Identification of candidate virulence loci in Striga hermonthica, a devastating parasite of African cereal crops

Parasites have evolved suites of proteins, Virulence Factors (VFs), that are delivered into host plants to facilitate colonization. Whilst VFs mediating plant-microbe and plant-nematode interactions have been characterised extensively, less is known about VFs mediating parasitic plant interactions with their hosts. Striga hermonthica is an obligate, root-parasitic plant capable of parasitizing multiple cereal hosts in sub-Saharan Africa, causing devastating losses in yields. An understanding of the molecular nature and allelic variation of VFs in S. hermonthica is essential for breeding durable resistance and delaying the evolution of parasite virulence. To address this issue, we assembled a genome for Striga hermonthica and identified candidate VFs by combining in silico prediction of secreted proteins with pooled sequencing of parasites growing on a susceptible and a strongly resistant rice host. Consistent with predictions for parasites, like S. hermonthica, that can interact with multiple hosts, we identified multiple loci, potentially with a wide range of functions, implicated in overcoming host resistance. Extremely different allele frequencies were observed at 152 non-secreted and 38 putatively secreted VFs between S. hermonthica parasitising the resistant and susceptible rice varieties. Our candidate, secreted VFs encompassed functions such as host cell wall modification, protease inhibitors, oxidoreductase and kinase activities, as well as several with unknown functions. Consistent with maintenance of variation at virulence loci by balancing selection the candidate loci had significantly higher Tajima’s D on average than the genomic background. Our results show that diverse strategies are used by S. hermonthica to overcome different layers of host resistance. Understanding the maintenance of variation at virulence loci by balancing selection will be critical to managing the evolution of virulence as a part of a sustainable control strategy.

Aphyllon ludovicianum (Orobanchaceae), newly reported in coastal Alabama and Florida, U.S.A.

We describe the first records of the parasitic plant Aphyllon ludovicianum in Alabama and Florida, a range extension and disjunction of over 400 miles eastward and over 500 miles southward. A key to the two species of Aphyllon in Alabama and Florida is included.

Genetic Diversity of Orobanche cumana Populations in Serbia

In this study, we report genetic characterization of Orobanche cumana, the causal agent of sunflower wilting in Serbia. The genetic diversity of this parasitic plant in Serbia was not studied before. Random amplified polymorphic DNA (RAPD) markers and partial rbcL gene sequences analysis were used to characterize the O. cumana populations at the molecular level. While phylogenetic analyses of RAPD-PCR amplicons were performed using unweighted pair-group Method analyses, rbcL gene sequences were analyzed using neigbor joining method and minimum spanning tree. Molecular analyses of RAPD-PCR analysis revealed high genetic diversity of O. cumana populations which indicated high adaptive potential of this parasitic weed in Serbia. Further analyses of rbcL gene using minimum spanning tree revealed clear differences among diverse sections of Orobanche genus. Although this molecular marker lacked the resolution to display intrapopulation diversity it could be a useful tool for understanding the evolution of this parasitic plant. Our results suggested that O. cumana has great genetic potential which can lead to differentiation of more virulent races which is important for determining crop breeding strategies for their control.

Comparative study of some physicochemical and biological properties of effect host species variation on the relationship Saharan parasitic plant Cistanche violaceae (Desf.) Beck.

This work aims to study the effect of different host species on physicochemical and biological properties of the Saharan parasitic plant Cistanche violacea that grows parasitized on two hosts Haloxylon articulatum and a Limonistrum guyonianum in the eastern desert of Algeria. The physicochemical characteristics of C. violcea showed an affinity for the results of both ash and pH and it showed a difference in the amount content of carbohydrates and the value of electrical conductivity. For the content of polyphenols, flavonoids, anthocyanins and tannins the highest values were recorded in C. violcea, which was parasitized on H. articulatum. While, the results of HPLC have identified nine compounds in the crude extracts of the parasitic plants and their hosts in different concentrations. In antioxidant activity, the tannin and anthocyanin extracts from C. violcea parasitized on H. articulatum showed better inhibition of DPPH• radical and best the total antioxidant capacity respectively, but the tannins extract of C. violcea parasitized on L. guyonianum given best reducing power capacity. In SPF assay by UV-Vis spectrophotometry method, all extracts of the parasitic plants showed mild to moderate sun protection. Statically the host variation did not show any significant differences in the physicochemical analysis and the quantitative and qualitative total content of polyphenols. While the significant differences appeared through the antioxidant activity tests, especially between C. violcea and its host H. articulatum, between C. violacea and its host H. articulatum and between the two samples of parasitic plants.

