Morphopathological and molecular morphometric characterization of Waitea circinata var. prodigus causing a novel sheath spot disease of maize in India

Maize brown sheath spot (MBSS), a new disease of maize, was discovered while surveying for maize leaf and sheath blight diseases in the Indian states of Assam, Jharkhand, Meghalaya, Manipur, and Odisha. Maize is the third most important cereal after rice and wheat in India. Unlike banded leaf and sheath blight (BLSB) disease caused by Rhizoctonia solani, MBSS symptoms on maize were discrete and limited to sheaths only. Symptoms of MBSS in the field were initially water soaked necrotic lesions of 1 to 2 cm in diameter on the lowermost leaf sheaths, which then progressed to the upper sheaths. Lesions coalesced and covered approximately 2 to 5% of the sheath area. Infected dried lower leaves were shed while infected upper leaves remained on the stem. The pathogen was isolated, characterized morphologically, pathologically, and molecularly, and identified as Waitea circinata var. prodigus (Wcp); a basidiomycete known to cause basal leaf blight of seashore paspalum. The internal transcribed spacer sequence 2 (ITS2) of rDNA from MBSS isolates formed a well-supported clade with known Wcp isolates. Molecular morphometric analysis of the ITS2 regions of the five known varieties of W. circinata detected distinguishing variations in GC content, compensatory base changes (CBCs), hemi-compensatory base changes (hCBCs), indels, and altered base-pairing of helices. Variation in these characteristics may indicate that varieties are distinct biological species within W. circinata sensu lato. The geographical distribution and potential impacts of MBSS on the maize crop in India necessitates further investigations on pathogen identification and disease management.

Efficiency of a new Waitea circinata extract against rice pathogens

ABSTRACT Waitea circinata (Warcup & Talbot) is an orchid antagonist mycorrhizal fungus with biocontrol potential against rice pathogens. This study aimed to optimize the extraction method, obtain a new extract and evaluate its efficiency against rice pathogens in vitro and in vivo, as well as to compare it with other extraction methods and W. circinata. The extracts were obtained and screened for in vitro growth inhibition against the pathogens Cochliobolus miyabeanus, Monographella albescens and Sarocladium oryzae, using the following extracts: mycelial, crude, lyophilized and mycelial mass. An additional in vitro assay was performed with the principal rice pathogen (Magnaporthe oryzae), in order to evaluate the conidial germination and appressorium formation. Based on this evaluation, the lyophilized and mycelial mass extracts were tested in vivo against rice blast (M. oryzae) and compared to the W. circinata mycelial suspension, in different application forms (simultaneous and previous). The mycelial mass extract inhibited all the pathogens, and the crude and lyophilized extracts inhibited C. miyabeanus and M. albescens, respectively. The mycelial mass extract inhibited the M. oryzae conidial germination and appressorium formation by 80 %, and the simultaneous and previous applications suppressed the rice blast by 94 %. These results indicate that the new extract can be used to control rice pathogens.

Waitea circinata var. zeae causing root rot of cabbage and oilseed rape

Cabbage, a widely used and popular vegetable, and oilseed rape, the second most valuable oilseed crop in the world, are two important species from the Brassicaceae family. Two geographically separated outbreaks of cabbage and oilseed rape root rot with estimated incidence of 15% and 20%, respectively, were recorded during 2017 in the Vojvodina region, Serbia. Twelve hyphal-tip isolates were obtained from symptomatic cabbage and oilseed rape plants and identified as Waitea circinata var. zeae based on morphological and molecular features. This indicates that W. circinata var. zeae has expanded its host range to the Brassicaceae family. Sequence analyses of ITS and LSU of the rDNA, RPB2, and β-tubulin genes revealed the highest similarity with multiple W. circinata var. zeae. Neighbor-joining analyses of ITS sequences resulted in a phylogenetic tree with one well-defined branch of W. circinata var. zeae, with two separate groups. All Serbian isolates and the majority of isolates originating from natural infection of dicotyledonous plants grouped together in Group I. Following artificial inoculation, W. circinata var. zeae isolates caused mild to medium root necrosis of seedlings of 2 monocotyledonous and 12 dicotyledonous plant species, implying a wider host range than known for W. circinata var. zeae. Additionally, this is the first occurrence of W. circinata var. zeae on dicotyledonous host plants in Europe. As cabbage and oilseed rape are important crops grown worldwide, the occurrence of this new soil-borne pathogen with a broad host range imposes the necessity for changes in routine disease control practice, particularly crop rotation.

