No abstract

Among the abiotic stresses, drought is the first environmental stress responsible for a decrease in agricultural production worldwide; it affects plants in various ways, including slowing down plant growth and disrupting its general physiology. Arbuscular mycorrhizal symbiosis and plant growth-promoting rhizobacteria (PGPR) are considered to be the bioameliorators of the plant’s resistance to water stress. The present study investigated the effects of inoculation with arbuscular mycorrhizal fungi (AMF) and PGPR on the water status and antioxidant enzyme activities of date palm seedlings grown under water stress conditions. The parameters related to the plant’s water status were significantly ( p < 0.05 ) higher in the plants treated with mycorrhizae and mycorrhizae + bacteria compared with their respective controls, especially under water stress conditions. The maximum proline content was obtained in plants inoculated with the AMF species and PGPR (combined) under severe water stress conditions reaching a value of 2.588 ± 0.034 in 25% field capacity, compared with 0.978 ± 0.024 for the control. In addition, the inoculated seedlings showed notably lower activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and glutathione S-transferase (GST) in response to severe water stress compared with nonmycorrhizal seedling. Overall, the arbuscular mycorrhizal symbiosis and PGPR bacteria inoculation could be promising methods to enhance date palm resistance against oxidative stress.

In October 2010, a Colletotrichum species was isolated from white Phalaenopsis flowers growing in a greenhouse in San Francisco, CA. This Phalaenopsis is a common commercial orchid hybrid generated mostly likely from Phalaenopsis amabilis and P. aphrodite. The white petals showed anthracnose-like lesions where necrotic tissue is surrounded by a ring of green tissue. The green halo tissues around the necrotic tissue contain functional chloroplasts. One-centimeter disks were cut around the necrotic sites and surface-sterilized with 95% ethanol and 0.6% sodium hypochlorite. The disks were placed on potato dextrose agar (PDA) medium to establish cultures. Pure cultures were obtained by subculturing hyphal tips onto fresh PDA plates. The generated colonies had white aerial mycelia and orange conidial mass. The color of the reverse colony varies between colorless and pale orange. Microscopic observations identified the conidia as cylindrical, straight, and rounded at both ends. In addition, the conidia were approximately 15.0 to 18.0 μm long and 5.0 to 6.5 μm in diameter. These observed morphological features suggested that these isolates possessed the same characteristics as previously described for Colletotrichum karstii, a species considered as part of the C. boninense species complex (1). Four putative independent Colletotrichum isolates were recovered (DED9596, DED9597, DED9598, and DED9599). To confirm the Colletotrichum isolates as the causative pathogen, healthy white Phalaenopsis flowers (five total) in a whole plant were sprayed with a conidial suspension (approximately 1.2 × 106 conidia/ml) of the isolates and incubated at 20°C and 100% relative humidity with cycles of 16 h light and 8 h of darkness. Approximately 1 ml of conidial suspension solution was used for each flower. The plants were watered regularly and flowers were sprayed with sterile double-distilled water daily. As negative controls, five flowers in a whole plant were sprayed with water. Fifteen to twenty days after inoculation, lesions started to form on the petals sprayed with the putative Colletotrichum isolates. All controls remained healthy. The Colletotrichum-inoculated flowers remained alive and did not die as a result of the infection. This same experiment was repeated and the same results were obtained. DNA was extracted from the necrotic regions of the petals infected by the pure cultures of the four isolates and used to sequence the 18S rRNA ITS (internal transcribed spacer) region. All four isolates gave identical ITS sequences. Analysis of the obtained representative sequences (GenBank Accession No. JQ277352) suggested that the isolated pathogen as C. karstii. Using the published ITS data for the C. boninense species complex (1), a phylogenetic tree was generated via the maximum likelihood method. This created tree places the isolates in the same group as C. karstii. This type of C. karstii infection in Phalaenopsis orchid petals was not documented in the U.S. before, although it has been reported in China and Thailand (2). To our knowledge, this is the first report of infection and green island formation caused by C. karstii on orchid flower in the United States. References: (1) Damm et al. Studies in Mycology 73:1, 2012. (2) Yang et al. Cryptogamie Mycologie 32:229, 2011.

Le cyprès de l’Atlas, Cupressus atlantica Gaussen, est endémique stricte de l’ouest du Haut Atlas marocain. Cette espèce joue un rôle écologique et socio-économique très important dans son aire de distribution : pour produire du bois de feu, aider à protéger les sols contre l’érosion, et comme plante médicinale chez les populations locales. Malheureusement, subissant diverses pressions, principalement le surpâturage et les activités humaines excessives, l’espèce souffre d’une détérioration alarmante et de perte de territoire. La variabilité des champignons mycorhiziens arbusculaires et sa réponse à l’inoculation mycorhizienne des plantules sous serre ont été étudiées pour différentes provenances. Douze populations naturelles représentant l’aire de distribution du cyprès de l’Atlas ont été sondées, à Adebdi, Aghbar, Allous, Idni, Ighil, Ighzer, Mzouzit, Rikt, Tiouna, Taghzout, Talat N’os and Taws. L’analyse des variations des champignons mycorhiziens associés aux racines de cyprès de l’Atlas ont révélé la présence d’au moins sept morphotypes appartenant aux genres Rhizophagus, Glomus, Gigaspora et Acaulospora. Le taux de colonisation mycorhizienne dans les racines du cyprès de l’Atlas a été examiné dans son milieu naturel, montrant une variation de 25 % à 45 %. Dans les conditions sous serre, la croissance des plantules, avec ou sans inoculation avec un complexe mycrohizien, a été surveillée pour les plantules provenant des douze lieux échantillonnés. Les résultats montrent qu’en absence des champignons bénéfiques dans le substrat de culture, la croissance et la nutrition des plantules ont été hautement dépendantes de l’origine des graines. En revanche, en présence du champignon dans le substrat de culture, les paramètres de croissance et de nutrition des plantules des douze provenances ne différaient pas de manière significative. Deux groupes principaux ont été identifiés par l’analyse en composantes principales et la classification ascendante hiérarchique basées sur les caractères analysés. Le premier groupe comprend les populations de la vallée de N’Fis, à savoir Allous, Idni, Ighil, Ighzer, Mzouzit, Rikt, Talat N’os et Taws, alors que le second groupe est composé des populations du côté sud, Aghbar, Adebdi, Taghzout et Tiouna.