Fusarium solani f. sp. cucurbitae race 1, a potential pathogen of grafted watermelon production in Spain*

A crown, root and fruit rot of squash (Cucurbita maxima and Cucurbita moschata) has been observed in eastern provinces of Spain over the past 4 years. Isolations from the crown of symptomatic plants and fruits yielded primarily a Fusarium solani that was identified as F. solani f. sp. cucurbitae race 1 on the basis of pathogenicity tests and disease symptoms in the field. In Spain, more than 90% of watermelon plants are grafted, using different Cucurbita hybrids (C. maxima × C. moschata) as rootstocks. In 1998, some grafted watermelon plants were first found to be affected by F. s. cucurbitae race 1. The purpose of this study was to evaluate the pathogenicity of this fungus on several rootstocks commonly used for grafting watermelon (Brava, Titan, Shintoza, RS‐841, TZ‐148 and TW‐1) in order to prevent a possible spread of this fungus that could cause serious economic losses in watermelon production. None of them proved to be resistant.     

Fusarium wilt of basil in Greece: Foliar infection and cultivar evaluation for resistance

Fusarium wilt of basil (Ocimum basilicum), caused byFusarium oxysporum f.sp.basilici, is reported for the first time in Greece. Foliage inoculation of young plants resulted in a downward movement of the pathogen to the crown and roots and 20–30% plant mortality. Of 14 commercial basil cultivars evaluated for possible disease resistance using young plants, six out of eight large-leaved cultivars were found resistant, while all six small-leaved ones were susceptible. http://www.phytoparasitica.org posting Feb. 23, 2004.     

Evaluation of herbicides for selective weed control in grafted watermelons

Grafted watermelon is a combination of two plants, aCucurbita rootstock and a watermelon scion. Therefore, weed control for this crop faces a unique problem: the safety of the selected herbicide has to be tested for both plants that make up the grafted plant. In the current study, we evaluated the usage safety of selected herbicides forCucurbita rootstocks as well as for non-grafted and grafted watermelons, and the control ofAmaranthus retroflexus by the same herbicides. In addition, the residual effect of the herbicides was tested for seeded and transplanted melons representing the next crop following cultivation of the grafted watermelons. The herbicides ethalfluralin, pendimethalin, ethalfluralin, sulfentrazone, oxyfluorfen, chlorsulfuron and clomazone were chosen for their potential to controlA. retroflexus. Pendimethalin and trifluralin were less effective than the other herbicides in controllingA. retroflexus; sulfentrazone, chlorsulfuron and clomazone were not safe for use on the tested cucurbits and thus cannot be recommended for weed control in grafted watermelons. Therefore, by eliminating the herbicides that are toxic to cucurbits and those that are ineffective forA. retroflexus control, it was concluded that the herbicides ethalfluralin and oxyfluorfen can be considered effective and safe for weed control in grafted watermelons. It was shown that trifluralin and oxyfluorfen have the potential to be applied effectively through the drip irrigation system. http://www.phytoparasitica.org posting Jan. 10, 2008.     

Effect of antagonistic<Emphasis Type="Italic">Fusarium</Emphasis> spp. and of different commercial biofungicide formulations on Fusarium wilt of lettuce

Five experimental trials were carried out to test different biological control agents against Fusarium wilt of lettuce, cause byFusarium oxysporum f.sp.lactucae. In the presence of a very high disease incidence, the best results in terms of disease control as well as increased growth response were shown byTrichoderma harzianum T 22 (RootShield), which, at 3 gl ⁻¹ of substrate, provided very consistent results.F. oxysporum IF 23 gave good disease control but in two out of five trials reduced the biomass produced. Less consistent, but still significant results were provided byF oxysporium MSA 25, at 3 gl ⁻¹ of substrate, and byTrichoderma viride TV 1. The twoF. oxysporum agents Fo 251/2 and Fo 47 and the mixture ofT. harzianum + T. viride (Remedier) partially reduced disease incidence but were less effective than the above mentioned. Less interesting results were offered byStreptomyces griseoviridis (Mycostop). The results obtained show that biological control can play a role in the management of Fusarium wilt of lettuce.     

