Root Rot Of Corn Research Articles

First report of sweet corn root rot caused by Pythium graminicola in southeast China.

Sweet corn (Zea mays L.) is widely consumed as fresh or frozen vegetable worldwide, and Zhengtian68 is a popular commercial variety cultivated extensively in southeast China. In May 2021, 40% of the inbred line YK063 (the female parent of Zhengtian68) showed early yellowing of the leaves at flowering time in a commercial seed production field with a total area of 0.5 ha in Guangzhou, Guangdong Province after a heavy rain. Black and rotten roots were observed in the diseased plants after digging the whole plant out of the soil. Grain filling was also severely affected, adversely impacting seed production. Diseased plants were more easily found in the lower section of the field, where water accumulated after rainfall. Three plants with rotten roots were collected randomly from the field to identify the causal pathogen. The diseased roots were cut into 2-3 mm sections, washed in 75% ethanol for 2 minutes and rinsed three times in sterile distilled water. Four to five sections per plant were placed on potato dextrose agar (PDA) and incubated at 28℃ in the dark for three days. Three isolates GF1, GF2, and GF3 from different plants were purified by hyphal tip isolation and transferred to new PDA and 10% V8 juice agar (16 g agar, 3 g CaCO3, 100 ml V8 juice, and 900 ml distilled water) and incubated at 28℃ for 10 days in darkness for further investigation. Translucent, glassy mycelial growth was observed on the PDA media. Morphological characteristics of the 3 isolates were observed under a microscope from the 10%V8 media. The hyphae were aseptate and 2.7 to 4.5 μm wide (mean±SD,3.3±0.44μm, n=44). Sporangia were inflated, or lobulate, terminal, or intercalary. Oogonia were globose, smooth-walled, terminal, or occasionally intercalary, with a diameter of 17.2-24.1 μm (mean±SD, 21.3±2.14μm, n=29). Oospores were globose, plerotic, smooth, and 14.5-21.2 μm (mean±SD, 18.7±2.07μm, n=35) in diameter. The antheridia were diclinous or monoclinous, not intercalary, and one to six antheridia were attached to each oogonium. Based on these morphological characteristics, 3 isolates were identified as Pythium spp. including Pythium graminicola (Van der Plaats-Niterink 1981). Genomic DNA was extracted from the mycelia grown on PDA using a Fungal Genomic DNA kit (Scintol, Beijing, China) according to the manufacturer's instructions. The cytochrome oxidase II (Cox II) gene and internal transcribed spacer (ITS) region of the rDNA were amplified using the primers FM58/FM66 (Martin 2000) and ITS4/ITS5 (White et al. 1990) respectively. Amplification was performed in a 50μl reaction volume using 25 μl PCR Mix (Trans Gene, Beijing, China), 3 μl genomic DNA (50 ng/μl), 1 μl each forward and reverse primer (10 μM), and 20 μl ddH2O. The PCR program was as follows: initial denaturation at 95°C for 30 s, 35 cycles of denaturation at 95°C for 30 s, annealing at 60°C for 60 s, extension at 72°C for 60 s, and a final extension at 72°C for 10 min. PCR products were sequenced and submitted to GenBank (accession no. OQ504322, OQ933130, and OQ933212 for ITS; OQ512002, OQ942203, and OQ942204 for Cox II). BLASTn analysis revealed that the ITS and Cox II sequences showed more than 98.62% similarity (721/724bp, 722/724bp,723/724bp for ITS; 514/514bp, 506/507bp, 500/507bp for Cox II) to P. graminicola ATCC96234 (accession no. AB095045 for ITS, and AB160849 for Cox II), respectively, supporting the morphological analysis. A neighbor-joining phylogenetic analysis of the ITS and Cox II concatenated sequence further confirmed that the isolates were P. graminicola. To test the pathogenicity of GF1, GF2, and GF3 a wheat seed inoculum was prepared as previously described (Qu et al. 2016). Sweet corn YK063 plants were planted in sterilized nutrient soil in plastic pots (one plant per pot) and grown in a greenhouse at 28℃ with 60% humidity and a 12-h/12-h light-dark cycle. For each isolate,10 plants were inoculated with 20 infected wheat seeds around the roots at the V5 stage, while 10 other YK063 plants were inoculated with the non-infected wheat seeds as a control. The experiment was repeated once. Three weeks later, the non-inoculated plants were asymptomatic. In contrast, inoculated plants showed stunning, yellowing of the leaves, root rot, and decreased production of lateral roots, exhibiting symptoms similar to those originally described for the disease. P. graminicola was successfully reisolated from the diseased roots and identified by morphological characteristics and sequencing of the ITS and Cox II as the causal agent for this root rot disease, fulfilling Koch's postulate for defining a causal agent. P. graminicola was reported as a causal agent of damping-off on dent corn in Georgia (Li et al. 2018). To our knowledge, this is the first report of P. graminicola causing root rot in sweet corn in southeast China. Identification of this pathogen will facilitate further research on this disease and the development of effective strategies to control the disease.

