Host-status of sweet potato cultivars to South Africa root-knot nematodes

Globally, most of the crop-related developmental projects collapsed due to the existence of aggressive plant-parasitic nematodes. Intensive South African biofortification efforts using exotic and local sweet potato (Ipomoea batatas) cultivars have hardly considered the inclusion of nematode resistance in plant breeding, despite the withdrawal of most nematicides from agrochemical markets. The objective of this study was to screen 12 selected biofortification sweet potato cultivars for host-status to South Africa tropical root-knot (Meloidogyne species) nematodes. Three exotic orange-fleshed, three local orange-fleshed and six cream-fleshed cultivars were used in three separate experiments of M. javanica and races 2 and 4 of M. incognita. In each experiment, 6000 eggs and second-stage juveniles/plant were used for inoculation, with nematode assessment performed at 56 days after inoculation. All tested biofortification exotic (except for cv. ‘W-119’) and local cultivars were hosts to Meloidogyne species and races, whereas three non-biofortication local cultivars, namely, ‘Bosbok’, ‘Blesbok’ and ‘Mvuvhelo’ were non-hosts. In conclusion, the findings suggested the likelihood of the existence of non-host-status in certain exotic and local sweet potato cultivars for use in plant breeding programmes against South African Meloidogyne species and races.     

Interrelations between commercial beetroot (Beta vulgaris) cultivars and Meloidogyne species

Most beetroot (Beta vulgaris) cultivars in South Africa are exotic and were specifically bred for root-knot (Meloidogyne species) nematode populations in their countries of origin. Due to the widespread distribution of different Meloidogyne species and races, exotic cultivars should be matched with nematode populations in importing countries. The objective of this study was to determine the interrelations between exotic beetroot cultivars ‘Detroit Red Dark’ and ‘Crimson Globe’ with Meloidogyne species in the predominant beetroot-producing regions in South Africa. Different inoculum series of M. incognita and M. javanica were used on the two beetroot cultivars. At 56 days after initiating the treatments, roots of both cultivars had small undeveloped root galls, with the reproductive factor values of M. incognita on ‘Detroit Dark Red’ being above and below unity at low (≤125 inoculation) and high (≥250 inoculation) nematode levels, respectively. Growth of ‘Detroit Dark Red’ was significantly stimulated and inhibited at low and high nematode infection levels, respectively. In contrast, RF values for M. javanica on ‘Crimson Globe’ were below unity, without any significant effects on plant growth. In conclusion, ‘Detroit Dark Red’ was tolerant to M. incognita, whereas ‘Crimson Globe’ was resistant to M. javanica.     

Host response of Capsicum frutens cultivar ‘Capistrano’ to Meloidogyne incognita race 2

Abstract

Host resistance in managing the southern root-knot nematode (Meloidogyne incognita) is limited by the existence of races of this nematode species. Pepper (Capistrano frutens) cultivar ‘Capistrano’ released for resistance against M. incognita races 3 and 4 in Central and South America, was evaluated for host-status and host-sensitivity to M. incognita race 2 in Limpopo Province, South Africa. Plants in pots uninoculated or inoculated with nematodes were arranged in a completely randomized design, with 15 replications. At 120 days after inoculation, the reproductive factor was less than unity, while nematode infection had no effect on plant growth. Thus, the cultivar is resistant to M. incognita race 2 and could be included in crop rotation systems intended to suppress population densities of M. incognita race 2.     

