Sources of resistance to ascochyta blight in wild Cicer species

Ascochyta blight [Ascochyta rabiei (Pass.) Lab.] is the major foliar disease of chickpea (Cicer arietinum L.). In search of better sources of resistance to ascochyta blight, 201 accessions of 8 annual wildCicer species were evaluated in field and greenhouse for 3 years (1988 to 1991) at Tel Hadya, Syria. One accession each ofC. judaicum Boiss (ILWC 165) andC. pinnatifidum Jaub. & Spach. (ILWC 159) were consistently rated resistant in both field and greenhouse evaluations. Another three accessions ofC. judaicum (ILWC 61, ILWC 154, ILWC 199) and six accessions ofC. pinnatifidum (ILWC 78, ILWC 88, ILWC 155, ILWC 160, ILWC 162, ILWC 203) were resistant or moderately resistant. The blight-resistant accessions ofC. judaicum originated from Jordan, Lebanon, Syria, and Turkey; and those ofC. pinnatifidum from Syria and Turkey. None of the accessions ofC. bijugum, C. chorassanicum, C. cuneatum, C. echinospermum, C. reticulatum andC. yamashitae were resistant to blight.     

Aggressiveness of eight <Emphasis Type="Italic">Didymella rabiei</Emphasis> isolates from domesticated and wild chickpea native to Turkey and Israel,a case study

Ascochyta blight, caused by Didymella rabiei, affects both domesticated chickpea and its congeneric wild relatives. The aim of this study was to compare the aggressiveness of D. rabiei isolates from wild and domesticated Cicer spp. in Turkey and Israel on wild and domesticated hosts from both countries. A total of eight isolates of D. rabiei sampled from C. pinnatifidum, C. judaicum and C. arietinum in Turkey and Israel was tested on two domesticated chickpea cultivars and two wild Cicer accessions from Turkey and Israel. Using cross-inoculation experiments, we compared pathogen aggressiveness across the different pathogen and host origin combinations. Two measures of aggressiveness were used, incubation period and relative area under the disease progress curve. The eight tested isolates infected all of the host plants, but were more aggressive on their original hosts with one exception; Turkish domesticated isolates were less aggressive on their domesticated host in comparison to the aggressiveness of Israeli domesticated isolates on Turkish domesticated chickpea. C. judaicum plants were highly resistant against all of the isolates from different origins except for their own isolates. Regardless of the country of origin, the wild isolates were highly aggressive on domesticated chickpea while the domesticated isolates were less aggressive on the wild hosts compared with the wild isolates. These results suggest that the aggressiveness pattern of D. rabiei on different hosts could have been shaped by adaptation to the distinct ecological niches of wild vs. domesticated chickpea.     

A comparative study of Turkish and Israeli populations of Didymella rabiei,the ascochyta blight pathogen of chickpea

The Fertile Crescent is the centre of domestication of chickpea (Cicer arietinum) and also the place of origin of its pathogens. Agrosystems provide different environments to natural eco‐systems, thus imposing different types of selection on pathogens. Here, the genetic structure and in vitro temperature growth response of the chickpea pathogen Didymella rabiei from domesticated chickpea (59 isolates from Turkey and 31 from Israel) and wild Cicer spp. (three isolates from Turkish C. pinnatifidum and 35 from Israeli C. judaicum) were studied. Six sequence‐tagged microsatellite site (STMS) primer pairs were used to determine the genetic structure of the 128 D. rabiei isolates. Turkish isolates exhibited the highest genetic diversity (H = 0·69). Turkish and Israeli D. rabiei from domesticated chickpea were genetically closer to each other than isolates from the wild Cicer spp. Analysis of molecular variance showed that 54% of the genetic variation resided between isolates from wild and domesticated origins. EF1‐α sequences distinguished between D. rabiei isolates from domesticated and wild Cicer spp. by four polymorphic sites. Nevertheless, a certain degree of mixing between isolates from wild and domesticated origin was demonstrated using the Bayesian algorithm as well as with principal coordinates analysis. Isolates sampled from domesticated chickpea from both countries were better adapted to temperatures typical of Levantine spring and had a significantly larger colony area at 25°C than at 15°C (typical Levantine winter temperature). These observations were in accordance to the heritability values of the temperature growth response.     

