Useful Sources Of Resistance Research Articles

Seeing red: a modified RUBY reporter assay for visualizing inplanta protein-protein interactions.

Seeing red: a modified RUBY reporter assay for visualizing inplanta protein-protein interactions.

Virulence of Blumeria graminis f. sp. tritici in Brazil, South Africa, Turkey, Russia, and Australia

The globally distributed causal agent of powdery mildew on wheat, Blumeria graminis f. sp. tritici (Bgt), is one of the most rapidly adapting plant pathogens and requires monitoring for shifts in virulence to wheat resistance (Pm) genes. Virulence frequencies were assessed in a total of 346 Bgt isolates from several countries that had either lately recorded increasing powdery mildew epidemics (Brazil, South Africa, and Australia) or not recently been surveyed (Turkey and Russia). The results were compared to previously published surveys of United States and Egyptian Bgt (390 isolates). Many of the Pm genes that have potentially been employed longer (Pm1a–Pm17) were shown to have lost effectiveness, and the complexity of virulence to those genes was higher among Brazilian isolates than those from any other country. Some cases of high virulence frequency could be linked to specific Pm gene deployments, such as the widespread planting of cultivar Wyalkatchem (Pm1a) in Australia. Virulence was also assessed to a set of Pm genes recently introgressed from diploid and tetraploid wheat relatives into a hexaploid winter wheat background and not yet commercially deployed. The isolate collections from Fertile Crescent countries (Egypt and Turkey) stood out for their generally moderate frequencies of virulence to both the older and newer Pm genes, consistent with that region’s status as the center of origin for both host and pathogen. It appeared that the recently introgressed Pm genes could be the useful sources of resistance in wheat breeding for other surveyed regions.

Resistance to Callosobruchus maculatus among cowpea (Vigna unguiculata (L.) Walp) genotypes

ABSTRACT Callosobruchus maculatus is an important field-to-store pest that causes close to 100% losses in stored produce. This study aimed at assessing the resistance of cowpea genotypes to C. maculatus infestation. Thirteen cowpea advanced breeding lines pre-selected on the basis of their high grain yield, and three released varieties (Padi-tuya, Kirkhouse Benga and Wangkae) were evaluated in a no-choice experiment. The experiment was laid out in a completely randomized design with four replications under laboratory conditions. Data were collected on mean number of eggs per seed (MEPS), days to first emergence (DFE), adult bruchid emergence (ABE), percentage weight loss (PWL), percentage seed damage (PSD) and median development period (MDP). Dobie’s susceptibility index (DSI) was computed and used to classify the genotypes as resistant or susceptible. Significant differences were found among the genotypes for the measured traits, except for DFE and MDP. IT13K-1070-2 had the lowest MEPS, ABE, PWL and PSD. C. maculatus, with high ABE, developed best on Kirkhouse Benga and Wangkae. Wangkae had 100% seed damage at the end of the experiment. Based on the DSI score, IT13K-1070-2 was found to be moderately resistant; the rest of the genotypes were susceptible. Among the susceptible genotypes, IT10K-817-3, IT07K-303-1, SARI-2-50-80, SARI-3-11-100, IT10K-837-1, IT13K-1424-12 and SARVX-09-004 had PWL of less than 16%, indicating tolerance to bruchid infestation. DSI was significantly and positively correlated with ABE (r = 0.81), PSD (r = 0.93) and PWL (r = 0.79). DSI had a significant negative correlation with the final seed weight (r = −0.83). IT13K-1070-2 could serve as a useful source of resistance to the cowpea bruchid in cowpea breeding programs or released as a variety for cultivation.

Evaluation of Disease Severity and Molecular Relationships Between Peronospora variabilis Isolates on Chenopodium Species in New Hampshire.

