Amendment of soil with African marigold and sunn hemp for management of Meloidogyne incognita in selected legumes

Field experiments were conducted in 2008 and 2009 in the tropical rainforest zone of Nigeria to investigate the effects of amendment of soil with seedlings of African marigold (Tagetes erecta) and sunn hemp (Crotalaria juncea) incorporated singly in plots on Meloidogyne incognita and yield of cowpea and soybean. The experimental field, which was naturally free of plant-parasitic nematodes, was inoculated with chopped roots of M. incognita race 2-infected Celosia argentea roots and planted to tomato to increase M. incognita population at the site.Eight week-old marigold seedlings were incorporated in cowpea or soybean field and eight week-old sunn hemp seedlings were also incorporated in cowpea or soybean field. At the ends of the experiments, M. incognita population densities were significantly higher in control plots than those of the plots amended with marigold or sunn hemp with correspondingly higher grain yield in the amended plots in both cowpea and soybean fields in both years. A significantly higher population of the nematode and consequently, lower yield was associated with cultivar Ife Brown than cultivar Ife Bimpe of cowpea for each treatment whereas in soybean cultivars, the pattern was not definite. Also twelve seedlings of marigold or sunn hemp per plot incorporated into the soil produced significantly higher grain yield in cultivar Ife Brown of cowpea and cultivar TGX 1440 of soybean compared to six seedlings per plot. The results of this study suggest that incorporating marigold or sunn hemp in M. incognita-infected cowpea or soybean field has potentials to suppress M. incognita population and reduce nematode damage on yield of the associated leguminous crops.     

Utilizing management zones for Rotylenchulus reniformis in cotton: Effects on nematode levels,crop damage,and Pasteuria sp.

Nematode management zones (MZs) based on soil electrical conductivity (EC, a proxy for soil texture) have not been published for Rotylenchulus reniformis. We tested 1) whether R. reniformis levels and the amount of damage caused to cotton differed among MZs, 2) if the relative effectiveness of nematicides differed among MZs, and 3) whether the prevalence of Pasteuria sp. on R. reniformis differed among MZs and nematicide treatments. A field was divided into three MZs where MZ3 had sandier soil than MZ1 or MZ2, which were the same, and MZ2 had higher elevation than MZ1 or MZ3, which were the same. Levels of R. reniformis near planting in plots not receiving nematicide averaged 1342 (per 150 cm³ soil) in 2008, 610 in 2009, and 869 in 2010. Both soil texture and elevation influenced R. reniformis population levels with greater reproduction in finer-textured soil and reduced R. reniformis levels at higher elevation. Treatment effects on R. reniformis levels were the same in all MZs (no MZ × treatment interactions). The effects of texture and elevation on yield were similar to the effects on nematode levels. We observed endospores of Pasteuria sp., a bacterial parasite of nematodes, on R. reniformis at the field site used for this study. Pasteuria sp. generally had greater spore attachment to juvenile R. reniformis than to adults with no differences among MZs in percentage of nematodes with endospores, but the number of spores per nematode was lower in MZ3, which had the greatest sand content. The percentage of R. reniformis with endospores and the number of attached endospores were reduced by 1,3-dichloropropene + aldicarb. We documented that R. reniformis levels are affected by modest differences in soil texture and elevation, but levels of R. reniformis were above the action threshold in all MZs, therefore a uniform rate of nematicide would have been recommended and there would have been no cost savings from utilizing MZs in this field.     

Introgression of resistance to reniform nematode (Rotylenchulus reniformis) into upland cotton (Gossypium hirsutum) from Gossypium arboreum and a G. hirsutum/Gossypium aridum bridging line

Gossypium hirsutum L. is the predominant cotton of commerce and all cultivars of this species are susceptible to the reniform nematode, Rotylenchulus reniformis. To introgress resistance to R. reniformis into the tetraploid 2(AD₁) G. hirsutum, a resistant diploid A₂-genome Gossypium arboreum accession (A₂-190) was crossed with a hexaploid 2((AD₁)D₄) bridging line (G 371) to obtain a tetraploid triple-species hybrid. The triple-species hybrid was back-crossed to G. hirsutum and a population of 277 BC₁ individuals was produced. The BC₁s and controls were assayed in growth chambers for resistance to R. reniformis. Fortuitously, the hexaploid bridging line G 371 was also found to be resistant to R. reniformis. The BC₁ segregated 3:1, resistant:susceptible, indicating that resistance was conferred by dominant genes at two different loci, with each originating from a distinct germplasm source. This study demonstrated that it is possible to introgress and pyramid genes for resistance to R. reniformis in G. hirsutum.     

