IRANIAN JOURNAL OF PLANT PATHOLOGY
Year:2001 | Volume:37 | Issue:3-4|Papers Count:12

Field experiment was conducted to evaluate the effect of competition of different wild oat densities on wheat cultivars using replacement and additive series designs. Factorial experiment with randomized complete block design was used with 3 replications in research station of college of agriculture, Shiraz University in 1997. The design consisted of wild oat densities (0, 63, 125, 188, 250 plants m-2) and three wheat cultivars with constant density of 250 plants m-2 (CROSS AZADI, NIKNEJAD and DARAB2 with heights of 100-1\5, 95-100 and 75-85 cm, respectively). With increase in density of wild oat, final height of wheat cultivars was reduced, but it was not statistically significant. In all wild oat densities, the difference in height of wild oat and DARAB2 was significant. DARAB2 showed the greatest decrease in tiller number. Number of wild oat tillers in competition with this cultivar was significantly more than other cultivars. Yield and it*s components and also harvest index (HI) were affected by wild oat densities and decreased significantly. At higher densities, number of spikelets in panicle and 1000 seed weight of wild oat in mixture with CROSS AZADI were minimum while these were maximum in mixture with DARAB2. At the highest wild oat density, grain yield in CROSS AZADI, NIKNEJAD and DARAB2 was reduced 66, 73 and 88 percent, respectively.

In the present investigation, the effect of soil depth, moisture and temperature on sclerotium survival and germination of Sclerotinia sclerotionlln and the rate of sunflower infection were studied. Sclerotia needed for experimental purposes were obtained on mixed wheat kernel and carrot pieces. Mature sclerotia were placed0, 2, 5, 8, 11, 14, 16 and 20 cm deep in soil in plastic pots with and or without host plant. It was revealed that sclerotia embedded at lower depth of soil up to 5 cm showed high percent of 0, 2 and 5 cm. Results on the effect of soil moisture indicated that, the most suitable condition required for sclerotium germination was at 24% moisture content of soil. This was achieved by watering of pots every other day. Lower or higher ranges of soil moisture resultedin lower percent germination. Average temperature of soil (5-10cm in depth) during growing season of sunflower in rain-fed area measured above 30°C.Due to low soil moisture and high temperature. Sclerotia are presumed to remained ungerminated in the soil. In order to manage the disease, it is recommended that cultivation of sunflower in West-Azarbaidjan to be established in rainfed areas.

Phenotypic diversity of 54 isolates of Fusarium graminearum, the causal agent of wheat head blight, was studied using pectinase, cellulase, lipase, fatty acid esterase, protease (casein hydrolysis) and gelatinase activities. On the basis of these enzymatic activities, the isolates were differentiated into four categories. Also a new genetic marker for this species was developed using selenate mutagenesis. A mycelial disk of each isolate was transferred onto a minimal medium containing I g sodium selenate and 0.1 g taurine. Cultures were monitored daily for two weeks starting one week after incubation and the selenate resistant mutants were selected. Two classes of mutants A and B, were identified. Isolates of class A had a high germination rate ranging from 61-91% (average 67%), produced fast growing colonies on MM+SeO4 and were resistant to chromate. Class B mutants had a low germination rate <35%), produced restricted slow growing colonies (4-2mm) however, like calss A isolates were resistant to chromate. No mutant belonging to class C and susceptible to chromate was recovered. This is the first report on production of selenate resistant mutants in F. graminearum. Such mutants are potentially useful for genetic analysis in this species.

This investigation was carried out in Switzerland, in two locations, Hausweid with sandy loam soil and Langwiese with clay loam soil. At these two locations an experiment has been in progress since 1987 to study the effects of tillage practices on agricultural crops. The crop rotation has been winter wheat, maize, winter wheat and rape seed. During 1996 when corn was planted, effects of 3 tillage treatments (plow, chizel and no-till) on the activities of AM mycorrhizae at the two locations and with four replications at each location were studied. Root and leaf samples were taken at different dates and degree of root colonization by mycorrhizal fungi and leaf concentration of elements were measured. Maize roots in no-till fields were colonized by AM fungi much earlier in the season and much more during the whole season. Maize leaves in the no-till plots contained higher concentrations of P, Cu and Zn and less Mn as compared with plants in the plowed fields.