Effect of Allelochemicals from Cereal Rye Cultivar and Pythium lutarium on Corn Growth and Disease

Allelopathic chemicals produced by a cereal rye (CR; Secale cereale L.) cover crop have been implicated in the negative effect of CR on corn planted into decomposing CR residue. Production of allelochemicals varies among CR cultivars. In the current study, the allelopathic effect of crude extracts from five CR cultivars (Elbon, Hazlet, Serafino, Tayo, and Yankee) was evaluated on corn seedling growth, mycelial growth of Pythium lutarium, and root rot of corn caused by P. lutarium using a plate assay. In general, crude extracts from all CR cultivars slowed pathogen growth and reduced corn coleoptile and radicle lengths. When corn was grown on media amended with crude extracts from the CR cultivars and colonized with P. lutarium, corn growth was reduced and root rot severity increased compared with the check (no extract with pathogen). Subsequently, a cup assay was used to further investigate the allelopathic effect of Elbon, Hazlet, and Serafino on corn seedling growth and root rot. Corn grown in cups into which each cultivar had been planted had shorter radicles and coleoptiles compared with the check (no CR), regardless of the CR cultivar. Results from this study suggest that allelochemicals released from decomposing CR vary among cultivars, and their interaction with Pythium spp. could affect seedling disease on corn. Consequently, choice of CR cultivar may be an important management decision to reduce the negative effects of CR on corn. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Pratylenchus zeae a causative agent of Corn Root Rot in Jiangsu Province of China.