Reniform nematode resistance in potato clones

SeveralSolatium tuberosum clones were tested for resistance to the reniform nematode,Rotylenchulus reniformis. Commercial cultivars La Rouge and possibly Red La Soda had high levels of resistance to the reniform nematode.R. reniformis resistance was found to exist independently of the H₁, H₂, or H₃ genes for resistance to races of potato cyst nematodes,Globodera rostochiensis andG. pallida. In addition to reniform nematode resistance, B7642-2, B7154-8 and B7680-6 contained the H₁ gene and breeding linePI 377741 contains the H₁ and H₂ gene for potato cyst nematode resistance. Over a three month period reniform nematode counts were significantly lower in pots where resistant varieties were grown.     

Evaluation of resistance to root-knot nematode (Meloidogyne incognita) in okra cultivars

The root-knot nematode, Meloidogyne incognita, is one of the major limiting factors affecting plant growth and yield causing an estimated $100 billion loss per year worldwide. Synthetic pesticides, though instantaneously effective, are usually prohibitively expensive, not readily available, may cause hazards to both man and livestock, and inflict injury to the environment. Notable among the alternatives to nematicides is the use of resistant cultivars which are inexpensive and eco-friendly. In the present studies, twelve okra (Abelmoschus esculentus L) cultivars were evaluated for their resistance against M. incognita under field conditions. Ten-day old okra plants of test cultivars were inoculated with 3000 freshly hatched second stage juveniles of M. incognita. The nematode caused reductions in various growth parameters of all the cultivars to varying levels over their respective controls. None of the cultivars was found completely resistant. The cultivar ‘Sharmeeli’ was highly susceptible as >100 galls were recorded on the roots. Sharmeeli also showed maximum reductions in growth among the cultivars evaluated. The cultivars Anmol and Sindha were susceptible with 71–100 galls. The cultivars Sabz Pari, Super Star, PMS-55 and PMS Beauty were moderately susceptible with 31–70 galls and comparatively less reductions in growth. Cultivars Sanam, Dikshah, Arka Anamika, Ikra-1 and Ikra-2 with 11–30 galls were rated as moderately resistant and showed less damage by the nematode as compared to susceptible cultivars and their planting could provide a useful tool to control root-knot nematodes.     

Host suitability of peppers to the false root-knot nematode Nacobbus aberrans

The false root-knot nematode, Nacobbus aberrans, causes severe damage to field and greenhouse pepper crops in several localities of the American continent. No commercial peppers (Capsicum annuum) resistant to this nematode are available up to the present. Host suitability of 6 experimental and 3 commercial peppers (some of them carrying Me1 and Me7 resistance genes to Meloidogyne spp.) to two N. aberrans populations were evaluated under greenhouse experiments. None of the peppers was found to be resistant to the nematode. The evaluated parameters exhibited significant differences among some peppers tested within a single population and between populations for a single plant material. Some peppers carrying resistance showed higher nematode reproduction than some lines that did not possess resistance genes. These results confirmed that the genes conferring resistance to Meloidogyne spp. do not provide protection against this species of root-galling nematode. Host suitability of pepper lines carrying Me1 or Me7 resistance genes against N. aberrans is evaluated for the first time. Search for resistant genes against this nematode in wild peppers growing in areas where this nematode is indigenous should be promoted.     

