Biofumigation: An alternative strategy for the control of plant parasitic nematodes

Plant-parasitic nematodes wreak havoc on the yield and quality of crops worldwide.Damage from these pests is estimated to exceed US$100 bllion annually but is likely higher due to misdiagnosis.Nematode damage may be catastrophic,but historically the solution has been damaging as well.Use of the synthetic nematicide methyl bromide(MBr)poses risks to the environment and to human health.Biofumigation,the use of plant material and naturally produced compounds to control pests,is an increasingly feasible method of pest management.The process acts through the growth or incorporation of plant material into the soil,that,over the course of its degradation,releases glucosinolates that break down into nematotoxic isothiocyanates.These secondary plant metabolites exist naturally in commonly grown plants,most of which belong to the Brassicaceae family.Research endeavors have increasingly explored the potential of biofumigation.The reaction of target pests,the selection of biofumigant,and ideal environments for efficacy continue to be evaluated.This review seeks to provide a cost and benefit assessment of the status of biofumigation for the control of plant-parasitic nematodes as an alternative to conventional methyl bromide usage.

Biofumigation for Weed Management in Cabbage

Field studies were conducted in Lebanon to investigate the effect of solarization with/without cover crop green manure on weed population in subsequent planting of cabbage. Cover crops （alfalfa, barley, clover, lathrus and vetch） or crushed olive pulp were planted/added in i 8 m2 plots 75 days prior to planting cabbage. Crops and crushed olive pulps were ploughed under （CCGM） and then half the plots in each treatment were solarized （Biofumigation） by covering each plot with a clear polyethylene sheet for 40 days. Solarization with or without biofumigation significantly reduced weed population in subsequent cabbage planting as compared to nonsolarized CCGM or to the control. Solarization and biofumigation significantly increased fresh weight of cabbage as compared to the control and to nonsolarized CCGM treatments. Optimal weed control was observed in plots which were biofumigated with clover as a CCGM,

Control of Southern Root-knot Nematodes on Tomato and Regulation of Soil Bacterial Community by Biofumigation with Zanthoxylum bungeanum Seed

Biofumigation is an environmentally friendly strategy used to control nematodes and plant diseases.The volatile oil of Zanthoxylum bungeanum has high insecticidal and antibacterial activity.However,it is not known if the seed of Z.bungeanum is a suitable material for biofumigation to control southern root-knot nematodes(SRKN)on tomato,and how it may regulate the soil bacterial community structure.We used pot experiments in the greenhouse to determine the effects of Z.bungeanum seeds on SRKN,plant growth parameters,soil physicochemical and microbial characteristics.A total of 26 volatile components,including nematicidally active substances,were identified from Z.bungeanum seeds.Z.bungeanum seed biofumigation significantly reduced the SRKN population by 88.89%and 81.55%on the 50th and 100th day after transplanting,respectively.Compared to the control,the total soluble sugar,soluble solids,soluble protein,titratable acid,root activity and the fruit yield per tomato plant increased significantly.The content of soil alkali-hydrolyzed nitrogen,available potassium and the soil enzyme activities were also significantly increased.The soil bacterial diversity and the co-occurrence network complexity were increased by Z.bungeanum seed biofumigation.Relativelymore keystone OTUs in biofumigation soil had potential plant growth-promoting capabilities.The function of Z.bungeanum seed increasing tomato production in SRKN-infected soil depends on directly killing SRKN and improving soil properties.These results indicate that Z.bungeanum seed can be used as both a nematicide and a high quality organic fertilizer in tomato production.

