فصلنامه بیماریهای گیاهی
سال چهل و ششم شماره 2 (تابستان 1389)

Plant samples infected with Ditylenchus dipsaci were collected from alfalfa and garlic fields in different regions of Iran. The nematodes were cultured on monoxenic carrot discs to obtain sufficient inocula. The host ranges of three garlic populations were tested on garlic, onion, fababean, common bean, sugar beet, pea and soybean. Alfalfa, Melilotus sp., common bean, clover, onion, garlic and sainfoin (Onobrychis viciaefolia Scop.) were tested with four alfalfa populations of D. dipsaci. The plants were inoculated with 200 D. dipsaci in 10µl of 1% CMC (Carboxymethyl cellulose) suspension, maintained in growth chamber at 20°C ± 2 for 16-hour light and 8-hours dark period, and high humidity was sustained for one week. The plants were harvested after eight weeks (some after four weeks) and the above ground parts were examined. The results indicated that onion and garlic were suitable hosts, pea and sugar beet and common bean (in two populations) poor hosts but Soybean was not a host for garlic populations. The alfalfa populations multiplied on common bean, alfalfa and mostly Melilotus sp. thus were suitable hosts while clover was a weak host and sainfoin and garlic were non host for alfalfa populations. We demonstrated the existence of at least two races of D. dipsaci in Iran, and proved that garlic race is a seed-borne pathogen on onion and the mature individuals and fourth stage juveniles were observed inside inflorescence and seeds of the tested onion plants. In the present study it was revealed that D. dipsaci is widespread in garlic and alfalfa growing regions and could be involved in crop losses.

order to identify the Aphelenchina species nematodes of crop plants, 250 soil samples were collected from different fields in Jiroft and Kahnoj regions, Kerman province. The nematodes were extracted from soil by centrifugal flotation technique. The extracted nematodes were transferred to glycerin. The permanent slides were mounted. The nematodes were identified by morphological and morphometrical characters. In this study nine species of three genera Aphelenchoides, Aphelenchus and Paraphelenchus from suborder Aphelenchina were identified viz, Aphelenchoides. astrecaudatus, A. curiolis, A. limberi, A. obtosicaudatus, A. parabicaudatus, A. sacchari, A. spicomucronatus, Aphelenchus avenae and Paraphelenchus. amblyurus. Among these species Aphelenchoides curiolis, A. obtusicaudatus and Paraphelenchus amblyurus is reported from Iran for the first time.

Almond witche's broom (AlmWB) is an economically important disease in Iran and Lebanon. It is caused by Candidatus Phytoplasma phoenicium, a pigeon pea related (16SrIX) phytoplasma. Graft inoculation was used to study the reaction of stone fruit cultivars to AlmWB phytoplasma. Two years after inoculation, apricot (cultivars Asefi and Talkh), nectarine (cultivar Red), peach (cultivars Zaferani, Elberta and Shaftalou), plum (cultivars Santa Roza and Shiro), prune (cultivars Sadi and Barghan) and sour cherry (cultivar Schattenmorele) showed little leaf, internode shortening, leaf rolling, yellowing, witche's broom and stunting. Incubation period in plants varied from five months in nectarine and peach to nine months in apricot. Growth expression of infected scions on stone fruit cultivars showed direct relationship with disease severity and inverse relationship with incubation period. Nested-PCR using P1/P7 followed by R16F2n/R16R2 primer pairs confirmed phytoplasmal infection of all symptomatic cultivars. Nested-PCR also showed that Meshki cultivar of sweet cherry and Holandi cultivar of prune (asymptomatic cultivars) were infected with AlmWB phytoplasma. Restriction fragment length polymorphism analysis of nested-PCR product (1.2 kbp) using AluI, HinfI and RsaI enzymes showed that phytoplasmas detected in almond and other stone fruits are identical. This is the first report of apricot, cherry, sweet cherry, Shaftalou, plum and prune as experimental hosts of Ca. Phytoplasma phoenicium in Iran. Transmission of this phytoplasma to peach and nectarine was previously reported.

