Oxidative burst elicited by Bacillus mycoides isolate Bac J, a biological control agent, occurs independently of hypersensitive cell death in sugar beet

Chemical Management Strategies for Halo Blight of Hop and In Vitro Sensitivity of Diaporthe humulicola Populations to Various Fungicide Classes

Halo blight of hop, caused by Diaporthe humulicola, has increased in eastern North America since 2018. When left untreated, the disease can cause yield loss ranging from 17 to 56%. Currently, there are no fungicides registered for use on halo blight of hop. From 2020 to 2022, field trials were conducted using 10 fungicides registered for use on powdery and downy mildew of hop to determine their efficacy against halo blight. To validate field results, the effective concentration of fungicide required for 50% growth inhibition (EC50) value was determined for each active ingredient including flutriafol, tebuconazole + fluopyram, cyflufenamid, and trifloxystrobin + salicylhydroxamic acid (SHAM). Each fungicide tested had an EC50 value less than 50 ppm. A discriminatory dose was used to test the sensitivity of 206 D. humulicola isolates collected from the eastern United States and Canada in a poison agar assay. Results showed that tebuconazole + fluopyram decreased the incidence and severity of halo blight in the field. Also, this fungicide combination had EC50 values of 2.26 × 10-1 ppm and significantly reduced the growth of most of the isolates tested. Trifloxystrobin + SHAM decreased the presence of halo blight in the field trial, but some isolates were less sensitive in discriminatory dose testing. Our results show that fungicides in FRAC groups 3, 7, and 11 were the most effective to control halo blight. Analyses of field trials showed a positive correlation between the severity of early-season downy mildew infections and late-season halo blight infections.

Genomic Insights into the Bactericidal and Fungicidal Potential of Bacillus mycoides b12.3 Isolated in the Soil of Olkhon Island in Lake Baikal, Russia

The dispersal of plant pathogens is a threat to the global economy and food industry which necessitates the need to discover efficient biocontrol agents such as bacteria, fungi, etc., inhibiting them. Here, we describe the Bacillus mycoides strain b12.3 isolated from the soil of Olkhon Island in Lake Baikal, Russia. By applying the co-cultivation technique, we found that the strain inhibits the growth of plant pathogens, such as the bacteria Xanthomonas campestris, Clavibacter michiganensis, and Pectobacterium atrospecticum, as well as the fungus Alternaria solani. To elucidate the genomic fundament explaining these activities, we leveraged next-generation whole-genome sequencing and obtained a high-quality assembly based on short reads. The isolate bore seven known BGCs (biosynthetic gene clusters), including those responsible for producing bacillibactin, fengycin, and petrobactin. Moreover, the genome contained insecticidal genes encoding for App4Aa1, Tpp78Ba1, and Spp1Aa1 toxins, thus implicating possible pesticidal potential. We compared the genome with the 50 closest assemblies and found that b12.3 is enriched with BGCs. The genomic analysis also revealed that genomic architecture corresponds to the experimentally observed activity spectrum implying that the combination of produced secondary metabolites delineates the range of inhibited phytopathogens Therefore, this study deepens our knowledge of the biology and ecology of B. mycoides residing in the Lake Baikal region.

Biocontrol of rusted root rot in Panax ginseng by a combination of extracts from Bacillus amyloliquefaciens YY8 crude protein and Enterobacteriaceae YY115 ethyl acetate

BACKGROUND

Rusted root rot is one of the most common root diseases in Panax ginseng, and Cylindrocarpon destructans is one of the main pathogenic fungus. The objective of this study was to screen and explore the extracts of biocontrol bacteria isolated from ginseng rhizosphere soil against Cylindrocarpon destructans.

RESULTS

Bacterial strains Bacillus amyloliquefaciens YY8 and Enterobacteriacea YY115 were isolated and found to exhibit in vitro antifungal activity against C. destructans. A combination of crude protein extract from B. amyloliquefaciens YY8 and ethyl acetate extract from Enterobacteriacea YY115 in a 6:4 ratio exhibited the strongest antifungal activity against C. destructans. Measurements of electrical conductivity, protein content, and nucleic acid content in suspension cultures of C. destructans treated with a mixture extracts indicated that the extracts disrupted the cell membranes of rusted root rot mycelia, resulting in the leakage of electrolytes, proteins, and nucleic acids from the cells, and ultimately inhibiting the growth of C. destructans. The combined extracts suppressed the infection of ginseng roots discs by C. destructans effectively.

