Efficacy of Potential Control Agents Against Rosellinia necatrix and Their Physiological Impact on Avocado

Rosellinia necatrix is the causal agent of white root rot (WRR), a fatal disease affecting many woody plants, including avocado (Persea americana). As with other root diseases, an integrated approach is required to control WRR. No fully effective control methods are available, and no chemical or biological agents against R. necatrix have been registered for use on avocado in South Africa. Fluazinam has shown promising results in the greenhouse and field in other countries, including Spain. The current study aimed to investigate the potential of a fumigant, chloropicrin, and biological control agents (B-Rus, Beta-Bak, Mity-Gro, and Trichoderma) against R. necatrix both in vitro and in vivo as compared with fluazinam. In a greenhouse trial, results showed that Trichoderma and B-Rus were as effective as fluazinam at inhibiting R. necatrix in vitro and suppressed WRR symptoms when applied before inoculation with R. necatrix. In contrast, Mity-Gro and Beta-Bak failed to inhibit the pathogen in vitro and in the greenhouse trial, despite application of the products to plants before R. necatrix infection. Fluazinam suppressed WRR symptoms in plants when applied at the early stages of infection, whereas chloropicrin rendered the pathogen nonviable when used as a preplant treatment. Plants treated with Trichoderma, B-Rus, and fluazinam sustained dry mass production and net CO2 assimilation by maintaining the green leaf tissues despite being infected with the pathogen. This study has important implications for the integrated management of WRR.

Biochar for Circular Horticulture: Feedstock Related Effects in Soilless Cultivation

Biochar has previously been used in growing media blends as fertilizer or for improving plant growth, disease suppression, and as a sustainable replacement of peat. To achieve optimal circular horticulture, we propose here to reuse the biochar from spent growing media. However, it is unclear to what extent the biochar feedstock determines the mode of action of the biochar and if use of spent growing media biochar may encounter nutrient or salt problems. Differences in chemical characteristics, nutrient release, and interaction in a leaching experiment and effects on plant growth, nutrient uptake, and disease suppression in a strawberry greenhouse trial were studied for 11 biochars either processed from spent growing media or from lignocellulosic biomass. A well-studied biochar produced from oak wood was set as reference. Biochars produced from spent growing media were characterized by higher electrical conductivity, extractable and total nutrient concentrations compared with biochars produced from lignocellulosic biomass. Especially in the first phase of the leaching experiment, all biochars showed nutrient and salt release, with most prominent effects for spent growing media biochars and the reference biochar. The latter biochars were an important source of phosphorus and in particular of potassium. Only for the reference biochar, strawberry plants showed increased uptake of phosphorus, potassium and calcium, and increased chlorophyll concentration. No Bortrytis cinerea disease suppression and no increase in plant growth was observed for the tested biochars. It is concluded that spent growing media can be recycled as biochar in growing media without adverse effects compared to biochars produced from lignocellulosic biomass.

Multiple stressors in multiple species: effects of different RDX soil concentrations and differential water-resourcing on RDX fate, plant health, and plant survival

Response to simultaneous stressors is an important facet of plant ecology and land management. In a greenhouse trial, we studied how eight plant species responded to single and combined effects of three RDX soil concentrations and two levels of water-resourcing. In an outdoor trial, we studied the effects of high RDX soil concentration and two levels of water-resourcing in three plant species. Multiple endpoints related to RDX fate, plant health, and plant survival were evaluated in both trials. Starting RDX concentration was the most frequent factor influencing all endpoints. Water-resourcing also had significant impacts, but in fewer cases. For most endpoints, significant interaction effects between RDX concentration and water-resourcing were observed for some species and treatments. Main and interaction effects were typically variable (significant in one treatment, but not in another; associated with increasing endpoint values for one treatment and/or with decreasing endpoint values in another). This complexity has implications for understanding how RDX and water-availability combine to impact plants, as well as for applications like phytoremediation. Two plant species native to the southeastern United States, Ruellia caroliniensis and Salvia coccinea, exhibited treatment responses that suggest they may be useful for phytoremediation, even within complex and changing environments.

Evaluation of Thirty-Eight Models of Drippers Using Reclaimed Water: Effect on Distribution Uniformity and Emitter Clogging

Emitter clogging is a problem in drip irrigation systems, and it is accentuated when using reclaimed water. The objective of this work was to evaluate the different commercial models of drippers used for irrigation with reclaimed water in greenhouse horticultural crops. Thirty-eight commercial emitter models were selected. The selection was based on recommended models from different irrigation installation companies and manufacturers for this type of water. These emitters had different types of pipeline insertion (inter-line, in-line, and on-line) and different pressure compensation (compensating and non-compensating pressure). The emitter models were analyzed in the laboratory, determining the manufacturing variation coefficient (Cv) and the emitter equation (Ee), and subsequently two consecutive tests were established in the greenhouse, with a period of irrigation inactivation between tests, as well as different reclaimed water qualities. The reclaimed water was regenerated urban wastewater from the city of Almería. Distribution uniformity coefficient (DU) and clogging of the emitter (Ec) were evaluated in the greenhouse tests. Of the 38 models analyzed, only one of them did not comply with the International Organization for Standardization (ISO) standard, providing a Cv greater than 0.07. At the commencement of the greenhouse trial (0 h of irrigation), 14 dripper models performed with an excellent DU, above 95%, and all emitter models presented a DU above 85%. At the end of the second greenhouse trial (206 h of irrigation), three models recorded a DU of less than 85%. The application of reclaimed wastewater produced events of clogging and reducing uniformity in the studied models. On-line pressure-compensating emitter models had the worst performance. The irrigation inactivation period produced an improvement in uniformity values. By improving the quality of reclaimed water, all types of emitters showed a better performance during the irrigation season. Notably, pressure-compensating emitter models even showed some cleaning capacity, because their clogging was reduced in the second trial.