Host-status and host-sensitivity of wild Cucumis species to Meloidogyne incognita race 4

Abstract

Wild watermelon (Cucumis africanus) and wild cucumber (Cucumis myriocarpus), which are highly resistant to the southern root-knot nematode (Meloidogyne incognita) race 2, have the potential for serving as seedling rootstocks for the highly nematode-susceptible watermelon (Citrullus lanatus) cultivars. In South Africa, due to high labour costs, most cotton farmers are turning to watermelon production. In these regions, there is high incidence of M. incognita race 4. A pot experiment in the greenhouse was, therefore, initiated to investigate the host-status and host-sensitivity of Cucumis africanus and Cucumis myriocarpus to M. incognita race 4, when inoculated with 0, 200, 600, 100, 1400, 1800 and 2200 eggs and second-stage juveniles (J2s). At harvest, 56 days after inoculation, the reproductive factor values at all levels of inoculation were less than one. Penetration indices on both plant species were greater than one, suggesting that the resistance was post-infectional and therefore, introgressible. Sex (male: female) ratios of M. incognita race 4 on the two Cucumis species were greater than one, suggesting that more J2s were converted into males. Infection of Cucumis species by the test nematode had no effect on yield components of the two plant species due to poor feeding sites. The two Cucumis species were, therefore, resistant to M. incognita race 4, with post-infectional resistance, where the sex ratio was skewed towards maleness. Thus, the two Cucumis species have the potential to be used as nematode-resistant rootstocks in watermelon production.     

Response of mineral malnutrition elements in African ginger pseudo-stems to nematode infection

Interference of nematode infection with mineral malnutrition (MMN) elements in biofortificated cultigens could devalue the health potential of such crops for humans. A pot trial was conducted to determine the response of selected MMN elements in African ginger (Siphonochilus aethiopicus) pseudo-stems to the southern root-knot (Meloidogyne incognita) nematode. Fifty-six days after inoculation, the sensitivity of the pseudo-stems to nematode infection was confirmed, with 23–45% reduced potassium in pseudo-stem tissues, but had no effect on other MMN elements. In conclusion, population densities of M. incognita race 2 should be managed to enhance the potential uses of S. aethiopicus as a biofortification crop.     

Interactive effects of Nemarioc-AL phytonematicide,Steinernema feltiae and Trichoderma harzianum on the reproduction of Meloidogyne incognita race 2 under greenhouse conditions

Interactive effects of alternatives to methyl bromide on root-knot (Meloidogyne species) nematodes could provide information on whether to use the products combined or singularly. The objective of this study was to investigate the interactive effects of Nemarioc-AL phytonematicide, Steinernema feltiae and Trichoderma harzianum on eggs and reproductive factors of Meloidogyne incognita race 2 under greenhouse conditions. The interactive effects of Nemarioc-AL phytonematicide (N), S. feltiae (S) and T. harzianum (T) on population densities of M. incognita were examined in a 2?×?2?×?2 factorial experiment in pots filled with steam-pasteurised soil. Each tomato seedling was inoculated with 2000 eggs and second-stage juveniles (J2), with phytonematicide and biocontrol agents applied at commercial rates. At 56 days after the treatments, the second-order (N₁S₁T₁) interaction reduced eggs and the reproductive factor (RF) in roots by 100% and 93%, respectively. Similarly, the first-order (N₁S₀T₁) interaction reduced the two variables by 92% and 72%, respectively, whereas N₁S₁T₀ interaction had 63% and 55% reduction effects, respectively. Nemarioc-AL phytonematicide was compatible with S. feltiae and T. harzianum and could, therefore, be used collectively to manage population densities of M. incognita.     

Confirmation of bioactivities of active ingredients of nemarioc-AL and nemafric-BL phytonematicides