CONCLUSION

The extracts obtained from the two bacterial strains effectively inhibited C. destructans in P. ginseng. It can provide scientific basis for the development of new biological control pesticides, reduce the use of chemical pesticides, and promote the sustainable development of agriculture.

Understanding the sugar beet holobiont for sustainable agriculture

The importance of crop-associated microbiomes for the health and field performance of plants has been demonstrated in the last decades. Sugar beet is the most important source of sucrose in temperate climates, and-as a root crop-yield heavily depends on genetics as well as on the soil and rhizosphere microbiomes. Bacteria, fungi, and archaea are found in all organs and life stages of the plant, and research on sugar beet microbiomes contributed to our understanding of the plant microbiome in general, especially of microbiome-based control strategies against phytopathogens. Attempts to make sugar beet cultivation more sustainable are increasing, raising the interest in biocontrol of plant pathogens and pests, biofertilization and -stimulation as well as microbiome-assisted breeding. This review first summarizes already achieved results on sugar beet-associated microbiomes and their unique traits, correlating to their physical, chemical, and biological peculiarities. Temporal and spatial microbiome dynamics during sugar beet ontogenesis are discussed, emphasizing the rhizosphere formation and highlighting knowledge gaps. Secondly, potential or already tested biocontrol agents and application strategies are discussed, providing an overview of how microbiome-based sugar beet farming could be performed in the future. Thus, this review is intended as a reference and baseline for further sugar beet-microbiome research, aiming to promote investigations in rhizosphere modulation-based biocontrol options.

Exploring plant-microbe interactions of the rhizobacteria Bacillus subtilis and Bacillus mycoides by use of the CRISPR-Cas9 system

Bacillus subtilis HS3 and Bacillus mycoides EC18 are two rhizosphere-associated bacteria with plant growth-promoting activity. The CRISPR-Cas9 system was implemented to study various aspects of plant-microbe interaction mechanisms of these two environmental isolates. The results show that fengycin and surfactin are involved in the antifungal activity of B. subtilis HS3. Moreover, this strain emits several other volatile organic compounds than 2,3-butanediol, contributing to plant growth promotion. Confocal laser scanning microscopy observations of the GFP-labelled strain showed that HS3 selectively colonizes root hairs of grass (Lolium perenne) in a hydroponic system. For B. mycoides EC18, we found that the wild-type EC18 strain and a ΔasbA (petropectin-deficient) mutant, but not the ΔdhbB (bacillibactin-deficient) and ADKO (asbA and dhbB double knockout) mutants, can increase the plant biomass and total chlorophyll. All the mutant strains have a reduced colonization capability on Chinese cabbage (Brassica rapa) roots, at the root tip and root hair region compared with the wild-type strain. These results indicate that the siderophore, bacillibactin, is involved in the plant growth promoting activity and could affect the root colonization of B. mycoides. Collectively, the CRISPR-Cas9 system we developed for environmental isolates is broadly applicable and will facilitate deciphering the mechanisms of Bacillus-plant interactions. © 2018 The Authors.

Manipulation of the rhizosphere microbial community through application of a new bio-organic fertilizer improves watermelon quality and health

Bio-organic fertilizers (BOFs) combine functional microbes with a suitable substrate and have been shown to effectively suppress soil-borne diseases and promote plant growth. Here, we developed a novel bio-organic fertilizer (BOF) by fermentation of a cow plus chicken manure (M) compost using Fen-liquor Daqu (FLD) as a fermentation starter and compared the compositions of bacterial and fungal communities in the rhizosphere soil of watermelon plants after treatment with different fertilizers. Further, we aimed to explore the mechanisms underlying plant-promoting and disease (Fusarium wilt)-suppressing activities of each rhizosphere microbial community. The microbial communities of soil amended with cow plus chicken manure compost (S+M), soil amended with the BOF (S+BOF), and untreated control soil (S) without plants were analyzed through sequence analysis using the Illumina MiSeq platform. The results showed that a new microbial community was formed in the manure compost after fermentation by the Daqu. Application of the BOF to the soil induced remarkable changes in the rhizosphere microbial communities, with increased bacterial diversity and decreased fungal diversity. Most importantly, S+BOF showed the lowest abundance of Fusarium. Moreover, watermelon quality was higher (P < 0.05) in the S+BOF than in the S+M treatment. Thus, application of the BOF favorably altered the composition of the rhizosphere microbial community, suppressing Fusarium wilt disease and promoting plant quality.

