IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2005 | Volume:41 | Issue:1|Papers Count:12

Experiments were carried out to determine the effects of organic and fertilizer amendments on severity of Meloidogyne javanica in cucumber cultivar PS. The treatments were undecomposed farm yard manure (10t/ha) poultry manure (40t/ha), green manure i.e. cabbage leaf waste (40t/ha), compost (40t/ha), and chemical fertilizers including urea (500Kg/ha), ammonium phosphate (500Kg/ha), and potassium sulphate (500Kg/ha) which were used alone and /or in combination with the organic matters. The combination of poultry manure and chemical fertilizers (NPK) resulted in greatest reduction of number of eggs and juveniles in soil and roots of cucumber and also of few other tylenchids viz Tylenchus,Paratylenchus, Psilenchus and Helicotylenchus. Whereas the population of saprophytic nematodes viz aphelenchids, rhabditids, diplogasterids and cephalobids was increased. The growth of cucumber plants was also greatest as compared with the other treatments. The treatments of poultry manure, combinations of farm yard manure, waste cabbage leaf with chemical fertilizers and farm yard manure were the next effective ones in reduction of egg and juvenile numbers of M.javanica respectively. Cabbage leaf waste, compost and the chemical fertilizer treatments were respectively the least effective treatments.  

Downy mildew of sunflower is considered to be one of the important diseases of this crop in Iran. To determine physiological races of the pathogen and its distribution in the country, 253 diseased samples were collected from 100 sunflower growing regions including: Golestan, Mazandaran East and West Azarbaijan, Ardabil, Hamadan, Lorestan, Kordestan, Kermanshah, Central and Tehran Provinces during 1995- 1997. Spore suspension was prepared from sporulating samples and inoculated on a susceptible cultivar (Record) immediately after transferring specimens to the laboratory. However, those specimens lacking sporulation due to unfavorable conditions in the regions were first induced to form spores and then used.One-hundred and one representative isolates from 57 regions of the country were selected for race determination using differential lines obtained from Canada (DM-2, RHA-274, RHA-266, HA-300, RHA-340, PHA-325, DM3) and France (HA-335, HA-25). Three-day old seedlings were inoculated for three hr- with spore suspension (2x 104 spores/ml) using the whole seedling immersion (WSI) inoculation method. The inoculated seedlings were then planted in the pots containing sand-perlite (2: 3 V/V) and transferred to a greenhouse at 20-24 °C. Reaction of the lines was recorded 2 weeks after inoculation on the basis of sporulation and /or lack of sporulation on cotytodon and true leaves. The majority of isolates caused similar reaction on differential lines, indicating the presence of only a single race dominantly exists in most sunflower growing regions of the country. This race is different from previously recorded races of the fungus (Gulya et al. 1998) and is being reported for the first time from Iran. In addition, two more pathotypes, were identified one with a low frequency existing in most affected areas and the other, collected only from three regions. The precise nature of these pathotypes needs further investigation.  

Five isolates of Trichoderma (T. virens DAR 74290, T. harzianum T39, T. harzianum M,T. viride and Trichoderma sp.96) were evaluated for biocontrol of Fusarium wilt of melon (Fusarium oxysprum f.sp melonis). Dual culture and cellophane overlays techniques were used in vitro assay. Colony area was recorded, compared with controls and percentage inhibition of growth was calculated. Greenhouse experiments were performed to test the efficacy of Trichderma isolates for biological control of Fusarium wilt of melon. Colonized wheat bran with Trichoderma and infested wheat grain with pathogen were incorporated to potting mix as a rate of 10 and 14g per Kg respectively. Percentage of plants surviving determined 30 days after planting. Percentage of growth inhibition varied significantly among the antagonist isolate (P<0.01) and ranged from 0 to 100%. Cell free metabolite of T.virens DAR 74290 completely inhibited growth of the pathogen in vitro and appeared to be fungicidal. Percent of plants survival in pots treated with antagonist or healthy control was 100 and those of Trichoderma + pathogen varied from 5.3 to 61.06%. Population (cfu/g) of pathogen was stable and population of Trichoderma slightly decreased during the greenhouse experiments.  

