فصلنامه بیماریهای گیاهی
سال پنجاه و هشتم شماره 3 (بهار 1402)

The rice white tip nematode Aphelenchoides besseyi is the causal agent of summer dwarf disease of the strawberry plant, which causes significant crop damage worldwide each year. Considering the environmental hazards of chemical pesticides, identification of resistance sources in different strawberry cultivars and their application could be one of the effective strategies to control this nematode. To this end, a population of A. besseyi was collected from a strawberry field in Kurdistan province and identified based on the morphological characteristics and sequence of D2-D3 expansion segments of 28S rDNA. Then, the responses of 12 commercial and common strawberry cultivars in the province were studied under greenhouse conditions. The results showed that the effects of nematode infestation on most plant growth and reproduction traits and on the final nematode population in the cultivars were significant at the 1% level. Based on the nematode reproduction factor, 12 cultivars were divided into four groups: The cultivar Missionary with a nematode reproduction factor of 9.04, was recognized as a suitable host for A. besseyi and had the greatest impact on growth and reproductive traits compared to the other cultivars. The cultivars Yalova and Chandler with nematode reproduction factors of 6.73 and 7.20, were classified as relatively suitable hosts, while the cultivars Kurdistan, Aromas and Aliso with nematode reproduction factors of 4.27-4.76 were classified as relatively poor hosts. These cultivars were less affected than Missionary in terms of growth and reproductive characteristics. Krasnayy berg, Selva, Queen Elisa, Camarosa, Mrak and Paros cultivars with nematode reproduction...

Citrus yellow vein clearing virus (CYVCV), is the causal agent of a destructive disease that has been spreading in Iran and a number of countries in the region in recent years. To identify susceptible hosts of the disease, the budwoods of the important lime and lemon genotypes of Iran were collected from asymptomatic mother trees. Then the samples were confirmed to be CYVCV-free by biological indexing using the indicator plant. The buds of the genotypes were then propagated on sour orange (Citrus aurantium) rootstocks and the plants were simultaneously graft-inoculated with the Iranian LEN isolate (GenBank accession number: KX902488). The inoculated and control plants were maintained under controlled temperature conditions (24°C during the day and 18°C at night). Persian lime (C. latifolia) and nine lemon (C. limon) varieties were identified as disease-susceptible cultivars among the 21 studied genotypes. To confirm infection in symptomatic inoculated plants, total RNA was extracted from the bark and midrib of new flushes and a two-step RT-PCR was performed. No symptoms were observed in the other genotypes studied until one year after inoculation. Disease severity in susceptible genotypes was graded from 0 to 4 based on the severity of symptoms on the lateral veins and cultivars were divided into three groups according to the intensity of the response. The relationship between ancestral affinity of lemon cultivars and susceptibility to Citrus yellow vein clearing virus was discussed.

Alfalfa is an important agricultural crop and the most important forage crop in Iran, playing a crucial role in providing feed for livestock. Hephomycetous fungi are considered as part of the factors associated with the leaf spot disease of alfalfa. In this study, according to the importance of alfalfa cultivation in West Azerbaijan province, in November 2020, samples of alfalfa plants with leaf spot symptoms were collected from various farms in the southern regions of this province, including Miandoab, Mahabad and Naghadeh. After direct examination and single-spore isolations from the leaf spots, 66 fungal isolates from different fungal genera were obtained. After growing the isolated fungi on standard culture media and primary morphological identification, molecular analysis of representative isolates was performed using the ITS ribosomal region and or parts of the gapdh gene. Based on morphological and molecular characteristics, eight species belonging to five genera of hyphomycetes including Albifimbria verrucaria, Alternaria atra, Alternaria kordkuyana, Alternari sp. (section Alternaria), Cercospora zebrina, Curvularia inaequalis, Stemphylium botryosum and Stemphilium vesicarium were identified. Following pathogenicity test under greenhouse condition, the pathogenicity of Alb. verrucaria, A. kordkuyana, C. zebrina, S. botryosum and S. vesicarium species was confirmed. Among the identified species, A. atra, A. kordkuyana and Cu. inaequalis are first world records on alfalfa.

