BackgroundPlant-parasitic nematodes developed strategies to invade and colonize their host plants, including expression of immune suppressors to overcome host defenses. Meloidogyne graminicola and M. incognita are root-knot nematode (RKN) species reported to damage rice (Oryza sativa L.) cultivated in upland and irrigated systems. Despite M. incognita wide host range, study of the molecular plant - RKN interaction has been so far limited to a few dicotyledonous model plants. The aim of this study was to investigate if the rice cv. Nipponbare widely used in rice genomic studies could be used as a suitable monocotyledon host plant for studying M. incognita pathogenicity mechanisms. Here we compared the ability of M. graminicola and M. incognita to develop and reproduce in Nipponbare roots. Next, we tested if RKNs modulates rice immunity-related genes expression in galls during infection and express the Mi-crt gene encoding an immune suppressor.ResultsRoot galling, mature females, eggs and newly formed J2s nematodes were obtained for both species in rice cultivated in hydroponic culture system after 4-5 weeks. Meloidogyne graminicola reproduced at higher rates than M. incognita on Nipponbare and the timing of infection was shorter. In contrast, the infection characteristics compared by histological analysis were similar for both nematode species. Giant cells formed from 2 days after infection (DAI) with M. graminicola and from 6 DAI with M. incognita. Real-time PCR (qRT-PCR) data indicated that RKNs are able to suppress transcription of immune regulators genes, such as OsEDS1, OsPAD4 and OsWRKY13 in young galls. Four M. incognita reference genes (Mi-eif-3, Mi-GDP-2, Mi-Y45F10D.4, and Mi-actin) were selected for normalizing nematode gene expression studies in planta and in pre-parasitic J2s. Meloidogyne incognita expressed the immune suppressor calreticulin gene (Mi-crt) in rice roots all along its infection cycle.ConclusionRKNs repress the transcription of key immune regulators in rice, likely in order to lower basal defence in newly-formed galls. The calreticulin Mi-CRT can be one of the immune-modulator effectors secreted by M. incognita in rice root tissues. Together, these data show that rice is a well suited model system to study host- M. incognita molecular interactions in monocotyledons.Electronic supplementary materialThe online version of this article (doi:10.1186/s12284-014-0023-4) contains supplementary material, which is available to authorized users.

Root and rhizospheric soil of diseased black pepper plants from Binh Phuoc Province were collected. Based on morphological characteristics and molecular markers, the presence of Meloidogyne javanica was confirmed. In greenhouse conditions, nematode completed the life cycle in 35 days after inoculation on black pepper (Piper nigrum) cv. Vinh Linh. To our knowledge, this is the first report of M. javanica on black pepper in Vietnam. Keywords Morphology. Pathogenicity. Root-knot nematode Black pepper (Piper nigrum) is a high-value tropical plant in Vietnam. Root-knot nematodes (Meloidogyne spp.) were recorded on black pepper many years ago in the south of Vietnam (Khương 1983). In 2002, a survey conducted from more than four hundred soil and root samples resulted in thirty-five plant-parasitic nematode taxa belonging to 19 genera and 11 families. It is worth noting that all root-knot nematode populations collected on black pepper plants were identified exclusively as M. incognita (Thuy et al. 2012). In recent years, soil-borne diseases and plantparasitic nematodes have caused severe damage in many black pepper growing areas in the Central Highlands (Gia Lai, Dak Nong) and Southeast (Ba Ria-Vung Tau, Đong Nai, and Binh Phuoc). Leaves of diseased vines turn yellowish-green, and the infected leaves gradually fall from the lower to the upper parts of the vine (Fig. 1a). The rhizosphere soil samples and galled roots were collected from slowly declining vines in the Bu Dang and Bu Dop districts, Binh Phuoc Province (Fig. 1b).

In this study, the extracts of Kaempferia rotunda L. were investigated by GC/MS (Gas chromatography/mass spectrometry). There were 25 compounds in tuberous rhizome: alpha-pinene (4.48%), camphene (20.85%), pentadecane (15.47%), camphor (10.15%), alpha terpinolene (1.01%), bornyl acetate (5.65%), alpha-selinene (2.32%), gamma-curcumene (3.22%), heptadecane (3.80%), alpha-cedrene (3.64%), alpha-amorphene (4.92%), alpha-curcumine (2.68%), benzyl-benzoate (7.56%), eucalyptol (1.01%), and some important other compounds. The protocol for in vitro propagation was conducted. The MS medium supplemented with 2 mg/L of Benzyl adenine and 0.2 mg/L of Kinetin gave the highest number of shoots (4.67 shoots/explant). The MS 1/2 medium supplemented with 0.5 mg/L of Naphthalene acetic acid was suitable for plantlet formation (shoot height: 12.05 cm and 14.56 roots/explant). The greenhouse-acclimated in vitro plants reached a 100% survival rate.

This study was conducted to determine some conditions for transformation via Agrobacterium rhizogenes on soybean cultivars HLDN29 and DT84. Cotyledon explants were more efficient in hairy root induction compared with hypocotyl explants in both cultivars of soybean. The highest root induction rate and average root number were observed in HLDN29 explants infected with ATCC11325 and ATCC15834 strains (approx. 96% - 100% and 8 roots per explant) and in DT84 explants infected with ATCC15834. Six to eight day - old cotyledonary leaves after sowing were optimal and appropriate for hairy root induction. Direct inoculation and immersion methods showed no significant difference in root induction rate and average root number in both HLDN29 and DT84 cultivars. Transgenic root lines were identified based on PCR analysis with virD and rolC sequences - specific primers.