Quinoa is a potential new crop for New England; however, its susceptibility to downy mildew, caused by Peronospora variabilis, is a key obstacle for cultivation. The objectives of this study were to evaluate differential resistance within the Chenopodium genus, identify novel sources of resistance for use in future genetic studies or breeding programs, and investigate phylogenetic relationships of P. variabilis isolates from different Chenopodium hosts. The long-term goal of this research is to develop a resistant variety of quinoa to be grown in New England. Field trials conducted at the University of New Hampshire evaluated downy mildew disease severity on 10 Chenopodium accessions representing four species. Disease severity for each treatment was compared and significant differences in disease severity were observed between accessions. C. berlandieri var. macrocalycium ecotypes collected from Rye Beach, New Hampshire and Appledore Island, Maine exhibited the lowest disease severity over the growing season. P. variabilis was isolated from each accession, and COX2 sequences were compared. Phylogenetic analyses suggest no effect of host species on P. variabilis sequence similarity; however, isolates are shown to cluster by geographic location. This research provides the first step in identifying potential New England native sources of resistance to downy mildew within the genus Chenopodium and provides preliminary information needed to further investigate resistance at the genomic level in Chenopodium spp.

Genome‐wide association study reveals molecular markers and genes potentially associated with soybean (Glycine max) resistance to Xanthomonas citri pv. glycines

AbstractSoybean bacterial pustule is caused by the gram‐negative bacterium Xanthonomas citri pv. glycines. The identification of sources of resistance for use in molecular breeding is a challenge due to the existence of complex interactions between pathogenic strains and soybean cultivars. This study aimed to evaluate the reaction of 118 soybean cultivars to inoculation with strains 2440P and 2447 of X. citri pv. glycines and to identify molecular markers associated with the resistance. The genome‐wide association study approach was used to identify association between the phenotype and the single nucleotide polymorphisms (SNP) markers. The positions of significant SNPs were mapped to the soybean Williams 82 genome, and protein‐coding genes near them were identified. One and 116 cultivars were resistant to strains 2440P and 2447, respectively. Eleven SNPs were significantly associated with resistance to strain 2440P and five to 2447. Two significant SNPs are predicted to result in amino acid changes in benzyl alcohol O‐benzoyltransferase‐like and MAIN‐LIKE 1‐like proteins, which after confirmation, could be used in marker‐assisted selection in order to increase the frequency of resistant alleles in new cultivars.

Registration of HA‐R14, HA‐R15, HA‐R16, and HA‐R17 oilseed sunflower germplasm with broad resistance to rust and downy mildew

AbstractRust and downy mildew (DM) are two of the most important sunflower diseases in the world. The development of sunflower hybrids with enhanced levels of genetic resistance to both diseases is a goal for sunflower breeding. Four oilseed sunflower (Helianthus annuus L.) germplasm lines, HA‐R14 (Reg. no. GP‐371, PI 698193), HA‐R15 (Reg. no. GP‐372, PI 698194), HA‐R16 (Reg. no. GP‐373, PI 698195), and HA‐R17 (Reg. no. GP‐374, PI 698196) are multiple rust‐ and DM‐resistant lines that were developed and released by the USDA‐ARS Sunflower and Plant Biology Research Unit in collaboration with the North Dakota Agricultural Experiment Station in January 2020. Three lines, HA‐R14 (R4R4/R12R12/PlArgPlArg), HA‐R15 (R5R5/R12R12/PlArgPlArg), and HA‐R16 (R13bR13b/R12R12/PlArgPlArg), stack two different rust genes with a common DM gene PlArg, and HA‐R17 (R13bR13b/R15R15) possesses two rust genes, R13b and R15. These germplasm lines will provide a broad spectrum of useful sources of resistance to all known races of rust and DM.