Aggressiveness of Phytophthora medicaginis on chickpea: Phenotyping method determines isolate ranking and host genotype-by-isolate interactions

Phytophthora medicaginis causing Phytophthora root rot of chickpea (Cicer arietinum) is an important disease, with genetic resistance using C. arietinum × Cicer echinospermum crosses as the main disease management strategy. We evaluated pathogenic variation in P. medicaginis populations with the aim of improving phenotyping methods for disease resistance. We addressed the question of individual isolate aggressiveness across four different seedling-based phenotyping methods conducted in glasshouses and one field-based phenotyping method. Our results revealed that a seedling media surface inoculation method used on a susceptible C. arietinum variety and a moderately resistant C. arietinum × C. echinospermum backcross detected the greatest variability in aggressiveness among 37 P. medicaginis isolates. Evaluations of different components of resistance, using our different phenotyping methods, revealed that differential pathogen–isolate reactions occur with some phenotyping methods. We found support for our hypotheses that the level of aggressiveness of P. medicaginis isolates depends on the phenotyping method, and that phenotyping methods interact with both isolate and host genotype reactions. Our cup-based root inoculation method showed promise as a non-field-based phenotyping method, as it provided significant correlations with genotype–isolate rankings in the field experiment for a number of disease parameters.     

Variation in resistance to Orobanche crenata in species of Cicer

Crenate broomrape (Orobanche crenata) is a major constraint for legume cultivation in Mediterranean agriculture. Field trials, pot and in vitro experiments demonstrated that resistance to O. crenata is present in chickpea and wild species of Cicer. The resistance is the result of the combination of several mechanisms, including low induction of parasite seed germination and in some accessions, either a darkening at the infection site on the host root that prevents establishment, or a reduced development of established parasite tubercles.     

Partial stem and leaf resistance against the fungal pathogen <Emphasis Type="Italic">Botrytis cinerea</Emphasis> in wild relatives of tomato

Tomato (Solanum lycopersicum) is one of many greenhouse crops that can be infected by the necrotrophic ascomycete Botrytis cinerea. Commercial cultivation of tomato is hampered by the lack of resistance. Quantitative resistance has been reported in wild tomato relatives, mostly based on leaf assays. We aimed to identify wild tomato relatives with resistance to B. cinerea based on quantitative assays both on leaves and stem segments, monitoring infection frequency and disease expansion rate as parameters. A quantitative tomato stem segment assay was developed. This stem assay and a previously described leaf assay were used to screen a collection of 22 Solanum accessions. Significant differences in disease parameters were observed among accessions. Resistance to B. cinerea was observed in a number of wild Solanum species, including accessions of S. chilense, S. habrochaites and S. neorickii, both in the leaf assay and the stem segment assay. A number of resistant and susceptible accessions were evaluated as adult plants under greenhouse conditions. The data obtained in greenhouse assays confirmed the leaf and stem disease data. The expression of several defence-related genes was studied in a subset of accessions. There was no apparent correlation between the expression levels of the genes tested and the quantitative resistance level to B. cinerea. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Resistant accessions of wild Psidium spp. to Meloidogyne enterolobii and histological characterization of resistance

