Histopathology of Andean Potato (Solanum tuberosum Andigenum group) varieties parasitized by the false root-knot nematode, Nacobbus aberrans.

Landraces of the Solanum tuberosum Andigenum group are abundant and diverse. They are a valuable genetic resource possessing resistance to pests, diseases, and environmental stresses. In the Andean region, populations of the false root-knot nematode Nacobbus aberrans became specialized to infect native potatoes, being one of the major limiting factors affecting this crop. A better understanding of the host plant-parasite interactions is important in order to select tolerant or resistant plants to be included in management programs. Despite the close of association of N. aberrans with potato, and the great diversity of the S. tuberosum Andigenum group, few histopathological studies have been conducted. The aim of this work was to analyze histological alterations induced by different Argentine populations of the nematode in naturally infested roots of four Andean potato varieties (Collareja, Negra Imilla, Ojo de Señorita and Colorada). All the varieties showed hyperplastic tissue in the central zone of galls, where syncytia developed in close association with the nematode female. Syncytia were composed of modified hyperplastic tissue and parenchyma xylem cells. The results showed differences among varieties in their response to nematode populations, with Ojo de Señorita and Negra Imilla being the most susceptible ones. This study is the first describing histopathological alterations induced by N. aberrans in susceptible Andean potato landraces.

Cross-modal reorganization and speech perception in cochlear implant users.

Recent work suggests that once the auditory cortex of deaf persons has been reorganized by cross-modal plasticity, it can no longer respond to signals from a cochlear implant (CI) installed subsequently. To further examine this issue, we compared the evoked potentials involved in the processing of visual stimuli between CI users and hearing controls. The stimuli were concentric circles replaced by a different overlapping shape, inducing a shape transformation, known to activate the ventral visual pathway in human adults. All CI users had their device implanted for >1 year, but obtained different levels of auditory performance following training to establish language comprehension. Seven of the 13 patients showed good capacities for speech recognition with the CI (good performers) while the six others demonstrated poor speech recognition abilities (poor performers). The evoked potentials of all patients showed larger amplitudes, with different distributions of scalp activations between the two groups. The poor performers exhibited broader, anteriorly distributed, high P2 amplitudes over the cortex whereas the good performers showed significantly higher P2 amplitudes over visual occipital areas. These results suggest the existence of a profound cross-modal reorganization in the poor performers and an intramodal reorganization in the good performers. We interpret these data on the basis of enhanced audiovisual coupling as the key to a long-term functional improvement in speech discrimination in CI users.

Occurrence of Meloidogyne spp. in Argentina.

A record of 84 plant species in 32 families that are hosts to the root-knot nematode species found in Argentina is presented. The genus Meloidogyne appears to be widely distributed in the country, with Meloidogyne incognita and M. javanica the most frequently detected species. Other species found in Argentina include M. arenaria, M. cruciani, M. decalineata, M. hapla, and M. ottersoni. The present survey is supplemented with existing published information.

Histopathology of Andean Potato (Solanum tuberosum Andigenum group) varieties parasitized by the false root-knot nematode, Nacobbus aberrans / Histopatologia de variedades de batata andina (Solanum tuberosum grupo Andigenum) parasitadas pelo falso nematóide das galhas, Nacobbus aberrans

Abstract Landraces of the Solanum tuberosum Andigenum group are abundant and diverse. They are a valuable genetic resource possessing resistance to pests, diseases, and environmental stresses. In the Andean region, populations of the false root-knot nematode Nacobbus aberrans became specialized to infect native potatoes, being one of the major limiting factors affecting this crop. A better understanding of the host plant-parasite interactions is important in order to select tolerant or resistant plants to be included in management programs. Despite the close of association of N. aberrans with potato, and the great diversity of the S. tuberosum Andigenum group, few histopathological studies have been conducted. The aim of this work was to analyze histological alterations induced by different Argentine populations of the nematode in naturally infested roots of four Andean potato varieties (Collareja, Negra Imilla, Ojo de Señorita and Colorada). All the varieties showed hyperplastic tissue in the central zone of galls, where syncytia developed in close association with the nematode female. Syncytia were composed of modified hyperplastic tissue and parenchyma xylem cells. The results showed differences among varieties in their response to nematode populations, with Ojo de Señorita and Negra Imilla being the most susceptible ones. This study is the first describing histopathological alterations induced by N. aberrans in susceptible Andean potato landraces.

Resumo As variedades de Solanum tuberosum grupo Andigenum são abundantes e diversas, além de serem uma fonte importante de recursos genéticos antea resistência de pragas, doenças e estresse ambiental. Na região andina, populações de Nacobbus aberrans se especializaram em parasitar batatas nativas e representam o principal fator limitante que afeta a produção desse cultivo. Um melhor entendimento da interação hospedeiro-parasita é importante para a seleção de plantas tolerantes ou resistentes a serem incluídas nos programas de manejo. Apesar da íntima associação de N. aberrans com a batata e a grande diversidade de S. tuberosum grupo Andigenum, os estudos histopatológicos desenvolvidos são limitados. O objetivo do presente trabalho foi analisar as alterações histológicas de raízes de quatro variedades de batata andina (Collareja, Negra Imilla, Ojo de Señorita e Colorada) parasitadas naturalmente por distintas populações argentinas do nematóide. Em todas as variedades se observou tecido hiperplásico na zona central das galhas onde, também, se desenvolveram os sincícios em íntima relação com as fêmeas do nematóide. Os sincícios estavam constituídos por tecido hiperplásico modificado e por células parenquimáticas do xilema. Os resultados mostraram diferenças entre as variedades de batata frente às populações do nematóide, sendo Ojo de Señorita e Negra Imilla as que evidenciaram maior susceptibilidade. Este estudo constitui a primeira avaliação da histopalogia induzida por N. aberrans em variedades suscetíveis de batata andina.

Blind subjects process auditory spectral cues more efficiently than sighted individuals.

The goal of the present study was to investigate how monaural sound localization on the horizontal plane in blind humans is affected by manipulating spectral cues. As reported in a previous study (Lessard et al. 1998), blind subjects are able to calibrate their auditory space despite their congenital lack of vision. Moreover, the performance level of half of the blind subjects was superior to that of sighted subjects under monaural listening conditions. Here, we first tested ten blind subjects and five controls in free-field (1) binaural and (2) monaural sound localization tasks. Results showed that, contrary to controls and half the blind subjects, five of the blind listeners were able to localize the sounds with one ear blocked. The blind subjects who showed good monaural localization performances were then re-tested in three additional monaural tasks, but we manipulated their ability to use spectral cues to carry out their discrimination. These subjects thus localized these same sounds: (3) with acoustical paste on the pinna, (4) with high-pass sounds and unobstructed pinna and (5) with low-pass sounds and unobstructed pinna. A significant increase in localization errors was observed when their ability to use spectral cues was altered. We conclude that one of the reasons why some blind subjects show supra-normal performances might be that they more effectively utilize auditory spectral cues.