Evaluation of Maize Inbreds for Maize stripe virus and Maize mosaic virus Resistance: Disease Progress in Relation to Time and the Cumulative Number of Planthoppers

ABSTRACT Five tropical maize lines were tested and compared with the susceptible control line B73 for resistance to Maize stripe virus (MStV) and Maize mosaic virus (MMV), both propagatively transmitted by the planthopper Peregrinus maidis (Homoptera: Delphacidae). Resistance to each virus was evaluated separately by artificial inoculations with planthoppers viruliferous for either one virus or the other. Disease incidence and symptom severity progression were quantified in relation to time and the cumulative number of planthoppers. Line Hi40 was found to be susceptible to MStV and highly resistant to MMV. Generally, no MMV symptoms developed on Hi40, even under intense inoculation pressure by a large number of viruliferous planthoppers. Line Rev81 showed a partial but strong resistance to MStV, which mainly reduced disease incidence. Nevertheless, this resistance to MStV was the highest ever reported and held up, even when challenged by large numbers of planthoppers. The percentage of infected plants in line Rev81 never exceeded 30 to 40% in our experiments. Moderate levels of resistance to MStV, and to a lesser extent MMV, were found in lines 37-2, A211, and Mp705. However, resistance in these lines was completely overcome using a large number of insects transmitting either of the two viruses. These results suggest that different types of resistance to MMV and MStV are available in maize lines from Caribbean and Mascarene germ plasm. The expression of virus-specific resistance identified in Hi40 and Rev81 lines was not affected by intense inoculation pressure. In contrast, the moderate resistance in 37-2, A211, and Mp705 was partially effective against both viruses but not at high inoculation pressure. These different types of resistance, when present in the same genotype, could provide protection against both viruses.     

SPINAL SUB ARACHNOID CYSTS IN 13 DOGS

Thirteen dogs, including 6 Rottweiler dogs, exhibiting clinical signs of spinal cord dysfunction and myelographically confirmed subarachnoid space enlargement were investigated. To characterize the lesions and to get a better understanding of their pathogenesis, different imaging techniques were used in association with explorative surgical procedures (12 dogs) and histopathologic techniques (5 dogs). All subjects underwent preoperative myelography, five of which were examined by computed tomography (CT) scanning and one by magnetic resonance imaging (MRI) as well as cerebrospinal fluid (CSF) flow measurement (velocimetry). Most animals were <12 months old (7/13 dogs) and Rottweilers were over-represented (6/13 dogs). The lesions were mainly located dorsally with respect to the spinal cord (10/13 dogs) and in the cranial cervical area (8/13 dogs). MRI suggested spinal cord deviation with signs of ventral leptomeningeal adhesion opposite the enlarged space. In one dog, velocimetry confirmed that the "cyst" was freely communicating with the surrounding CSF space. Surgical investigation confirmed leptomeninges-induced ventral adhesion in 4/5 dogs. Follow-up studies, carried out from 6 months to 2.5 years postoperatively, showed there was full recovery in 8/13 dogs. This study suggests that the compression of the spinal cord is possibly not caused by a cyst. Adhesion resulting from a combination of microtrauma and chronic inflammatory processes induces a secondary enlargement of the subarachnoid space and may be a significant causative factor in spinal cord compression and dysfunction. The over-representation of Rottweilers and the young age of the animals in the study suggest a possible genetic predisposition and an inherited etiology.     

Flowering synchronisation between male and female West African cultivated yams (Dioscorea cayenensis-rotundata complex)

It has long been admitted that male and female cultivars of Dioscorea cayenensis-rotundata complex do not flower at the same period and consequently natural outcrossing rarely occurs. Flowering in thirteen (7 males and 6 females) traditional cultivars were studied. Four main results were obtained: i) the first bud emergence occurred 25 days earlier in males; ii) the male and female first flower opening overlapped for 10 days (85 to 95 days after sprouting); iii) for both sexes, highest frequency of flower opening occurred at mid-day; and iv) the female cultivar 1800 could flower for 8 consecutive days, with a peak between day 4 and day 8. These results are discussed in relation to intercrossing success. This revised version was published online in July 2006 with corrections to the Cover Date.     

Deep Subseafloor Fungi as an Untapped Reservoir of Amphipathic Antimicrobial Compounds

The evolving global threat of antimicrobial resistance requires a deep renewal of the antibiotic arsenal including the isolation and characterization of new drugs. Underexplored marine ecosystems may represent an untapped reservoir of novel bioactive molecules. Deep-sea fungi isolated from a record-depth sediment core of almost 2000 m below the seafloor were investigated for antimicrobial activities. This antimicrobial screening, using 16 microbial targets, revealed 33% of filamentous fungi synthesizing bioactive compounds with activities against pathogenic bacteria and fungi. Interestingly, occurrence of antimicrobial producing isolates was well correlated with the complexity of the habitat (in term of microbial richness), as higher antimicrobial activities were obtained at specific layers of the sediment core. It clearly highlights complex deep-sea habitats as chemical battlefields where synthesis of numerous bioactive compounds appears critical for microbial competition. The six most promising deep subseafloor fungal isolates were selected for the production and extraction of bioactive compounds. Depending on the fungal isolates, antimicrobial compounds were only biosynthesized in semi-liquid or solid-state conditions as no antimicrobial activities were ever detected using liquid fermentation. An exception was made for one fungal isolate, and the extraction procedure designed to extract amphipathic compounds was successful and highlighted the amphiphilic profile of the bioactive metabolites.