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.

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.

Meiotic abnormalities underlying pollen sterility in wild potato hybrids and spontaneous populations.

Wild potato species are widely distributed in the Americas, where they spontaneously grow in very diverse habitats. These species - with low chromosome differentiation - form polyploid series with 2n = 2x, 3x, 4x and 6x (x =12). They are isolated in nature by external and internal hybridisation barriers that can be incomplete, allowing hybridisation in areas of sympatry. Nevertheless, most accessions in germplasm banks, regardless of genetic background of the sampled spontaneous populations, have been assigned specific categories based on morphological characters. To further investigate the extent of hybridisation in the group and for comparative purposes, pollen viability was estimated in (i) artificial hybrids between a commercial cultivar (Calén INTA) of the common potato (tetraploid Solanum tuberosum ssp. tuberosum) and the tetraploid cytotype of the related wild species S. gourlayi, and (ii) samples of plants (accessions) and inflorescences of natural populations from Argentina, tentatively classified as 'presumed hybrids' (S. infundibuliforme-S. gourlayi) and 'species' (S. infundibuliforme, S. gourlayi and S. chacoense). Regardless of origin, 98 out of 103 plants analysed had zero to 70% pollen viability (zero to 40% in eight of them). Pollen grains were of variable size and morphology and, in mostly male sterile plants, the only viable pollen grains were 2n and/or 4n. Furthermore, male sterile plants shared various abnormalities in meiosis I and II (unpaired chromosomes, unequal chromosome distribution, precocious/lagging chromosomes, parallel, tripolar, fused and multiple spindles, unequal size nuclei, dyads, triads and pentads in addition to normal tetrads, among others). These results provide novel evidence to support field observations of early potato botanists on the extent of spontaneous hybridisation in wild Argentinian potato populations, which is not reflected in the current taxonomy and has significant consequences for germplasm conservation and breeding.

Evaluating the ability of different characterization parameters to describe the surface of fried foods.

The objective of this work is to identify surface topography characterization parameters that are capable of discriminating the surfaces of different fried foods. Three fried food model systems with clearly different surfaces were formulated from vital wheat gluten, native wheat starch, and potato flakes. The surfaces were measured with a scanning laser microscope (SLM), and the ability of several parameters to discriminate between them was tested. Two conventional parameters, the root mean square roughness (Sq) and the surface Kurtosis (Sku), were calculated, along with parameters derived from area-scale fractal analysis: smooth-rough crossover (SRC), fractal dimension, and relative area as a function of scale. The coefficient of variation (COV) of Sq, Sku, and SRC and fractal dimension of different sizes of measurement regions were calculated for the surface of the roughest product in order to specify a measurement region that would be sufficiently large to be representative. The size of the representative region was found to be 25 mm². Among the parameters evaluated in this study, the most reliable parameter for discriminating the surfaces of fried foods is the relative area calculated from area-scale fractal analysis.