Nemarioc-AL and Nemafric-BL phytonematicides consistently reduced populations of plant-parasitic nematodes. The contribution of juvenile hatch inhibition to the overall reduction of the nematode numbers by the two phytonematicides, with cucurbitacin A and B as active ingredients, respectively, remains undocumented. The objectives of this study were to examine (i) the response of Meloidogyne incognita second-stage juveniles (J2) hatch to increasing concentration of cucurbitacins A and B, (ii) the potential saturation of J2 hatch when exposed to cucurbitacins for extended incubation periods, (iii) the minimum inhibition concentration for J2 hatch and (iv) the reversibility of J2 hatch inhibition.. Eggs of M. incognita were exposed to a series of purified cucurbitacin A and B concentrations over five incubation periods of 24, 48, 72?h and extended incubation periods of 7 and 10 days. Methanol-dissolved cucurbitacin A and B were each diluted and pipetted into well-plates making 11 concentrations, ranging from 0.0 to 2.5 µg.ml^?1 water solvent. Juvenile counts were made after 24, 48 and 72?h, with those for saturation assessed at 7 and 10 days. Thereafter, treatments were diluted five times, incubated again for 5 days and counted to establish reversibility of J2 hatch inhibition. In all incubation periods, treatment effects were highly significant (P?≤?0.01), with J2 hatch and cucurbitacin concentrations exhibiting quadratic relations. Minimum inhibition concentrations of the two cucurbitacins were between 1.13 and 1.40?µg.ml^?1. Treatment effects for reversibility to J2 hatch inhibition were not significant (P?>?0.05). In conclusion, J2 hatch inhibition could be one of the waysthrough which the two phytonematicides reduced population densities of Meloidogyne species.     

Effects of AM fungi and organic fertilizers on the reproduction of the nematode <Emphasis Type="Italic">Meloidogyne incognita</Emphasis> and on the growth and water loss of tomato

Glasshouse experiments were conducted to assess the influence of arbuscular mycorrhizal (AM) fungi (Glomus mosseae and Gigaspora margarita) and organic fertilizers (cow dung, horse dung, goat dung and poultry manure) alone and in combination on the reproduction of the nematode Meloidogyne incognita and on growth and water loss of tomato. Meloidogyne incognita decreased water loss of tomato from the first week onwards after inoculation. AM fungi increased water loss of both nematode-infected and uninfected plants. Glomus mosseae was better at improving growth of tomato and reducing galling and nematode multiplication than G. margarita, but the rate of water loss was similar with both fungi. Addition of organic fertilizers improved growth of tomato, but decreased the rate of water loss. There was less galling and nematode multiplication with poultry manure, which improved tomato growth more than goat dung, while cow dung was the least effective organic fertilizer. Greatest plant growth and least nematode reproduction were observed in plants inoculated with M. incognita along with G. mosseae and poultry manure.     

Response to root-knot nematodes of a germplasm collection of red clover and related species

A germplasm collection of red clover (Trifolium pratense L.) and seven related species was evaluated in greenhouse tests for resistance to Meloidogyne arenaria (Neal) Chitwood, M. hapla Chitwood, M. incognita (Kofoid & White) Chitwood, and M. Javanica (Treub) Chitwood. Plants were rated for root galling severity and nematode egg production at eight weeks after inoculation with 1500 nematode eggs. A resistance index, RI = (gall₂; + egg₂;), was generated to assess the plants' reaction to nematode infection as immune, highly resistant, resistant, moderately resistant, intermediate, moderately susceptible, susceptible, or highly susceptible. More than 98% of red clover accessions were intermediately to highly susceptible to all four root-knot nematode species. Only one accession, PI 271627 introduced from India, had a moderate resistance level to the four nematodes tested. About one third of the T. medium accessions were resistant or highly resistant to M. arenaria, M. incognita, and M. javanica whereas more than 50% of the T. alpestre accessions were highly resistant or immune to all four nematodes species. Genetic factors for resistance to root-knot nematode could be introduced into T. pratense through interspecific hybridization with T. medium and/or T. alpestre     

