فصلنامه بیماریهای گیاهی
سال چهل و هشتم شماره 4 (زمستان 1391)

Different clones of Myzus persicae, the main vector of Potato leafroll virus (PLRV), vary in reproductive performance, host-plant adaptation, insecticide resistance and vector efficiency. In this study some important life parameters related to population increase of five major genotypes of Scottish M. persicae, characterized by the ribosomal DNA intergenic spacer fingerprinting technique, denoted type A, B, C, J, and I along with clone 4010 of M. antirrhinii were analyzed. The life parameters measured were average daily offspring production, reproduction time, total offspring production and longevity. These were measured by putting fourth instar nymphs from each genotype on detached leaves of oilseed rape and potato, recording the number of offspring produced by each individual and removing them from the leaves daily until each individual died. The developmental time of the genotypes was also determined by putting one day old offspring of each genotype on detached leaves of the same plants and recording the period from birth to maturity. Significant differences in life parameters of the genotypes were observed. Genotype A was one of the most reproductive genotypes on both hosts and genotype B was so, on potato. It has already been shown that these two genotypes were resistant to insecticides and more efficient vectors of PLRV. Taking these matters into account, it is clear that the existence of such genotypes that are very reproductive, resistant to insecticides and efficient in transmitting PLRV, can potentially increase the spread of the virus if they become established as the predominant genotypes in each area. This in turn, further reinforces the necessity of monitoring M. persicae genotypes with regard to resistance to insecticides, virus transmission efficiency and reproduction capacity in each specific region.

An add-in for MS Excel 2007 was developed to fit discrete distributions to the frequency of disease incidence, weed, insect and nematode in the form of count per sampling unit data. Probability distributions such as binomial, Poisson, negative binomial and beta binomial are discrete distributions, which are respectively appropriate for describing uniform, random and aggregated or clustered binary data such as disease incidence or insect/nematode/weed count per quadrate observations. The fit discrete distribution (FDD) program is a very user-friendly and flexible add-in and can take data in the form of either Table of raw observations or a frequency Table. The program estimates distribution parameters and their standard errors using a maximum likelihood procedure and determine the expected (theoretical) values of the distribution for any distribution from its list. It also calculates both chi-square and log-likelihood ratio goodness of fit statistics to test the null hypothesis of goodness of fit and plot the expected frequencies according to all used distributions against observed values in one single bar graph for comparison purposes. Application of the program in studying spatial pattern of plant pests is discussed.

Sunflower downy mildew is one of the most important and destructive diseases of this crop in West-Azarbaijan. The disease causes epidemic damages and yield losses at favorite environmental conditions for the pathogen activity. Application of disease resistant cultivars is considered as one of the effective control methods. During the growing season of 2009 in West-Azarbaijan, infected sunflower plants were collected and used as a source of Plasmopara halstedii for inoculation of standard differential lines to identify the variation of pathogenicity. The resistance of seven open-pollinating cultivars and two hybrids of sunflower to the dominant race (race 100) of P. halstedii, was evaluated employing the whole seedling immersion (WSI) method in the greenhouse. In this investigation, nine macroscopic disease symptoms including damping-off, sporulation on cotyledons and leaves, sporulation on leaves, stunting, sporulation on cotyledons, mosaic on leaves, deformation of leaves, lesion on hypocotyls and root reduction on the inoculated plants were considered for disease rating and calculating the disease severity index (D.S.I). The experiment was conducted in three replications for each cultivar. The analysis of variance (ANOVA) was performed and the means were compared using Duncan multiple range test (P = 0.05) in SAS ver. 9.1 (SAS institute Inc., Cary, NC.). According to the analysis of variance (ANOVA) for disease severity index, cultivars and hybrids were classified into five significantly different groups (P< 0.05): resistant, moderately resistant, moderately susceptible, susceptible, and highly susceptible. Cultivars Lakumka and Master were in the same group as resistant cultivars, whereas Record was highly susceptible.

Cucumber damping-off is a limiting factor in commercial greenhouse production. To determine the causal agents of disease, sampling and fungal isolation were performed during 2009 and 2011. A total of 23 isolates of Pythium sp. were obtained using selective media. Their pathogenicity was evaluated on cucumber seedlings under greenhouse conditions. All isolates were pathogenic. Morphological and molecular identifications of the isolates were performed. P. aphanidermatum was identified based on microscopic characteristics. The complete sequences of ribosomal DNA internal transcribed spacers regions of selected isolates were determined and submitted to GenBank. The GenBank-BLAST homology search revealed P. aphanidermatum as the most similar sequence (> 99% identity) with GenBank entry AB355599. PCR primers were designed for the identification of P. aphanidermatum in which had a unique ITS sequence. The PCR primer combination Paph54F/ITS2 was species-specific with no cross-reaction to other Pythium species or to soil borne cucumber fungal pathogens tested. The detection limit was as little as 200 fg pure genomic DNA. P. aphanidermatum could be detected in lesions of infected cucumber stem tissue. No signals were obtained from healthy cucumber tissue DNA.