Characterization of phytoplasmas is primarily based on sequence analysis of their highly conserved 16S rRNA gene sequences. Even minor changes in the sequence of 16S rRNA gene can elucidate long-term evolutionary events along with modification of ecological characteristics within bacterial communities. The presence of any error and anomalies in 16S rRNA gene sequences can confound downstream analyses such as taxonomy and phylogenetic analyses. The most common sequence anomalies in the bacterial 16S rRNA gene sequences are chimera and sequencing errors. This investigation employed bioinformatics tools to examine the presence of such anomalies in the 16S rRNA gene sequence of representative phytoplasma strains from more than 170 subgroups within 40 16Sr groups. The findings suggested that the 16S rRNA gene sequences of eight phytoplasma strains contained anomalies, characteristics of chimeras, or some sorts of sequencing errors. Most of these strains were resolved on atypically elongated branches in the phylogenetic tree. The most notable strains with likely anomalous 16S rRNA gene sequences were reference strains of ‘Ca. P. wodyetiae, ‘Ca. P. allocasuarinae’ and ‘Ca. P. lycopersici’ as well as representative strains of the 16Sr groups XXVI and XXVII. The findings of this study suggest that anomalous 16S rRNA gene sequences are probably not restricted to the eight strains detected by the bioinformatics tools employed in this study.

Diseases caused by Begomovirus species are playing a crucial role in Thai agriculture. Effective disease management requires an understanding of the viruses that associate with weeds as alternative hosts. Sida spp. (Malvaceae) are a prevalent weed in Thailand that has been mostly associated with symptoms similar to viral infections. Globally, there are 38 begomoviruses known to exist from Sida species. Sida cordifolia L. samples that showed yellowing, vein clearing, and upward leaf curling or cupping were collected in Mueang Chiang Mai District. The partial coat protein (CP) gene of DNA-A was amplified using degenerate primers, Deng A and Deng B. Sequences of Sida samples (CM-BM01; OQ459361 and CM-BM02; OQ459362) showed greater similarities with those of the Sida leaf curl virus (SiLCV) isolates (MW465952: SiLCV-[HN] - 97%; AM050731: SiLCV-[Hn60] - 93%; and AM050730: SiLCV-[Hn57] - 93%). CM-BM01 and CM-BM02 clustered with SiLCV isolates and were sister to SiLCV-[HN] in the maximum likelihood phylogeny. SiLCV has been reported in China in association with S. cordifolia. A Sida species with an unidentified begomovirus and a SiLCV associated with Abutilon indicum L. (Malvaceae) have both been found in Thailand. This is the first known report of the SiLCV associated with S. cordifolia from Thailand. The potential of Sida weeds as alternate hosts and the effectiveness of virus transmission to crop plants are currently unresolved. Continued research into the role of weeds as alternative hosts for vector-borne viruses is vital for successful disease management.

Associated betasatellites with begomoviruses and mastreviruses are small single stranded circular DNA molecules ~1.4 kb in size which have been detected in various infected plants and cause enhanced accumulation of helper viruses as well as induction of severe symptoms (Navas-Castillo & Fiallo-Olivé 2021). In previous study, Sesame curly top virus (SeCTV) (genus Turncurtovirus, family Geminiviridae) was detected in infected watermelon plants showing severe leaf curling in Rudbar-e-Jonub farms (Kerman province, southeastern Iran) (Fig. 1a). Whereas, agroinoculation of watermelon plants with constructed infectious clone of SeCTV resulted in somewhat mild symptoms showing dwarfing and mild yellowing of plants (Fig. 1b) in compared with the natural SeCTV infection of watermelon plants (Hasanvand et al. 2021). In order to investigate the causal agent of severe symptoms in watermelon plant, total DNA were extracted from SeCTV infected sample (isolate 1W) followed by enrichment of circular DNA molecules using (RCA). Initially, possible co-infection of sample with other common geminiviruses in the region including beet curly top Iran virus (BCTIV), chickpea chlorotic dwarf virus (CpCDV) and begomoviruses was tested using PCR assay, specific or degenerate (in case of begomoviruses) primer pairs and RCA product as template.