Meloidogyne enterolobii has been reported in some states of Brazil and other countries causing severe damage on commercial guava (Psidium guajava). The use of resistant varieties is the most effective way to manage nematode parasitism. This study screened 51 accessions of Psidium spp. selected from the Psidium Germplasm Collection (Embrapa) to look for resistance against M. enterolobii. Six months after inoculation, nematode reproduction factor (RF) was used to assess resistance. The following species were resistant to M. enterolobii: P. cattleianum (yellow guava), P. friedrichsthalianum (Costa Rican guava), Acca sellowiana (feijoa) and P. rufum (purple guava). All 43 wild accessions of P. guajava were susceptible, as well as three accessions of P. guineense (Brazilian guava), one of P. acutangulum (pear guava) and the susceptible control P. guajava cv. Paluma. When used as rootstocks under greenhouse conditions, P. cattleianum and P. friedrichsthalianum were compatible with cv. Paluma; however, in greenhouse and field conditions only 50% of both scions survived. No apparent hypersensitive response (HR) was seen in the resistant guava P. cattleianum and P. friedrichsthalianum. Juveniles were able to develop normal feeding sites similar to those in susceptible roots 6–13 days after inoculation (dai). From 27 to 32 dai, giant cell deterioration was observed and nematodes showed arrested development. The majority of nematodes failed to reach maturity and did not begin laying eggs in resistant roots. These results suggested that the induction of resistance is relatively late in this pathosystem.     

Identification of novel sources of resistance to Pea enation mosaic virus in chickpea germplasm

Chickpea can be seriously affected by Pea enation mosaic virus (PEMV) in the Pacific Northwest region of the USA and other areas of the world. Use of pesticides to manage PEMV vector transmission is ineffective and PEMV-resistant chickpeas have not been identified. Therefore, the Cicer core collection consisting of 499 wild Plant Introduction (PI) accessions and improved cultivars representing 25 countries and two chickpea phenotypes (Desi and Kabuli) was evaluated for resistance to PEMV based on a 1 to 5 scale where 1 = symptomless and 5 = severe mosaic and stunting. Eight accessions were considered resistant to PEMV based on mean disease severity values equal to or less than 1·9 in repeated greenhouse tests. All of the resistant accessions to PEMV were of the Desi type and all originated from Iran or India. PI 450763 was the only Kabuli accession that demonstrated tolerance to PEMV. PEMV resistance was not detected in commercial chickpea cultivars or advanced breeding lines currently grown in the USA and Canada. This is the first report of chickpea germplasm with resistance to PEMV.     

Alternative hosts and plant tissues for the survival,sporulation and spread of the Ascochyta blight pathogen of chickpea

Various crop and weed species were infected naturally by Didymella rabiei (anamorph: Ascochyta rabiei) in blight-affected chickpea fields in the Palouse region of eastern Washington and northern Idaho, USA. The fungus was isolated from asymptomatic plants of 16 species commonly found in commercial crops in this region. Isolates of the pathogen from crop and weed species were pathogenic to chickpea and indistinguishable in cultural and morphological characteristics from isolates of D. rabiei from chickpea. Both mating types of D. rabiei were isolated from eight naturally infected plant species. Chickpeas were infected by D. rabiei when plants emerged through infested debris of seven crop and weed species. The teleomorph developed on overwintered tissues of seven plant species infected naturally by D. rabiei in a blight screening nursery and on debris of wheat, white sweet clover and pea inoculated with ascospores of D. rabiei or conidia of two compatible isolates of the pathogen. Didymella rabiei naturally infected 31 accessions of 12 Cicer spp. and the teleomorph developed on the overwintered debris of all accessions, including those of three highly resistant perennial species. The fungus developed on the stem and leaf pieces of ten plant species common to southern Spain inoculated with conidia of two compatible isolates of D. rabiei, and formed pseudothecia with asci and viable ascospores on six of ten species and pycnidia with conidia on all plant species.     