Registration of PR1572‐19 and PR1572‐26 pinto bean germplasm lines with broad resistance to rust, BGYMV, BCMV, and BCMNV

AbstractCommon bean rust, Bean golden yellow mosaic virus (BGYMV), Bean common mosaic virus (BCMV), and Bean common mosaic necrosis virus (BCMNV) are devastating diseases of dry bean (Phaseolus vulgaris L.) in Central America and the Caribbean. The development of dry bean cultivars with enhanced levels of genetic resistance to these and other diseases is an important goal of the University of Puerto Rico (UPR) and other dry bean breeding programs in Central America and the Caribbean. PR1572‐19 (Reg. no. GP‐308, PI 692976) and PR1572‐26 (Reg. no. GP‐307, PI 692975) are multiple virus‐ and rust‐resistant pinto bean germplasm lines adapted to the humid tropics that were developed and released cooperatively in 2019 by the UPR Agricultural Experiment Station, the Instituto Dominicano de Investigaciones Agropecuarias y Forestales, and the USDA–ARS. Both PR1572‐19 and PR1572‐26 possess the bgm‐1 gene for resistance to BGYMV, the I and bc‐3 loci that provide broad resistance to all strains of BCMV and BCMNV in the United States and the Caribbean, and the Ur‐3 and Ur‐11 loci that confer comprehensive resistance to all known races of the bean rust pathogen. PR1572‐26 also has the SW12 quantitative trait locus marker associated with resistance to BGYMV. PR1572‐19 and PR1572‐26 produced mean seed yields similar to the check cultivar ‘Santa Fe’ in trials conducted in Puerto Rico and mean seed yields comparable to the pinto cultivar ‘La Paz’ in the Cooperative Dry Bean Nursery conducted in Puerto Rico. Both lines should serve as useful sources of resistance to BGYMV, BCMV, BCMNV, and bean rust for common beans of the Durango race that includes the pinto and great northern market classes.

Characterization of species of Fusarium causing root rot of Soybean (Glycine max L.) in South Dakota, USA

In 2014, 2000 plants showing root rot symptoms were collected from 200 commercial soybean (Glycine max L.) fields in South Dakota, USA. One thousand one hundred thirty fungal isolates obtained from the samples were identified as Fusarium species by morphology and sequencing of the translation elongation factor 1-alpha gene. Fifty-one percent were F. graminearum, 30.0% were F. acuminatum, 8.0% belonged to the F. oxysporum species complex, 3.4% were F. armeniacum, 2.0% were F. proliferatum, 1.6% were F. virguliforme, 1.2% belonged to the F. solani species complex, 0.4% were F. nanum (syn. F. incarnatum-equiseti species complex), 0.1% were F. bulbicola (syn. F. fujikuroi species complex) and 0.1% were F. commune. The pathogenicity of 57 isolates was evaluated on the soybean ‘Asgrow 1835’ under greenhouse conditions. Root rot severity was rated 14 days after inoculation on a 1-to-5 scale and expressed as relative treatment effects (RTE). Nine isolates of F. oxysporum, and one each of F. armeniacum and F. commune, caused significantly greater RTE than in the non-inoculated control. Twenty-one accessions were screened for resistance in the greenhouse using one isolate each of F. graminearum, F. proliferatum and F. sporotrichioides. Accession PI361090 was less susceptible to F. graminearum and F. proliferatum than the susceptible controls, ‘Williams 82’ and ‘Asgrow 1835’. All accessions were more susceptible to F. sporotrichioides. These findings suggest that 11 Fusarium species or species complexes are pathogenic to soybean in South Dakota, and PI361090 may be a useful source of resistance to F. graminearum and F. proliferatum.

Identification of Fusarium wilt resistance sources in melon (Cucumis melo L.) landraces of Iran using marker-assisted selection technique

