First Report of Stemphylium vesicarium Causing Onion Stemphylium Leaf Blight in Mauritius

In August 2021, severe leaf blight symptoms were observed on onion (Allium cepa L. cvs Francia and Askari F1 hybrid) in commercial fields located in Mauritius, namely La Forêt (20°19'56.1"S57°30'04.9"E), St Aubin (20°29'47.0"S57°32'29.4"E) and Chapiron (20°20'46.8"S 57°29'12.8"E). Infected leaves displayed small circular to oblong yellow-pale-brown and spindle shaped lesions which later coalesced and formed necrotic areas with black sporulation. Three fields were selected from each region, and along a W-pattern across the fields a disease incidence ranging 53-93% and a severity of 9-28% were recorded. Ten symptomatic leaves were collected in each region and small pieces of infected tissue were surface disinfected using 1% NaOCl for 2 min, rinsed with sterile distilled water, air-dried, transferred to potato dextrose agar (PDA) and incubated for 7 days at 20°C under a 12-h light/dark cycle. Fungal cultures with uniform appearance forming multi-septated conidia typical of the genus Stemphylium (Simmons 1969) were consistently isolated. Monosporic colony of isolates SVCWLF24/3, SVSSA23/1 and SVCWLMC26/1 developed similar olivaceous green to light and dark grey mycelium with an average daily growth rate of 6.5 mm at 25°C in the dark. Conidiophores were straight, light brown with a distinct swollen apex on which olive brown to dark brown, oblong to ovoid, septate conidia formed with dimensions 16.2-44.7 × 8.0-22.9 μm (av. 29.5 x 14.7 μm; n = 50) typical of Stemphylium vesicarium (Wallr) E.G. Simmons 1969 (Woudenberg et al. 2017). Genomic DNA of the three isolates was extracted from fungal mycelium (Ranghoo and Hyde 2000).. The ITS, cmdA and gapdh genes of the isolates were amplified with primers ITS4/ITS5 (White et al. 1990), CALDF1/CALDR1 (Lawrence et al. 2013) and Gpd1/Gpd2 (Beerbee et al. 1999) and sequenced. Sequences were submitted to GenBank under accession numbers OR131271, ON620213, OR188702 (ITS), OR350623, OR350622, OR166368 (cmdA) and OR684516, OR684517, OR684518 (Gapdh). The BLAST search of the sequences showed 100% similarity with S. vesicarium strain CBS 155.24 under accession numbers KU850555 (ITS), KU850702 (Gapdh) and KU850845 (cmdA) (Woudenberg et al. 2017). Phylogenetic trees inferred from the ITS, cmdA and Gapdh concatenated datasets with the maximum-likelihood algorithm allowed clustering of the isolates within S. vesicarium clade, confirming the morphological identification. Pathogenicity tests were performed using all three isolates, cultured on PDA at 25°C in a 12-h dark/light cycle. Ten 60-day-old onion plants (cv. Francia) were spray inoculated each with 10 ml of conidial suspension (1 × 104/ml) of each isolate while 10 healthy plants sprayed with sterile distilled water served as control. They were incubated in a greenhouse at 25°C with a 12-h photoperiod and > 80% humidity. Necrotic circular lesions appeared on leaves after 7-10 days while control plants remained symptomless. Re-isolations made from symptomatic leaf tissues on PDA consistently yielded cultures with similar morphology as the original isolates, thus fulfilling Koch's postulates. This is the first report of S. vesicarium as the causal agent of leaf blight of onion in Mauritius. It is a re-emerging fungal disease (Hay et al. 2021) with a wide host range threatening local onion production. This finding will contribute to early detection of leaf blight, implementation of surveillance and integrated disease management in affected regions.

Parafermionic Zero Modes in Ultracold Bosonic Systems

Exotic topologically protected zero modes with parafermionic statistics (also called fractionalized Majorana modes) have been proposed to emerge in devices fabricated from a fractional quantum Hall system and a superconductor. The fractionalized statistics of these modes takes them an important step beyond the simplest non-Abelian anyons, Majorana fermions. Building on recent advances towards the realization of fractional quantum Hall states of bosonic ultracold atoms, we propose a realization of parafermions in a system consisting of Bose-Einstein-condensate trenches within a bosonic fractional quantum Hall state. We show that parafermionic zero modes emerge at the end points of the trenches and give rise to a topologically protected degeneracy. We also discuss methods for preparing and detecting these modes.

Human immunodeficiency virus type 1 genetic evolution in children with different rates of development of disease

The rate of development of disease varies considerably among human immunodeficiency virus type 1 (HIV-1)-infected children. The reasons for these observed differences are not clearly understood but most probably depend on the dynamic interplay between the HIV-1 quasispecies virus population and the immune constraints imposed by the host. To study the relationship between disease progression and genetic diversity, we analyzed the evolution of viral sequences within six perinatally infected children by examining proviral sequences spanning the C2 through V5 regions of the viral envelope gene by PCR of blood samples obtained at sequential visits. PCR product DNAs from four sample time points per child were cloned, and 10 to 13 clones from each sample were sequenced. Greater genetic distances relative to the time of infection were found for children with low virion-associated RNA burdens and slow progression to disease relative to those found for children with high virion-associated RNA burdens and rapid progression to disease. The greater branch lengths observed in the phylogenetic reconstructions correlated with a higher accumulation rate of nonsynonymous base substitutions per potential nonsynonymous site, consistent with positive selection for change rather than a difference in replication kinetics. Viral sequences from children with slow progression to disease also showed a tendency to form clusters that associated with different sampling times. These progressive shifts in the viral population were not found in viral sequences from children with rapid progression to disease. Therefore, despite the HIV-1 quasispecies being a diverse, rapidly evolving, and competing population of genetic variants, different rates of genetic evolution could be found under different selective constraints. These data suggest that the evolutionary dynamics exhibited by the HIV-1 quasispecies virus populations are compatible with a Darwinian system evolving under the constraints of natural selection.

An improved cellophane method for in vitro germination of recalcitrant pollen

The cellophane technique of La Cour and Faberge has been improved by the use of a booklet of filter paper. The booklet consists of seven squares of filter paper stapled together; the cellophane on which the pollen is germinated is placed between the two top leaves of the booklet and the whole soaked in a sucrose-based nutrient medium for 15 min. This arrangement keeps the cellophane flat as it absorbs medium. The top leaf of the booklet is then removed, the pollen dusted on it and the completed preparation closed in a plastic-wrapped Petri dish. The lower leaves of the booklet keep the cellophane moist for up to 24 hr. Proportions of pollen grains germinating are at least as high as in the hanging drop method; pollen of species that germinate poorly or not all in hanging drops do well in this technique. Because the pollen tubes adhere tightly to the cellophane, staining, observation, and studies of various sorts are facilitated.