Reduction of Pythium Damping-Off in Soybean by Biocontrol Seed Treatment.

Pythium spp. is one of the major groups of pathogens that cause seedling diseases on soybean, leading to both preemergence and postemergence damping-off and root rot. More than 100 species have been identified within this genus, with Pythium irregulare, P. sylvaticum, P. ultimum var ultimum, and P. torulosum being particularly important for soybean production given their aggressiveness, prevalence, and abundance in production fields. This study investigated the antagonistic activity of potential biological control agents (BCAs) native to the U.S. Midwest against Pythium spp. First, in vitro screening identified BCAs that inhibit P. ultimum var. ultimum growth. Scanning electron microscopy demonstrated evidence of mycoparasitism of all potential biocontrol isolates against P. ultimum var. ultimum and P. torulosum, with the formation of appressorium-like structures, short hyphal branches around host hyphae, hook-shaped structures, coiling, and parallel growth of the mycoparasite along the host hyphae. Based on these promising results, selected BCAs were tested under field conditions against six different Pythium spp. Trichoderma afroharzianum 26 used alone and a mix of T. hamatum 16 + T. afroharzianum 19 used as seed treatments protected soybean seedlings from Pythium spp. infection, as BCA-treated plots had on average 15 to 20% greater plant stand and vigor than control plots. Our results also indicate that some of these potential BCAs could be added with a fungicide seed treatment with minimum inhibition occurring, depending on the fungicide active ingredient. This research highlights the need to develop tools incorporating biological control as a facet of soybean seedling disease management programs. The harnessing of native BCAs could be integrated with other management strategies to provide efficient control of seedling diseases.

Trichoderma Isolates Inhibit Fusarium virguliforme Growth, Reduce Root Rot, and Induce Defense-Related Genes on Soybean Seedlings.

Sudden death syndrome (SDS) caused by Fusarium virguliforme is among the most important diseases affecting soybean in the United States. The use of biological control agents (BCAs) such as Trichoderma spp. can be a valuable resource to suppress F. virguliforme populations. Therefore, this research focused on screening possible BCAs against F. virguliforme and evaluating mycoparasitism and the induction of systemic resistance as mechanisms underlying the antagonistic activity of selected BCAs against F. virguliforme. In total, 47 potential BCAs, including 41 Trichoderma isolates and 6 Mortierella isolates, were screened in a dual-plate assay. The most effective isolates belonged to the Trichoderma harzianum species and were able to inhibit F. virguliforme radial growth by up to 92%. Selected Trichoderma isolates were tested in the greenhouse and in a microplot study. They reduced root rot caused by F. virguliforme when the plants were coinoculated with the pathogen and the BCA. The tested BCA's ability to reduce F. virguliforme growth may be related to several mechanisms of action, including mycoparasitism and induction of defense-related genes in plants, as revealed by monitoring the expression of defense-related genes in soybean. Our results highlight the potential of native Trichoderma isolates to inhibit F. virguliforme growth and reduce SDS severity, providing the basis for future implementation of biological control in soybean production. More efforts are needed to implement the use of these approaches in production fields, and to deepen the current knowledge on the biology of these highly antagonistic isolates.

Recuperación del genoma del padre recurrente en un programa de retrocruzas asistido por marcadores en arroz / Recurrent parent genome recovery in a marker assisted backcross breeding program in rice

La piricularia (Pyricularia grisea (Cooke) Sacc.) es una de las enfermedades más destructivas del arroz a nivel mundial. El uso de cultivares resistentes es la vía más efectiva y económica de controlar la enfermedad. El método de la retrocruza es el más empleado para la incorporación de genes simples de resistencia. Sin embargo, el proceso se dificulta cuando existe ligamiento de estos genes con características indeseables, el cual puede ser difícil de romper, aún después de muchas generaciones de retrocruzas. La selección asistida por marcadores (SAM) contribuye a facilitar la recuperación del genoma del padre recurrente (PR) en un menor número de generaciones. El objetivo del presente estudio fue la recuperación del genoma del PR utilizando marcadores moleculares en generaciones tempranas de un programa de retrocruzas para la incorporación de un gen de resistencia a P. grisea. En los parentales se evaluaron 36 microsatélites ubicados en los 12 cromosomas del arroz; aquellos que mostraron polimorfismo se evaluaron en plantas de las generaciones RC2F2 y RC3F1. La SAM permitió identificar plantas 100 por ciento similares al PR para los loci evaluados en ambas generaciones de retrocruzas; sin embargo, la proporción fue mayor en la RC3F1 que en RC2F2. Se identificaron regiones cromosómicas candidatas en los cromosomas 4 y 7 para la futura identificación del gen de resistencia incorporado. La aplicación de SAM en el programa de retrocruzas permitió la recuperación del genoma del PR en pocas generaciones, reduciendo el tiempo necesario en el proceso de mejoramiento para incorporar resistencia a piricularia