Melon (Cucumis melo L.) is an important popular high-consumption product in the world. Melon Fusarium wilt (Fusarium oxysporum f.sp. melonis: FOM) is a global destructive disease. In this research, 88 melon landraces from different geographical regions of Iran together with reference genotypes as control genotypes were screened for resistance to 0 and 1 races of Fusarium wilt disease agent using artificial inoculation and two functional markers for the presence or absence of Fom-2 gene. The landraces in multiple replicates were examined in a greenhouse experiment. Thirty-five out of the 88 landraces were selected to determine the disease incidence percentage (DIP), disease severity percentage (DSP) and area under disease progress curve (AUDPC). Based on the results of marker-assisted selection, 83 genotypes had at least one susceptible allele, while 43 heterozygote genotypes had at least one resistance allele. Among genotypes evaluated in artificial inoculation test, three landraces including Shahd-e-Shiraz Gosht Narenji, Korki and Alam Gorgor indicated the highest level of resistance. It seems that these landraces can be considered as the most useful sources of resistance in breeding programs for introducing Fusarium resistant melons. In contrast, Jalali, Petra falat and Habib-Abad landraces were the most sensitive genotypes, which can be used to produce sensitive standard check lines.

Characterization of a bean rugose mosaic virus isolate and search for virus resistance in a germplasm bank of Phaseolus vulgaris

Common bean is an economically important crop grown in several areas in the world. Among the constraints for this crop development, bean rugose mosaic virus (BRMV) infections can potentially lead to serious yield reduction. Genetic resistance is the most effective control method, and the search for sources of resistance is an essential step. The objective of this study was to biologically characterize the BRMVGO isolate and search for virus resistance in germplasm accessions of Phaseolus vulgaris L. To biologically characterize the isolate, 15 plants, selected from a list of indicators, were inoculated, among them soybean (Glycine max L) and pea (Pisum sativum L). The host range demonstrated that the virus can infect different plant species, reinforcing the need for resistance sources. In order to screen for resistance, 172 P. vulgaris accessions were inoculated with the isolate and scored for disease symptoms at 5, 21 and 30 days after inoculation. Among the evaluated accessions, four exhibited hypersensitive reactions (HR) while the remaining showed typical susceptible reactions. The virus seemed to be restricted and could not be retrieved from the common bean accessions showing HR and they are likely interesting sources of resistance for use in breeding programs.

Assessment of Breeding Materials for Resistance to Fusarium Wilt in Cotton under Greenhouse Conditions in 2019

The germplasm evaluated in this study was a part of the National Screening Program for Fusarium Wilt Resistance. This program is conducted annually in the glasshouses of (Cotton and Fiber Crops Diseases Research Dept.), PPRI. The current study included 50 of Lower Egypt experimental genotypes, this experimental genotypes and 931families of seven common cultivars. The investigational genotypes were supplied by Cotton Breeding Dept., while the families of the seven common cultivars were supplied by Cotton Research Institute . Healthy survival rate of seedlings of the genotypes was used as a criterion to evaluate their reactions when the genotypes were grown in autoclaved soil highly infested with a mixture of race 3 of Fusarium oxysporum f. sp. vasinfectum isolates. All the lower Egypt genotypes (100%) were very highly resistant. The majority of the Upper Egypt genotypes 68 % were very highly resistant while 4% were very highly susceptible. The other reaction classed ranged from 4 to 16% of the tested genotypes. The distribution of Upper Egypt genotypes to reaction classes in 2017, 2018 and 2019 showed steady and considerable increases in the VHR genotypes, which were 48, 54 and 68% in 2017, 2018 and 2019 respectively. Over the three year period, the majority (56.67%) of the Upper Egypt genotypes were VHR. . All families of the common cultivars were VHR. The present study provides new and useful sources of resistance to Fusarium wilt caused by race 3 isolates

Search for sources of genetic resistance to Meloidogyne enterolobii in tomato and in wild Solanum (section Lycopersicon) accessions