Corn (Zea mays L.) plays an important role in China's cash crops, not only as food, but a vital raw material for animal husbandry and industry (Li et al. 2022). Pratylenchus zeae is one of the most damaging root-lesion nematodes (RLN) that can result in decreased yield and quality of crops (Liu et al. 2017). In September 2020, five root/soil samples were collected from the rhizosphere of corn (cv. Zhengdan 958), which had weak growth and root brown lesions in Chenzhou Village, Taolin Town, Donghai County, Lianyungang City, Jiangsu Province of China. Nematodes were extracted from the collected samples using the modified Baermann funnel method (Hooper et al. 2005). RLN were found in all samples, an average of 46 RLN per gram of root and 138 RLN per 100 cm3 of soil. The obtained RLN females were sterilized with 0.3% streptomycin sulfate and then inoculated on each carrot disks individually to obtain the purified population. RLN were examined by morphological and molecular characteristics to confirm the species indentification. The main morphological measurements of adult (n = 15) included body length = 524.7 μm (mean) ± 15.1 (standard deviation) (range = 490.7 to 543.6 μm), stylet = 15.2 μm ± 0.8 (14.2 to 16.8 μm), tail length = 30.3 μm ± 2.5 (26.3 to 35.3 μm), a = 25.6 ± 1.3 (24.4 to 29.3), b = 5.3 ± 0.3 (4.7 to 5.8), c = 17.4 ± 1.4 (14.9 to 19.3), two annules on the lip region. No males were found in the specimens. The morphological characters of this population are consistent with the description of P. zeae (Castillo and Vovlas, 2007). Furthermore, DNA was extracted from individual nematodes. The primers of TW81/AB28 and D2A/D3B (Subbotin et al. 2006) were used to amplified the rDNA-ITS region and rDNA 28S D2-D3 region, respectively. The purified PCR products were ligated into One step ZTOPO-Blunt/TA vector and transformed to Escherichia coli strain DH5α, and then sequenced by Sunya Biotechnology Co., Ltd (Henan, China). The obtained seqences were submitted to NCBI. The rDNA-ITS sequences (669 bp, GenBank Accession No: OP456372 and OP466367) exhibited 95.0% to 97.1% of identity with P. zeae sequences (KU198980 and KU198975). The obtained D2-D3 region of the 28S rDNA sequences (782 bp, OP441397 and OP448675) exhibited 99.7% to 100% identity with P. zeae sequences (EU130893 and KY424269). Consequently, both morphological and molecular data confirmed the identity of P. zeae. To further confirm reproduction on corn, single corn seeds (cv. Zhengdan 958) were sown in eight 2-liter pots filled with 1.8-liter of sterilized soil in greenhouse at 28°C. About 15 days after sowing, each pot with one corn plant with the same growth status was selected to inoculate with 1,000 mixed stage nematodes of P. zeae , Eight pots of uninoculated corn plants were used as controls. After 60 days, the inoculated plants were harvested and brown lesions were observed on roots. No symptoms and nematodes was detected in the control. An average number of RLN per pot was 3,752 in soil and 1,183 in roots were extracted, the reproduction factor (final population/initial population) was 4.94, indicating that P. zeae infects and reproduces well on this corn cultivar. P. zeae has only been reported on corn in Guangxi Province, southern in China(Fang et al. 1994). To our knowledge, this is the fist report of P. zeae infecting corn in Jiangsu Province, eastern in China. As P. zeae can cause great damage to corn, necessary measures should be taken to prevent the spread of P. zeae to other areas.

Features of allelopathy between fusarium species and concomitant Trichoderma longibrachiatum in the maize rhizosphere in Kuban

The purpose of these studies was to study the interaction of pathogens of corn root rot in the agricultural sector of the Northern region of Krasnodar region. Corn root rot in the agricultural farms of the region annually cause significant damage to the harvest of silage and corn grain. In the course of research, the biological feature of the relationship between two species of the genus Fusarium: Fusarium concentricum Nirenberg & O'donnell and Fusarium proliferatum Matsush., optimizing the five-fold increase in the first species of mushroom compared to the growth of the second. PCR analysis revealed Fusarium oxysporum strain IMI 58289 with increased ability to exhibit elements of aggressive synergism. These fungi belong to the Department Ascomycota, order Hypocreales. In the soil of the studied rhizosphere, a natural hyperparasite – Trichoderma was detected, which can be used to minimize Fusarium infection.

First Report of Pythium torulosum Causing Corn Root Rot in Northeastern China.