Fusarium wilt on sweet basil: Cause and sources in southeastern Spain

This study concerned a new disease detected in 1997 in southeastern Spain — Fusarium wilt in basil (Ocimum basilicum L.), caused byFusarium oxysporum f.sp.basilici. Its importance was evaluated at two locations in the Almería area, where 14% of the plants presented symptoms of the disease after 4 months of cropping. The search for sources of the disease inoculum was centered on the health of the seeds and the polypropylene trays that were reused for plant production. Analysis of four lots of seeds from Germany and Italy showed that two of them harboredF. oxysporum f.sp.basilici. This finding was confirmed by the analysis of seeds collected from diseased plants. Furthermore, analysis of three reused trays revealed the presence of the pathogen on them and it was concluded that the trays acted as the source of dispersion of the mycosis. http://www.phytoparasitica.org posting July 14, 2004.     

Extracts of killedPenicillium chrysogenum Induce resistance against Fusarium wilt of melon

Dry fungal biomass ofPenicillium chrysogenum (dry mycelium), a waste product of the pharmaceutical industry, was extracted with water and applied to the roots of melon plants before or after inoculation withFusarium oxysporum f.sp.melonis (Font). Seedlings (4–6 days after emergence) treated with either acidic dry mycelium extract (DME) or neutralized dry mycelium extract (NDME) were protected against challenge infection withFom. A single drench with 2–5% DME applied 12–72 h before inoculation provided significant control of the disease compared with water-drenched, challenged seedlings. No protection was seen in plants treated 0–6 h before inoculation or 0–48 h after inoculation. Neither DME nor NDME (0.5–5%) had any effect on fungal growthin vitro, which implied that disease controlin vivo was mediated by induced resistance. The resistance induced by DME protected melon plants not only against race 1,2, but also against the three other races of the pathogen, indicating a race-non-specific resistance againstFom. Both DME and NDME significantly increased peroxidase activity and free L-proline content in seedlings 12 h and 48 h after soil drench, respectively. Resistance to Fusarium wilt was significantly associated with elevated levels of peroxidase activity but not with free L-proline content. Thus, peroxidase might be involved in the defense mechanisms activated by DME or NDME. http://www.phytoparasitica.org posting Aug. 31, 2001.     

Nitrogen metabolism disorder in watermelon leaf caused by fusaric acid

The effect of fusaric acid (FA) on the activity of leaf nitrogen (N) metabolism enzymes in watermelon seedlings supplied with different N forms was studied. The results showed that FA inhibited nitrogen uptake and caused decreased leaf amide and protein but increased the content of ammonium and amino acids. When treated with FA the activities of enzymes in the pathway for the synthesis of amino acid in leaves (GS, GOGAT, and GDH) were decreased by 15–23%, 13–40%, and 71–86%, respectively. The activity of asparagine synthetase was decreased by 34–57%. The proteinase activity was initially increased by 37–125% at 12 h after treatment of FA but then subsequently decreased. The activity of glutamate-pyruvate aminotransferase was increased by 280–400%, though the activity of glutamate-oxaloacetate aminotransferase was decreased by 30–63%. It was suggested that FA inhibited the uptake of ammonium in seedlings and suppressed the activities of amino acid and amide synthases, while stimulating proteinase activity.A new pathogenic mechanism of watermelon infection by Fusarium spp. was found as FA caused the complete disorder and collapse of the host plant's nitrogen metabolism. This work provides a new insight into the progression of watermelon wilting caused by Fusarium oxysporum f.sp. niveum.     

Induced resistance in cotton seedlings against fusarium wilt by dried biomass of<Emphasis Type="Italic">Penicillium chrysogenum</Emphasis> and its water extract

Dry mycelium (DM) of killedPenicillium chrysogenum and its water extract (DME) were used to induce resistance in cotton plants againstFusarium oxysporum f.sp.vasinfectum (Fov). Results showed that the efficacy of either DM or DME in controlling the disease depends on both the concentration and the mode of application. DM amended to the soil at 0.25–2% (w/w) provided 32–75% protection againstFov. Soil drench with 2–5% DME (w/v) and pre-sowing seed soakage with 5–10% DME provided 51–77% and 28–35% protection against the wilt disease, respectively, whereas no protection was obtained with foliar sprays of 1–10% DME. DM and its water extract had no direct antifungal activity on growth ofFov in vitro, suggesting that disease control with DM or DME resulted from the induction of natural defense mechanisms in the cotton plants. Soil drench with 5% DME was as effective as 2% DM powder in inducing resistance againstFov, implying that the resistance-inducing substances were mostly water-soluble. Four cotton cultivars with various genetic resistance levels againstFov were tested at the seedling stage: two resistant ‘Pima’ cultivars and two susceptible ‘Acala’ cultivars. The level of protection achieved in the two susceptible cultivars with DME was equal to, or higher than, that of the two resistant cultivars treated with water. Innate and induced peroxidase activity in cotyledons or hypocotyls and roots coincided with the level of genetic resistance and DME-induced resistance, respectively. Based on our results, an integrated control strategy ofFov with both genetic resistance and induced resistance is suggested.     