Meloidogyne enterolobii (syn. M. mayaguensis) is an emerging plant pathogen capable of inducing root galls and yield reduction in a wide range of host species. This pathogen has also been reported as a global threat for tomato (Solanum lycopersicum L.) crop production mainly due to its ability to overcome the Meloidogyne resistance meditated by the Mi-1 gene. Despite the potential importance of this nematode, sources of resistance to M. enterolobii are not yet available for breeding purposes. The main objective of the present work was to evaluate a large Solanum (section Lycopersicon) germplasm (comprising nine species and one botanic variety) aiming to identify useful sources of resistance to M. enterolobii. In the first screening assay, 101 accessions and the susceptible standard S. lycopersicum ‘Santa Cruz’ were inoculated and evaluated under controlled (greenhouse) conditions. Twenty-day-old seedlings were inoculated with a suspension of M. enterolobii eggs (710 eggs per plant) and maintained in expanded 128-cell polystyrene trays during the entire course of the experiment. The phenotypic criteria used for evaluation (done at 45 days after inoculation) were the number of root galls, gall index, number of eggs, and the reproduction factor. Twenty accessions with promising resistant reaction to M. enterolobii in the first screening test were selected and employed in a subsequent assay. Plants of the 20 selected accessions were cultivated in 400 cm3 pots filled with sterile soil. Inoculation procedures were identical to the first assay, but with higher inoculum pressure (3,300 eggs per plant). Three accessions with superior tolerance levels to M. enterolobii were identified viz. S. lycopersicum ‘Yoshimatsu’, S. lycopersicum ‘CNPH 1246’ and S. pimpinelifolium CGO 7650 (= CNPH 1195). These accessions were re-evaluated against a distinct M. enterolobii population as well as against two other root-knot nematode species (M. javanica and one M. incognita race 1). Under higher inoculum pressure, ‘Yoshimatsu’ was found to be resistant to M. javanica and M. incognita race 1, but susceptible to a M. enterolobii from guava. The other two sources displayed susceptibility to all three nematodes. The results indicated additional germplasm screening since no source of stable genetic resistance to M. enterolobii was found so far.

Novel Sources of Wheat Head Blast Resistance in Modern Breeding Lines and Wheat Wild Relatives.

Wheat head blast (WHB), caused by the fungus Magnaporthe oryzae pathotype triticum, is a devastating disease affecting South America and South Asia. Despite 30 years of intensive effort, the 2NVS translocation from Aegilops ventricosa contains the only useful source of resistance to WHB effective against M. oryzae triticum isolates. The objective of this study was to identify non-2NVS sources of resistance to WHB among elite cultivars, breeding lines, landraces, and wild-relative accessions. Over 780 accessions were evaluated under field and greenhouse conditions in Bolivia, greenhouse conditions in Brazil, and at two biosafety level-3 laboratories in the United States. The M. oryzae triticum isolates B-71 (2012), 008 (2015), and 16MoT001 (2016) were used for controlled experiments, while isolate 008 was used for field experiments. Resistant and susceptible checks were included in all experiments. Under field conditions, susceptible spreaders were inoculated at the tillering stage to guarantee sufficient inoculum. Disease incidence and severity were evaluated as the average rating for each 1-m-row plot. Under controlled conditions, heads were inoculated after full emergence and individually rated for percentage of diseased spikelets. The diagnostic marker Ventriup-LN2 was used to test for the presence of the 2NVS translocation. Four non-2NVS spring wheat International Maize and Wheat Improvement Center breeding lines (CM22, CM49, CM52, and CM61) and four wheat wild-relatives (A. tauschii TA10142, TA1624, TA1667, and TA10140) were identified as resistant (<5% of severity) or moderately resistant (5 to <25% severity) to WHB. Experiments conducted at the seedling stage showed little correlation with disease severity at the head stage. M. oryzae triticum isolate 16MoT001 was significantly more aggressive against 2NVS-based varieties. The low frequency of WHB resistance and the increase in aggressiveness of newer M. oryzae triticum isolates highlight the threat that the disease poses to wheat production worldwide and the urgent need to identify and characterize new resistance genes that can be used in breeding for durably resistant varieties.