Sympatric ascochyta complex of wild Cicer judaicum and domesticated chickpea

The aim of this study was to isolate, identify and characterize ascochyta blight pathogens from Cicer judaicum , a wild annual Cicer species which grows in Israel and other Mediterranean countries in sympatric distribution with legume crops, and determine their virulence and aggressiveness to other wild and domesticated legumes. Native C. judaicum plants exhibited symptoms resembling ascochyta diseases of grain legume crops. Two distinct pathogens were isolated and identified as Phoma pinodella and Didymella rabiei using morphological and molecular tools; their infectivity was verified using Koch's postulates. The virulence of these pathogens was examined on 13 legume species, of which P. pinodella was virulent to Pisum sativum , P. fulvum , C. judaicum , C. arietinum , C. reticulatum , C. pinnatifidum and C. bijugum . Didymella rabiei infected all these Cicer species, but not the other legume species tested. Aggressiveness of the pathogens was tested on wild and domesticated chickpea and pea. Didymella rabiei isolated from C. judaicum had significantly higher ( P  < 0·001) aggressiveness than P. pinodella from C. judaicum on both wild and domesticated chickpea. Disease severity on the former species ranged from 62·5% to 70% and on the latter from 41% to 56%. Phoma pinodella isolates from C. judaicum were more aggressive on C. arietinum and P. sativum than on C. judaicum and P. fulvum . Results of the current study suggest that C. judaicum may serve as an alternative host to ascochyta pathogens that endanger chickpea and possibly other crops and wild species growing in close proximity.     

Molecular and biological characterization of two potyviruses infecting lettuce in southeastern France

Several potyviruses affect lettuce (Lactuca sativa) and chicory (Cichorium spp.) crops worldwide and are important constraints for production because of the direct losses that they induce and/or because of their seed transmission. Here, the molecular and biological properties are described of two potyviruses that were recently isolated from lettuce plants showing mosaic or strong necrotic symptoms in an experimental field in southeastern France. The first potyvirus belongs to the species Endive necrotic mosaic virus and is present in a large number of wild plant species, especially Tragopogon pratensis. It is unable to infect lettuce cultivars with a resistance to Turnip mosaic virus that is present in many European cultivars and probably conferred by the Tu gene. The second potyvirus belongs to the tentative species lettuce Italian necrotic virus and was not observed in wild plants. It infected all tested lettuce cultivars. Wild accessions of Lactuca serriola, Lactuca saligna, Lactuca virosa and Lactuca perennis were identified as resistant to one or the other potyvirus and could be used for resistance breeding in lettuce. No resistance against these two potyviruses was observed in the tested Cichorium endivia cultivars. In contrast, all tested Cichorium intybus cultivars or accessions were resistant.     

Assessment of the pest status of Pratylenchus curvicauda and ultrastructural changes in roots of infected wheat and barley

Pratylenchus curvicauda, which was first described in metropolitan Perth in 1991, was recently identified in grain-growing areas in Western Australia. The biology of this root-lesion nematode, and especially its pest status, is unknown. We investigated its life cycle and interaction with host plants, because such information is essential for its management. The life cycle took 45 days to complete in a wheat cultivar maintained at 23°C. Over 10 weeks, the nematode multiplied in 26 of 61 genotypes; these host plants were all cereals and included widely grown cultivars of wheat and barley. Eighteen other cereal genotypes and 13 cultivars including canola, chickpea, ryegrass, lupin, soybean, and tomato, sustained the nematodes to different degrees without multiplication. Four cover crops were not suitable hosts. The patterns of attraction of the nematodes and penetration into roots of the host and tolerant plants were similar. The nonhosts attracted fewer nematodes, none of which penetrated the roots. Browning of infected roots was atypical—it occurred late in some roots, 55 days after inoculation, and in the presence of a fungus. The nematodes were confined to, and fed from, cortical cells. The ultrastructure of infected wheat and barley cells showed typical signs of damage caused by Pratylenchus spp. and included cell disorganization and lack of membrane integrity, disintegration of cytoplasm, hypertrophy of some nuclei, and deposition of tannin-like granules. This detailed characterization of P. curvicauda–host interaction indicates the nematode is likely to be a pest of major crops, and attention should be given to its management.     