In October 2017, we collected five soil samples from each of several fields with a history of severe corn (Zea mays) seedling disease in Heilongjiang province of China. Affected seedlings were wilted with severe root rot, and a high incidence of seedling death was observed in the fields. Corn seeds were seeded in the collected soil samples and grown in a growth chamber for 21 days set at the following incubation temperatures: 21℃/7℃ for 6 days, 10℃/3℃ for 4 days, 16℃/7℃ for 5 days, 20℃/20℃ for 6 days (16 h/8 h, light/dark) (Tang et al. 2019). The corn seedlings in the growth chamber showed the same symptoms observed in the field as mentioned above. Corn root rot samples were collected from several symptomatic plants in the growth chamber to isolate the possible pathogen. Symptomatic roots were washed in 0.5% NaOCl for 2 min, rinsed in sterile water and cut into 1-2 mm segments and then plated on corn meal agar amended with pimaricin (5 μg/ml), ampicillin (250 μg/ml), rifampicin (10 μg/ml), pentachloronitrobenzene (50 μg/ml), and benomyl (10 μg/ml) (PARP+B), which is selective for oomycetes (Jeffers and Martin 1986). After 3 days of incubation in the dark at 25℃, colonies were transferred to 10% V8 juice agar and incubated at 25℃ for 2 weeks. Six isolates were identified as Pythium torulosum based on the morphology of sexual and asexual structures following van der Plaats-Niterink's key (van der Plaats-Niterink 1981). On 10% V8 juice agar, the hypha were aseptate and colonies had filamentous sporangia with a dendroid or globose structure. The oogonia were globose or subglobose, laevis, terminal, rarely intercalary, ranging from 12-19 (average 16) μm. Antheridia were mostly sessile or brachypodous, and each oogonium was supplied by 1-2 antheridia cells. Oospores were globose, plerotic, ranging from 9-16 (average 13) μm. For the molecular identification, two molecular targets, the internal transcribed spacer (ITS) region of ribosomal DNA and cytochrome c oxidase subunit II (CoII), were amplified and sequenced using universal primer sets DC6/ITS4 (Cooke et al. 2000) and FM58/FM66 (Villa et al. 2006), respectively for one isolate, "copt". BLAST analyses of a 971 bp ITS segment amplified from copt (GenBank Accession No. MT830918) showed 99.79% identity with a P. torulosum isolate (GenBank Accession No. AY598624.2). For the COⅡ gene of copt, BLAST analyses of a 553 bp segment (GenBank Accession MT843570) showed 98.37% identity with P. torulosum isolate (GenBank Accession No. AB095065.1). Thus, the isolate, copt, was identified as P. torulosum based on morphological characteristics and molecular analysis. To confirm pathogenicity and Koch's postulates, a pathogenicity test was conducted as described by Zhang et al. (2000). Briefly, a 5 mm culture plug from the P. torulosum isolate, copt, was transferred to a 9-cm petri dish containing 20mL 10% V8 juice agar and incubated in the dark at 25℃ for 7 days. The culture was cut into small pieces and mixed with a sterilized soil mix (40% organic peat substrate, 40% perlite, and 20% soil) at a ratio of one petri dish per 100 g soil mix. Ten corn seeds were planted at a depth of 2 cm in a 500-mL pot containing the inoculated soil mix. The control pots were mock inoculated with plain 10% V8 juice agar. Pots were incubated in a greenhouse at temperatures ranging from 21 to 23℃. There were four replications. After 14 days, corn roots brown and rotted were observed, which was similar to those observed in the field and growth chamber. Control plants remained symptomless and healthy. P. torulosum copt was consistently re-isolated from the symptomatic roots. To our knowledge, this is the first report of P. torulosum causing root rot of corn in Northeastern China. Corn is an important crop in Heilongjiang and the occurrence of root rot caused by this pathogen may be a new threat to corn plants. There is a need to develop management measures to control the disease.

First Report of Binucleate Rhizoctonia AG-F Causing Stalk and Root Rot of Corn (Zea mays) in Turkey

First Report of Binucleate <i>Rhizoctonia</i> AG-F Causing Stalk and Root Rot of Corn (<i>Zea mays</i>) in Turkey

The Relationship Analysis on Corn Stalk Rot and Ear Rot According to Fusarium Species and Fumonisin Contamination in Kernels.