Resistance to fusarium basal rot of onion in greenhouse and field and associated expression of antifungal compounds

Greenhouse and field evaluations of onion for resistance to Fusarium basal rot caused byFusarium oxysporum f.sp.cepae were conducted on cultivars ‘Akgün 12’ and ‘Rossa Savonese’ previously described as resistant at the seedling stage. In the greenhouse experiments inoculations were carried out on seeds or soil; in the field experiments evaluation was performed on onion sets from plants grown in naturally infested soils. Akgün 12 and to a lesser extent Rossa Savonese were resistant to the disease at the bulb stage in all experiments. Results were also consistent with those obtained from a previous screening at the seedling stage. Onion sets were also extracted and fractionated by thin layer chromatography to determine their content of antifungal compounds. Extracts were characterized by the expression of distinct antifungal components, which may be involved in resistance to the pathogen. http://www.phytoparasitica.org posting July 14, 2004.     

Efficacy of bacterial antagonists and different commercial products against Fusarium wilt on rocket

Seven experimental trials were carried out to evaluate the efficacy of the bacterial strains Achromobacter xylosoxydans AM1 and Serratia sp. DM1 obtained from suppressive soils and from soilless used rockwool substrates (Pseudomonas putida FC6B, Pseudomonas sp. FC7B, Pseudomonas putida FC8B, Pseudomonas sp. FC9B and Pseudomonas sp. FC24B) against Fusarium wilt on rocket caused by Fusarium oxysporum ff. spp. raphani and conglutinans. Along with these strains, two commercial bioproducts (RootShield—Trichoderma harzianum T22; Cedomon—Pseudomonas chlororaphis MA342) were also tested. Different application strategies such as soil treatment (trials I to VI; 10⁷ and 10⁸ CFU ml⁻¹) and root dipping (trial VII; 10⁸ and 10⁹ CFU ml⁻¹) were performed in a glasshouse in order to test the efficacy of the bacterial strains against Fusarium oxysporum ff. spp. raphani and conglutinans. The lowest disease incidence (16.7%) was observed with the application of Achromobacter sp. AM1, Serratia sp. DM1 at 10⁸ CFU ml⁻¹ and Pseudomonas sp. FC9B at 10⁷ CFU ml⁻¹ against F. oxysporum f. sp. conglutinans (experiment I). Maximum plant biomass (5.0 g/plant) was registered in Serratia sp. DM1 at 10⁸ CFU ml⁻¹ treated plants in trial IV. The trials against F. oxysporum f. sp. raphani (experiment II) showed that the application of Pseudomonas sp. FC7B, P. putida FC8B at 10⁸ CFU ml⁻¹ and P. chlororaphis MA342 at 7.5 × 10⁶ CFU ml⁻¹ significantly reduced disease incidence to values ranging between 87% and 92%. The highest plant biomass was recorded with the application of Achromobacter sp. AM1 and P. putida FC6B at 10⁷ CFU ml⁻¹ (3.9 to 4.2 g) carried out 7 days before the artificial inoculation of the pathogens (trial IV). The present study showed the potential biocontrol activity of the bacterial strains Achromobacter sp. AM1, Serratia sp. DM1 and Pseudomonas sp. FC9B against F. oxysporum f. sp. conglutinans and of Pseudomonas sp. FC7B, P. putida FC8B, P. chlororaphis MA342, Achromobacter sp. AM1 and P. putida FC6B against F. oxysporum f. sp. raphani. Growth-promoting activity of biocontrol bacteria used during the trials was observed.     