Screening of three sweet potato (Ipomoea batatas L.) cultivars for resistance to different virulence groups of root-knot nematodes (Meloidogyne spp.) under controlled conditions

The susceptibility of three sweet potato cultivars (Ipomoea batatas L.) C4, TIS 3290 and TIS 9162 was evaluated against 156 isolates of Meloidogyne spp. with the aim to include resistant/tolerant sweet potato cultivars in a crop rotation scheme for the management of root-knot nematodes. The nematode isolates corresponded to races 1, 2 and 3 of Meloidogyne arenaria (n = 7), races 1, 2, 3 and 4 of M. incognita (n = 131) and Meloidogyne javanica (n = 18). Also, the isolates of M. incognita were differentiated in virulence groups: Pepper (n = 35), Pepper-Mi (n = 25), Tomato (n = 41) and Tomato-Mi (n = 30), depending on their ability to parasitize resistant pepper and tomato cultivars. The tested isolates of M. javanica parasitized C4 and TIS 3290, but not TIS 9162, whereas M. arenaria parasitized C4 and TIS 9162, but not TIS 3290, and M. incognita was able to parasitize the three sweet potato cultivars tested. C4 was the most susceptible cultivar to all nematode species tested, especially M. incognita, TIS 3290 was the most resistant and TIS 9162 was in between (7.2, 62.9 and 26.9% of resistant plants, respectively). Susceptibility of the sweet potato cultivars showed slight variations depending on the race or virulence group of M. incognita. The results suggest that sweet potato cultivars TIS 3290 and TIS 9162 may be used as rotation crops in fields where root-knot nematodes are present, their selection depending on the Meloidogyne isolates present. The use of resistant sweet potato cultivars would be preferably combined with other management practices to avoid virulence selection in nematode isolates.     

Resistance in tuber-bearing solanum species to root knot nematode,Meloidogyne incognita

Forty-one clones of 34 accessions belonging to 25 tuber-bearingSolanum species were tested for their reaction to root knot nematode,Meloidogyne incognita. A high degree of resistance was found inS. bulbocastanum, S. gandarillasii, S. lignicaule, S. ajanhuiri andS. tuberosum groupandigena. S. vernei andS. spegazzinii were the most resistant species.     

Management of the root-knot nematode Meloidogyne incognita on tomato with combinations of different biocontrol organisms

The nematicidal effect of Pseudomonas fluorescens, Paecilomyces lilacinus, Pichia guilliermondii and Calothrix parietina singly or in combination was tested against root-knot nematode, Meloidogyne incognita. Treatments with P. fluorescens and P. lilacinus caused mortality of M. incognita as 45% and 30% of juveniles after 48 h of exposures, respectively compared to water control in vitro. Under greenhouse conditions, all treatments reduced the disease severity and enhanced plant growth compared to untreated control. Application of P. fluorescens, P. lilacinus and P. guilliermondii Moh 10 was more effective compared to C. parietina. There was a negative interaction between C. parietina and either P. lilacinus or P. guilliermondii. Fresh and dry weight of shoots and roots of plants were significantly reduced as a result of infection with M. incognita, however application of biocontrol agents singly or in mix recovered this reduction. Moreover, they enhanced the growth parameters compared with the control. Our results proved that application of different biocontrol agents (P. fluorescens, P. lilacinus and P. guilliermondii) not only has a lethal effect on nematode, but also enhances the plant growth, supplying many nutritional elements and induction the systemic resistance in plants. Presence of C. parietina as a soil inhabitant cyanobacterium could antagonize biocontrol agents leading to the reduction of their practical efficiency in soil.     

Weed control in sunn hemp and its ability to suppress weed growth

Sunn hemp is a tropical, herbaceous annual legume that has potential as a cover crop during the summer in temperate climates. Due to the recent increased interest in sunn hemp breeding and seed production for temperate climates, there is a need for weed control in sunn hemp production. No herbicide product currently on the market specifically identifies sunn hemp as a tolerant crop. The aims of this research were 1) to evaluate herbicides with the intent of identifying a herbicide program that can assure near weed free sunn hemp intended for seed harvest and 2) to demonstrate and quantify sunn hemp-weed suppression. Pre-emergence applied treatments consisted of pendimethalin alone, imazethapyr alone, and pendimethalin plus imazethapyr. Pendimethalin alone provided consistent effective weed control and maximum sunn hemp biomass, but when yellow nutsedge was present, imazethapyr was required for effective control and greater sunn hemp biomass. The combination of pendimethalin and imazethapyr was detrimental to sunn hemp biomass yield. Results also established that sunn hemp is tolerant of 2,4-DB applied post-emergence, but was not necessary for weed control in these studies because of the lack of broadleaf weed pressure. In a separate study with variable sunn hemp densities, weed biomass reductions of ≥50% were obtained with sunn hemp densities of only 20 to 50 plants m⁻². This degree of weed suppression obtained from relatively modest sunn hemp densities is likely indicative of the ability of sunn hemp to grow faster and taller than other plants.     