The competitive ability of wheat against rye was evaluated at Agricultural Research Center of Varamin during growing season of 2001 and 2002. The experimental design was randomized complete block with 24 treatments and 4 replications. The competition design was bivariate factorial. The treatments included the pure stands of wheat at densities of 350,450, 550 and 650 plant/m2 and rye at 10, 30, 50 and 60 plant/m2 and mixed stands of the two plants at complete factorial densities. In this experiment, the competitive ability of wheat (CV. Mahdavi) was investigated against rye, using reciprocal yield model. Results indicated that under low precipitation conditions, rye was a stronger competitor compared to wheat. With increase in precipitation, wheat was an equal competitor with rye. At the first year of experiment, biological and economic yields of wheat were mainly affected by inter-specific competition whereas, at the second year of experiment, biological and economic yields of wheat were affected equally by inter and intra-specific competition. Economic yield was more affected compared to biologic yield by rye densities. Evaluation of competitive ability, using regression coefficients showed that the effect of each rye plant on reciprocal grain yield of wheat at first and second years were equivalent to 3 and 1.1 plants of wheat, respectively. In other words, each 0.36 and 0.9 plants of rye had an equivalent effect of one wheat on reciprocal economic yields at first and second years, respectively.    

Leaf tissue extract from Artemisia siebery, A. auchary and A. scoparia were evaluated for their allelopathic effects on seed germination and seedling growth of Amaranthus retroflexus. The experiment was arranged in a completely randomized layout with three replications. The treatments were three species of Artemisia, and nine levels of leaf extracts (0, 6250, 10000, 12500, 20000, 40000, 80000, 125000 and 162500 ppm). Results showed that Amaranthus seed germination, root and shoot length were reduced by Artemisia species extracts. A. auchary had more effect on Amaranthus seed germination. Estimated reduction of Amaranthus seed germination by 80000 ppm extract was 36.1, 86.3 and 82.5 % for A. scoparia, A. auchary and A. siebery, respectively. The maximum inhibitory effects on root and shoot length was observed by A. auchary. The estimated rates of A. auchary extract required for a 50% reduction in Amaranthus root and shoot length were, 19520 and 21960 ppm, respectively.  

The effects of inter cover crops on density and biomass of Sisymbrium officinalis and Fumaria vaillantii were investigated in Varamin Research Experimental Field from 1999 to 2001. The experiment was arranged as a complete randomized block with four treatments (rye monoculture, vetch monoculture, mixture of vetch and rye and without of cover crop) and three replications. Rye monoculture and mixture of rye and vetch had more biomass than vetch monoculture. The light passage by canopy of rye and mixture of rye and vetch was less than vetch monoculture. Live mulch of rye, mixture of rye and vetch and vetch, 120 days after planting reduced Sisymbrium density and biomass. In the first year rye, mixture of rye and vetch and vetch reduced 94, 56 and 89% Sisymbrium density and 94, 38 and 95% Sisymbrium biomass compared to control, respectively. In first year, Fumaria biomass in the rye, vetch and mixture of rye and vetch treatments was 98, 36 and 99% less than control, respectively. We may conclude that, live mulch of rye, vetch and mixture of rye and vetch can reduced competition of weeds with main crops in spring and also reduced seed bank of them in soil.    

Competitive interactions of rice (Oryza sativa L.) and barnyardgrass (Echinochloa Crusgalli) in relation to variation in weed densities ( 10, 20, 30 and 40 plant /m2)were determined in the field under irrigation and four levels of nitrogen application (0, 40, 80, and 120kg/ ha) and two rice plant spacings (20×20, 25×25 cm). The experiment was conducted at the experimental station of the college of agriculture, Shiraz University at Kushkak in 1998.Analysis of variance was conducted for each measured variable for all plantings as a splits plot based on RCBD with three replications. The main factor was four levels of N application, and the sub factor was two rice plant spacings and the sub-sub factor was different weed densities. Results indicated that rice grain yield was decreased as barnyardgrass per unit area increased. Among yield components, the number of panicles per plant and the number of seeds increased significantly. Rice grain yield increased by increasing nitrogen rate, but there was no significant difference between 80 and 120 kg N ha-1 .This means that the efficiency of nitrogen use at 120 kg N ha-1 has diminished. The increase of Echinchloa crus-galli density has reduced the use efficiency of the excess nitrogen in rice. Therefore, increase in N-rate not only cannot diminish the effect of weed competition but also emphasizes the weed competition strength over the crop. In fact the reduction in rice grain yield was more under the influence of weed density as compared to the nitrogen fertilizer.  

