In Vitro Studies of Endophytic Bacteria Isolated from Ginger (Zingiber officinale) as Potential Plant-Growth-Promoting and Biocontrol Agents against Botrytis cinerea and Colletotrichum acutatum.

Agriculture currently confronts a multitude of challenges arising from the excessive utilization of chemical pesticides and the proliferation of phytopathogenic fungi strains that exhibit resistance to commonly employed active compounds in the field. Botrytis cinerea and Colletotrichum acutatum are phytopathogenic fungi that inflict substantial economic losses within agriculture and food due to their high impacts on crops both pre- and post-harvest. Furthermore, the emergence of fungal strains that are resistant to commercial fungicides has exacerbated this problem. To explore more environmentally sustainable alternatives for the control of these pathogens, an investigation into the endophytic bacteria associated with ginger (Zingiber officinale Rosc.) was conducted. The primary focus of this study involved evaluating their inhibitory efficacy against the fungi and assessing their potential for promoting plant growth. The endophytic bacteria genera Lelliottia, Lysinibacillus, Kocuria, Agrococcus, Acinetobacter, Agrobacterium, Zymobacter, and Mycolicibacterium were identified. All isolates showed remarkable in vitro antagonistic ability against B. cinerea (>94%) and C. acutatum (>74%). Notably, the Lelliottia amnigena J29 strain exhibited a notable proficiency in producing extracellular enzymes and indole compounds (IAA), solubilizing phosphate and potassium, and forming biofilm. Furthermore, the Lysinibacillus capsici J26, Agrococcus citreus J28, and Mycolicibacterium sp. J5 strains displayed the capacity for atmospheric nitrogen fixation and siderophore production. These findings underscore the agricultural and biotechnological potential of endophytic bacteria derived from ginger plants and suggest the feasibility of developing alternative approaches to manage these two phytopathogenic fungi.

A Cost-Benefit Analysis of Soil Disinfestation Methods against Root-Knot Nematodes in Mediterranean Intensive Horticulture.

Losses caused by phytoparasitic nematodes in crops depend directly on their soil densities at the start of the crop, so reducing their populations before planting is the main aim of nematological management. Efficacies in reducing Meloidogyne soil populations of soil disinfestation methods, such as agrochemicals, botanicals, or biosolarization were estimated on multiple field trials conducted over fourteen years in intensive horticultural crops. Soil nematode populations were reduced by 87 to 78% after fumigation with 1,3-dichloropropene + chloropicrin and dimethyl-disulphide, respectively. Non-fumigant nematicides such as azadirachtin, dazomet, fenamiphos, fluopyram, fosthiazate, metam-sodium, and oxamyl showed efficacies ranging from 51 to 64%, whereas the efficacy of natural products, such as abamectin, garlic extracts, or essential oils was 41 to 48%. Biosolarization with chicken manure had an efficacy of 73%. An economic cost-benefit study of nematode management methods was performed for seven vegetable-M. incognita pathosystems. Fumigation with 1,3-dichloropropene + chloropicrin and biosolarization with chicken manure were the only treatments able to reduce RKN populations above 1000 and 750 J2 per 100 cm3 of soil, respectively, to levels below the nematode economic damage threshold, keeping profitability. Fumigation was able to manage RKN soil densities up to 350 J2 per 100 cm3 of soil in most susceptible crops as aubergine or cucumber and up to 1000 J2 per 100 cm3 of soil for more tolerant crops, such as other cucurbits, pepper, or tomato. Other nematicidal treatments were not able to reduce RKN populations above 200-300 J2/100 cm3 of soil below the economic thresholds but were profitable when RKN densities were below the limits of 200-300 J2/100 cm3 of soil.

Nematicidal Efficacy of Milbemectin against Root-Knot Nematodes.

The nematicidal efficacy of milbemectin and its commercial formulate Milbeknock® on (i) egg hatching, (ii) juvenile motility and (iii) infective capacity of root-knot nematodes was evaluated in vitro and in planta assays. Serial dilutions of pure milbemectin were tested against nematode eggs and juveniles and lethal concentrations LC50 and LC90 calculated. Exposure of egg masses to milbemectin at a concentration of 30 µg/mL for 72 h reduced egg hatching by 52%. The increase in exposure time to 240 h did not increase the egg hatching inhibition at the highest concentration 30 µg/mL (53%) but reduced egg hatching at 15 and 7 µg/mL by 35 and 24%, respectively, when compared to untreated controls. The inhibitory effect of milbemectin on juvenile motility ranged from 41 to 87% depending on its concentration, and this effect was persistent after rinsing the juveniles in water. The probabilistic dose-response model indicated that lethal concentrations of milbemectin for juvenile motility were LC50: 7.4 µg/mL and LC90: 29.9 µg/mL. The pre-plant application of Milbeknock® to soils infested with the nematode reduced its infective capacity by 98-99% compared to untreated soils in pot experiments. Milbeknock® reduced nematode soil population densities by 50-60% in natural infestations under field conditions. Milbemectin shows a high level of efficacy against root-knot nematodes as it reduces egg hatching, persistently immobilizes nematode juveniles, and reduces tomato root infection.