During 2005-2007, soil, leaf and fig fruit samples from fig plantation in Estahban in Fars Province and several samples of dried figs from markets in Shiraz city were collected. Ninety four isolates of Aspergillus species were recovered from soil, leaf and fig fruit samples. Based on cultural characteristic, temperature and morphological criteria the following Aspergillus species with their percentage frequencies were identified: A. alliaceus (3.13), A. carbonarius (7.44) A. flavus (35.1), A. fumigatus (6.38), A. japonicus (4.25), A. niger var niger (39.6), A. ochraceus (2.13), and A. terreus (2.13). A. japonicus and A. ochraceus are as a new report for Iran and Fars province mycoflora respectively. The genetic diversity of a population of A. flavus from various substrates using nit mutants and their aflatoxin production was determined. Seven vegetative compatibility groups (VCGs) were identified among the nit mutants. The in vitro ability of A. flavus isolates in aflatoxin production was assessed using yeast extract sucrose agar medium supplemented with 0.2% methylated --cyclodextrin. There was a relationship between a VCG and the amount of mycotoxin produced by the isolate.

The distribution of Phytophthora parsiana a high-temperature tolerant newly described species was studied in southern Iran and examined its host range in woody perennial plant species in greenhouse condition under high inoculum potential. Among different plant species examined, almonds were highly susceptible by different isolates. From 24 woody plants inoculated, the disease severity in descending orders were: Prunus dulcis, P. armeniaca, Pistacia vera cv. Sarakhs, Prunus dulcis var. fragilis, Carica papaya, Pistacia khinjuk, P. vera cv. Badami, Mangifera indica, P. mutica, Platanus orientalis,, Ficus carica and Juglans regia. The pathogen was detected from soil and infected trees only in pistachio orchard in Rafsanjan in Kerman province and adjacent province Yazd.

Deoxynivalenol (DON) contamination of 227 wheat samples from Golestan, Ardabil, Azarbaijan, and 154 barley samples from Golestan province all located in the north and northwest of Iran produced in 2006 were determined using ELISA method. DON was detected in 44.97 % of the wheat samples collected from Golestan province at levels from 18.53 to 192.81 ng g-1, with the average level of 40.99 ng g-1. Also 78.36 percent of Golestan's barley samples were contaminated to DON with the average level of 57.60 ng g-1 and at levels from 15.19 to 280.6 ng g-1. DON was not found in wheat samples of west Azarbaijan and only one sample from East Azarbaiejan was contaminated in this year, while it was detected in 92.30% of Ardabil's samples at levels from 32 to 316 ng g-1 with the average level of 130.23 ng g-1. DON contamination of wheat and barley produced at north and northwest of Iran in 2006 was much lower than the world regulatory limit for cereals. Thirty five wheat samples collected from Parsabad Moqan area to determine frequency of Fusarium graminearum incidence and natural DON contamination levels in 2011 using HPLC - IAC. Mean of the incidence of F. graminearum was 70. 91% in irrigated system cultivars and DON was detected in 90% of samples ranged from 1.06 to 2.06 µg g-1, at harvest time and 3.08 to 7.49 µg g-1 after storing. DON potential production of 29 F. graminearum isolates obtained from wheat of north and northwest ranged from 17.82 to 2397.33 ng g-1.

Ten grapevine cultivars include of “Yaghuti Siah”, “Askari Zarghan”, “Khalil Bavanat”, “Bidane Ghermez Ghazvin”, “Bidane Sefid Ghazvin”, “Yaghuti Sefid”, “Rish Baba”, “Rotabi”, “Siah Sisakht”, “Siah” and 14 trees include of pistachio, almond, peach, apple, apricot, willow, sycamore, fig, service, elm, acacia, mulberry, ash and pomegranate were evaluated to infection by Neofusicoccum parvum and Diplodia seriata which were isolated from grapevines showing decline symptoms in Iran. Artificial inoculations were made on rooted cuttings of grapevine and trees branches in the greenhouse and field conditions respectively. Data were collected by recording the external symptoms and length of the resulting necrosis 4 months later. Based on the pathogenicity tests on grapevine cultivars both species gave the longest and the smallest lesions on “Yaghuti Siah” and “Siah” cultivars respectively. Based on the pathogenicity tests on the trees in the field, N. parvum and D. seriata gave the least lesions on pomegranate. In this regards N. parvum produced the longest lesions on pistachio while D. seriata caused the longest lesions on apple. Generally, this study indicated that the presence of trunk pathogens such as D. seriata and N. parvum in native vegetation and orchards planted in close proximity to vineyards, as an alternative hosts and potential source of inoculum, may affect the health of the vineyards.