Wheat streak mosaic virus (WSMV) caused serious losses in wheat in some regions of Fars province in 2000-2001. Sampling was done to assess WSMV losses in a field in the college of Agriculture, Shiraz University. All plants in each of 10 randomly selected squaremeter plots were pulled and grouped in three categories of severely diseased, stunted and healthy, on the basis of symptoms. Their agronomical characters were measured. There was significant difference in all characters between healthy and infected plants. Difference in height and weight of tillers and number of seeds per spike in healthy and infected plants was significant at 1% level. The difference was significant at 5% level for number of tillers per plant. Yield of each plot, percent of infected plants and tillers, relative (%) weight of infected kernels, yield per plant and tillers and percentage of potential yield were calculated. There are significant difference at 1% level between yield per plant and tillers in healthy and infected plants. Percentage of potential yield is a ratio of yield of an infected plot to healthy one on the basis of one plant. For calculation of yield and percentage of potential yield and regression analysis, sampling was done in the 20 randomly selected square-meter plots. Thousand-kernel weights of two adjacent fields with 43% and 100% infection, had 18.73% and 41.04% weight reduction, respectively .Sieving of kernels showed severe reduction in kernel size due to disease. Up to 98% of healthy seeds, but only ca 13% of infected seeds germinatd.Comparative analysis of infected and healthy plant yields, yield per plant and per tiller and percentage of potential yield, showed that percentage of potential yield is a better representative of yield reduction. Among different characters and variables, percent of infected plants had a higher correlation with the percentage of potential yield. Therefore, the regression equation between percent of infected plants, and the percentage of potential yield was calculated. This equation, y= 101.164-0.755x(r=0.969)had the best fitness for the disease loss assessment. Evaluation and statistical analysis indicated that the virus had serious effect on all agronomical properties and yield components. In addition, seeds from severely infected plants were not suitable for planting.The calculated rate of loss in totally infected field was 74.38% while the field with 43.67% infection had a loss of 31.83%.

Cytology of Tilletia indica, the causal agent of Karnal or partial bunt of wheat, was investigated by light and fluorescent microscopy. Following meiosis and mitosis at teliospore germination, promycelia were observed multinuclate. Promycelia bear a cluster of primary filifom sporidia which initially were single, monokaryotic cells. After abstraction cell division occured, bu t each cell stayed momokaryotic. Primary sporidia were directly germinated to bear somatic mycelia or bear secondry allantoid sporidia on strigmata which both monokaryotic. The promycelial, allantoid sporidial and sporogenous mycelial nuclei were subglobose or ovoid, whereas the nuclei of filiform sporidia and somatic hyphae were consistently elongated. Dikarytic sporogenous mycelia isolated from infected wheat caryopses were formed teliospores on potato dextrose agar amended with 0.1% yeast extract after 15-20 days. During teliospore formation in vitro two nuclei were migrated from sporogenous mycelia to probasidial initials which formed at right angles. The dikaryotic probasidia usually were subtended by Y-shaped septa. The evidences of this study suggested that karyogamy was occured during very early stages of probasidial development because even immature teliospore were monokaryotic. Nuclear condition of teliospore formation were easily observed in cultures, but in vivo the gelatinoid nature of the mycelia in host tissue made this much more difficult.

Mechanical inoculation of the Iranian isolate of Pea enation mosaic virus (PEMV-I) induced local lesions in Chenopodium amaranticolor and C. quiona and systemic vein clearing and mosaic in Lathyrus odoratus, Lens culinaris, Medicago sativa, Melilotus officinalis, Phaseolus vulgaris cv. Bountiful, Pisum sativum, Trifolium alexandrinum, T. repens and Vicia faba. Infected Glycyrrhiza glabra showed no symptoms. Amaranthus retroflexus,Chenopodium album, Glycine max, Phaseolus vulgaris cv. Goli, Top crop, and Kentucky, Pheseolus aureus cv. Gohar and Vigna unguiculata were not susceptible.PEMV-I was purified by methods of lzadpanah and Shepherd (1966) and Mahmood and Peters (1973). In density-gradient centrifugation two bands were distinguished, a weak top (T) and a strong bottom (B) band. Both components contained small polyhedral particles of 28-30 nm diameter as revealed byelecteron microscopy. Virus yield was 35 mg and 12.6 mg per 100g of infected tissue by the methods of Izadpanah and Shepher (1966) and Mahmood and Peters (1973), respectively. Use of Triton X-100 increased the yield.DAS-ELISA with PEMV-I-IgG showed that Trifolium alexandrinum, T. repens, Medicago sativa, Melilotus officinalis and Glycyrrhiza glabra are natural sources of PEMV-I in Bajgah and Trifolium alexandrinumn is a natural host of the virus in Karaj. This is the first report of G. glabra and T. alexandrinum as the hosts of PEMV. In SDS-PAGE and western blot analysis, the molecular weight of the virus structral proteins were estimated at about 56000 and 22000 daItons. A 44000 daiton protein band detected in SDS-PAGE and western blot was probably a dimer of 22000 daiton protein. In agarose gel electerophoresis, values of 1.7x106 and l.4x106 daltons were obtained for RNA-1 and RNA-2, respectively. No satellite RNA was detected.On the basis of biological and serological properties, the Iranian isolate of PEMV is quite similar to the isolates reported elsewhere. Also, it was found that Pisum salivum, Cicer arietinum, Vicia saliva, ViCia faba and Glycine max are natural hosts of PEMV in Fars, Ghazvin, Golestan, Lorestan, Mazandaran and Tehran provinces of Iran.