In vitro inhibitory activity of xylem exudates from cucurbits towardsFusarium oxysporum microconidia

Experiments were conducted to determine if xylem exudates from three cucurbitaceous plants as well as non-cucurbit species were inhibitory to the growth of microconidia ofFusarium oxysporum f. sp.niveum, causal agent of Fusarium wilt of watermelon. Inhibitory effects of xylem exudates from watermelon(Citrullus lanatus) cultivars differentially susceptible toF.o. f.sp.niveum as well as from watermelon plants previously inoculated with virulent or avirulent races ofF. oxysporum, were compared. Results indicated that xylem fluid contained an inhibitory component that was independent of the resistance status of the cultivar or previous inoculation with virulent or avirulentF.o. f.sp.niveum races. Xylem exudates from cucumber(Cucumis sativis) also inhibited microconidia growth and colony formation while muskmelon(Cucumis melo) and tomato(Lycopersicon esculentum) xylem exudates had little inhibitory activity. Incubation with proteinase K, lysozyme, or boiled xylem fluid suggested that the active component had proteinaceous properties with an oligosaccharide moiety.     

Fungi on roots and stem bases of asparagus in the Netherlands: species and pathogenicity

A survey was made to identify the most important soilborne fungal pathogens of asparagus crops in the Netherlands. Ten plants were selected from each of five fields with a young (1–4 y) first planting, five fields with an old (6–13 y) first planting and five fields with a young replanting. The analysis included fungi present in the stem base and the roots of plants with symptoms of foot and root rot or showing growth decline without specific disease symptoms. Isolates of each species were tested for pathogenicity to asparagus on aseptically grown plantlets on Knop's agar. Symptoms were caused byFusarium oxysporum, F. culmorum, Botrytis cinerea, Penicillium verrucosum var.cyclopium, Cylindrocarpon didymum, Phialophora malorum, Phoma terrestris andAcremonium strictum. F. oxysporum was by far the most common species and was isolated from 80% of the plants. Not all of its isolates were pathogenic to asparagus. Symptoms were caused by 67%, 78% and 93% of the isolates obtained from young first plantings, old first plantings and replantings, respectively.F. culmorum was isolated from 31% of the plants. Two other notorious pathogens of asparagus,F. moniliforme andF. proliferatum, did not occur in our samples.Species causing symptoms in the vitro test that were found on more than 5% of the plants were additionally tested for their pathogenicity in pot experiments.F. oxysporum f.sp.asparagi caused severe foot and root rot, significantly reduced root weights and killed most of the plants.F. culmorum caused lesions on the stem base often resulting in death of the plant.P. terrestris, a fungus only once reported as a pathogen of asparagus, caused an extensive root rot, mainly of secondary roots that became reddish. The fungus was isolated in only a few samples and is not to be regarded as an important pathogen in Dutch asparagus crops.P. malorum caused many small brown lesions on the stem base and incidentally also on the upper part of small main roots. This is the first report of its pathogenicity to asparagus. The fungus is one of the organisms inciting spear rust and it reduced crop quality rather than crop yield.P. verrucosum var.cyclopium andC. didymum did not cause symptoms in pot experiments.Because of its predominance on plants with foot and root rot and its high virulence,F. oxysporum f.sp.asparagi was considered to be the main soilborne pathogen of asparagus in the Netherlands.     

Biological control ofBotrytis cinerea in residues and flowers of Rose (Rosa hybrida)

Microbial isolates from living petals, petal residues and leaf residues of rose, and from laboratory collections, were evaluated for control ofBotrytis cinerea in rose. In leaf residues artificially infested withB. cinerea, isolates of the filamentous fungiGliocladium roseum, FR136 (unidentified) andTrichoderma inhamatum reduced sporulation of the pathogen by >90%, other filamentous fungi were 25–90% effective, and those of yeasts and bacteria were <50% effective. In artificially inoculated petal residues, no microbe reduced sporulation ofB. cinerea by >75%, but isolates ofCladosporium oxysporum and four yeasts were 51–75% effective, and three filamentous fungi, eight yeasts andBacillus subtilis isolates were 26–50% effective. Isolates ofT. inhamatum, C. oxysporum andG. roseum performed best againstB. cinerea among isolates evaluated in leaf residues naturally infested with the pathogen and indigenous microorganisms. Totals of ten isolates of filamentous fungi (includingC. oxysporum andC. cladosporioides), two of yeasts and five ofBacillus subtilis completely prevented lesion production byB. cinerea in detached petals, and a further six isolates of filamentous fungi (includingG. roseum) and six yeasts were 90–99% effective. Isolates ofC. oxysporum, C. cladosporioides andB. subtilis, the most effective microorganisms againstB. cinerea in flower buds, reduced number of lesions in the range of 42–65% compared with 59–89% for à standard fungicide (vinclozolin). It is suggested that application of leading antagonists Jo living rose leaves and flowers should optimize control of inoculum production byB. cinerea when the tissues die. Optimal biocontrol of lesion production in flower buds requires a better understanding of the microenvironment of petals.     

