Biofumigation: A Cover Crop Option 12 Months of the Year to Manage Three Soilborne Pathogens Ailing the Australian Vegetable Industry

Brassica biofumigant cover crops are being increasingly considered in vegetable crop rotations as part of an integrated disease management strategy and simply as a cover cropping choice. Nine biofumigant varieties were assessed to see if they could be grown year-round in the Lockyer Valley South East Queensland region, for yield, days to incorporation and glucosinolate concentrations, as well as efficacy against 3 soilborne pathogens; Sclerotinia sclerotiorum, Sclerotium rolfsii and Macrophomina phaseolina. The fastest growing brassica biofumigant was BQ Mulch which reached 25% flowering in 36 and 59 days from planting to incorporation with a summer and winter planting respectively. Nemcon and Nemclear took the longest to incorporation when planted in summer, 101 days and failed to flower, while Caliente, Tillage Radish and Biofum reached 25% flowering and incorporation in 98 days when planted in winter. BQ Mulch produced the least amount of biomass, 30.93 t/ha fresh weight and 2.92 t/ha dry weight with a summer planting. Biofum producing the greatest amount of biomass, 185.76 t/ha fresh weight and 17.34 t/ha dry weight with a summer and winter planting respectively. Most varieties produced more total glucosinolates during summer compared to winter. Caliente produced the highest levels of Total GSLs with 53.47 µmol/g DW in summer compared to 23.78 µmol/g DW in winter. This was reflected in their efficacy against the soilborne pathogens. Caliente and Mustclean were more efficacious at controlling Macrophomina and Sclerotinia in summer compared to winter while all varieties were more efficacious at controlling Sclerotinia with a summer planting compared to a winter planting.

Genomic Analysis Reveals Potential Mechanisms Underlying Promotion of Tomato Plant Growth and Antagonism of Soilborne Pathogens by Bacillus amyloliquefaciens Ba13

Microbial agents are considered the optimal alternative for chemical agents. Exploring the mechanisms underlying the beneficial effects of microbial agents is essential for rational applications in the field.

Effects of Interspecific Grafting Between Capsicum Species on Scion Fruit Quality Characteristics

Production of Capsicum annuum peppers is often limited, especially in tropical environments, by susceptibility to soil pathogens including Ralstonia solanacearum. Grafting desirable cultivars onto selected rootstocks can increase adaptation to abiotic stress and is an alternative to pesticides for managing soilborne pathogens. Cultivars of two other pepper species, Capsicum baccatum and Capsicum chinense, are tolerant or resistant to an array of soilborne pathogens and have potential as rootstocks; however, knowledge of how interspecific grafting may affect scion fruit quality is lacking. Flowering time, yield, and fruit quality characteristics were evaluated in 2017 and 2020 for C. annuum cultivars Dulcitico, Nathalie (2017), Gypsy (2020), and California Wonder used as scions grafted onto Aji Rico (C. baccatum) and Primero Red (C. chinense) rootstocks, including self-grafted and nongrafted scion checks. In 2020, the rootstocks per se were evaluated. The two rootstocks (‘Aji Rico’ and ‘Primero Red’), three scions, and self- and nongrafted scions were evaluated using a factorial, replicated, completely randomized design in fields at the West Madison and Eagle Heights Agricultural Research Stations located in Madison, WI, in 2017 and 2020, respectively. Differences among the main effects for scion fruit quality characteristics were consistent with cultivar descriptions. No scion × rootstock interactions were observed. Rootstocks did not result in changes in total fruit number, yield, fruit shape (length-to-width ratio), or soluble solids of scion fruit compared with self- and nongrafted checks. The rootstock ‘Primero Red’ increased fruit weight and decreased time to flowering regardless of scion compared with self- and nongrafted checks. All scions were sweet (nonpungent) cultivars and both rootstocks were pungent cultivars. No capsaicinoids were detected in the fruit of sweet pepper scions grafted onto pungent pepper rootstocks. The results indicate that interspecific grafts involving ‘Aji Rico’ and ‘Primero Red’ will not have deleterious effects on fruit quality characteristics of sweet pepper scions.