氮肥用量对滨海滩涂区甘薯干物质积累、氮素效率和钾钠吸收的影响

我国沿海滩涂种植能源作物甘薯有广阔的前景。为确定苏北滩涂区甘薯适宜施氮量,比较了6个施氮水平下甘薯的成活率(SR)、商品率(CR)、蔓薯比(V/T)、干物质积累(DMA)、氮素累积值(NAV)、氮利用效率(NUE)、氮收获指数(NHI)及钾钠吸收的差异。结果表明:(1)施氮量与甘薯地上部分DMA和NAV均呈极显著正相关(P<0.01,余同),对地下部分NAV影响较小(P>0.05)。(2)与不施氮比较,施氮60 kg(N)·hm-2对甘薯的V/T、SR、NUE和NHI均无显著影响。(3)甘薯的CR、地下部分和块根DMA以及理论产量(NAV×NUE×NHI)均以施氮60 kg(N)·hm-2显著高于其他处理。施氮量超过60 kg(N)·hm-2,施氮量与甘薯的V/T值呈极显著正相关,与SR、CR、NUE、NHI、地下部分和块根DMA均呈极显著负相关。(4)甘薯对钾钠的吸收量均随施氮量的增加而增加,二者呈极显著正相关。甘薯地上部分钾钠含量均在施氮量为60 kg(N)·hm-2时达到最高值。施氮量对钾钠含量比没有影响。因此,苏北滩涂区甘薯适宜施氮量为60 kg(N)·hm-2。     

Efficacy of fresh fruit from Cucumis myriocarpus as Nemarioc-AL phytonematicide on suppression of root-knot nematodes in tomato plant production

Experimental System: Fermented dried fruit of wild cucumber (Cucumis myriocarpus Naude.) Had been successfully used as Nemarioc-AL phytonematicide in managing plant-parasitic nematodes in various cropping systems. However, the specialised oven-drying equipment are inaccessible to most resource-poor smallholder farmers in marginalised communities. Procedures: The objective of this study was to determine the efficacy of fermented crudes extracts of C. myriocarpus fruit when used in fresh form as Nemarioc-AL phytonematicide on management of population densities of root-knot (Meloidogyne species) nematodes and growth of tomato (Solanum lycorpersicum L.) plants. Seedlings at five leaf-stage were transplanted into pots containing 2700?ml steam-pasteurised river sand and Hygromix at 3:1 (v/v) ratio. Each seedling was inoculated with approximately 3000 eggs and second-stage juveniles (J2) at transplanting. The phytonematicide was applied at 0%, 2%, 4%, 8%, 16%, 32% and 64%, arranged in a randomised complete block design, with five replications and validated in time. Results: At 56 days after treatment, nematode variables and phytonematicide concentrations exhibited negative quadratic relations, with coeffients of determination (COD) ranging from 93% to 97%. Similarly, plant variables and phytonematicide concentrations exhibited positive quadratic relations, with COD from 96% to 98%. Conclusions: In conclusion, when prepared from fresh fruit of C. myriocarpus, Nemarioc-AL phytonematicide was suitable for use in managing nematode population densities of Meloidogyne species in tomato production.     

Role of effective microorganisms in efficacy of Nemarioc-AG phytonematicide on suppression of Meloidogyne incognita and growth of tomato plants

The release of active ingredient chemicals in conventional organic amendments is primarily through microbial degradation, whereas in granular phytonematicides, leaching through irrigation water had been implied as a probable mechanism. The objective of this study was to determine the role of effective microorganisms (EM) on the efficacy of Nemarioc-AG (NAG; G?=?granular formulation) phytonematicide on suppression of root-knot (Meloidogyne species) nematodes and growth of tomato (Solanum lycopersicum) plants. A 5?×?6 factorial experiment, with EM at 0%, 0.14%, 0.17%, 0.20% and 0.25% and phytonematicide at 0, 3, 6, 9, 12 and 15?g per plant, was conducted under microplot conditions. Each plant was inoculated with 11,000 eggs and second-stage juveniles (J2) of Meloidogyne incognita. Seventy days after initiating the treatments, the interactions were not significant (P?≥?.05) on all variables, but the main factors were highly significant. Regression of nematode population densities, root gall and dry shoot mass over increasing phytonematicide concentration exhibited quadratic relations, which were explained by 93%, 97% and 99%, respectively. In contrast, stem diameter and phytonematicide concentration had a positive linear relation, which was explained by 98%. Nematode numbers over increasing EM concentration exhibited quadratic relation, which was explained by 97%. All plant variables and EM had no significant relations. In conclusion, the efficacy of NAG phytonematicide on nematode suppression and plant growth was independent of EM activities, suggesting that irrigation water played a major role in the efficacy of the product in granular formulation.     