Population dynamics of arthropods in a sunn-hemp zucchini interplanting system

Zucchini, Cucurbita pepo L., is often colonized by economically important insect pests such as the striped (Acalymma vittatum Fab.) and spotted (Diabrotica undecimpunctata howardi Barber) cucumber beetles. To evaluate the impact of an interplanted cover crop on arthropods associated with zucchini, field experiments were conducted in which sunn hemp (Crotalaria juncea L.) was interplanted with zucchini as a living mulch and compared with zucchini monoculture (bare-ground) during 2009, 2010 and 2011 growing seasons. The experiment consisted also of two types of fertilizer usage including the application of synthetic or organic fertilizer in the form of chicken manure. Foliar counts of arthropods conducted on zucchini plants showed significantly lower numbers of the striped cucumber beetle in sunn hemp interplanted plots compared to bare-ground treatment plots. Also, fewer spotted cucumber beetles were found on zucchini plants in sunn hemp plots. Aphid abundances were variable during the study and significantly lower in sunn hemp treatment plots at one study site in 2009. Among predators, spiders were significantly more abundant in sunn hemp treatment plots during 2009. Fertilizer type did not have a significant effect on arthropod numbers on zucchini plants. Potential causes of arthropod population differences among the two treatments are discussed.     

Differential response of two pineapple cultivars (Ananas comosus (L.) Merr.) to SAR and ISR inducers against the nematode Rotylenchulus reniformis

We hypothesized that inducing systemic resistances can contribute to the control of the nematode Rotylenchulus reniformis in pineapple. In greenhouse experiments conducted in Martinique, the pineapple cultivars Smooth Cayenne and MD-2 were treated with methyljasmonate (JAME) and salicylic acid (SA), elicitors of induced systemic resistance (ISR) and systemic acquired resistance (SAR). The efficacy of the elicitors was tested by inoculating plantlets grown in individual pots with a monospecific population of R. reniformis reared on Vigna unguiculata. The final nematode populations, 45 days after inoculation on MD-2 treated with JAME were reduced by 67.0% (p = 0.006). Nematode populations on MD-2 plants treated with SA were reduced by 55.8% (p = 0.016). Nematode populations on SC were not reduced by the elicitors. In a second experiment, using split-root systems, JAME was applied to MD-2 plantlets and enzymatic activities involved in plant defense and stress responses were monitored for 14 h after treatment. Additional pots were inoculated with nematodes 24 h after JAME treatment and examined ten days later. Transient stress was observed along with an increase in enzymatic response after inoculation with nematodes. These results showed that the MD-2 was primed through an ISR by JAME. The question now arises whether ISR can be specifically induced only in certain pineapple cultivars. Results are discussed from the perspective of introducing new strategies to manage pineapple nematodes.     

Management of Meloidogyne incognita in yam-based cropping systems with cover crops

The effect of intercropping cover crops was with yam was assessed for nematode management both in pot and field conditions in Nigeria. The cover crops were sown with yams in pots containing sterile soil and inoculated with 5000 eggs of Meloidogyne incognita. In the field, each cover crop was separately intercropped with yams inoculated with 10,000 nematodes. From both pot and field experiments, no nematode damage was observed on yam tubers that were intercropped with Aeschynomene histrix, Crotolaria juncea, and Tagetes erecta. Damage in intercropped tubers was reduced by 72.7% with Mucuna pruriens, Centrosema pubescens, and Pueraria phaseoloides and by 58.3% with Stylosanthes guianensis compared to yams planted without cover crops; they also had lower (p ≤ 0.05) nematode populations. Cajanus cajan, Lablab purpureus and Vigna unguiculata however, supported high nematode populations and led to nematode damage in intercropped yams. Tubers from M. incognita-inoculated plants were more damaged and lost 42% more weight (p ≤ 0.05) following three months of storage than tubers from uninoculated plants. Intercropping yams with selected cover crops can be useful in managing M. incognita without reducing yam yields.     