Screening and identification of Cucurbita germplasm resistant to Xanthomonas cucurbitae,incitant of cucurbit bacterial spot

Bacterial spot of cucurbits, caused by Xanthomonas cucurbitae, is an emerging disease of cucurbits. This study was conducted to identify Cucurbita species that are resistant to X. cucurbitae. We developed a reliable method for inoculating cucurbit plants by spraying plants with X. cucurbitae suspensions containing carborundum. Symptoms of the disease developed within 7 days after inoculation. Subsequently, we evaluated the virulence of six isolates of X. cucurbitae in the greenhouse and observed that X. cucurbitae isolated from cucurbit fields in Illinois, Michigan, Kansas, Ohio, and Wisconsin were more virulent than the reference ATCC 23378 strain. Then, we screened 81 commercial cultivars of gourds, pumpkins, and squashes, as well as 300 Cucurbita spp. accessions, for their resistance to X. cucurbitae under greenhouse and field conditions. In the greenhouse study, all commercial cultivars and some of the accessions developed typical symptoms of bacterial spot disease, while some of the accessions developed fewer lesions. In the field studies, infection of leaves and fruits was caused by both natural inoculum and spray-inoculation of plants with a suspension of the X. cucurbitae isolate from Illinois. Among 300 accessions tested, 9 and 21 accessions were classified as resistant and less resistant, respectively. Resistant and less resistant accessions belong to the species Cucurbita maxima, C. maxima subsp. maxima, C. maxima subsp. andreana, and C. okeechobeensis subsp. martinezii. This is the first report of potential resistance to bacterial spot of cucurbits.     

Revealing of resistant sources in <Emphasis Type="Italic">Cicer</Emphasis> species to chickpea leaf miner, <Emphasis Type="Italic">Liriomyza cicerina</Emphasis> (Rondani)

The chickpea leaf miner, Liriomyza cicerina (Rondani) (Diptera: Agromyzidae), is an important pest of cultivated chickpea (Cicer arietinum L.). A 2-year field study was carried out to screen a total of 126 Cicer germplasm for resistance to the leaf miner during the 2012 and 2013 growing seasons. Resistance was evaluated using a visual scale of 1–9, where 1?=?highly resistant and 9?=?very highly susceptible under natural infestation conditions. The results showed that two C. arietinum accessions, ILC 3397 and Sierra, had a score of 9 on the scale, being very highly susceptible. Three germplasm, one mutant (3304) and two breeding lines (LMR 140 and LMR 160) of C. arietinum, were found to be highly resistant with the scores ranging from 1.5 to 2 for resistance to the leaf miner. The mutant, 3304, was detected for the first time in this study as a highly leaf miner-resistant mutant of the cultivated chickpeas while the other two breeding lines had been previously reported as highly resistant against the leaf miner. In addition, two mutants and 14 breeding lines of C. arietinum and two mutants and one germplasm of C. reticulatum were identified as resistant having the scores from 2.1 to 3 on the 1–9 scale. The results suggest that these resistant germplasm may add a new dimension to chickpea breeding programs because they possess valuable traits for resistance against the pest. The resistant chickpeas that can be grown without using pesticides are important as environmental protection and reliable food source for human health.     

Host status and reaction of <Emphasis Type="Italic">Medicago truncatula</Emphasis> accessions to infection by three major pathogens of pea (<Emphasis Type="Italic">Pisum sativum</Emphasis>) and alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis>)

Ditylenchus dipsaci, the stem nematode of alfalfa (Medicago sativa), Mycosphaerella pinodes, cause of Ascochyta blight in pea (Pisum sativum) and Aphanomyces euteiches, cause of pea root rot, result in major yield losses in French alfalfa and pea crops. These diseases are difficult to control and the partial resistances currently available are not effective enough. Medicago truncatula, the barrel medic, is the legume model for genetic studies, which should lead to the identification and characterization of new resistance genes for pathogens. We evaluated a collection of 34 accessions of M. truncatula and nine accessions from three other species (two from M. italica, six from M. littoralis and one from M. polymorpha) for resistance to these three major diseases. We developed screening tests, including standard host references, for each pathogen. Most of the accessions tested were resistant to D. dipsaci, with only three accessions classified as susceptible. A very high level of resistance to M. pinodes was observed among the accessions, none of which was susceptible to this pathogen. Conversely, a high level of variation, from resistant to susceptible accessions, was identified in response to infection by A. euteiches.     