Effects of Pseudomonas fluorescens and fertilizers on the reproduction of Meloidogyne incognita and growth of tomato

A 60-day glasshouse experiment was conducted to assess the influence of two strains of Pseudomonas fluorescens (GRP3 and PRS9), organic manure, and inorganic fertilizers (urea, diammonium phosphate (DAP), muriate of potash and monocalcium phosphate) alone and in combination on the multiplication of Meloidogyne incognita and growth of tomato. Pseudomonas fluorescens GRP3 was better at improving tomato growth and reducing galling and nematode multiplication than PRS9. Organic manuring resulted in less galling and nematode multiplication than occurred with DAP. However, DAP was found better in reducing nematode multiplication and improving plant growth than urea. Muriate of potash was the inorganic fertilizer least effective in reducing galling and nematode multiplication. Pseudomonas fluorescens GRP3 with organic manure was the best combination for the management of M. incognita on tomato but improved management of M. incognita can also be obtained if DAP is used with the GRP3 strain of P. fluorescens.     

Control of tomato bacterial wilt and root-knot diseases by Bacillus thuringiensis CR-371 and Streptomyces avermectinius NBRC14893

Ralstonia solanacearum and Meloidogyne incognita are two soilborne pathogens that cause serious damage and great losses in the production of tomato. For this purpose, a bacterial isolate, Bacillus thuringiensis CR-371, and an actinomyces isolate, Streptomyces avermectinius NBRC14893, were examined for their ability to protect tomato from root-knot nematode and bacterial wilt diseases under glasshouse conditions. Treatment of tomato roots with B. thuringiensis CR-371 and S. avermectinius NBRC14893 followed by challenge inoculation with R. solanacearum and M. incognita significantly decreased disease severity of bacterial wilt alone, root-knot nematode alone, or mixed infection by both pathogens compared to the control. Furthermore, pretreatment of tomato roots with B. thuringiensis CR-371 and S. avermectinius NBRC14893 significantly reduced bacterial proliferation of R. solanacearum both in pathogen alone inoculated plants and in plants co-inoculated with R. solanacearum and M. incognita. In conclusion, our results suggest that the treatment of tomato roots with B. thuringiensis CR-371 and S. avermectinius NBRC14893 simultaneously suppresses bacterial wilt and root-knot nematode diseases. Therefore, B. thuringiensis CR-371 and S. avermectinius NBRC14893 could provide new options for integrated pest management strategies against plant diseases, especially against bacterial-nematode disease complexes that cause synergistic yield losses.     

Nematicidal activity of volatile organic compounds emitted by Brassica juncea,Azadirachta indica,Canavalia ensiformis,Mucuna pruriens and Cajanus cajan against Meloidogyne incognita

