Biology of Gaeumannomyces graminis var. graminis isolates from rice and grasses and epidemiological aspects of crown sheath rot of rice

Abstract

A collection of Gaeumannomyces graminis var. graminis isolates obtained from symptomatic rice and grass plants in central and northern Brazil were studied in regard to pathogenicity on rice and cultural characteristics. For all isolates, only one type of lobed hyphopodia was observed both in the field and artificially inoculated plants. Perithecia were formed on artificial media and inoculated leaf sheaths. Hyphopodia were formed from ascosporic germ tubes. The hyphae under moist stress conditions produced dark brown chlamydospores that were initially hyaline. Large variation in the number of chlamydospores produced and duration of perithecia formation was observed among the isolates. Pathogenicity assays showed that 60-day old rice plants were more susceptible than 35-day old plants. The isolates from rice and grasses varied significantly in regard to disease severity on both rice seedlings and adult rice plants. In general, the isolates from rice were more aggressive than the isolates from grasses. Spontaneous infection of rice plants by ascosporic inoculum from perithecia on rice stubbles was observed in the greenhouse, suggesting their role as a source of primary inoculum in the field, which deserves further investigation.

Infection process of Gaeumannomyces graminis var. graminis on the roots and culms of rice

“…graminis were abundantly noticed on both the surface and inside of the rice roots and caused the symptoms of crown sheath rot. By contrast, Peixoto et al (2013) did not find mycelium of G. graminis var.…”

“…Peixoto et al. () reported the occurrence of ascosporic infection by G. graminis var. graminis in rice grown in a greenhouse exposed to infected rice stubbles.…”

“…graminis , was reported for the first time in some Brazilian states in the 1997/1998 growing season (Prabhu & Filippi, ). The disease can cause early grain maturation and reduce the number of grains per panicle and even the death of the tillers depending on the rice growth stage that fungal infection takes place (Ou, ; Peixoto, Ottoni, Filippi, Silva‐Lobo, & Prabhu, ; Prabhu & Filippi, ). Curiously, most of the information available in the literature regarding the biology of the genus Gaeumannomyces and the epidemiological aspects of the disease caused by this pathogen and its control is reported for wheat in contrast to rice (Prabhu & Filippi, ).…”

“…The fungus G. graminis var. graminis can survive in infected rice stubbles and on several alternative hosts (Datnoff, Eliott, & Krausz, ; Peixoto, Ottoni, Silva‐Lobo, Filippi, & Prabhu, ; Peixoto et al., ). Crown sheath rot management is quite difficult to achieve due to the absence of resistant cultivars and the unavailability of effective fungicides (Nunes, ; Peixoto et al., ; Prabhu & Filippi, ).…”

“…graminis, was reported for the first time in some Brazilian states in the 1997/1998 growing season (Prabhu & Filippi, 2002). The disease can cause early grain maturation and reduce the number of grains per panicle and even the death of the tillers depending on the rice growth stage that fungal infection takes place (Ou, 1985;Peixoto, Ottoni, Filippi, Silva-Lobo, & Prabhu, 2013;Prabhu & Filippi, 2002).…”