In order to compare probability of allelopathic, potential of Berseem and Persian clovers extracts on seedling growth of Amaranthus retroflexus, Convolvulus arvensis,Secale cereale, and Sinapis arvensis, this experiment was conducted. Above ground tissue of the clovers (Berseem and Persian) were collected during flowering and were dried. 5 grs of dried tissue were added to 150ml of distilled water (aqueous extract) or methanol (methanolic extract), and agitated for 12 hrs at room temperature. Three concentrations of aqueous and methanolic extracts were used: full-strength (33.3 g/L), half-strength (16.7 g/L), and quarter-strength (8.3 g/L). The weed seeds were placed in petri dishes that contained the legume extract, or distilled water (control). Seedling growth was measured after two weeks. In general, seedling root growth declined progressively with increasing concentrations of both clover extracts. Amaranth and field bindweed exhibited the greatest and the least decrease seedling growth, respectivcly. The response of hypocotyl, depended on weed species and the kind of extract. Sinapis and field bindweed exhibited the greatest and the least decrease, respectively. Compared with aqueous extract, methanolic extract caused more inhibition in seedling growth. Compared with Persian clover, Berseem clover was a stronger inhibitor of seedling growth. It is thus concluded that the allelochemical contents of the two clovers are not similar. It seemed that field bindweed had probably more tolerance to these allelochemicals.  

In a 1998-2000 survey, witches' broom disease of sugar beet (Beat vulgaris) was found in several fields in Chahgeer region in Abarque (Yazd Province). The associated agent was transmitted from sugar beet to sugar beet, periwinkle and eggplant and from periwinkle to sugar beet via dodder inoculation and from periwinkle to periwinkle and from eggplant to eggplant, ornamental eggplant and tomato by grafting. Polymerase chain reaction (PCR) using universal phytoplasma primer pairs P1/P7 and R16F2 / R16R2 consistently amplified segments of expected size (1.8 and 1.2kb, respectively) when DNA extracts of midrib samples of affected sugar beet plants were used as template. Phylogenetic and putative restriction site analyses and percent similarity values showed that sugar beet witches' broom phytoplasma is closest to yet distinct from members of peanut witches' broom phytoplasma group (16Srll). It is related only distantly to two phytoplasmas reported from sugar beet, i. e., the phytoplasma associated with low sugar disease in France (stolbur group, 16SrXII) and another phytoplasma associated with a similar but distinct disease in Hungary (aster yellows group,16SrI). This is the first report of a 16Srll related phytoplasma group in sugar beet.  

Detection of barley yellow dwarf viruses (BYDVs) and Cereal yellow dwarf virus (CYDV) is very important for disease management. In the present study several serological and molecular methods for rapid detection of these viruses were compared. Among the serological methods that were used in this study, TPIA and cocktail-ELISA had more advantages. TPIA needs few equipments and can be used widely in the field. Cocktail-ELISA was time-saving. Both methods can differentiate and detect serotypes. By RT-PCR with degenerate primers 400 bp and 1200 bp long segments for RPV and PAV, respectively, were amplified. Segments of 700 bp and 800 bp were amplified by using RPV and PAV specific primers, respectively. In this study, regular RT-PCR was unable to detect serotypes in crude saps of the infected plants, while IC-RT-PCR by using polyclonal antibodies of these two serotypes (to trap virus particles) was able to amplify the expected segments. Our findings suggest that TPIA and IC-RT-PCR can be used routinely with high efficiency for BYDVs and CYDV detection.