Suppressive Effect of Brassica juncea on the Root-Lesion Nematode （ Pratylenchus penetrans）

Incorporation of sulfur-rich crucifer tissues into soil is known to suppress a variety of soil-bome plant pathogens and pests. The potentials of using Brassica juncea as green manure to kill the root lesion nematode Pratylenchus penetrans m soil and to decrease damages to subsequent crops were assessed in field and pot experiments. In the first trial, green manures containing B. juncea were grown and incorporated during spring to summer 2009. Japanese radish was then cultivated in each plot. In the second trial in spring 2010, green manure was grown and incorporated during summer to autumn 2009, and greater burdock was cultivated in pots containing soil sampled from each plot. Neither trial showed clear effects on nematode populations in the soil. However, in the first trial, Japanese radish grown following a B. juncea breeding line with a high content of sinigrin had a lower root lesion index and a higher number of marketable taproots than grown in the fallow soil. In the second trail, greater burdock cultivated in pots following incorporation ofB. juncea had a lower root lesion index with the incorporation of white mustard, which is widely used as a landscape plant. These findings suggest that B. juncea used as green manure can potentially decrease damage to subsequent crops caused by the root-lesion nematode, although it had no positive effect on decreasing populations of the root-lesion nematode in the soil.

The Concentration of 2-Propenyl Glucosinolate in Biofumigant Crops Influences Their Anti-Fungal Activity (In-Vitro) against Soil-Borne Pathogens

This study investigated the biofumigation potential of nine Brassica species/cultivars by determining the levels of 2-propenyl glucosinolate in their roots and shoots, and their in-vitro suppression of four major soil-borne pathogens of vegetable crops. Hydrolysis of 2-propenyl GSL produces volatile isothiocyanate (ITC) compounds which are known to have anti-fungal activity. HPLC results showed that 2-propenyl GSL only occurred in root and shoot residue of flowering plants of four Brassica cultivars developed for green manuring (Caliente 199?, Mustclean?, Nemfix? and BQ Mulch?) and in the standard (mustard seed meal) treatment Fumafert?. Levels of 2-propenyl GSL varied several fold within the four Brassica cultivars, with 77-88% of the total concentrations recorded in the shoot tissues. In in vitro assays, the level of fungal suppression by volatiles emitted by hydrated shoot and root residues related to their content of 2-propenyl GSL, and the dose of residue applied to five soilborne test pathogens (S. minor, Rhizoctonia solani, Fusarium oxysporum, Pythium dissotocum and Rhizoctonia solani). The variation in 2-propenyl GLS levels found in the Brassica green manure crops tested provides scope for selecting cultivars with greater potential for biofumigation, and to control multiple soil-borne disease problems in vegetable farms.

Bacillus cereus X5 Enhanced Bio-Organic Fertilizers Effectively Control Root-Knot Nematodes(Meloidogyne sp.)

The efficacy of Bacillus cereus X5 as a potential biological control agent against root-knot nematodes was evaluated in vitro by examining second-stage juvenile mortality and egg hatching rate under addition of culture filtrate and in planta by application of bio-organic fertilizers enhanced with B. cereus X5, B. thuringiensis BTG, or Trichoderma harzianum SQR-T037 alone or together in greenhouse and field experiments. The biofumigation of the root-knot nematode-infested soil with organic materials (chicken manure, pig manure and rice straw) alone or in combination with B. cereus X5 was also conducted in greenhouse experiments. In laboratory, the filtrate of B. cereus X5 more effectively reduced egg hatching rates during the incubation period for 14 d and more effectively killed the second-stage juvenile during the incubation period of 24 h than that of B. thuringiensis BTG. The highest dry shoot weights for greenhouse tomatoes and field muskmelons were found in both the treatment consisting of the bio-organic fertilizer enhanced with the three biocontrol agents and the treatment consisting of the bio-organic fertilizer enhanced only with B. cereus X5. The two bio-organic fertilizers achieved better nematicidal effects than those enhanced only with B. thuringiensis BTG or T. harzianum SQR-T037. B. cereus X5 also enhanced effect of biofumigation, which resulted in increased plant biomass and reduced nematode counts in the roots and rhizosphere soil. Therefore, these results suggested that biological control of root-knot nematodes both in greenhouses and fields could be effectively achieved by using B. cereus X5 and agricultural wastes.