotch of various commercial cultivars
as well as breeding and wild lines of melon, using seed-transmission assays and seedling-inoculation experiments. Selected
cultivars were also tested in a greenhouse experiment with mature plants. All tested cultivars/lines were found to be susceptible
to the pathogen, and most of them showed different responses (relative tolerance vs. susceptibility) in the different assays;
however, some consistent trends were found: cv. ADIR339 was relatively tolerant in all tested assays, and cv. 6407 and wild
lines BLB-B and EAD-B were relatively tolerant in seed-transmission assays. We also provide evidence supporting a strong correlation
between the level of susceptibility of a cultivar/line and the ability of the pathogen to adhere to or penetrate the seed.
To the best of our knowledge, this is the first attempt to assess melon cultivars/lines for bacterial fruit blotch response. 相似文献
The cover image, by Ofir Lidor et al., is based on the Research Article Introduction of a putative biocontrol agent into a range of phytoplasma‐ and liberibacter‐susceptible crop plants, DOI: 10.1002/ps.4775 .
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