Evaluation of root-knot nematode disease control and plant growth promotion potential of biofertilizer Ning shield on Trichosanthes kirilowii in the field

Biofertilizer Ning shield was composed of different strains of plant growth promotion bacteria. In this study, the plant growth promotion and root-knot nematode disease control potential on Trichosanthes kirilowii in the field were evaluated. The application of Ning shield significantly reduced the diseases severity caused by Meloidogyne incognita, the biocontrol efficacy could reached up to 51.08%. Ning shield could also promote the growth of T. kirilowii in the field by increasing seedling emergence, height and the root weight. The results showed that the Ning shield could enhance the production yield up to 36.26%. Ning shield could also promote the plant growth by increasing the contents of available nitrogen, phosphorus, potassium and organic matter, and increasing the contents of leaf chlorophyll and carotenoid pigment. Moreover, Ning shield could efficiently enhance the medicinal compositions of Trichosanthes, referring to the polysaccharides and trichosanthin. Therefore, Ning shield is a promising biofertilizer, which can offer beneficial effects to T. kirilowii growers, including the plant growth promotion, the biological control of root-knot disease and enhancement of the yield and the medicinal quality.

Proteomic Analysis Reveals the Positive Roles of the Plant-Growth-Promoting Rhizobacterium NSY50 in the Response of Cucumber Roots to Fusarium oxysporum f. sp. cucumerinum Inoculation

Plant-growth-promoting rhizobacteria (PGPR) can both improve plant growth and enhance plant resistance against a variety of environmental stresses. To investigate the mechanisms that PGPR use to protect plants under pathogenic attack, transmission electron microscopy analysis and a proteomic approach were designed to test the effects of the new potential PGPR strain Paenibacillus polymyxa NSY50 on cucumber seedling roots after they were inoculated with the destructive phytopathogen Fusarium oxysporum f. sp. cucumerinum (FOC). NSY50 could apparently mitigate the injury caused by the FOC infection and maintain the stability of cell structures. The two-dimensional electrophoresis (2-DE) approach in conjunction with MALDI-TOF/TOF analysis revealed a total of 56 proteins that were differentially expressed in response to NSY50 and/or FOC. The application of NSY50 up-regulated most of the identified proteins that were involved in carbohydrate metabolism and amino acid metabolism under normal conditions, which implied that both energy generation and the production of amino acids were enhanced, thereby ensuring an adequate supply of amino acids for the synthesis of new proteins in cucumber seedlings to promote plant growth. Inoculation with FOC inhibited most of the proteins related to carbohydrate and energy metabolism and to protein metabolism. The combined inoculation treatment (NSY50+FOC) accumulated abundant proteins involved in defense mechanisms against oxidation and detoxification as well as carbohydrate metabolism, which might play important roles in preventing pathogens from attacking. Meanwhile, western blotting was used to analyze the accumulation of enolase (ENO) and S-adenosylmethionine synthase (SAMs). NSY50 further increased the expression of ENO and SAMs under FOC stress. In addition, NSY50 adjusted the transcription levels of genes related to those proteins. Taken together, these results suggest that P. polymyxa NSY50 may promote plant growth and alleviate FOC-induced damage by improving the metabolism and activation of defense-related proteins in cucumber roots.

Study on screening and antagonistic mechanisms of Bacillus amyloliquefaciens 54 against bacterial fruit blotch (BFB) caused by Acidovorax avenae subsp. citrulli

