Esmat Mahdikhani Moghadam

Pistachio is one of the most economically important horticultural crops worldwide, and its yield is annually reduced due to damages caused by root-knot nematodes (RKNs). To identify the species of RKNs associated with pistachio trees in Kerman and Khorasan Razavi provinces of Iran, 84 localities were investigated and 37 isolates of the predominant species, Meloidogyne javanica , were identified based on the perineal pattern of females and species-specific primers Fjav and Rjav. Eight isolates (KS1-1, KS1-10, KN7-1, KR3-1, KR8-1, KSh1-1, KhF1-4, and KhF2-1) were further characterized using morphological, morphometric, and molecular data (Small subunit [SSU] rDNA, COII-16S , and NADH dehydrogenase subunit 5 [ Nad5 ] mtDNA sequences). The SSU sequences of these eight isolates showed over 98% identity with several sequences of tropical Meloidogyne species. The COII-16S and Nad5 sequences displayed 99.63 and 100% identity with other available M. javanica sequences, respectively. This study provided, for the first time, comprehensive morphometric, molecular, and geographical distribution data of M. javanica isolates parasitizing pistachio in two main pistachio-producing provinces of Iran. Based on the results of this research, the prevalence of M. javanica in the pistachio orchards of the studied regions was 44.04%, indicating its widespread distribution. Rafsanjan in Kerman province and Mahvelat in Khorasan Razavi province were two highly infested cities based on the present study. Therefore, regular monitoring is essential for effective management of this pest.

Root‐knot nematodes (RKNs) are one of the most serious pests of carrot plants. Resistance cultivars are a cost‐effective and ecofriendly management strategy for nematodes. To develop these, it is essential to understand the genetic, molecular and biochemical aspects underpinning RKN infection. Here, Meloidogyne javanica penetration and development, defence reactions and antioxidant enzyme activity were investigated in a resistant carrot cultivar (TN‐99‐129) compared to the susceptible cultivar TN‐99‐62. No significant difference was found in the number of J2s penetrating the roots of both cultivars. At 2 days post‐inoculation (DPI), necrosis symptoms were observed around the head of penetrated nematodes. Cell death also increased in the roots of the nematode‐infected TN‐99‐129 cultivar. Callose deposition happened at 6 DPI, and lignin content increased with delay (21 DPI) in the inoculated resistant cultivar. In addition, the reactive oxygen species metabolism process in resistant and susceptible cultivars was significantly different. In TN‐99‐129, catalase activity inhibition was observed at the early (2 DPI) phases of infection, and increasing superoxide dismutase activity and a relative decrease in catalase activity during nematode development. The activity of guaiacol peroxidase also increased significantly in the resistant cultivar, but no significant difference was observed in the activity of ascorbate peroxidase. This study explains the process of defence reactions in the TN‐99‐129 carrot cultivar during RKN penetration and development. The exhaustive characterization of the defence mechanism of a novel source of resistance to RKN in carrots constitutes a significant step toward their use in crop breeding.

Root-knot nematodes (RKNs) are the most destructive nematode species in main pistachio cultivation areas of Iran, and adversely affect crop quality and yield. So far, Meloidogyne incognita and M. javanica have been reported infecting pistachio. In this study, four populations of M. arenaria were found infecting pistachio in Kerman and Khorasan Razavi provinces. The morphology and morphometrics of the recovered populations closely match the data given for other populations of the species. Molecular characterization of the recovered populations was performed by sequencing three genomic and mitochondrial regions, including D2-D3 of LSU rDNA, COII-16S and Nad5 mtDNA. The D2-D3 sequences had more than 99% identity with many sequences of tropical species. The COII-16S sequences had more than 99% identity with sequences of M. arenaria, M. morocciensis and M. thailandica. The Nad5 sequences had 99.81% identity with some sequences of M. arenaria. The D2-D3 and COII-16S sequences of M. arenaria did not form independent clades in corresponding Bayesian trees, but Nad5 sequences formed a monophyletic group in corresponding phylogeny. Based on this study, M. arenaria is present in Iran’s pistachio gardens, necessitating appropriate management measures.

