فصلنامه بیماریهای گیاهی
سال پنجاه و دوم شماره 4 (زمستان 1395)

Root-knot nematodes (Meloidogyne spp.) are the most important plant pathogenic nematodes that reduce yield of economic plants worldwide. Infection by the root-knot nematodes cause gall formation on roots, prevent the normal growth and finally severe reduction in tomato production. In this experiment, effect of two plant species including Prangos ferulacea and Satureja hortensis against M. javanica, were investigated under greenhouse and laboratory conditions. The experiment was laid out in a randomized complete design with four replicates. Under laboratory conditions, combination treatment were used with 1: leaves of Prangos ferulacea and Satureja hortensis and 2: seven concentrations of leaves extract including 0.5, 1, 2, 3, 5, 7 and 9% w/v. Results showed that at 9% w/v, the highest percentage of mortality of second stage larvae (100%) was caused by both extract under. Under greenhouse conditions, five doses of leaf powder including 0.1%, 0.15%, 0.25%, 0.35% and 0.45% were applied. In greenhouse experiment, 0.45% of leaves powder of both plants showed more efficiency than the other doses.

The life cycle of Heterodera avenae type B on the spring wheat cv. Chamran was studied in an infested field in Behbahan District, Khuzestan Province, during 2009-2010. Soil and plant samples were taken from planting to harvest. The results showed that, the penetration of the second stage juveniles happened at temperatures of 15°C and 12°C for 17 and 15 days after the wheat sowing in early December and mid-January during 2009 and 2010, respectively. White females were observed on the roots in the late January and February in first and second year, with soil temperature 12°C to 18°C for 88-90 days after planting respectively. The male were observed in the soil, in early and late of March of the first and second year, with soil temperature ranges 16°C to 17°C, 100-118 days after planting respectively. Changing of white females to brown cysts containing eggs happened in mid-March and early April in the first and second years, at soil temperatures of 20°C to 21°C, 114-126 days after planting respectively. H. avenae type B developed only one generation per growing season and completed its life-cycle within 81-120 in Behbahan District. Total effective degree-days for completing the generation were measured 557 and 446 day degrees in 2009 and 2010 years, respectively.

Root rot and vine decline caused by Monosporascus cannonballus is the most destructive diseases of cucurbitaceous plants in arid and semi-arid regions across the world. Control strategies of this disease in Iran have remained elusive so far, despite its devastating importance. In this study, pathogenicity potential of eight isolates of M. cannonballus was assessed on a susceptible landrace of melon, locally named Zard-e-Garmsar. The most virulent isolate was then used to inoculate 31 landraces and cultivars of cantaloupe and muskmelon in two independent experiments. The reaction of the landraces was assessed through measuring disease incidence, disease severity and the weight of root and shoot. The minimum disease incidence was observed as 62.5, 66.67, 70.84, 79.17 and 79.17 in landraces Ghasri Mashhadi, Biarjmand, Minoo095, Shah Abadi and Zeydary respectively. The minimum disease severity was measured as 27.5%, 29.5%, 31.5%, 32% and 27% in these landraces accordingly. The maximum weight of roots and shoots were measured for these landraces. This study showed that disease incidence and disease severity was occurred in lower amounts in landraces of Ghasri Mashhadi, Zeydary, Biarjmand, Minoo 095 and Shah Abadi in which produced higher amounts of root and shoot tissues among landraces tested. These landraces therefore, can be recommended for field trials.