Fusarium diseases, including corn root rot, sheath rot, stalk rot, and ear rot are frequently occurring in maize producing areas of China. Fusarium stalk rot and ear rot are the most serious diseases and often occur at the same time, but it is unclear whether there is a correlation between Fusarium composition and disease occurrence. This study was conducted to clarify the relationship between the two diseases. A total of 49 corn stalk rot samples were collected from 15 regions of eight provinces in China from 2016 to 2018. The pathogens were isolated and identified separately from stalks, ear stems, and kernels. The contents of the fumonisins (FB1 and FB2) were detected in kernels. The results showed that the main Fusarium species were found in corn kernels, ear stems and stalks at the same time. The results showed that 1201 strains of Fusarium verticillioides, 668 strains of Fusarium oxysporum, 574 strains of Fusarium graminearum species complex (FGSC), 318 strains of Fusarium equiseti, 95 strains of Fusarium proliferatum, and 40 strains of Fusarium subglutinans were isolated from 1470 corn kernels, 245 ear stems, and 1225 stalks randomly selected from 49 samples. The contamination rate of fumonisins in the 49 samples was 57.1% with an average content of 1.9 μg/g, of which four samples exhibited higher levels as set by the European Commission (4.0 μg/g). These results provide a certain association between stalk rot and ear rot and lay a foundation to study the relationships among Fusarium maize diseases.

Eight Species of Fusarium Cause Root Rot of Corn (Zea mays) in South Dakota

Fusarium root rot of corn (Zea mays L.) is yield-limiting in the United States, but there is no information available on the disease in South Dakota. In 2015, corn seedlings with discolored roots were arbitrarily sampled from 50 South Dakota fields, and 198 isolates were recovered. Eight species (F. acuminatum, F. boothii, F. equiseti-incarnatum complex, F. graminearum, F. oxysporum, F. proliferatum, F. solani, and F. subglutinans) were identified by morphology and translation elongation factor 1-α gene sequencing. F. graminearum (26.8%) was the most common fungus, and F. boothii (0.5%) was the least recovered. Fourteen isolates, representing the eight species, were evaluated for their pathogenicity on 2-week-old seedlings of inbred ‘B73’ using the inoculum layer method in the greenhouse. Fourteen days postinoculation, root rot severity was evaluated on a 1-to-5 rating scale and expressed as relative treatment effects (RTEs). F. proliferatum isolate P2 caused significantly greater RTE (based on 95% confidence intervals) on seedlings than the other isolates and the noninoculated control, except F. graminearum isolate FG23. This study indicates that the eight species of Fusarium are aggressive root rot pathogens of corn in South Dakota, and this information will help evaluate strategies for producers to manage these pathogens in their fields.

Compost and Manure Mediated Impacts on Soilborne Pathogens and Soil Quality

Root rots of snap bean (Phaseolus vulgaris L.) and sweet corn (Zea mays L.) cause economic losses to farmers. This study was conducted to determine whether dairy manure amendments suppressed root diseases and to describe relationships between disease severity and soil characteristics. Field plots were amended with high or low rates of fresh or composted dairy manure solids in 2001 and 2002. Soils were collected at 2 and 12 mo after the first amendment and 2 and 6 mo after the second amendment. Greenhouse bioassays were conducted to assess severity of damping‐off (DO) of cucumber (Cucumis sativus L.) and root rots of bean and corn. Soils were analyzed for soil free (fPOM) and occluded (oPOM) particulate organic matter content, rate of hydrolysis of fluorescein diacetate (FDA), arylsulfatase activity, microbial biomass C, and water‐stable aggregation (WSA). Two months after amendment, all amendments (except the low rate of manure) reduced the severity of DO 30%, bean root rot 29%, and corn root rot 67%. Twelve months after amendment, amended soils were no longer suppressive. All amendments were suppressive after re‐amendment the following year and no longer suppressive 6 mo later. In Year 1, significant suppression was observed across all diseases when fPOM content was ≥12.1 g cm−3, FDA activity was ≥2.88 μg FDA min−1 g−1 dry wt, and microbial biomass was ≥91.6 μg C g−1 dry wt, and these levels were proposed as suppressive thresholds. Only the FDA threshold held up over all sampling times.

First Report of Rhizoctonia solani AG-2-4 on Carrot in Georgia.

