Variation in virulence of Septoria tritici Rob ex Desm isolates on wheat

To identify physiologic races, the variation in virulence of 10 local Septoria tritici Rob ex Desm isolates was evaluated on 10 wheat differentials selected in Israel and 7 previously tested Argentine cultivars (cvs). Pycnidial leaf coverage percentage (PC) and necrotic lesion percentage (NL) were used to determine cvs reaction in order to compare their efficiency in isolate differentiation. Isolates behaved differently on the different wheat cvs. The 2 variables showed which isolates behaved similarly, and which behaved differently; PC was more sensitive in detecting these differences. The ranking of varieties for PC and NL was different for every isolate x cv combination, and few ordering patterns coincided (Bobwhite "S", lassul 20 and Bordenave Puán). In general, local isolates induced more PC than NL on national cvs. Two isolates (I11, I19) behaved in the most virulent manner; 2 others (I21, I25) provoked the highest resistant reaction percentage on the cvs tested. Isolate x cv interaction varied according to the parameter evaluated. The analysis of variance for PC indicated significant interaction between the 2 main factors (P = 0.01) which may be considered as an index of pathogen physiologic specialization. However, a non-significant interaction (P = 0.01) for NL indicated only differences between isolates degree of aggressiveness. Low degree of specificity of the interactions and similar order in the ranking of disease severity on some cvs showed no "true physiologic races". The international set did not supply any major variation range in lesion type and percentage or more consistent cv reactions in differentiating biotypes. Thus, the standardization of research methodologies is necessary to study S tritici-Triticum sp interactions. This would contribute to the reproducibility of results obtained by different authors throughout the world and thus avoid different interpretations of varietal reaction.Variation de la virulence d'isolats de Septoria tritici Rob ex Desm sur blé. La variation de virulence de 10 isolats de Septoria tritici a été évaluée sur 17 variétés de blé sélectionnées : 10 en Israël et en Argentine, pour identifier des races physiologiques (tableau I). La réaction des variétés est déterminée afin d'estimer l'effet de la méthode d'évaluation de la différenciation des souches et montrer les différences de comportement des variétés de blé par l'emploi de 2 variables : - le pourcentage de lésions nécrotiques avec pycnides (NL), - le pourcentage de couverture de la surface foliaire totale par des pycnides (PC). Les 2 variables, PC et PN, permettent de séparer les isolats en fonction de leur comportement, mais avec un net avantage pour PC. La magnitude de la surface nécrosée et la couverture pycnidiale donnent des résultats différents pour chaque combinaison : souche/variété (tableau III). II existe peu de concordance entre les classements (variétés Bobwhite "S", lassul 20 et Bordenave Puán). Les isolats locaux ont, en général, révélé plus de PC que de NL dans les variétés nationales (tableaux IV et V). Deux d'entre eux (I11 et I19) se sont montrés plus virulents alors que 2 autres (I 21 et I25) ont le pourcentage le plus élevé de réactions de résistance sur les 17 variétés testées. L'interaction souche/variété varie selon le paramètre d'évaluation considéré : une valeur significative (P = 0,01) pour PC peut être considérée comme un indice de spécialisation physiologique de l'agent pathogène mais, une interaction non significative (P = 0,01) pour NL n'a montré que des différences dans le degré d'agressivité des isolats. En outre, le faible degré de spécificité des interactions, et l'ordre similaire de l'évaluation de la gravité de la maladie sur certaines variétés montrent qu'ils n'ont pas mis en évidence de «vraies races physiologiques». L'emploi de la gamme internationale d'hôtes différentiels n'a pas fourni plus de variation pour le type et le pourcentage de lésion, ni de réactions des variétés, plus solides et plus claires, dans le but de différencier des biotypes. Enfin, il faut insister sur le besoin de standardiser les conditions d'inoculation et d'évaluation des études d'interactions S tritici/Triticum sp, afin d'assurer la reproductibilité des résultats au niveau mondial et d'éviter les différences d'interprétation de réaction des variétés qui surgissent par l'emploi de méthodologies variables

Effects of distal and proximal arm muscles fatigue on multi-joint movement organization

International audienc

Selection and characterization of Argentine isolates of Trichoderma harzianum for effective biocontrol of Septoria leaf blotch of wheat

Species of the genus Trichoderma are economically important as biocontrol agents, serving as a potential alternative to chemical control. The applicability of Trichoderma isolates to different ecozones will depend on the behavior of the strains selected from each zone. The present study was undertaken to isolate biocontrol populations of Trichoderma spp. from the Argentine wheat regions and to select and characterize the best strains of Trichoderma harzianum by means of molecular techniques. A total of 84 out of the 240 strains of Trichoderma were able to reduce the disease severity of the leaf blotch of wheat. Thirty-seven strains were selected for the reduction equal to or greater than 50 % of the severity, compared with the control. The percentage values of reduction of the pycnidial coverage ranged between 45 and 80 %. The same last strains were confirmed as T. harzianum by polymerase chain reaction amplification of internal transcribed spacers, followed by sequencing. Inter-simple sequence repeat was used to examine the genetic variability among isolates. This resulted in a total of 132 bands. Further numerical analysis revealed 19 haplotypes, grouped in three clusters (I, II, III). Shared strains, with different geographical origins and isolated in different years, were observed within each cluster. The origin of the isolates and the genetic group were partially related. All isolates from Parana were in cluster I, all isolates from Loberia were in cluster II, and all isolates from Pergamino and Santa Fe were in cluster III. Our results suggest that the 37 native strains of T. harzianum are important in biocontrol programs and could be advantageous for the preparation of biopesticides adapted to the agroecological conditions of wheat culture.Centro de Investigaciones en Fitopatologí

Immediate changes in feedforward postural adjustments following voluntary motor training

There is limited evidence that preprogrammed feedforward adjustments, which are modified in people with neurological and musculoskeletal conditions, can be trained and whether this depends on the type of training. As previous findings demonstrate consistent delays in feedforward activation of the deep abdominal muscle, transversus abdominis (TrA), in people with recurrent low back pain (LBP), we investigated whether training involving voluntary muscle activation can change feedforward mechanisms, and whether this depends on the manner in which the muscle is trained. Twenty-two volunteers with recurrent LBP were randomly assigned to undertake either training of isolated voluntary activation of TrA or sit-up training to activate TrA in a non-isolated manner to identical amplitude. Subjects performed a trunk perturbation task involving arm movement prior to and after training, and surface and fine-wire electromyography (EMG) recordings were made from trunk and arm muscles. Following a single session of training of isolated voluntary activation of TrA, onset of TrA EMG was earlier during rapid arm flexion and extension, to more closely resemble the responses in pain-free individuals. The magnitude of change in TrA EMG onset was correlated with the quality of isolated training. In contrast, all of the abdominal muscles were recruited earlier during arm flexion after sit-up training, while onset of TrA EMG was further delayed during arm extension. The results provide evidence that training of isolated muscle activation leads to changes in feedforward postural strategies, and the magnitude of the effect is dependent on the type and quality of motor training