Understanding the effect of plant volatile organic compounds (VOCs) on soil nematodes and water may explain plant damage in the field and how some nematode management strategies reduce soil nematode populations. M. incognita is a damaging plant pathogenic nematode that affects crops worldwide. The aims of this study were to evaluate the effect of the VOCs emitted by five common crops used for soil incorporation to control the second-stage juveniles (J₂) of Meloidogyne incognita. To investigate the “in vitro” role of water in the relationship between nematodes and plant VOCs. And to identify the volatile molecules by gas chromatography (GC/MS). The method used permitted the volatile molecules from macerated plant organs to only contact the J₂ nematodes by air. Plants organs from all plants macerated with and without water emitted VOCs that immobilized J₂ nematodes, with higher levels emitted when the plant organs were macerated without water. Only water exposed to VOCs from neem and mustard leaves were capable of immobilizing M. incognita J₂. The M. incognita J₂ exposed to neem and mustard VOCs and inoculated in tomato seedlings resulted in reduced gall formation and nematode reproduction, showing the nematicidal effect of the plant-emitted VOCs. GC/MS analysis revealed the presence of 58 and 32 molecules in the VOCs emitted from neem and mustard macerates, respectively. Alcohols were found in both the neem and mustard VOCs. Esters were found in the neem VOCs, and sulfur-containing compounds, mostly isothiocyanates, were found in mustard. Our results demonstrate that plant VOCs contain diversified molecules that affect M. incognita mobility, pathogenicity and reproduction. Nematode toxic VOCs may be retained in water, which prevents the VOCs from escaping into the air and causing the water to become toxic to nematodes. These data may explain part of the role of VOCs in the biofumigation process, through plant incorporation with the soil, and suggests that irrigation performed directly after incorporation may trap the VOCs in soil water and thereafter retain nematode toxicity longer than incorporation that is performed later.     

Sources of resistance to cyst nematode in cultivated and wild Cicer species

Summary Among the nematodes infesting chickpea (Cicer arietinum L.) plants in Syria, cyst nematode (Heterodera ciceri Vovlas, Greco et Di Vito) is the most important. It is uneconomical to grow chickpea in fields infested with cyst nematode and to control this nematode with nematicide. Therefore, investigations were conducted at ICARDA, Syria from 1987 to 1991 to identify sources of resistance to cyst nematode in 7258 lines of C. arietinum and 102 lines of eight annual Cicer species including C. bijugum K.R. Rech. (13 lines), C. chorassanicum (Bge) M. Pop. (3 lines), C. cuneatum Hochst. ex Rich. (3 lines), C. echinospermum P.H. Davis (8 lines), C. judaicum Boiss. (18 lines), C. pinnatifidum Jaub. & Sp. (18 lines), C. reticulatum Ladiz. (36 lines), and C. yamashitae Kitamura (3 lines). All lines were grown in a greenhouse at 15–25°C in pots containing soil infested with 20 eggs of the nematode g^-1 soil. Nematode infestation was evaluated on a 0 to 5 scale based on number of females and cysts on roots. Resistance was found in one line of C. bijugum, six lines of C. pinnatifidum, and one line of C. reticulatum. No lines of C. arietinum, C. chorassanicum, C. cuneatum, C. echinospermum, C. judaicum, or C. yamashitae was resistant to cyst nematode. Plants with resistance have been recovered in the F₃ generation from crosses between the cultigen and C. reticulatum, indicating the possibility of transfer of gene(s) for resistance to cyst nematode from wild to cultivated Cicer species.Joint contribution from Istituto di Nematologia Agraria, ICARDA and ICRISAT (International Crops Research Institute for the Semi-Arid Tropics), Patancheru P.O., A.P. 502 324, India.     

Potential existence of multiple Tylenchulus semipenetrans biotypes in South Africa

The existence of multiple Tylenchulus semipenetrans biotypes within a citrus-producing region complicates the selection of nematode-resistant rootstocks for managing the slow decline of citrus. The potential existence of multiple T. semipenetrans biotypes in South Africa was investigated under greenhouse conditions on differential host plants using nematode isolates from 18 citrus-producing districts with at least six diverse soil groups and three different climates. After three nematode generations, the regional effects had no influence on final nematode population densities, whereas the differential host plants significantly segregated the nematode reproductive potentials. On Olea europaea reproductive potentials (eggs and juveniles/g) were zero, whereas those on Citrus jambhiri and Poncirus trifoliata ranged from 79 to 482 and 86 to 433, respectively. All T. semipenetrans isolates, regardless of the soil group and climate type, behaved similarly to the Poncirus biotype, which therefore rules out the existence of multiple T. semipenetrans biotypes in South Africa.     