Search for sources of resistance to Meloidogyne enterolobii in commercial and wild tomatoes

ABSTRACT Meloidogyne enterolobii (=M. mayaguensis) is an emerging plant pathogen capable of inducing root galls and yield reduction in a wide range of host species. This pathogen has also been reported as a global threat for tomato (Solanum lycopersicum) crop production mainly due to its ability to overcome the resistance meditated by the Mi-1 gene. Despite the potential importance of this nematode, sources of resistance to M. enterolobii are not yet available for breeding purposes. The main objective of the present work was to evaluate a large Solanum (section Lycopersicum) germplasm (comprising nine species and one botanic variety) aiming to identify useful sources of resistance to M. enterolobii. In the first screening assay, 101 accessions and the susceptible standard S. lycopersicum ‘Santa Cruz’ were inoculated and evaluated under controlled conditions. The phenotypic criteria used for evaluation were the number of root galls, gall index, number of eggs, and the reproduction factor. Plants of the 20 selected accessions were cultivated in 0.4 L pots filled with sterile soil. Inoculation procedures were identical to the first assay, but with higher inoculum pressure (3,300 eggs per plant). Three accessions with superior tolerance levels to M. enterolobii were identified viz. S. lycopersicum ‘Yoshimatsu’, S. lycopersicum ‘CNPH 1246’ and S. pimpinelifolium CGO 7650 (= CNPH 1195). These accessions were re-evaluated against a distinct M. enterolobii population as well as against two other root-knot nematode species (M. javanica and one M. incognita race 1). Under higher inoculum pressure, ‘Yoshimatsu’ was found to be resistant to M. javanica and M. incognita race 1, but susceptible to M. enterolobii from guava. The other two sources displayed susceptibility to all three nematodes. Additional germplasm screening is needed since no source of stable genetic resistance to M. enterolobii was found so far.

Progress breeding for resistance to eastern filbert blight in the eastern United States

Eastern filbert blight (EFB) is a hazelnut disease caused by Anisogramma anomala, a fungus endemic to North America where it can be found associated with the wild hazelnut Corylus americana. While C. americana is resistant to EFB, the commercial hazelnut C. avellana is highly susceptible and typically dies within 5 years from exposure. A hazelnut breeding program was initiated in 1996 at Rutgers University in New Brunswick, New Jersey. The early objective was to identify sources of resistance to EFB for use in breeding regionally adapted, EFB-resistant plants to support the establishment of a hazelnut industry in eastern USA. By working with Oregon State University (OSU) and international colleagues, germplasm collections were made in Russia, Ukraine, Poland, Georgia, Latvia, Lithuania, Estonia, Italy, and Turkey. Over 5,000 seedlings were grown and evaluated for response to EFB. While most plants succumbed to EFB, about three percent were found to be resistant. Interestingly, the resistant plants spanned nearly all collection locations and molecular markers have shown them to be highly diverse. Today, we have access to over 100 EFB-resistant accessions selected from more than 60 locations, which represents a significant pool of germplasm to support breeding. Recent studies have shown that most resistance seems to be controlled by only one or a few major genes; R-gene mapping projects are underway at Rutgers as well as Oregon State University. We continue to study new sources of resistance for use in a focused cultivar improvement program.

Evaluation of Major Ancestors of North American Soybean Cultivars for Resistance to Three Pythium Species that Cause Seedling Blight.

Pythium seedling blight, which can be caused by a number of Pythium spp., is a disease that affects soybean (Glycine max) in the United States and Canada. Pythium ultimum var. ultimum, one of the most common pathogenic species, is favored by cool, wet conditions in early spring and causes seed decay, root rot, and seedling damping-off. In all, 102 major ancestors of modern North American cultivars and "first progeny" cultivars developed directly from ancestral lines were evaluated for resistance to P. ultimum var. ultimum and two other species of Pythium in greenhouse assays. Several ancestors and first progeny cultivars, as well as the resistant check Archer, had varying levels of partial resistance to an Illinois isolate of P. ultimum var. ultimum. In a subsequent experiment, four of the most resistant lines (PI 84637, Maple Isle, Fiskeby III, and Fiskeby 840-7-3) and the susceptible cultivar Kanro were screened for resistance against isolates of P. irregulare and P. sylvaticum, and resistance to P. ultimum var. ultimum was confirmed. The lines that were partially resistant to P. ultimum var. ultimum in the first experiment were also partially resistant to P. irregulare and P. sylvaticum. The P. ultimum var. ultimum isolate was the most aggressive of the three isolates, followed by the P. irregulare and P. sylvaticum isolates. Modern cultivars descended from the soybean lines with partial resistance to these pathogens could be useful sources of resistance to Pythium seedling blight if they are found to have similar levels of resistance.