The influence of rainfed and limited irrigation conditions and early vs. late plantings on kenaf as a potential industrial crop in the southern High Plains,USA

Kenaf (Hibiscus cannabinus L.) is a nonwoody fiber source with many uses. To evaluate the dry matter yield potential of kenaf at two locations in the southern High Plains of the USA and the effects of late planting/late emergence as a possible replacement for hail damaged cotton, four varieties were grown in 2004 and 2005 at New Mexico State University's Agricultural Science Centers at Clovis, under limited irrigation, and Tucumcari, under rainfed conditions. Each study was a randomized complete block design having four replicates. A year × location interaction existed (P < 0.0469) for kenaf yield largely due to precipitation amount and distribution. Either late planting or late emergence due to low soil moisture at planting significantly reduced yields (3.62 vs. 0.63 Mg ha^?1 for mid-May planting and emergence and early July emergence or planting, respectively, P < 0.0001). Consequently, kenaf would not be suitable for recovering input costs when planted after failure of cotton. The very late maturing variety Gregg had consistently lower numeric yields than Dowling, Everglades 41, and Tainung 2 in all comparisons, with the strongest trend within the emergence date comparison (P < 0.0912). Kenaf varieties should be selected for any location that finish blooming approximately three to four weeks prior to the average first autumn freeze to allow for maximum growth.     

More about the potato nematode,Heterodera rostochiensis Woll., in Peru

Thirteen resistant selections ofS. tuberosum hybrids bred in the U.S.A. and Europe and 44 diploid clones derived fromS. vernei, S. spegazzinii, S. neohawkesii, andS. sanctaerosae each with resistance to one or more pathotypes ofH. rostochiensis were tested for their resistance to three Peruvian populations of this nematode. Only one diploid clone ofS. sanctatrosae was found to be resistant to the three populations of nematodes, but several clones were resistant to one or another of the nematode populations. More clones were found to resist the nematode population collected near Cuzco than those populations collected near Huancayo or Otuzco. Morphometric measurements of body length, stylet length, and distance of median valve to excretory pore, of second stage larvae showed great variation and no clear difference among the three populations. The measurements obtained were closer to pathotype E from England than to any other recognized pathotypes.     

Rapid detection of Meloidogyne spp. by LAMP assay in soil and roots

Loop-mediated isothermal amplification (LAMP), a novel DNA amplification technique, has been used to detect a variety of pathogens including viruses, fungi, bacteria and parasites. However, diagnosis of sedentary plant-parasitic nematode (PPN) species has not yet been attempted. In this study, we developed a universal LAMP set (RKN-LAMP) for the diagnosis of four common Meloidogyne species (Meloidogyne incognita, M. arenaria, M. javanica and M. hapla), and M. incognita-specific LAMP set (Mi-LAMP). In both assays, a typical ladder-like pattern on gel electrophoresis was observed in all positive samples but not in the negative controls. Amplification products were further confirmed using restriction analysis of the Hpa II enzyme, detection by visual inspection using SYBR Green I and the lateral flow dipstick (LFD) assay. The two LAMP sets were specifically able to detect four common Meloidogyne species and M. incognita populations having several different geographical origins and pathotypes. No cross reaction with DNA of other PPNs was observed. Sensitivity of the RKN- and Mi-LAMP was 10 and 100 fg of pure genome DNA respectively. Both LAMP sets could also amplified crude DNA isolated from the galled root tissue and from soil containing juveniles of M. incognita. The RKN- and Mi-LAMP sets offer the advantages of simplicity, rapidity and cost effectiveness. Both LAMP sets will be instrumental for the diagnosis of Meloidogyne spp. by local extension and regulatory personnel.     

Multiple buds are an alternative target to genetic manipulation of kenaf (Hibiscus cannabinus L.)