Chemical- and microbial-enhanced phytoremediation of cadmium-contaminated calcareous soil by maize

Phytoremediation is an appropriate technology used to remove pollutants from environment components. A greenhouse trial was conducted to test the hypothesis that application of surfactant levels and inoculation with Pseudomonas fluorescens bacterium and/or Piriformospora indica fungus enhances the phytoremediation of cadmium (Cd). Maize seeds were sown in Cd-polluted soil, and after 2 months Cd status in plant tissues and Cd phytoremediation criteria was determined. Results showed that application of surfactant increased root and shoot dry weight. Mean Cd uptake in roots and shoots increased following the application of 2 and 4 mmol kg−1 Tween 80, respectively. Application of 2 mmol kg−1 Tween 80 increased mean Cd uptake efficiency, while application of 4 mmol kg−1 Tween 80 increased phytoextraction and translocation efficiencies. Inoculation with P. indica and P. fluorescens was mostly effective in increasing Cd uptake and Cd phytoextraction efficiency, respectively. Co-inoculation with P. indica and P. fluorescens had no superiority to application of each inoculant alone. Since most of the Cd remained in roots, phytostabilization is probably the main mechanism controlling Cd phytoremediation by maize. According to the results, application of Tween 80 and inoculation with P. indica and P. fluorescens effectively enhanced phytoremediation of Cd-contaminated soil by maize.

Pengaruh Bahan Organik dan Azotobacter terhadap pertumbuhan Jagung di Tailing terkontaminasi merkuri dari Pulau Buru

Characteristics of mineral-mine tailings deposited in agricultural areas do not meet the requirements for food crop cultivation. The objective of the experiment was to obtain the information on the improvement of plant growth planted in mercury-contaminated tailings after adding organic matter and nitrogen fixing bacteria, Azotobacter. The greenhouse trial was set up in randomized factorial design which tested the Azotobacter inoculation consentrations and organic matter doses. There was no interaction effect between the two treatments on the growth of four-week old corn. Both organic matter and Azotobacter had a positive impact on vegetative growth of corn.

Interference and Control of ALS-Resistant Mouse-Ear Cress (Arabidopsis thaliana) in Winter Wheat

In 2015, winter wheat growers in Virginia reported commercial failures of thifensulfuron to control mouse-ear cress. This was the first reported case of field-evolved acetolactate synthase (ALS) resistance in mouse-ear cress, so research was conducted to evaluate alternative herbicide options as well as to document potential yield loss in winter wheat from mouse-ear cress. Efficacy studies were conducted at three site-years in 2015 to 2016 and 2016 to 2017 as well as a POST greenhouse trial. In the PRE study, flumioxazin, pyroxasulfone, saflufenacil, and metribuzin resulted in more than 80% mouse-ear cress control 15 wk after planting across all sites with no observable wheat injury. No differences were observed in wheat yield in two of three sites in the PRE herbicide study; yield differences were attributed to common chickweed and not to mouse-ear cress. In the POST herbicide study, 2,4-D, dicamba, and metribuzin resulted in greater than 75% control in the field and greenhouse. Metribuzin, dicamba, and pyroxsulam resulted in crop injury 3 wk after treatment at some sites, but injury was transient. Yield from all POST treatments was similar to the nontreated plots. No yield loss was observed by mouse-ear cress densities greater than 300 plants m–2, indicating that mouse-ear cress is not very competitive with winter wheat. Growers should make herbicide decisions based on other weeds in the field and can incorporate the aforementioned herbicides for mouse-ear cress control.

Bottle Gourd Genotypes Vary in Clomazone Tolerance

A greenhouse trial was used to evaluate 159 accessions of bottle gourd [Lagenaria siceraria (Mol.) Standl.] obtained from the U.S. National Plant Germplasm for tolerance to clomazone herbicide. Most accessions tested were moderately or severely injured by clomazone at 3.0 mg·kg−1 incorporated into greenhouse potting medium; however, several exhibited lower injury. Seeds were produced from tolerant and susceptible plants for use in a greenhouse concentration–response experiment. About three to four times higher clomazone concentrations were required to cause moderate injury to tolerant bottle genotypes in comparison with susceptible genotypes. The differences in tolerance among genotypes were observed with injury ratings, chlorophyll measurements, and shoot weights. Clomazone may be used safely on tolerant bottle gourd genotypes, but the herbicide may not be safe for susceptible genotypes. Also, tolerant genotypes such as Grif 11942 may be desirable for use as rootstocks in grafted watermelon production.