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Herb dodder (Cuscuta spp.) is one of the most important parasitic plants that can severely affect crop yields in the world. So far, interactions of this parasitic plant with hosts were not investigated adequately. Here, we conducted a differential expression analyzes and identified a number of genes that were differentially expressed in haustorium tissue compared with the stem of Cuscuta campestris growing on Alfalfa. We obtained 439 cDNA fragments from haustoria (parasite-host connection zone) and stems (25 cm away from connections zones) using the cDNA-AFLP (Amplified Fragment Length Polymorphism) method with eight different primer combinations. Of 439 transcript-derived fragments (TDFs) that were detected, 145 fragments were identified as differentially expressed genes. Five TDF sequences were similar to known functional genes involved in signal transduction, metabolism, respiration, and stress responses. Genes encoding DEAD-box ATP-dependent RNA helicase, potential heme-binding protein, lysine-specific demethylase 5A were selected for qRT-PCR. The qRT-PCR analyzes confirmed the results obtained using cDNA-AFLP. Our findings shed light on the elicitation of dodder defense responses in the connection zone to overcome plant defense reactions.

In vitro screening techniques were used to evaluate 46 genotypes of Iranian potato collection for resistance to bacterial soft rot caused by Pectobacterium carotovorum subsp. carotovorum (Pcc). One month old in vitro rooted potato plantlets were inoculated by two inoculation techniques under in vitro conditions: 1) sterile toothpicks dipped into bacterial suspension and pressed into the crown of plantlets and 2) the freshly cut crown of plantlets were dipped into bacterial suspension of 108 cfu ∙ ml-1 for 10 min. Typical soft rot disease symptoms, including the percentage of wilted leaves were recorded on inoculated plantlets 3, 6, 9, 12 and 15 days post-inoculation. The potato genotypes which were examined responded differently to Pcc and varying levels of resistance were observed. Potato genotype AG showed the highest level of resistance. Results obtained from in vitro screening were then verified by classical tuber slice assay. The verifications were conducted using five representative cultivars: Milva, Ramus, Picaso, Marfona and Agria which responded similarly to both in vitro and classical evaluation systems. Similar results obtained from these tests indicated that the in vitro screening technique developed in this study could provide a simple and rapid whole plant assay in selecting resistant potato genotypes against bacterial soft rot.

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One of the best strategies to control bacterial wilt caused by Ralstonia solanacearum (Smith) is generally based on breeding resistant cultivars. The information obtained from the expression of plant defense genes will provide new insight for improving plant resistance against pathogens. This study was to identify inducible genes under defense no death (DND) reaction of tobacco (Nicotiana tabacum)-R. solanacearum interaction using cDNA-AFLP technique. In this assay five different primer combinations were used. Out of 1320 Transcript derived fragments (TDF) that were detected, 101 fragments were identified as differentially expressed genes in 0, 24, 48 and 72 hours post inoculation. Most of the differentially expressed genes were obtained 48 hours post inoculation. Following sequencing, most of sequenced TDFs showed homology to known genes interfering in signaling, regulation and defense functions. DND phenotype in tobacco has some similarities specially in signaling process with mechanism associated with induction of the hypersensitive reaction and it is distinct from general defense mechanisms.

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To find the best inoculation method for evaluation of the resistance in potato genotypes against bacterial blackleg caused by Pectobacterium atrosepticum under in vitro conditions, five inoculation methods were compared. In vitro grown explants of five potato genotypes were inoculated with different inoculation methods, then placed on MS solid medium and incubated at 23?C with 70% relative humidity under the light regime of 16 hours a day. After the appearance of symptoms, the efficiency of inoculation methods was then recorded based on the severity of disease symptoms in potato genotypes: Farmosa, Agria, Picaso, Marfona and a wild potato genotype ?Solanum phureja'. Plantlets inoculated by piercing the crown with sterile toothpick inoculated in bacterial suspension of 108 cfu/ml showed the most severe symptoms. Based on all experiments, cultivar Marfona showed higher resistance among all cultivars and, cultivar Agria was the most susceptible. Finally, after witnessing the reactions of different varieties to inoculation methods and comparing them with previous evaluations of resistance in greenhouse conditions, the crown treatment employing sterile toothpick after infection in 108 cfu/ml bacterial suspension was selected and introduced as the best evaluation method of in vitro potato explants against blackleg.