In summer 2015, cucumber and tomato plants with collaps and decline symptoms were collected from fields in Bajgah and Kaftarak regions in Fars province and transported to the laboratory. After isolation of the causal agent, single spore colonies were derived prior to morphological identification. Colonies on PDA plates were buff or salmon pink; the mycelium was slimy with sparse or absent aerial hyphae. Conidiophores were solitary, unbranched or rarely irregularly branched and the conidiogenous cells could be described as phialidic, hyaline and smooth. Occasionally the conidiogenous cells showed one septa near the base. Conidia were aggregated in slimy heads, hyaline, ellipsoidal, tapering gradually to rounded apex and base, septate or aseptate. These characteristics are typical of Plectosphaerella cucumerina (Lindf.) W. Gams. (anamorph: Plectsporium tabacinum). The internal transcribed spacer (ITS) region of the isolates was amplified using primers ITS1 and ITS4 and sequenced. Blast analysis of the sequences showed identity of the isolates to P. cucumerina. Based on sequence analysis of ITS region, the fungal isolates showed nucleotide variation. Bajgah and Kaftarak isolates were identified as two molecular subgroups. Pathogenicity tests were also conducted on tomato, cucumber, pepper, watermelon and melon plants. 3-4 weeks after inoculation, 70% inoculated plants showed symptoms including wilting, root and collar rot, dwarfing of stem and root and death of seedling. This is the first report of P. cucumerina causing tomato and cucumber collapse in Iran with characterization of the fungus based on morphological, pathogenicity and molecular data.

Viruses inducing yellowing and stunting syndrome in legumes including nanoviruses cause losses in several species particularly broad bean in Iran. One of the most damaging nanoviruses in legumes is Faba bean necrotic yellows virus (FBNYV). To detect nanoviruses in infected fields, symptomatic plants including broad bean and common bean were collected from Fars and Khuzestan provinces, respectively, in 2014-2015. DNA was extracted and subjected to PCR, cloning and sequencing using specific nanovirus primers. Four fragments of a nanovirus genome including DNA-R, DNA-M, DNA-U1 and DNA-U2 were amplified and sequenced. The results of sequencing showed that these fragments belong to Faba bean necrotic stunt virus (FBNSV). This is the first report of this virus in Iran. Sequence comparison of aforementioned genomic fragments with corresponding DNA fragments of FBNSV isolates and other nanoviruses for which nucleotide sequence information was available in GenBank indicated that both Iranian isolates of FBNSV are most similar to Azerbaijani isolates of this virus. Phylogenetic analysis showed that FBNSV is closer to FBNYV and Milk vetch dwarf virus (MDV) than to subterranean clover stunt virus. Dendrograms obtained by phylogenetic analyses of DNA-R and DNA-U2 sequences indicated that FBNSV was closest to FBNYV while in those obtained for DNA-M and DNA-U1, FBNSV was closer to MDV and Faba bean yellow leaf virus than to other nanoviruses. For all DNAs characterized in this study, FBNSV isolates from Azerbaijan, Ethiopia, Morocco and Iran formed a separate group distinct from FBNYV isolates. It seems that FBNSV and FBNYV are distinct nanovirus species.

During 2009-10, wheat fields in eight provinces of Iran including Tehran, Esfahan, Ardabil, Golestan, Mazandaran, Markazi, Qazvin and Zanjan were surveyed and samples were collected from plants showing crown rot disease symptoms. Fusarium species were identified based on morphological features and molecular markers (SCAR). Twelve Fusarium species including F. culmorum, F. pseudograminearum, F. equiseti, F. nygamai, F. proliferatum, F. oxysporum, F. solani, F. pseudonygamai, F. sambucinum, F. acuminatum, F. lateritium and F. verticillioides were identified. F. culmorum was the dominant species and had the highest (32%) frequency, followed by F. pseudograminearum (18%). Genetic diversity of 64 representative isolates of F. culmorum was studied using eight Simple Sequence Repeat (SSR) markers. There was a high level (0.81) of genetic diversity within the total population, where 89% of the variability was distributed within populations and 11% among populations. Number of alleles was between 7 to 22. In addition, there was significant difference among isolates in their aggressiveness. Isolates with a high level of aggressiveness from different geographical areas can be used for screening resistance to F. culmorum.