Validation of a QTL for resistance to ascochyta blight linked to resistance to fusarium wilt race 5 in chickpea (<Emphasis Type="Italic">Cicer arietinum</Emphasis> L.)

Ascochyta blight caused by Ascochyta rabiei and fusarium wilt caused by Fusarium oxysporum. f. sp. ciceris are the two most serious diseases of chickpea (Cicer arietinum). Quantitative trait loci (QTL) or genes for ascochyta blight resistance and a cluster of resistance genes for several fusarium wilt races (foc1, foc3, foc4 and foc5) located on LG2 of the chickpea map have been reported independently. In order to validate these results and study the linkage relationship between the loci that confer resistance to blight and wilt, an intraspecific chickpea recombinant inbred lines (RIL) population that segregates for resistance to both diseases was studied. A new LG2 was established using sequence tagged microsatellite sites (STMS) markers selected from other chickpea maps. Resistance to race 5 of F. oxysporum (foc5) was inherited as a single gene and mapped to LG2, flanked by the STMS markers TA110 (6.5 cM apart) and TA59 (8.9 cM apart). A QTL for resistance to ascochyta blight (QTL_AR3) was also detected on LG2 using evaluation data obtained separately in two cropping seasons. This genomic region, where QTL_AR3 is located, was highly saturated with STMS markers. STMS TA194 appeared tightly linked to QTL_AR3 and was flanked by the STMS markers TR58 and TS82 (6.5 cM apart). The genetic distance between foc5 and QTL_AR3 peak was around 24 cM including six markers within this interval. The markers linked to both loci could facilitate the pyramiding of resistance genes for both diseases through MAS.     

Sources of resistance to Pseudocercospora fijiensis,the cause of black Sigatoka in banana

Black Sigatoka, caused by Pseudocercospora fijiensis, is one of the most devastating diseases of banana. In commercial banana-growing systems, black Sigatoka is primarily managed by fungicides. This mode of disease management is not feasible for resource-limited smallholder farmers. Therefore, bananas resistant to P. fijiensis provide a practical solution for managing the disease, especially under smallholder farming systems. Most banana and plantain hybrids with resistance to P. fijiensis were developed using few sources of resistance, which include Calcutta 4 and Pisang Lilin. To broaden the pool of resistance sources to P. fijiensis, 95 banana accessions were evaluated under field conditions in Sendusu, Uganda. Eleven accessions were resistant to P. fijiensis. Black Sigatoka symptoms did not progress past Stage 2 (narrow brown streaks) in the diploid accessions Pahang (AA), Pisang KRA (AA), Malaccensis 0074 (AA), Long Tavoy (AA), M.A. Truncata (AA), Tani (BB), and Balbisiana (BB), a response similar to the resistant control Calcutta 4. These accessions are potential sources of P. fijiensis resistance and banana breeding programmes can use them to broaden the genetic base for resistance to P. fijiensis.     