Kenaf (Hibiscus cannabinus L.) is an annual fiber crop cultivated as an important source of cellulose and lignin. In the recent years, fibers have increased their economic importance as organic component in bio-composite materials. However, industry requires rheological improvements of these fibers. Genetic manipulation has been considered a feasible approach for fiber improvement; however, kenaf is considered a crop species difficult to manipulate. Here we propose meristematic cells from mature embryos as target for genetic modification driven by Agrobacterium tumefaciens. In vitro meristems proliferation and multiple shoots regeneration were evaluated by sowing kenaf mature seeds on medium containing three different concentration of thidiazuron, a substituted urea compound. The highest number of regenerated shoots was obtained from mature seeds germinated in presence of 10 μM thidiazuron after 14 days of culture. Interactions between two A. tumefaciens strains and two kenaf varieties were assessed. Transgene stable integration and its inheritance in T₁ generation were also verified, demonstrating that kenaf meristematic cells are an useful target for genetic manipulation by agroinfection.     

Response of selected cucumber cultivars to Meloidogyne incognita

Root-knot nematodes (Meloidogyne spp.) are one of the most destructive pathogens of vegetables. The cultivars resistant to root-knot nematodes have comparatively better crop yield than susceptible varieties and can be employed as a component of integrated nematode management. In the present study, 15 cultivars of cucumber (Cucumis sativus) were tested for their response to Meloidogyne incognita by inoculating with 3000 2nd stage juveniles of the nematode. All cultivars varied significantly in causing reductions in growth parameters over their controls. Likewise, all cultivars behaved differently regarding formation of galls and egg masses and reproductive factor. It was found that none of the tested cultivars was found immune or highly resistant. Long Green was the only cultivar which was found resistant against M. incognita as it showed minimum galls (8.2) and reductions in growth parameters. On the other hand, cultivars Mehran, Mirage, Thamin-II, and Royal Sluis were highly susceptible as evident by maximum galls (>100) on their roots and reductions in growth parameters. Similarly, the cultivars Green Wonder, Cucumber Citriolo and Poinsett were moderately susceptible (31–70 galls) while Babylon, Cobra and Falcon-560 (71–100 galls) were susceptible and reductions in growth parameters of these cultivars were less than those in highly susceptible cultivars. Four cultivars, Marketmore, Dynasty, Pioneer-II, and Summer Green, were rated as moderately resistant (11–30 galls) as these cultivars showed less damage by the nematode than moderately susceptible, susceptible and highly susceptible cultivars.     

Interactive effects of Meloidogyne incognita race 2, Bradyrhizobium japonicum and crude extracts of Cucumis myriocarpus fruit on Vigna unguiculata

Crude extracts of wild cucumber (Cucumis myriocarpus) fruit, without information on their effects on nodulation, had been touted as having potential as a nematicide and a fertiliser in low-input cowpea (Vigna unguiculata) production systems. Interactive effects of the southern root-knot nematode (Meloidogyne incognita), Bradyrhizobium japonicum and crude extracts of wild cucumber (C. myriocarpus) fruit on each other and growth of cowpea variety Eureka were investigated in a 23 factorial experiment. At harvest, 70 days after initiating the treatments, significant (P ≤ 0.05) first order interactions between any two of the three main factors on variables measured were observed, with interactive effects being either stimulatory or inhibitory. Crude extracts of C. myriocarpus fruit were basically suppressive on nematode numbers but stimulated nodulation and growth of cowpea. Consequently, the material is suitable for use in managing population densities of M. incognita on cowpea production in low-input cowpea production systems.     

Histopathological changes induced by Meloidogyne incognita in some ornamental plants

Histopathological changes induced by the root-knot nematode (Meloidogyne incognita) in five ornamental plants, specifically, Calendula (Calendula officinalis), Centaurea (Centaurea montana), Papaver (Papaver somniferum), Chrysanthemum (Chrysanthemum morifolium) and Dianthus (Dianthus caryophyllus), were investigated. Based on the galling index (GI), Centaurea was classified as susceptible, Calendula as moderately susceptible, and Papaver as moderately resistant, while Chrysanthemum and Dianthus were highly resistant to M. incognita infection. The histopathology of the galled roots of Centaurea, Calendula, and Papaver during later stages of infection showed that nematodes were localized entirely within the cortex and generally oriented horizontally to the vascular cylinder. Most of the females were mature, and a few of them were associated with egg masses. Giant cells with a variation in cell sizes were observed in the galled roots of all three of the plant species and exhibited a granular cytoplasm and hypertrophied nuclei as a typical reaction to nematode feeding.