Engineering Multigenerational Host-Modulated Microbiota against Soilborne Pathogens in Response to Global Climate Change

Crop migration caused by climatic events has favored the emergence of new soilborne diseases, resulting in the colonization of new niches (emerging infectious diseases, EIDs). Soilborne pathogens are extremely persistent in the environment. This is in large part due to their ability to reside in the soil for a long time, even without a host plant, using survival several strategies. In this regard, disease-suppressive soils, characterized by a low disease incidence due to the presence of antagonist microorganisms, can be an excellent opportunity for the study mechanisms of soil-induced immunity, which can be applied in the development of a new generation of bioinoculants. Therefore, here we review the main effects of climate change on crops and pathogens, as well as the potential use of soil-suppressive microbiota as a natural source of biocontrol agents. Based on results of previous studies, we also propose a strategy for the optimization of microbiota assemblages, selected using a host-mediated approach. This process involves an increase in and prevalence of specific taxa during the transition from a conducive to a suppressive soil. This strategy could be used as a model to engineer microbiota assemblages for pathogen suppression, as well as for the reduction of abiotic stresses created due to global climate change.

Response of Cover Crops to Phytopythium vexans, Phytophthora nicotianae, and Rhizoctonia solani, Major Soilborne Pathogens of Woody Ornamentals

Management of plant diseases is a subject of concern for researchers as well as growers. Different management practices are being developed and used to combat the rising number of plant pathogens, which threaten nursery crop production. Use of cover crops for sustainable management of soilborne diseases is being explored as an alternative strategy to the chemicals. However, the potential threat of these cover crops acting as a secondary host of these devastating soilborne pathogens has not been described. We studied the response of the major cover crops being used by woody ornamental growers in the Southeastern United States to Phytopythium vexans, Phytophthora nicotianae, and Rhizoctonia solani in greenhouse conditions to identify the effective cover crops that can be used in a nursery field production system. Data related to post-emergence damping-off and plant growth parameters (plant height increase and fresh weight) were recorded. Similarly, cover crop roots were assessed for root rot disease severity using a scale of 0–100% roots affected. Among the tested cover crops, the grass cover crops triticale (×Triticosecale Wittm. ex A. Camus.), annual ryegrass (Lolium multiflorum L.), Japanese millet (Echinochloa esculenta (A. Braun) H. Scholz), and the legumes Austrian winter pea (Pisum sativum var. arvense (L.) Poir) and cowpea ‘Iron and Clay’ (Vigna unguiculata (L.) Walp.), showed lower root rot disease severity and post-emergence damping-off in the soil inoculated with P. nicotianae, R. solani, or P. vexans compared to the other crops. Since these cover crops can act as non-host crops and benefit the main crop in one way or another, they can be used in the production system. Further research is recommended to evaluate their performance in a natural field setting.

Irreplaceable Role of Amendment-Based Strategies to Enhance Soil Health and Disease Suppression in Potato Production

Soilborne diseases are a major constraining factor to soil health and plant health in potato production. In the toolbox of crop management, soil amendments have shown benefits to control these diseases and improve soil quality. Most amendments provide nutrients to plants and suppress multiple soilborne pathogens. Soil amendments are naturally derived materials and products and can be classified into fresh or living plants, organic or inorganic matters, and microbial supplements. Fresh plants have unique functions and continuously exude chemicals to interact with soil microbes. Organic and inorganic matter contain high levels of nutrients, including nitrogen and carbon that plants and soil microorganisms need. Soil microorganisms, whether being artificially added or indigenously existing, are a key factor in plant health. Microbial communities can be considered as a biological reactor in an ecosystem, which suppress soilborne pathogens in various mechanisms and turn soil organic matter into absorbable forms for plants, regardless of amendment types. Therefore, soil amendments serve as an energy input, nutrient source, and a driving force of microbial activities. Advanced technologies, such as microbiome analyses, make it possible to analyze soil microbial communities and soil health. As research advances on mechanisms and functions, amendment-based strategies will play an important role in enhancing soil health and disease suppression for better potato production.

Holistic diagnosis and Cannabis microbiome.