Lipid metabolism in tomato and bean as a sensitive monitor for biocontrol of wilt diseases

The lipids metabolism of tomato and bean plants during biological control of wilt pathogens (Fusarium oxysporum f.sp.lycopersici andF. oxysporum f.sp.phaseoli, respectively) byBacillus subtilis was investigated. The interaction of wilt pathogens with both tomato and bean caused an imbalance and drastic reduction in total lipids, triacylglycerol, sterol and all phospholipd fractions except phosphatidic acid. The application of a formulated biocontrol agent,B. subtilis, eliminated the detrimental effect of both wilt pathogens and consequently prevented catabolism of lipid fractions in both tomato and bean. Moreover, the changes in the lipid fractions as a sensitive monitor for biocontrol of wilt diseases suggest a positive correlation between the application ofB. subtilis and improvement in the host metabolism towards anabolism. http://www.phytoparasitica.org posting Sept. 20, 2006.     

Influence of pH, nutrient solution disinfestation and antagonists application in a closed soilless system on severity of fusarium wilt of gerbera

Three trials were carried out during the years 2002–2005 at the Agricultural Experimental Center of Albenga (northern Italy) on gerbera plants grown in a closed soilless system. The efficacy of slow sand filtration and UV treatment in eliminatingFusarium oxysporum f.sp.chrysanthemi (Foc) propagules, naturally present or artificially added to the recirculating nutrient solution, was evaluated. These techniques were tested alone and in combination with the application into the soilless system of different antagonistic strains ofFusarium spp. andTrichoderma spp., isolated from gerbera rhizosphere, and of a commercial formulation ofStreptomyces griseoviridis. The role of the nutrient solution pH in reducingFoc infections was also evaluated. Results showed that slow sand filtration, alone and in combination with the application of biocontrol agents, and a nutrient solution pH higher than 6.0, may induce a significant reduction inFoc infections on gerbera plants grown in closed soilless systems. http://www.phytoparasitica.org posting June 8, 2008. Corresponding author     

四季豆枯萎病病原鉴定及防治

从南宁市郊11个病区采集的四季豆枯萎病株标样,经分离培养鉴定和致病性测定,证明其病原菌为尖孢镰刀菌菜豆专化型(Fusarium oxysporum f. sp. phaseoli Kend & Syd)。此病在南宁于4月上中旬四季豆初花期开始发生,5月中下旬盛花至结荚期为发病高峰期。用滤纸碟法进行药效试验的结果,40%灭病威300-500倍液的抑菌圈最大,田间灌根防治也有一定效果。可用种子重量的0.5%多菌灵可湿性粉拌种。品种间抗病性有显著差异,秋抗19号和秋抗6号较抗病。     

Differential reproduction of Meloidogyne incognita and M. javanica in watermelon cultivars and cucurbit rootstocks

The suitability of watermelon cultivars and cucurbit rootstocks as hosts to Meloidogyne incognita and M. javanica was determined in pot and field experiments. Meloidogyne incognita showed higher reproduction than did M. javanica on watermelon and cucurbit rootstocks. The watermelon cultivars did not differ in host status when challenged with these two species and supported lower nematode reproduction than the cucurbit rootstocks. Rootstocks Lagenaria siceraria cv. Pelops and Cucurbita pepo AK15 supported lower reproduction than did the squash hybrid rootstocks (C. maxima × C. moschata). Egg production increased (P < 0·05) with a rising initial inoculum level (Pi) in the non‐grafted Sugar Baby but the reproduction factor Rf (eggs per plant/Pi) was similar at two Pi levels. The total egg production in the plants grafted onto squash hybrids RS841 and Titan was greater (P < 0·05) at the higher Pi, but the Rf values were lower. The development of field‐grown non‐grafted watermelon plants was significantly stunted in plots where nematodes were detected at planting. However, no differences were observed in plots with grafted plants. In plots with nematodes, non‐grafted and Titan‐grafted plants had similar yields that were higher than that of RS841‐grafted plants. In the commercial plastic houses with grafted watermelon, the average Rf value was 42‐fold, confirming the high susceptibility of squash hybrids as rootstocks for grafted watermelon. The Titan–Sugar Baby combination was tolerant to M. javanica.     