Seed germination and development of orchid seedlings (Cyrtopodium saintlegerianum) with fungi

Fungi of Rhizoctonia complex are mycorrhizal of orchids and may to germinate yours seeds and development the seedlings. In this context, our objective was to select a fungal isolate to promote seed germination and seedling development of Cyrtopodium saintlegerianum. Pelotons were found in the roots and three mycorrhizal fungi were isolated. We tested mycorrhizal isolates obtained from C. saintlegerianum roots and six mycorrhizal fungi from other orchids as well three pathogenic isolates (of rice and bean) to germinate the seeds in oatmeal-agar medium. Seeds not inoculated were used as control. The isolates En07 (Waitea circinata), Cs10 (Tulasnella sp.) and Ro88 (Rhizoctonia oryzae) were efficient to promote seed germination, but only En07 differing statistically of the control. The non-specific isolate En07 promoted germination in 81% of seeds and the specific isolate (Cs10) promoted 60%, evidencing the non-specificity mycorrhizal association in this orchid during germination. Axenic seedlings were inoculated with four mycorrhizal fungi (non-inoculated seedlings - control). After six months, the isolates En07 and Cs10 were efficient in the interaction with the seedlings, but did not differ to the control. Therefore, our results suggested that fungi of the Rhizoctonia complex can be used in the germination and seedling development of C. saintlegerianum.

Diversity and Pathogenicity of Rhizoctonia Species from the Brazilian Cerrado

Eighty-one Rhizoctonia-like isolates were identified based on morphology and nuclei-staining methods from natural and agricultural soils of the Cerrado (Brazilian savanna). The nucleotide similarity analysis of ITS1-5.8S-ITS2 regions identified 14 different taxa, with 39.5% of isolates assigned to Waitea circinata (zeae, oryzae, and circinata varieties), while 37.0% belonged to Thanatephorus cucumeris anastomosis groups (AGs) AG1-IB, AG1-ID, AG1-IE, AG4-HGI, and AG4-HGIII. Ceratobasidium spp. AG-A, AG-F, AG-Fa, AG-P, and AG-R comprised 23.5%. Rhizoctonia zeae (19.8%), R. solani AG1-IE (18.6%), and binucleate Rhizoctonia AG-A (8.6%) were the most frequent anamorphic states found. Root rot severity caused by the different taxa varied from low to high on common beans, and tended to be low to average in maize. Twenty-two isolates were pathogenic to both hosts, suggesting difficulties in managing Rhizoctonia root rots with crop rotation. These results suggest that cropping history affects the geographical arrangement of AGs, with a prevalence of AG1 in the tropical zone from central to north Brazil while the AG4 group was most prevalent from central to subtropical south. W. circinata var. zeae was predominant in soils under maize production. To our knowledge, this is the first report on the occurrence of W. circinata var. circinata in Brazil.

Cultivo in vitro de Epidendrum nocturnum (Orchidaceae) ocorrente no Cerrado da região Centro-Oeste

Resumo As orquídeas podem ser propagadas in vitro em meios de cultivo assépticos ou em simbiose com fungos micorrízicos. Epidendrum nocturnum ocorre em áreas de Cerrado e neste estudo objetivou-se a visualização de fungos micorrízicos em suas raízes bem como o cultivo assimbiótico de suas plântulas em diferentes meios e a micorrização in vitro. No desenvolvimento assimbiótico testou-se três meios de cultura em um ensaio e, em outro ensaio, foram testadas formulações alternativas do meio Knudson C modificado, com a adição de polpa de frutas. Fungos micorrízicos de orquídeas foram usados na micorrização in vitro. Pelotons foram visualizados nas raízes de E. nocturnum. O meio Knudson C modificado diferiu estatisticamente dos demais, nas duas intensidades luminosas, no primeiro ensaio. No segundo ensaio, após sete meses, os meios com formulação alternativa não diferiram estatisticamente entre si. Na micorrização in vitro as plântulas com o isolado fúngico En07 (Waitea circinata) apresentaram maior vigor visual em relação aos demais tratamentos, mas não houve diferença estatística com o controle. Os meios com formulação alternativa e o Knudson C modificado podem ser utilizados no desenvolvimento in vitro de E. nocturnum e o isolado En07 pode ser usado na micorrização visando estratégias de conservação desta orquídea.

Varietal dependent response of barley to soil-borne Waitea circinata infection

The disease syndrome caused by Waitea circinata, a soil-borne pathogen introduced in the past decade into Carpathian basin, visually indistinguishable of those caused by various Rhizoctonia strains in diverse host plant. Dicotyledonaceous species in general proved to be more tolerant to this new pathogen than monotyledonaceous ones. This mesophilic fungus can seriously damage cereals. The barley varieties, similarly to other plants, exhibited highly different individual reaction to soil borne infection, Bivoy being the most while Maresi the less tolerant among the 9 tested varieties. Two groups could be separated on the base of their response to Rhizoctonia; Jubilant, Bivoy, Pasadena formed one group being moderately tolerant and Anabell, Scarlett, Rex and Omega the other group of more susceptibles. Three significant factors influence on the virulence of Rhizoctonia strains comprised 62% of total variation.