Bacterial fruit blotch (BFB) was a serious threat to cucurbitaceae crops. It was caused by the gram-negative bacterium Acidovorax avenae subsp. citrulli. Two hundred strains, which have the potential in controlling plant diseases in our laboratory's biocontrol strain library, were employed to this research to screen some antagonistic bacteria, which can efficiently control bacterial fruit blotch disease. Based on the results of antagonistic activity experiments, greenhouse tests and field trials, 5 of the test strains have high abilities to control BFB. One of the 5 bacteria strains has the highest potential to control BFB named 54. The biocontrol efficacy of 54 was up to 60%. To characterize the strain, we used series of methods to evaluate the bacterium, including morphology analysis, physiological biochemical test and biomolecular assay. We found that the bacterium 54 belongs to the species Bacillus amyloliquefaciens. The colonization test results showed that 54 had the highest colonization levels, and the density of the strain on leaves was up 10(5)colony forming units (CFU) per gram of leaf tissue. Our recent results show that B. amyloliquefaciens 54 can promote the plant growth due to raised the contents of available N, P, K and the leaf chlorophyll. The antagonistic bacterium 54 can significantly control the BF B by increasing the expression level of defense-related gene PR1 and the accumulation the hydrogen peroxide in the plant. The results of trail experiment was also verified this efficient results of bacterium. This is also the first report of B. amyloliquefaciens strain that is able to control BFB.

Copper chloride induces antioxidant gene expression but reduces ability to mediate H2O2 toxicity in Xanthomonas campestris

Copper (Cu)-based biocides are currently used as control measures for both fungal and bacterial diseases in agricultural fields. In this communication, we show that exposure of the bacterial plant pathogen Xanthomonas campestris to nonlethal concentrations of Cu2+ ions (75 µM) enhanced expression of genes in OxyR, OhrR and IscR regulons. High levels of catalase, Ohr peroxidase and superoxide dismutase diminished Cu2+-induced gene expression, suggesting that the production of hydrogen peroxide (H2O2) and organic hydroperoxides is responsible for Cu2+-induced gene expression. Despite high expression of antioxidant genes, the CuCl2-treated cells were more susceptible to H2O2 killing treatment than the uninduced cells. This phenotype arose from lowered catalase activity in the CuCl2-pretreated cells. Thus, exposure to a nonlethal dose of Cu2+ renders X. campestris vulnerable to H2O2, even when various genes for peroxide-metabolizing enzymes are highly expressed. Moreover, CuCl2-pretreated cells are sensitive to treatment with the redox cycling drug, menadione. No physiological cross-protection response was observed in CuCl2-treated cells in a subsequent challenge with killing concentrations of an organic hydroperoxide. As H2O2 production is an important initial plant immune response, defects in H2O2 protection are likely to reduce bacterial survival in plant hosts and enhance the usefulness of copper biocides in controlling bacterial pathogens.

Possible roles of reactive chlorine II: assessing biotic chlorination as a way for organisms to handle oxygen stress

Natural formation of organically bound chlorine is extensive in many environments. The enzymes associated with the formation of chlorinated organic matter are produced by a large variety of organisms. Little is known about the ecological role of the process, the key question being: why do microorganisms promote chlorination of organic matter? In a recent paper we discuss whether organic matter chlorination may be a result of antagonistic interactions among microorganisms. In the present paper we evaluate whether extracellular microbial formation of reactive chlorine may be used as a defence against oxygen stress, and we discuss whether this process is likely to contribute to the formation of chlorinated organic matter. Our analysis suggests that periodic exposure to elevated concentrations of reactive oxygen species is a common denominator among the multitude of organisms that are able to enzymatically catalyse formation of reactive chlorine. There is also some evidence suggesting that the production of such enzymes in algae and bacteria is induced by oxygen stress. The relative contribution from this process to the extensive formation of chlorinated organic matter in natural environments remains to be empirically assessed.

Study of the anti-sapstain fungus activity of Bacillus amyloliquefaciens CGMCC 5569 associated with Ginkgo biloba and identification of its active components

An endophytic bacterium, designated strain Bacillus amyloliquefaciens CGMCC 5569 was isolated from Chinese medicinal Ginkgo biloba collected from Xuzhou, China. Both the filtrate and the ethyl acetate extract of strain CGMCC 5569 showed growth inhibition activity against the sapstain fungi Lasiodiplodia rubropurpurea, L. crassispora, and L. theobromae obviously (>65%) based on the comparison of the length of zones on the petri dish. From the ethyl acetate extract of the filtrate, the antifungal compounds were obtained as a series of lipopeptides, which including series of fengycin, surfactin and bacillomycin. It showed strong growth inhibition activity in vitro against the L. rubropurpurea, L. crassispora and L. theobromae by about 70.22%, 69.53% and 78.76%, respectively. The strong anti-sapstain fungus activity indicated that the endophytic B. amyloliquefaciens CGMCC 5569 and its bioactive components might provide an alternative bio-resource for the bio-control of sapstain.