SCREENING A COLLECTION OF COTTON GENOTYPES FOR FUSARIUM WILT RESISTANCE UNDER GREENHOUSE CONDITIONS IN 2017

The genotypes evaluated in this study was a part of the National Screening Program for Fusarium Wilt Resistance. This program is conducted annually in the greenhouses of Cotton and Fiber Crops Diseases Research Dept., PPRI. The present study included 50 of Upper Egypt experimental genotypes and 875 families of six commercial cultivars. The experimental genotypes were supplied by Cotton Breeding Dept., and the six commercial cultivars were provided by Cotton Maintenance Dept., Cotton Research Institute. Healthy survival rate of seedlings of the genotypes was used as a criterion to evaluate the reactions when the genotypes were grown in autoclaved highly infested soil with a mixture of race 3 of Fusarium oxysporum f.sp.vasinfectum isolates. The majority of the tested genotypes (48%) were very highly resistant while 22% were very highly susceptible. All the families of the commercial cultivars Giza 90, Giza 95, Giza 86, Giza 87, and Giza 88 were very highly resistant while only 99.30% of Giza 92 families showed this level of resistance, which deserves more attention in monitoring its families in the future to Avoid any varietal deterioration. The present work provides new and useful sources of resistance to FOV race 3 isolates.

Vavilov wheat accessions provide useful sources of resistance to tan spot (syn. yellow spot) of wheat

Host genetic resistance is the most effective and sustainable means of managing tan spot or yellow spot of wheat. The disease is becoming increasingly problematic due to the adoption of minimum tillage practices, evolution of effector‐mediated pathogenicity, and widespread cultivation of susceptible cultivars from a narrow genetic base. This highlights the importance of broadening the diversity of resistance factors in modern breeding germplasm. This study explored 300 genetically diverse wheat accessions, originally sourced from the N. I. Vavilov Institute of Plant Genetic Resources (VIR), St Petersburg, Russia. The collection was screened for resistance to tan spot at seedling and adult stage under controlled conditions, and in the field across 2 years. The phenotypic datasets, coupled with ToxA bioassay screening, identified a number of accessions with useful sources of resistance. Seedling disease response corresponded well with ToxA sensitivity (r = 0.49, P &lt; 0.000), but not adult responses (r = −0.02 to −0.19, P &lt; 0.002), and overall reactions to ToxA appeared to show poor correspondence with disease response at the adult stage. ToxA‐insensitive accessions were generally found resistant across different growth stages (all‐stage resistance, ASR) in all experiments (seedling and adult stage under controlled conditions and field). ToxA‐sensitive accessions that were susceptible at seedling stage, but resistant at both adult‐plant stages, were deemed to carry adult‐plant resistance (APR). This study provides detailed information on the degree of tan spot resistance in the Vavilov wheat collection and discusses strategies to harness these sources to boost the diversity of resistance factors in modern wheat breeding germplasm.

Field Assessment of Agronomic Performance, Resistance to Aflatoxin, and Fumonisin Accumulation in Selected Maize Inbred Lines in Kenya

