Etiology of phomopsis root rot in soybean

Abstract

In the 2012/13 growing season, soybean was grown in an area of 27 million hectares, under no till and monoculture, which contributes to an increasing intensity of current and emergent diseases Soybean crop is attacked by many diseases caused by nematodes, viruses, bacteria and fungi. The latter cause root rot, damping-off, cankers, stem rot, leaf spots, and pod and seed diseases (1, 2, 4). In most soybean fields, weakened plants with thinner stems and leaf yellowing followed by early defoliation are observed. This symptomatology is similar to that of charcoal root rot caused by Macrophomina phaseolina (Tass.) Goid, which leads weakened plants to death next to harvest. Uneven crop ripening and yellowing and normal green areas characterize the secondary symptoms of the disease.In a survey of damages caused by root rot to soybean crops in southern Brazil for several years, a root rot caused by Phomopsis sp has been found as most frequent (4). The primary symptoms are seen when the main root is cut longitudinally, evidencing the death of the white-colored wood which shows well-defined lines forming no defined drawing. Plants manifesting the first secondary symptoms already have RESUMO Palavras-chave adicionais: Glycine max, geográfico, Phomopsis phaseoli, seca-da-haste e da-vagem.Em levantamento de danos causados por podridões radiculares da soja, em lavouras do sul do Brasil durante vários anos, tem sido encontrado com maior frequência uma podridão radicular causada por Phomopsis sp. Os sintomas primários são visualizados quando se corta longitudinalmente a raiz principal, observando-se a morte do lenho ostentando coloração branca, com linhas negras bem definidas, sem um formato definido. Por isso, por semelhança, tem sido chamada de podridão radicular de geográfico, pelo aspecto que lembra as linhas irregulares separando regiões num mapa. Isolamentos foram feitos durante várias Ghissi, V. V.; Reis, E. M.; Deuner, C. C. Etiologia da podridão radicular de Phomopsis em soja. Summa Phytopathologica, v.40, n.3, p.270-272, 2014. safras e feita a prova de patogenicidade. Nos isolamentos tem predominado colônias e os esporos alfa de Phomopsis sp. A prova de patogenicidade foi feita pela inoculação no colo de plantas cultivadas em câmara de crescimento. Reproduziram-se os sintomas de geográfico nas plantas e foi reisolado o fungo Phomopsis sp. Em hastes de soja naturalmente infectadas pela seca-da-haste e da-vagem são encontrados sintomas de geográfico causados por Phomopsis phaseoli. Aos sintomas conhecidos em hastes, vagens e grãos acrescenta-se agora o de podridão radicular causada por P. phaseoli. the geographic symptoms in the taproot. The primary symptoms can be observed even after mechanical harvesting in dead plant stumps. NOTAS CIENTÍFICAS Etiology of phomopsis root rot in soybeanTo diagnose the geographic root rot, removing the root epidermis and observing the presence of geographic symptoms is sufficient. Geographic root rot is easily recognized when the main root of dead or dying plants is cut longitudinally. T...

Association of Diaporthe longicolla with Black Zone Lines on Mature Soybean Plants

“…Previously, zone lines were characterized as produced by the Charcoal rot pathogen (M. phaseolina), Fusarium spp., or Diaporthe spp. (Ghissi et al 2014;Zaccaron et al 2014;T. Hughes, personal communication), when they were observed on soybean as the plants approached maturity.…”

“…More recently, zone lines were characterized as a symptom produced by either Macrophomina phaseolina (Tassi) Goid, Fusarium spp., or Diaporthe spp. on soybean (Ghissi et al 2014;Zaccaron et al 2014). The objective of this study was to establish the identity of the Diaporthe spp.…”

“…The D. longicolla isolates were assayed for pathogenicity using a modified toothpick inoculation method (Ghissi et al 2014;Keeling 1982). Seeds of a commercial soybean cultivar of relative maturity 1.8 (Monsanto Company, St. Louis, MO) were sown into a potting mix (Sunshine Mix #1, Sun Grow Horticulture Products, Belleview, WA) in 7.5-liter, circular, plastic pots, one seed per pot and grown for 4 weeks at 22°C in the greenhouse under a 14-h photoperiod with a light intensity of 450 μE/m 2 /s and watered daily.…”

“…2). Previously, Ghissi et al (2014) identified D. phaseolorum var. sojae to be associated with zone lines on soybean plants based on morphological characteristics.…”

“…In this study, the pathogenicity experiment to produce zone lines by D. longicolla on soybean plants was performed using a modified protocol of Ghissi et al (2014) and Keeling (1982). The protocol was modified from R5 developmental stage to stop watering the soybean plants and subject them to slow drying in the greenhouse; given previous studies suggested that zone lines may be formed in host tissues from the slow drying of the host plant (Nikandrow 1989;Hubert 1924).…”