Assessment of early blight (<Emphasis Type="Italic">Alternaria solani</Emphasis>) resistance in tomato using a droplet inoculation method

A droplet inoculation method was used for evaluation of tomato resistance to early blight, a destructive foliar disease of tomato caused by Alternaria solani (Ellis and Martin) Sorauer. In this test method, leaflets are inoculated with small droplets of a spore suspension in either water or a 0.1% agar solution. Early blight resistance was evaluated based on lesion size. The droplet method better discriminated the level of resistance (P < 0.001) for a range of spore densities in comparison with the more commonly used spray inoculation method. Lesions generated by droplet inoculation at 7 days after inoculation ranged from small flecks to almost complete blight with an exponential-like distribution of lesion sizes. Significant correlations (r = 0.52, 0.58, and 0.63, P < 0.001) were observed across three glasshouse tests of 54 accessions including wild species using the droplet method. The most resistant accessions included wild species: one accession of Solanum arcanum, three accessions of Solanum peruvianum, one accession of Solanum neorickii, and one of Solanum chilense. Solanum pennellii and Solanum pimpinellifolium accessions were susceptible, whereas Solanum habrochaites and Solanum lycopersicum accessions ranged from susceptible to moderately resistant. The droplet test method is simple to apply, offers a fine discrimination of early blight resistance levels, and allows objective evaluation.     

Identifying resistance in wild and ornamental cherry towards bacterial canker caused by Pseudomonas syringae

Bacterial canker is a major disease of stone fruits and is a critical limiting factor to sweet cherry (Prunus avium) production worldwide. One important strategy for disease control is the development of resistant varieties. Partial varietal resistance in sweet cherry is discernible using shoot or whole tree inoculations; however, these quantitative differences in resistance are not evident in detached leaf assays. To identify novel sources of resistance to canker, we used a rapid leaf pathogenicity test to screen a range of wild cherry, ornamental Prunus species and sweet cherry × ornamental cherry hybrids with the canker pathogens, Pseudomonas syringae pvs syringae, morsprunorum races 1 and 2, and avii. Several Prunus accessions exhibited limited symptom development following inoculation with each of the pathogens, and this resistance extended to 16 P. syringae strains pathogenic on sweet cherry and plum. Resistance was associated with reduced bacterial multiplication after inoculation, a phenotype similar to that of commercial sweet cherry towards nonhost strains of P. syringae. Progeny resulting from a cross of a resistant ornamental species Prunus incisa with susceptible sweet cherry (P. avium) exhibited resistance indicating it is an inherited trait. Identification of accessions with resistance to the major bacterial canker pathogens is the first step towards characterizing the underlying genetic mechanisms of resistance and introducing these traits into commercial germplasm.     

Genetic diversity of Meloidogyne spp. from rice and identification of multiresistant sources in Oryza spp. accessions

Recently a Meloidogyne species complex was detected parasitizing and causing damage to irrigated rice in southern Brazil, highlighting the need to study the genetic diversity of these species and their pathogenicity to Oryza spp. in order to select genotypes of rice with multiple resistance. This study compared the genetic diversity of Brazilian Meloidogyne spp. isolates from irrigated rice and evaluated the reaction of four wild accessions of Oryza species (O. glumaepatula, O. longistaminata, O. grandiglumis, and O. alta) and two cultivated species, O. glaberrima and O. sativa (control) to M. ottersoni, M. oryzae, and two variants of M. graminicola (Est G2 and Est G3). Genetic variability was assessed using RAPD and AFLP markers. M. graminicola and M. ottersoni showed high intraspecific variability: 83.76% and 41.14%, respectively. Cluster analysis showed a clear separation among rice root-knot nematodes (RKNs) into subclades according to their esterase phenotypes with 100% bootstrap. For rice resistance screening, plants were inoculated with 5,000 eggs, and the nematode reproduction factor evaluated 90–120 days postinoculation. O. glumaepatula, an American wild species, was highly resistant or resistant to all rice RKNs tested and is a valuable source of multiple resistance. Overall, the other rice species also showed different levels of resistance. Conversely, O. longistaminata exhibited low levels of resistance. M. graminicola Est G3 was the most aggressive isolate. Sources of resistance against RKN in wild Oryza genotypes, especially in an AA genome like O. glumaepatula, may be of great interest for future breeding programmes in cultivated rice.