Knowledge of the molecular changes in resistant and susceptible cultivars during nematode attack is essential for developing plant resistance. Increased expression of genes related to the synthesis and signaling of salicylic acid, jasmonic acid, and ethylene is known to induce expression of genes related to defense against plant parasitic nematodes. Here, we inoculated approximately 3000 s-stage juveniles (J2s) of Meloidogyne javanica to moderately resistant and highly susceptible tomato cultivars (ALYSTE F-1 and Dutch Mobil, respectively) to compare the developmental disease stages. The roots of each cultivar were collected daily until 30 days after inoculation (DAI). The roots were stained with acid-fuchsin and dissected under a microscope. The results showed that a few parasitic J2s were converted to J3s in the moderately resistant cultivar at 14 DAI, at which time, the highly susceptible cultivar had the highest number of J3s. Comparison of hormonal pathways in the two cultivars revealed that the expression of genes related to the ethylene pathway in ALYSTE F-1 was more strongly upregulated than in Dutch Mobil at 14 DAI. Moreover, the jasmonic acid pathway in the roots of both cultivars decreased at 14 DAI. The expression of genes related to salicylic acid synthesis and signaling was not significantly different between the two cultivars with regard to their non-inoculated controls, respectively, but ALYSTE F-1 in general showed constitutively higher levels of these genes compared to Dutch Mobil at 14 DAI. These results suggest that constitutive and induced expression of genes related to the salicylic acid pathway and ethylene pathway, respectively, delay the development of M. javanica J2s in ALYSTE F-1.

Pistachio yield is annually reduced due to root-knot nematode infections. In order to evaluate its resistance to Meloidogyne javanica, three domestic pistachio rootstocks, namely, Badami, Ghazvini and Sarakhs, and a wild pistachio, Baneh (Pistacia atlantica subsp. mutica), were selected. Their response to the nematode infection was evaluated based on different plant and nematode indexes, 120 days post-inoculation (dpi). The penetration and development rate of nematode in roots of these four pistachio rootstocks were evaluated at different time points by acid fuchsin staining. Based on the measured indexes, Badami, Ghazvini, Sarakhs, and Baneh rootstocks ranked as susceptible, moderately resistant, moderately resistant, and resistant, respectively. The penetration rate of second-stage nematode juveniles (J2) into four rootstocks was discussed. The first “midstage” or swollen juveniles appeared at 4 dpi but to a lesser extent in Ghazvini, Sarakhs, and Baneh cultivars. The first females were seen in Badami at 21 dpi, in Ghazvini and Sarakhs at 35 dpi, and in Baneh at 45 dpi. Three types of defense responses were distinguished and characterized in the examined pistachio rootstocks: (i) a hypersensitive response (HR)-like reaction in the cortex in Ghazvini, Sarakhs, and Baneh root tips at 4 dpi and 6 dpi; (ii) an HR response, degrading J2 which induce giant cells in the vascular cylinder of all rootstocks, at 6 dpi and 10 dpi; and (iii) an HR response, degrading females and giant cells in the vascular cylinder of all rootstocks at 15 dpi onward. These observations open new fields of study in breeding programs of this crop.

Ektaphelenchusberbericusn. sp. was recovered from soil samples collected in eastern Iran and is described and illustrated based on morphological, morphometric and molecular data. The new species is characterised by having female body 512-691 μm long, lip region separated from rest of body by a shallow depression, lips separated and equally sized, 19-22 μm long stylet with wide lumen and lacking knobs or swellings at its base, cuticle with fine, but distinct transverse annuli and three lines in lateral field, excretory pore located at base of metacorpus (with slight variation in position), reproductive system monodelphic-prodelphic with spheroid and fine sperm cells inside spermatheca in some individuals and short post-vulval uterine sac (PUS), rectum and anus vestigial (invisible in few individuals), conical posterior body end (tail), narrowing at mid-point between anus and rounded tail tip, and males lacking. The new species is typologically similar to species belonging to four genera:Devibursaphelenchus,Ektaphelenchoides,EktaphelenchusandSeinura, by a combination of morphological characters,e.g., gross morphology of stylet (lacking knobs or swellings at base), morphology of posterior body end (having short conical tail), PUS length, and having a vestigial anus and rectum in most individuals. In molecular phylogenetic analyses using sequences of the partial small subunit of the ribosomal RNA gene (SSU) and the D2-D3 expansion segments of the large subunit (LSU) ribosomal RNA gene, the new species is close to theEktaphelenchoides/Cryptaphelenchusclade in an inferred SSU tree, and formed a clade withEktaphelenchoidesandDevibursaphelenchusspp. in a D2-D3 LSU tree. Further phylogenetic analyses using full length sequences of the internal transcribed spacer region (ITS) (= ITS1 + 5.8S + ITS2) corroborated results from the SSU and D2-D3 LSU trees, and the multilocus analyses using the combined SSU and LSU data placed the new species in a robustly supported clade withEktaphelenchoides poinariandDevibursaphelenchus lini.