Calcium- and ROS-mediated defence responses in BY2 tobacco cells by nonpathogenic Streptomyces sp

AIMS

The early molecular events underlying the elicitation of plant defence reactions by Gram-positive bacteria are relatively unknown. In plants, calcium and reactive oxygen species are commonly involved as cellular messengers of a wide range of biotic stimuli from pathogenic to symbiotic bacteria. In the present work, we checked whether nonpathogenic Streptomyces sp. strains could induce early signalling events leading to defence responses in BY2 tobacco cell suspensions.

METHODS AND RESULTS

We have demonstrated that nonpathogenic Streptomyces sp. OE7 strain induced a cytosolic Ca(2+) increase and a biphasic oxidative burst in the upstream signalling events, leading to defence responses in BY2 tobacco cell suspensions. Streptomyces sp. OE7 also elicited delayed intracellular free scopoletin production and programmed cell death. In agreement with scopoletin production, OE7 induced accumulation of PAL transcripts and increased accumulation of transcripts of EREBP1 and AOX genes that are known to be regulated by the jasmonate/ethylene pathway. Transcript levels of PR1b and NIMIN2α, both salicylic acid pathway-linked genes, were not modified. Moreover, Streptomyces sp. OE7 culture filtrates could reduce Pectobacterium carotovorum- and Pectobacterium atrosepticum-induced death of BY2 cells and soft rot on potato slices.

CONCLUSIONS

New insights are thus provided into the interaction mechanisms between Streptomyces sp. and plants; Streptomyces sp. could be sensed by plant cells, and through cytosolic Ca(2+) changes and the generation of reactive oxygen species, defence responses were induced.

SIGNIFICANCE AND IMPACT OF THE STUDY

These induced defence responses appeared to participate in attenuating Pectobacterium-induced diseases in plants. Thus, Streptomyces sp. OE7 could be a biocontrol agent against Pectobacterium sp.

A survey on basal resistance and riboflavin-induced defense responses of sugar beet against Rhizoctonia solani

We examined basal defense responses and cytomolecular aspects of riboflavin-induced resistance (IR) in sugar beet-Rhizoctonia solani pathsystem by investigating H(2)O(2) burst, phenolics accumulation and analyzing the expression of phenylalanine ammonia-lyase (PAL) and peroxidase (cprx1) genes. Riboflavin was capable of priming plant defense responses via timely induction of H(2)O(2) production and phenolics accumulation. A correlation was found between induction of resistance by riboflavin and upregulation of PAL and cprx1 which are involved in phenylpropanoid signaling and phenolics metabolism. Application of peroxidase and PAL inhibitors suppressed not only basal resistance, but also riboflavin-IR of sugar beet to the pathogen. Treatment of the leaves with each inhibitor alone or together with riboflavin reduced phenolics accumulation which was correlated with higher level of disease progress. Together, these results demonstrate the indispensability of rapid H(2)O(2) accumulation, phenylpropanoid pathway and phenolics metabolism in basal defense and riboflavin-IR of sugar beet against R. solani.

Evaluation of the virulence of Xanthomonas campestris pv. campestris mutant strains lacking functional genes in the OxyR regulon

Xanthomonas campestris pv. campestris causes black rot in cruciferous crops. Hydrogen peroxide (H(2)O(2)) production and accumulation is an important initial response in plant defense against invading microbes. The role of genes involved in the bacterial H(2)O(2) protection system in pathogenicity was evaluated. Mutants of katA (encoding a monofunctional catalase) and, to a lesser extent, katG (encoding a catalase-peroxidase) and oxyR (encoding a H(2)O(2) sensor and a transcription regulator), are hypersensitive to H(2)O(2) treatments that mimic the plant H(2)O(2) burst. These data correlate with the results of pathogenicity testing that show katA, katG, and oxyR mutants are avirulent on a compatible plant. Moreover, exposure to H(2)O(2) (1, 2, and 4 mM) highly induces the expression of genes in the OxyR regulon, including katA, katG, and ahpC. The avirulent phenotype of the oxyR mutant is partly because of its inability to mount an adaptive response upon exposure to an H(2)O(2) burst. Our data provide insights into important roles of a transcription regulator and other genes involved in peroxide stress protection in the virulence of X. campestris pv. campestris.