Effect of Inoculation with the Arbuscular Mycorrhizal Fungus Glomus Intraradices on the Root-Knot Nematode Meloidogyne Incognita in Cucumber

ABSTRACT

A pot experiment was carried out to investigate the tolerance of cucumber plants (Cucumis sativus L.) to root-knot nematode after inoculation with Glomus intraradices. Plants were inoculated with G. intraradices for four weeks and then transplanted in soil treated with Meloidogyne incognita for a further five weeks. The low phosphorus (P) loamy soil was amended with 50 and 100 mg P kg^?1 soil. Mycorrhizal colonization increased shoot dry weight, shoot length, leaf numbers, root fresh weight and shoot P concentration, whereas nematode penetration and reproduction were significantly decreased. Similarly, P fertilization usually increased shoot growth and significantly decreased the number of galls and the number of egg masses and eggs per g root. Our results indicate that inoculation with G. intraradices and P fertilizer confer tolerance of cucumber plants to M. incognita by enhancing plant growth and by suppressing reproduction and/or galling of nematodes during the early stages of plant growth.     

Genetic diversity for root-knot nematode resistance in white clover and related species

A total of 237 Plant Introduction in eleven Trifolium species were evaluated for resistance to Meloidogyne arenaria (Neal) Chitwood race 1, M. hapla Chitwood, M. incognita (Kofoid & White) Chitwood race 3, and M. javanica (Treub) Chitwood. Plants were infected with 1500 nematode eggs collected from 'Rutgers' tomato (Lycoperiscon esculentum Mill.) roots with 0.5% NaOCl. Ratings of galling severity and egg mass production were assigned to each plant 8 wk after inoculation. Host plant reaction was classified as immune, highly resistant, resistant, moderately resistant, intermediate, moderately susceptible, susceptible, and highly susceptible according to the resistance index . More than 95% of 171 white clover accessions were moderately to highly susceptible to all four nematodes species. The best white clover accessions were only moderately resistant to either M. arenaria (PI 291843 and PI 306286) or M. hapla (PI 100250 and PI 204930). Accessions with moderate resistance or resistance to root-knot nematodes were found among relatives of white clover, with T. ambiguum M. Bieb. exhibiting the greatest resistance level. Among the other Trifolium species evaluated, T. carolinianum Michx. PI 516273 was immune or highly resistant to all four nematode species while accessions of T. hirtum All. showed a wide range of reaction to root-knot nematodes. Identified germplasm of white clover relatives with resistance to root knot nematodes should be useful for the selection of parents in white clover breeding programs.     

Effects of interaction of Meloidogyne incognita,Alternaria dauci and Rhizoctonia solani on the growth,chlorophyll, carotenoid and proline contents of carrot in three types of soil

Disease complex of carrot (Daucus carota L.) involving root knot nematode Meloidogyne incognita and two fungi Alternaria dauci and Rhizoctonia solani were studied in three soil types. More plant growth, chlorophyll, carotenoid and proline contents were found in carrot grown in fly ash mix soil than plants grown in sand mix soil and loamy soil. Inoculation of M. incognita, R. solani, and A. dauci reduced plant growth, chlorophyll and carotenoid but increased proline contents. Inoculation of M. incognita 20 days prior to a fungal pathogen caused a greater reduction in plant growth, chlorophyll and carotenoid than fungal pathogen was inoculated prior. Inoculation of A. dauci prior to R. solani or vice versa had a similar effect on plant growth, chlorophyll, and carotenoid. Nematode multiplication and galling was higher in plants grown in sand mix soil followed by loamy soil and fly ash mix soil. Both fungi had adverse effects on galling and nematode multiplication. Blight disease index caused by A. dauci was 3 and crown rot index by R. solani was also recorded 3. These disease indices were 5 when pathogens were inoculated in combinations.