Progress in grafting watermelon to manage Verticillium wilt

Vegetable grafting for disease management was first used successfully when watermelon grafted onto a Cucurbita moschata rootstock overcame Fusarium wilt. Interspecific grafting has since been used effectively to mitigate several soilborne pathogens in a variety of solanaceous and cucurbitaceous cropping systems. Verticillium wilt caused by Verticillium dahliae is a significant disease in watermelon crops and is difficult to manage. Current management practices, including crop rotation, soil fumigation, and host resistance, are insufficient due to the ability of microsclerotia to persist in absence of a host, lack of efficacy of soil fumigants, and limited availability of resistant cultivars. Watermelon grafted onto commercial cucurbit rootstocks have increased tolerance to Verticillium wilt, although no cucurbit rootstocks are known to be completely resistant. Verticillium wilt incidence decreased on grafted plants grown in artificially and naturally infested soils, while scion health and growth as well as rootstock root mass and vigour increased. Commonly used rootstocks are Lagenaria siceraria, C. moschata, and C. maxima × C. moschata; of these, only C. maxima × C. moschata ‘Tetsukabuto’ reduced severity of Verticillium wilt across several scion cultivars, locations, years, and soil densities of V. dahliae. Although studies on Verticillium wilt resistance of grafted watermelon are few, their combined results suggest the threshold of V. dahliae soil density for watermelon may be around 5–12 cfu/g. This review summarizes available information on Verticillium wilt of watermelon and effects of different rootstock × scion combinations, assisting growers and breeding programmes in decisions to adopt watermelon grafting for management of Verticillium wilt.     

Biofumigation with Brassica plants and its effect on the inoculum potential of Fusarium yellows of Brassica crops

The use of Brassica crops as green manure in the so-called biofumigation treatment has been successfully exploited for the management of soilborne pathogens and is gaining interest particularly in the case of less intensive agricultural systems. A study was undertaken to investigate possible negative side-effects of biofumigation in order to prevent possible damage caused by wilt pathogens able to attack both plants used for biofumigation as well as agricultural crops. To do so, firstly the response of different Brassicas, including some used in biofumigation, to the formae speciales of Fusarium oxysporum known for being pathogenic on Brassica crops was evaluated. Secondly, the effect of green manure treatments on yield, quality of crops, and inoculum densities, infection and survival of Fusarium oxysporum f. sp. conglutinans and F. oxysporum f. sp. raphani was evaluated. In the second part of the work, four Brassica crops, selected for their response (susceptibility or resistance) to F. oxysporum f. sp. conglutinans and to F. oxysporum f. sp. raphani were evaluated in order to determine their response to the two pathogens during subsequent crops grown in soil where plants were incorporated as green manure into the soil at the end of each cycle. Moreover, the dynamics of the populations of F. oxysporum f. sp. conglutinans and F. oxysporum f. sp. raphani in the soil after several biofumigation cycles was studied. Many of the Brassica crops used for biofumigation tested were susceptible to F. oxysporum f. sp. conglutinans and or to F. oxysporum f. sp. raphani. Green manure treatment, carried out by growing nine cycles of biocidal plants, with a short crop cycle of 30–35 days, did not reduce Fusarium wilts on susceptible Brassica hosts. The population of the pathogen was partially increased as a result of the incorporation of tissues of the susceptible plants. When Brassica crops grown were resistant to the two F. oxysporum pathogens used for soil infestation, green manure simulation did inhibit both pathogens, thus confirming its biocidal activity. The results obtained under our experimental conditions show that biofumigation treatment is not applicable for soil disinfestation on crops susceptible to the same formae speciales of F. oxysporum affecting Brassica species used for biofumigation. Brassica crops resistant to Fusarium yellows should be grown where biofumigation is applied. Moreover, alternation of crops used for biofumigation should be encouraged.