In field surveys of charcoal disease of Persian oak (CDO) trees caused by Biscogniauxia mediterranea in Iran, the fungal stroma-bearing (apparent infected) oaks have been regarded as infected trees. However, this disease has a latent phase that its ignoring leads to wrong estimations. Therefore, this research was performed to estimate percentage of latently infected oak trees and dieback related to the disease. Oak trees were sampled randomly to isolate fungi from inner bark in two regions of Zagros forests. Also altitude, diameter at breast height (DBH), crown diameter, CDO sign (fungal stroma), dieback severity (DS), severity of leaf loss by insects (SLLI), fire damage (FD), sign of damage by bark beetles (BB) and wood-boring insects (WBI) were recorded during sampling. The isolates of B. mediterranea were identified by characteristics of anamorph and teleomorph states and species specific primers (MED1-MED2). The results reveal that all oak trees have more or less dieback symptoms. Latent infection of causal agent of CDO occures in 12% of sign free oaks equivalent to 10% of all examined oak trees. Approximately, 16.7% of evaluated oaks tress has sign of CDO. On the whole, 26.7% of oaks have latent or apparent infection of B. mediterranea. CDO correlates positively with DS, FD, DBH, SLLI, BB and WBI, and negatively with altitude and crown diameter. The dieback severity of infected oaks with B. mediterranea is more than that of non-infected ones. Moreover, dieback severity of oak trees having apparent infection is more than that with latent infection.

The rapeseed (Brassica napus) is an important oilseed crop throughout the world for oil production. Blackleg disease which caused by Leptosphaeriamaculans is one of the most important disease of rapeseed in Iran. Among pathogenicity groups PG-1 (Leptosphaeria biglobosa) and PG-2, PGT (L. maculans) has been reported on rapeseed from Mazandaran and Golestan provinces of northern Iran (Fernando et al. 2007, Mirabadi et al. 2010). The samples (leaves, stem, flowers and seed) with symptoms of diseases such as discoloration, deformation, wrinkled and presence of pycnidia were collected during 2013-2016 from canola crops in North Iran. In addition, some of the stem debris with stem canker symptoms was examined for the presence and absence of pathogen sexual (perfect) state. Diseased tissues (leaves, stems, flowers and seed) were surface sterilized to obtain pathogen isolates following the procedure described by West et al. (2002) and Chen et al. (2010). Single ascosporic cultures of the fungus were isolated from psedothecia using the method developed by Li et al. (2004). In all 102 isolates when the causal pathogen was isolated from infected tissues, it was identified as L. maculans, by colony morphology/ pigment production on potato dextrose agar (PDA) and potato dextrose broth (PDB) respectively (Boerema et al. 2004), and species specific polymerase chain reaction (PCR) (Liu et al. 2006). The pycnidia of the fungus were black, globose to subglobose in shape, parts of pycnidia have pale pink droplet overflowed from the ostiole and Asci are clavate to cylindrical, bitunicate and 8 spores. Moreover, all isolates were classified as highly virulent using PCR with virulence type specific primers (Kuusk et al. 2002). Thirty-two isolates of L. maculans were used for determining the pathogenicity test using a cotyledon inoculation method. Pathogenicity of the isolates was confirmed by spraying a conidial suspension of the fungus (2×107 conidia mL-1) on cotyledons of Westar, Quinta and Glacier cultivars. All plants were maintained in a growth chamber at 22°C with 16 h light period and relative humidity of 80%. The first review of the plants was performed after 5 days and changes during experimenting plants have been observed after 12 days using the scale of 0–9 developed by Chen & Fernando (2006) which 0 to 3 reaction was considered as resistant (R), 4 to 6 as intermediate (I) and 7 to 9 as susceptible (S) (Fig. 1). Sixteen of isolates were classified as belonging to pathogenicity group PG-4. They were characterized by their ability to sporulate on the three differential hosts (S=7-9). Three isolates were PG-3, they sporulated on Westar and Glacier, and caused brown, non sporulating lesion on Quinta (I=4-6). The remaining isolates belonged to PG-2 and PGT. Moreover, our findings provided evidence that L. maculans (PG-4) is present on oilseed rape seeds in the North Iran. Our results showed that an understanding of possible shift in fungus populations will be of value in developing strategies for successful management of blackleg disease such as longer rotation between canola crops, new resistant cultivars against all PG isolates and strict regulations concerning crop seed trade. In addition, the current study is the first report on the identification of L. maculans (PG-3, PG-4) from oilseed in Northern Iran.