Differential occurrence of oxidative burst and antioxidative mechanism in compatible and incompatible interactions of Solanum lycopersicum and Ralstonia solanacearum

Striking increase in reactive oxygen species (ROS) such as hydrogen peroxide (H(2)O(2)) has been demonstrated to occur in plants in response to pathogen attack. The aim of this study was to investigate the biochemical aspects of ROS generation, antioxidative mechanism and cell wall reinforcement as responses of tomato cultivars Arka Meghali (AM; susceptible) and BT-10 (BT; resistant) against Ralstonia solanacearum (Ralsol). While the oxidative burst was characterized by a single phase ROS increase in AM, there was a clear bi-phasic ROS generation in BT. The first significant increase of H(2)O(2) production was noticed at 12 h post-inoculation (hpi) followed by a sharp increase in H(2)O(2) generation after 36 hpi. Lipid peroxidation was more in roots of AM than that of BT after pathogen inoculation. Superoxide dismutase and catalase activities were continuously at very high level in Ralsol-inoculated BT plants, whereas activities of the enzymes were observed to decrease at later stage in Ralsol-inoculated AM plants. Guaiacol peroxidase activity was high in Ralsol-inoculated roots of both cultivars, but BT recorded much higher activity than AM. Higher activity of ascorbate peroxidase in inoculated BT might be an indication of better scavenging activity of the enzyme. Total phenolic content and lignin deposition were significantly higher in Ralsol-inoculated BT compared to inoculated AM. Our results indicate that increased level of ROS production coupled with more efficient antioxidative system, lower rate of lipid peroxidation and high lignin deposition in cell wall may contribute to the resistance of tomato plants to Ralsol.

The catalase-peroxidase KatG is required for virulence of Xanthomonas campestris pv. campestris in a host plant by providing protection against low levels of H2O2

Xanthomonas campestris pv. campestris katG encodes a catalase-peroxidase that has a role in protecting the bacterium against micromolar concentrations of H(2)O(2). A knockout mutation in katG that causes loss of catalase-peroxidase activity correlates with increased susceptibility to H(2)O(2) and a superoxide generator and is avirulent in a plant model system. katG expression is induced by oxidants in an OxyR-dependent manner.

Sugarbeet leaf spot disease (Cercospora beticola Sacc.)dagger

SUMMARY Leaf spot disease caused by Cercospora beticola Sacc. is the most destructive foliar pathogen of sugarbeet worldwide. In addition to reducing yield and quality of sugarbeet, the control of leaf spot disease by extensive fungicide application incurs added costs to producers and repeatedly has selected for fungicide-tolerant C. beticola strains. The genetics and biochemistry of virulence have been examined less for C. beticola as compared with the related fungi C. nicotianae, C. kikuchii and C. zeae-maydis, fungi to which the physiology of C. beticola is often compared. C. beticola populations generally are not characterized as having race structure, although a case of race-specific resistance in sugarbeet to C. beticola has been reported. Resistance currently implemented in the field is quantitatively inherited and exhibits low to medium heritability.

TAXONOMY

Cercospora beticola Sacc.; Kingdom Fungi, Subdivision Deuteromycetes, Class Hyphomycetes, Order Hyphales, Genus Cercospora.

IDENTIFICATION

Circular, brown to red delimited spots with ashen-grey centre, 0.5-6 mm diameter; dark brown to black stromata against grey background; pale brown unbranched sparingly septate conidiophores, hyaline acicular conidia, multiseptate, from 2.5 to 4 microm wide and 50-200 microm long.

HOST RANGE

Propagative on Beta vulgaris and most species of Beta. Reported on members of the Chenopodiaceae and on Amaranthus. Disease symptoms: Infected leaves and petioles of B. vulgaris exhibit numerous circular leaf spots that coalesce in severe cases causing complete leaf collapse. Dark specks within a grey spot centre are characteristic for the disease. Older leaves exhibit a greater number of lesions with larger spot diameter. During the latter stage of severe epiphytotics, new leaf growth can be seen emerging from the plant surrounded by prostrate, collapsed leaves.

CONTROL

Fungicides in the benzimidazole and triazole class as well as organotin derivatives and strobilurins have successfully been used to control Cercospora leaf spot. Elevated levels of tolerance in populations of C. beticola to some of the chemicals registered for control has been documented. Partial genetic resistance also is used to reduce leaf spot disease.