The concept of holistic diagnosis used in this chapter has three layers of meaning. First, a plant is a system and all parts of the system should be viewed as a whole. Diagnosis should be based on an entire plant instead of on a single piece of plant material. Secondly, the approach of 'all things considered' should be practised when finding pests, pathogens, or factors that contribute to an observed plant problem. This approach considers the diagnosis process to be an investigation instead of a specific test for a single pathogen. Thirdly, all factors found in a disease are related and each of them may have a unique role in disease initiation and progression. Cannabis pest and disease complex holistic diagnosis, including disease complexes involving nematodes and soilborne pathogens are described, as well as microbiota and microbiome (including epiphytes and endophytes) and their benefits and drawbacks.

Efficacy of the Biopesticide NECO in the control of Ralstonia solancearum, causal agent of tomato bacterial wilt in Côte d’Ivoire

The tomato crop is confronted to numerous soilborne pathogens, including Ralstonia solanacearum, which considerably limits its production. In order to control this bacterium, a biological control approach has been considered by evaluating the efficacy of the NECO biopesticide against this bacteriosis. In vitro confrontations were carried out using a range of five concentrations of the biopesticide. In vivo, NECO solutions of 5 and 10 mL/L were incorporated into soil previously infested with R. solanacearum before transplanting tomato plants. Zones of bacterial growth inhibition were observed after the application of the NECO biopesticide. Results showed that the 20 mL/L concentration resulted in a higher inhibition rate. The biopesticide at the 10 mL/L concentration significantly reduced the incidence of bacterial wilt (54.05%) under in vivo conditions. The NECO biopesticide could be used as a control agent for Ralstonia solanacearum.

Fungal Pathogens Affecting the Production and Quality of Medical Cannabis in Israel

The use of and research on medical cannabis (MC) is becoming more common, yet there are still many challenges regarding plant diseases of this crop. For example, there is a lack of formal and professional knowledge regarding fungi that infect MC plants, and practical and effective methods for managing the casual agents of disease are limited. The purpose of this study was to identify foliar, stem, and soilborne pathogens affecting MC under commercial cultivation in Israel. The predominant major foliage pathogens were identified as Alternaria alternata and Botrytis cinerea, while the common stem and soilborne pathogens were identified as Fusarium oxysporum and F. solani. Other important fungi that were isolated from foliage were those producing various mycotoxins that can directly harm patients, such as Aspergillus spp. and Penicillium spp. The sampling and characterization of potential pathogenic fungi were conducted from infected MC plant parts that exhibited various disease symptoms. Koch postulates were conducted by inoculating healthy MC tissues and intact plants with fungi isolated from infected commercially cultivated symptomatic plants. In this study, we report on the major and most common plant pathogens of MC found in Israel, and determine the seasonal outbreak of each fungus.

Maltose and Totally Impermeable Film Enhanced Suppression of Anaerobic Soil Disinfestation on Soilborne Pathogens and Increased Strawberry Yield

Anaerobic soil disinfestation (ASD) is widely used to control soilborne diseases in organic crop production. The effect of ASD used different sealed films on soilborne pathogens and strawberry growth was evaluated in two laboratory studies and two field trials. Under maltose as carbon sources, 28 °C temperature and 30% of soil moisture optimal conditions ASD decreased Fusarium spp. and Phytophthora spp. by 100%. ASD used maltose as an organic amendment and sealed with totally impermeable film (TIF) obtained the highest suppression (>96%) against Fusarium spp. and Phytophthora spp. (>91%). According to the laboratory results, the efficacy of ASD utilizing 6 or 9 t/ha maltose and sealing with TIF was evaluated and compared with reference treatment with chloropicrin (Pic) or solarization (Sol) in the field trials. Compared with the untreated soil, ASD treatments greatly reduced the pathogenic population of Fusarium spp. and Phytophthora spp., and successfully controlled the damage of fusarium wilt with evidence of lower mortality (6%). ASD significantly increased soil nutrition promoted plant growth and increased strawberry yield, which was similar as the Pic, but better than Sol treatment. The analyzed fungal and bacterial microbiota did not show significant differences in the taxonomic richness and diversity between the compared treatments. Nevertheless, the abundance of some bacterial and fungal taxa tended to change between treated. The evidence showed that adding maltose and sealing TIF for ASD has the potential to replace Pic for pathogen control in commercial strawberry production.