First report of black rot caused by Xanthomonas nasturtii on watercress in Spain and Portugal

Xanthomonas nasturtii was first identified as the cause of black rot of watercress (Nasturtium officinale) on plants grown in Florida, USA (Vicente et al., 2017). Similar symptoms had been reported earlier in Hawaii (McHugh & Constantinides, 2004) and an unidentified Xanthomonas sp. was isolated in Portugal in 2003 from wild watercress (Cruz et al., 2017). Since 2017, watercress crops in southern Spain have occasionally exhibited small yellow leaf lesions around the hydathodes, leaf spots, V-shaped leaf lesions, wilt, distortion and senescence (Fig. 1). Symptoms were more frequent during mild and humid periods from November to February, reducing yields by up to 60% and leading to rejection of some crops (Lascelles, 2019). In 2021, symptoms were seen on watercress produced in Portugal and sold in the UK

Effects of Functionalization on Thermal Properties of Single-Wall and Multi-Wall Carbon Nanotube-Polymer Nanocomposites

Carboxylic functionalization (-COOH groups) of carbon nanotubes is known to improve their dispersion properties and increase the electrical conductivity of carbon-nanotube - polymer nanocomposites. We have studied experimentally the effects of this type of functionalization on the thermal conductivity of the nanocomposites. It was found that while even small quantities of carbon nanotubes (~1 wt%) can increase the electrical conductivity, a larger loading fraction (~3 wt%) is required to enhance the thermal conductivity of nanocomposites. Functionalized multi-wall carbon nanotubes performed the best as filler material leading to a simultaneous improvement of the electrical and thermal properties of the composites. Functionalization of the single-wall carbon nanotubes reduced the thermal conductivity enhancement. The observed trends were explained by the fact that while surface functionalization increases the coupling between carbon nanotube and polymer matrix it also leads to formation of defects, which impede the acoustic phonon transport in the single wall carbon nanotubes. The obtained results are important for applications of carbon nanotubes and graphene flakes as fillers for improving thermal, electrical and mechanical properties of composites.Comment: 25 pages; 6 figure