Anastomosis group-2-4 (AG-2-4) of Rhizoctonia solani Kühn was formally described in 2002 (1), but it was first collected in 1983 in Georgia from corn (Zea mays L.) exhibiting symptoms of crown and brace root rot. Although occasionally present on diseased corn roots, the role that isolates of AG-2-4 play in crown and brace root rot of corn is not specifically known (2). More recently, as part of a broad multi-year (1996 to 2000) survey of root diseases in field grown carrot (Daucus carota L.), isolates of R. solani AG-2-4 were recovered from diseased carrot plants in various stages of growth from fields of sandy loam soil at many locations in southern Georgia, including commercial fields in Coffee and Tift counties. During the 1996 to 2000 growing seasons, 123 isolates of Rhizoctonia sp. (including multinucleate and binucleate types) were collected from lesions on developing and mature carrot roots. Of these, 34% were AG-2-4, 10% were AG-2-2IV, 6% were AG-4, and 32% were binucleate Rhizoctonia sp. The remaining 18% were lost prior to AG typing. An additional 40 isolates were collected from carrot seedlings or soil and of these, 55% were AG-4, 18% were AG-2-2IV but none were AG-2-4. Virulence on carrot seedlings by two isolates of AG-2-4 (777R1P5-SL2 and 758C) was compared with virulence of isolates of AG-4, AG-2-2IV, AG-2-1, and binucleate Rhizoctonia sp. Carrot seeds soaked for 5 min in 0.5% NaOCl were planted in petri dishes containing moist autoclaved sandy loam soil. Each dish was inoculated in the center with a 10-mm-diameter disk cut from a 9-day-old potato dextrose agar (PDA) culture of the appropriate isolate. Petri dishes were placed in a 26°C incubator for 9 days, and then the seedlings were rated for disease. Virulence on mature carrot root tissue was also assessed on the same set of isolates. Cross sections of carrot roots (5 to 10 mm thick) were surface disinfested in 0.5% NaClO for 5 min. Three cross sections were placed on moist filter paper in sterile petri dishes and each was inoculated with a 5-mm-diameter disk of inoculum cut from 8- to 10-day-old cultures growing on PDA. All treatments were rated for damage following incubation on a lab bench at 21 to 24°C for 7 days. Isolate 777R1P5-SL2 caused moderate damage to seedlings but minimal rotting of mature carrot root tissue. Isolate 758C did no damage to either seedlings or root tissue. The AG-4 and AG-2-2IV isolates killed all seedlings and caused extensive rot on mature root tissue. The AG-2-1 isolate caused moderate damage to seedlings and mature root tissue, whereas isolates of binucleate Rhizoctonia sp. damaged neither seedling nor mature root tissue. These data suggest that some isolates of R. solani AG-2-4 may be capable of causing minor damage to carrot seedlings in the field in Georgia, but isolates of R. solani AG-4 and AG-2-2IV pose greater threat to seedlings and mature roots of carrot. Published data shows that isolates of AG-2-4 can kill seedlings of lettuce, cauliflower, and broccoli in the laboratory (1). R. solani AG-2-4 also may be capable of killing these crops in the field, all of which are grown commercially in Georgia. To our knowledge, this is the first report of R. solani AG-2-4 on carrot in Georgia.

Fumonisins in Maize: Can We Reduce Their Occurrence?

Fumonisins in Maize: Can We Reduce Their Occurrence?

Incidence of Phoma terrestris, Causal Agent of Red Root Rot, in Corn Roots and Soil in Delaware and on the Eastern Shore of Maryland.