<i>Aspergillus flavus</i> and <i>Fusarium verticilloides</i> cause contamination of maize (<i>Zea mays</i>) and concern to maize farmers because they reduce maize quantity and quality. These fungi produce mycotoxins, some of which are poisonous to both humans and animals. Over 300 mycotoxins are known but in this study aflatoxins and fumonisins produced by <i>A. flavus</i> and <i>F. verticilloides</i>, respectively, are reported due to their health concerns in Africa. Contamination of maize grain by these fungi occurs before harvest and selection of maize parental lines resistant to accumulation of aflatoxin, and fumonisin for breeding purposes is the easiest strategy to reduce consumption of maize grains contaminated by these toxins. In addition to selecting for resistant lines, breeders would prefer inbred lines with top performing agronomic traits. This study aimed at identifying possible source of resistance together with good agronomic traits among 23 maize inbred lines (13 sourced from the MAIZE Competitive Grants Initiative, International Maize and Wheat Improvement Centre and 10 from Agricultural Research Council, South Africa). The lines were planted in two blocks; <i>Aspergillus</i>, and <i>Fusarium</i>, in a randomized complete-block design for two seasons in one location in Kenya. Germination rate, days to silking, and days to anthesis were determined in each line. Inoculation of the maize ears was done at silking with three toxigenic strains of <i>A. flavus</i> for <i>Aspergillus</i> block, and <i>F. verticilloides</i> for <i>Fusarium</i> block. Aflatoxins and fumonisins concentration in the kernels was determined using Enzyme-linked immunosorbent assay (ELISA). A positive significant correlation (r = 0.9458846, P = < 9.845e-12) occurred between days to anthesis and days to silking, aflatoxins and fumonisins (r = 0.43149988, P ≤ 0.05) accumulated in the inbred lines. A negative correlation between germination and accumulated fumonisin levels (r = -0.5156961, P = 0.01178), days to pollen shed and aflatoxin (r = -0.4617732, P = 0.02654) was revealed. Apart from being good germinating lines and drought tolerant, CML 390 and CML 247 accumulated least fumonisin, and aflatoxin levels compared to the other germplasms. These two lines with consistent low aflatoxin, and fumonisin levels may, therefore be useful sources of resistance for maize breeding programs to reduce both aflatoxin and fumonisn contamination in maize. Four aflatoxin resistant lines (CB 222, CML 495 and CML 444) and one (CKL05003) fumonisin resistant line showed good agronomic traits. The lines may be suitable for breeding for resistance to aflatoxins, and fumonisins respectively in maize.

Field evaluation of resistance to aflatoxin accumulation in maize inbred lines in Kenya and South Africa

ABSTRACTAflatoxin, a carcinogenic toxin, is produced mainly by Aspergillus flavus and Aspergillus parasiticus. Contamination of maize (Zea mays L.) grain by these fungi occurs before harvest, and the easiest strategy to prevent this is to develop/use maize varieties resistant to Aspergillus spp. and aflatoxin accumulation. The objective of this investigation was to identify potential sources of resistance among 23 maize inbred lines (13 obtained from the MAIZE Competitive Grants Initiative, International Maize and Wheat Improvement Centre and 10 from Agricultural Research Council, South Africa). The inbred lines were planted in a randomized complete-block design at two locations each in Kenya and South Africa. Maize ears were inoculated at silking with three toxigenic strains of A. flavus. The inoculated ears in each plot were harvested at 12–18% moisture, dried, and visually assessed for Aspergillus ear rot (AER). Aflatoxin concentration in the kernels was determined using liquid chromatography–tandem mass spectrometry. Significant variation for both AER and aflatoxin concentration existed among the inbred lines at both locations in Kenya and one location in South Africa. Combined analysis revealed a significant (p < 0.001) lines × locations interaction for both AER and aflatoxin concentration. Higher incidences of AER (0–86.0%) and aflatoxin concentration (0.21–6.51 µg/kg) were recorded at Kiboko in Kenya than at the other three locations. A stronger genetic correlation (rG = 0.936, p < 0.0001) between the AER and aflatoxin concentration was recorded in Potchefstroom than at the other three locations. Repeatability of aflatoxin concentration was high at Kiboko (0.87) and Potchefstroom in South Africa (0.74). Three inbred lines, CML247, CML444, and CML495, emerged as potentially useful sources of resistance to AER and aflatoxin accumulation as they showed low levels of aflatoxin contamination in both localities in Kenya and in South Africa.