Viral diseases are among the most economically important diseases of wheat in Chahar Mahal Va Bakhtiari province and cause yield losses of up to 100% in early planting fields. The following viruses were identified in the area using DAS- ELISA or TAS- ELISA: barley yellow dwarf (BYDV- PAV and BYDV- MAV), cereal yellow dwarf (CYDV- RPV), wheat dwarf (WDV), wheat streak mosaic (WSMV), maize Iranian mosaic (MIMV) and barley yellow striate mosaic (BYSMV). About 64% of symptomatic samples were infected with one or more of these viruses. BYDVs (including BYDV-PAV,BYDV-MAV and CYDV-RPV), MIMV, BYSMV and WSMV were detected in 27, 25.5, 21.5 and 20.5 percent of the samples, respectively. Most mixed infections were by BYDV serotypes with WSMV or MIMV. In milder climates MIMV was dominant, while in colder regions WSMV and BYDVs serotypes were more prevalent. Field studies were conducted in Shahrekord, Lordegan and Broujen, in seven growing seasons from 2001 through 2007, to evaluate the effect of planting date, with and without a seed- treatment insecticide (Imidacloprid),on grain yield, yield components and control of viral diseases with natural vectors in winter wheat. The experimental design was a split plot arrangement of a randomized complete block with four replications. In each of the three regions, grain yields of plots planted in the first planting date were reduced significantly by viral infection. Planting dates of 22 October and 6 November resulted in the highest grain yields and yield components in three regions. Grain yield and yield component responses to seed-treatment insecticide, depended on planting dates. In Shahrekord experiment the incidence of viral diseases was higher than other regions. Also in this region seed treatment resulted in significant yield increase of 43% to 236% depending on planting date. The plots of planting date 7 October, 22 October and 1 November with seed-treatment gave the highest grain yield and yield components and reduced viral diseases in Broujen, Shahrekord and Lordegan, respectively. During 2003-2005, 414 advanced lines and cultivars of local and commercial soft wheat were evaluated in view of their resistance level to viral diseases in agricultural research station of Shahrekord. Seeds were planted on 23 September each year under natural infection conditions. We observed symptoms of yellow dwarf disease on all lines and cultivars of wheat. According to the results, 21 advanced lines of wheat were tolerant, the other lines and cultivars of wheat being very susceptible to viral diseases. Severity of yellow dwarf disease was more than other viruses on lines of wheat.

Numerous newly collected and herbarium specimens belonging to the genus Leveillula on Asteraceae were examined using light microscopy. A total of six species including L. guilanensis, L. lactucae-serriolae, L. lactucarum, L. picridis, L. simonianii and L. taurica s.lat. were identified. It was found that, Lactuca spp. in Iran are infected at least with two different Leveillula species (L. lactucae-serriolae and L. lactucarum). Examination of several specimens belonging to L. taurica s.l. from Asteraceae showed that these taxa posses different conidial morphology. However, most of them are not differentiable from already described species. According to conidial morphology, L. taurica on Asteraceous plants can be categorized at least into three morphological groups. Specimens with lanceollate to more or less ellipsoid primary conidia. L. taurica on Carthamus, Crepis, Gundellia, Helianthus, annuus Taraxacum are categorized in this group. Second group includes specimens with more or less ellipsoid to ovoid primary conidia. L. taurica on Anthemis, Circium, Cousinia, Echinops spp. showed this type of conidia. Third group includes specimens with subcylindric primary conidia which are pointed at apex. Lanceolate primary conidia were also present in this group. Specimens on Acroptilon, Artemisia, Centurea, Launaea and Helianthus are categorized in this group. It is mentionable that sunflower (Helianthus annuus) in Iran is infected at least with two morphologically different groups of Leveillula.

The susceptibility of Barley (Hordeum vulgar L.) cultivars were evaluated against an Iranian isolate of Gaeumannomyces graminis var. tritici (Ggt) the causal agent of take-all disease of wheat in a growth chamber using a sterile test tube technique. Seeds of naked, 2, 4 and 6-row barley cultivars were sown in test tubes of sterilized sand preinoculated with Ggt and placed in a naturally lighted growth room at 16±2˚C with a photoperiod of 16 hours light and eight hour darkness. After 4 weeks percentage of root infection, disease index, plant height and weight were assessed. The results indicated that 6-row barley cultivar had the lowest susceptibility rating whereas other barley types were severely or moderately infected. 2 and 4-row barley was moderately infected and no significant differences were found between them. The order rank of susceptibility assessed by other variables such as reduction in plant height and weight compared to control was as follows: naked barley> 2-row barley> 4 - row barley >6- row barley. The moderate susceptibility of some barley cultivars such as Karoon (6-row) to take-all fungus compared with wheat is noteworthy and could provide an alternative crop to wheat where the risk of take-all is high.

From aerial parts of declining shade trees, a fungus was consistantly recoverd and purified and based on morphological features was identified as Nattrassia mangiferae form 1.The pathogen was isolated from 16 species of plants in 16 families. Pathogenicity of 70 isolates of N. mangiferae was confirmed on 10 plant species under natural and greenhouse conditions. Disease symptoms on the detached stems in the laboratory appeared in three different types: canker, dense and thin sooty layers of arthrospores. On fresh detached shoots, although the pathogen produced canker but the progress of the disease was slow with little sporulation. Minimum, optimum and maximum temperatures for growth on potato dextrose agar; were 15-20, 30-35, 35-37° C, respectively. Surveying air spora in Shiraz during summer using vaseline coated microscopic slides and Petri plates contaning PDA supplemented with PCNB (100 mg/l) and Benomyl (100 mg/l) with lid off, yielded few spores of N. mangiferae.