A leaf spot and blight of sugarbeet (Beta vulgaris L.) of unknown etiology was observed in several sugarbeet production areas of Isfahan since 1993. Circular to irregular necrotic spots or blotches, less than one to several centimeters in diameter appear on leaves. The lesions progress inwards, expand and coalesce, giving the leaves a blighted appearance.A Gram-negative, aerobic, nonmotile, rod-shaped bacterium was consitently isolated from symptomatic leaves. Colonies on sucrose nutrient agar were nonmucoid, yellow, convex and smooth with entire margins. The strains were oxidase negative, nonfluorescent, and hydrolyzed casein, gelatin, esculin, starch and Tween-80. They were negative in tests for production of arginine dihydrolase, urease and lecithinase, reduction of nitrate and production of in,doleand acetoin. Some strains produced H2S from cysteine. Growth of the bacterium was inhibitedby 0.1% triphenyl tetrazolium chloride, 2.5% NaCI and 30% glucose. Fructose, glucose, cellobiose, trehalose, sucrose, maltose, melibiose, xylose, glycerol, starch, dextrin, amygdalin, arbutin, lactate, malate, D- and Lalanine and L- proline were among the carbon sources used for growth. No strain utilized adonitol, dulcitol, inositol, rhamnose or tartrates. Strains produced a xanthomonadin pigment.Pathogenicity of strains was confirmed through wound inoculation of young sugarbeet plants.Based on the biochemical, physiological and nutritional charactristics, the strains isolated from, and proved pathogenic on sugarbeet plants, were identified as Xanthomonas sp. The phenotypic features, electrophoretic profile of cell proteins and the type of symptoms produced by Xanthomonas sp. reported herein, are considerably different from those of Xanthomonas sp. betae (X campestris pv. betae) recorded in Brazil. Therefore, the blight of sugarbeet occurring in Iran, appe.1rs to be a previously unreported disease and the incita"nt bacterium a new species or pathovar of Xanthomonas.

In order to identify the plant parasitic nematodes (Tylenchida) of the rice fields in Guilan province, about 75 soil and root samples were collected from different fields during 1995 and 1996. The samples were washed and the nematodes were extracted by centrifugal suger-floating method. The nematodes were fixed and transfered to glycerin by modified seinhorst method (De Grisse, 1969). Then the permanent slides were prepared from nematodes including cone-top of cysts and some cross sections of some nematodes. The specimens were studied by light microscope.Cysts were also, prepared for scanning electron microscope (SEM) based on HIRSCHMANN and TRIANTAPHYLLOU's method (1979). Ten known plant parasitic nematodes belonging to 8 genera were identified including Aphelenchoides besseyi,A. bicaudatus ,Basiria graminophila, Criconemella paragoodeyi, Filenchus facultativus, F. polyhypnus, Helichotylenchus crenacaudatus, H. digitiformis, Heterodera oryzae and Tylenchorhynchus annulatus. F. polyhypnus, H. digitiformis and H. oryzae are new for nematode fauna of Iran as described in the text. In this study the morphological and morphometrical characters of these three species as well as H. digitifomis are described.

During 1996-2000 an investigation was carried out on the biology and establishment of Paecilomyces lilacinus in sour lemon rhizosphere. Among more than ten substrates used, chopped wheat straw and its enriched form with potato extract and dextrose (PD)were chosen. The survival of the fungus in three media [(sand+enriched wheat straw), (sand+wheat straw) and (sand)] was studied at 15,20,25 and 30°C. The results showed that except for 30°C, P. lilacinus survived for 480 and 280 days in media containing wheat straws and sand respectively. The longest survival time was at 20oC on "sand+wheat straw" medium (P<%1).The saprophytic competitive ability of P. lilacinus using wheat straw inoculum at different ratios mixed with soil from citrus orachard indicated that the fungus at high population can compete with soil microflora. Population changes of P. lilacinus in sour lemon rhizosphere was studied using enriched wheat straw in greenhouse and orchard. It was shown that the fungus was established in sour lemon rhizosphere for over 180 days in greenhouse and 300 days in orchard.