Red root rot of corn (Zea mays L.) has caused sporadic disease losses in Delmarva during the past 6 years. A survey was made between 21 August and 14 September 1995 in 11 counties in Delaware and on the eastern shore of Maryland to detect Phoma terrestris (E. M. Hans.) in corn roots and in the surrounding soil. Sampling was based on one field per 1,200 ha of corn production in each county. Three root samples and one soil sample were collected from each of 100 corn production fields from corn plants with diseased basal stalk tissue. The presence of P. terrestris was confirmed by cultures from root samples that produced a beet-red color on Watson's sterile wheat straw agar (2). Serial dilutions of soil samples in 0.1% water agar were mixed with unsolidified Watson's basal medium, followed by amendment with a 2-(4-thiazolyl)benzimidazole solution (1). P. terrestris was detected in root samples from 99% of the fields surveyed and from 82% of the soil samples. Soil populations ranged from 0.2 to 200 CFU per g of soil, with a mean of 12.5 CFU. This survey indicated that P. terrestris is widespread in corn production fields in Delaware and on the eastern shore of Maryland. Disease symptoms in surveyed fields indicated that pathogenicity on corn is variable, generally does not result in serious losses, and is related to hybrid susceptibility and growing conditions.

根朽病に対するトウモロコシのり病性と病原菌株の病原性の差異

Rhizoctonia root rot of corn is a recently occurring disease which has been reported since 1980. To clarify the background of the disease's occurrence, 20 native varieties, 66 foreign varieties and 27 inbred lines were tested for resistance to the pathogen, Rhizoctonia solani AG 2-2. The commercial Fi variety P3358 was used as a standard. All of the 113 varieties or lines were found to be susceptible as well as the standard used. These results showed that corn was originally susceptible to R. solani AG2-2, and the disease's occurrence is not related with the corn variety. On the other hand, the pathogenicity of R. solani AG2-2 isolated from diseased plants of sugar beet and corn was compared through cross inoculation tests. The pathogenicity of corn strains was strong both to corn and sugar beet. The sugar-beet strains were more pathogenic to sugar beet, but clearly weaker to corn.

Effects of Herbicide Antidotes on Sorghum Downy Mildew

Effects of Herbicide Antidotes on Sorghum Downy Mildew

Prevalence and Virulence of Pythium species Associated with Root Rot of Corn in Poorly Drained Soil

Prevalence and Virulence of Pythium species Associated with Root Rot of Corn in Poorly Drained Soil

PHIALOPHORA RADICICOLA CAIN, A CORN ROOTROT PATHOGEN

During the summer of 1950, Phialophora radicicola, was found on corn roots in soil near Chatham, Ridgetown, and Harrow, Ont. Owing to its color and parasite-host relations, it may have been mistaken previously for Rhizoctonia solani or a Rhizophagus species. It can be isolated only when a piece of apparently healthy corn root tissue with the adhering mycelium is removed from an infected root and placed on agar media. After two or three months of culture on nutrient and on potato dextrose agar, P. radicicola lost its ability to sporulate, but this ability was revived when it was cultured on moist corn roots. No sexual stage of the organism has been found. The fungus may attack corn roots at any time throughout the season and its brown runner-hyphae or macrohyphae grow parallel to the roots. The finer infection hyphae or microhyphae penetrate the outer root tissue and their infection threads are surrounded by "wall tubules". The fungus is quite aggressive, but not very pathogenic, and apparently it is followed by numerous secondary organisms. The similarity of this organism to Ophiobolus graminis is very noticeable.

STUDIES ON ROOT ROT OF CORN IN ONTARIO

Root rot of corn in Ontario is caused primarily by parasitic soil micro-organisms, the most important of which are species of Pythium, Helminthosporium, and Fusarium in that order. The disease causes a decrease in the stand by pre-emergence killing and a dwarfing of the plants by the parasitic invasion and destruction of their roots by the organisms. The pathogens have different optimum soil temperatures but the lower ranges favour those that cause the most severe damage. The roots of other field crops can be parasitized by the organisms found associated with corn root rot, but their effect on the development of the crop varies greatly. It has been proved under greenhouse conditions that the severity of the disease is greatly reduced if the corn is preceded by cover crops of soybeans and materially increased when preceded by timothy. Other crops tested have an intermediate effect.