Effets de Dix (10) Variétés de Sésame (Sesamum indicum (L.)) en Association avec Le Niébé (Vigna unguiculata (L.) Walp) dans la Lutte Contre Striga Gesnerioïdes (Willd.) Vatke. au Niger

Striga gesnerioïdes est une plante parasite qui cause des dégâts importants sur le niébé et les méthodes de lutte testées restent insatisfaisantes. L’étude vise à mettre au point, une référence de technique d’association sésame-niébé pour contribuer à lutter efficacement contre Striga gesnerioïdes. À cet effet, un dispositif en Split-Plot est utilisé sur un terrain naturellement infesté par Striga gesnerioïdes. Trois comptages à des périodes différentes (42, 56 et 70 jours après semis) du nombre de plants de Striga gesnerioïdes émergés par poquet de niébé ont été réalisés. Ainsi, en association dans le même poquet (sésame + niébé), les variétés de sésame EF 146, HC 110, ICN 130, HB 168, Vgr 156 et EF 147 sont efficaces pour atténuer l’émergence de striga. En alternance de poquets (niébé et sésame), les variétés de sésame EF 146, HC 110, ICN 137, EF 147 et 38-1-7 sont efficaces contre striga. Et les variétés de sésame EF 146, Vgr 156, HC 108 et 38-1-7 ont montré leurs efficacités en alternance de lignes avec le niébé. EF 146 est la seule variété de sésame efficace dans toutes les trois mesures de protections. Ces résultats pourraient être vulgarisés au niveau des producteurs de niébé pour booster sa production au niveau national, voir mondial. Striga gesnerioïdes is a parasitic plant that causes significant damage to cowpea and the control methods tested remain unsatisfactory. The study aims to develop a technical reference of sesame-cowpea association to contribute to the effective control of Striga gesnerioïdes. For this purpose, a Split-Plot device is used on land naturally infested by Striga gesnerioïdes. Three counts at different periods (42, 56 and 70 days) of the number of emerged Striga gesnerioïdes plants per cowpea were made. Thus, in combination in the same plot (sesame + cowpea), the sesame varieties EF 146,HC 110, ICN 130, HB 168, Vgr 156 and EF 147 are effective in mitigating Striga emergence. In alternating rows (cowpea and sesame), the sesame varieties EF 146, HC 110, ICN 137, EF 147 and 38-1-7 were effective against striga. And the sesame varieties EF 146, Vgr 156, HC 108 and 38-1-7 showed their efficacy in alternating rows with cowpea. EF 146 is the only sesame variety that is effective in all three protective measures. These results could be disseminated to cowpea producers to boost its production at the national and even global level.

A parasitic insect on a parasitic plant: a new species of the genus Formicoccus Takahashi (Hemiptera, Coccomorpha, Pseudococcidae) from Ishigaki Island, Japan

A new species of the genus Formicoccus Takahashi (Hemiptera, Coccomorpha, Pseudococcidae) collected from the holoparasitic plant Balanophora fungosa J. R. & G. Forst (Balanophoraceae), on Ishigaki Island, Japan, is described as Formicoccus yoshinoi Tanaka, sp. nov. based on the morphology of adult females. This species is similar to F. formicarius (1900) and F. erythrinae Williams, 2004, but differs from them by having fewer than six cerarii, and only one type of ventral oral collar tubular duct distributed on the medial area of the posterior abdominal segments. Keys to the Oriental species of the genus Formicoccus are provided.