Development and Genetic Characterization of Peanut Advanced Backcross Lines That Incorporate Root-Knot Nematode Resistance From Arachis stenosperma

Crop wild species are increasingly important for crop improvement. Peanut (Arachis hypogaea L.) wild relatives comprise a diverse genetic pool that is being used to broaden its narrow genetic base. Peanut is an allotetraploid species extremely susceptible to peanut root-knot nematode (PRKN) Meloidogyne arenaria. Current resistant cultivars rely on a single introgression for PRKN resistance incorporated from the wild relative Arachis cardenasii, which could be overcome as a result of the emergence of virulent nematode populations. Therefore, new sources of resistance may be needed. Near-immunity has been found in the peanut wild relative Arachis stenosperma. The two loci controlling the resistance, present on chromosomes A02 and A09, have been validated in tetraploid lines and have been shown to reduce nematode reproduction by up to 98%. To incorporate these new resistance QTL into cultivated peanut, we used a marker-assisted backcrossing approach, using PRKN A. stenosperma-derived resistant lines as donor parents. Four cycles of backcrossing were completed, and SNP assays linked to the QTL were used for foreground selection. In each backcross generation seed weight, length, and width were measured, and based on a statistical analysis we observed that only one generation of backcrossing was required to recover the elite peanut’s seed size. A populating of 271 BC3F1 lines was genome-wide genotyped to characterize the introgressions across the genome. Phenotypic information for leaf spot incidence and domestication traits (seed size, fertility, plant architecture, and flower color) were recorded. Correlations between the wild introgressions in different chromosomes and the phenotypic data allowed us to identify candidate regions controlling these domestication traits. Finally, PRKN resistance was validated in BC3F3 lines. We observed that the QTL in A02 and/or large introgression in A09 are needed for resistance. This present work represents an important step toward the development of new high-yielding and nematode-resistant peanut cultivars.

A Proof-of-Principle Study of Non-invasive Identification of Peanut Genotypes and Nematode Resistance Using Raman Spectroscopy

Identification of peanut cultivars for distinct phenotypic or genotypic traits whether using visual characterization or laboratory analysis requires substantial expertise, time, and resources. A less subjective and more precise method is needed for identification of peanut germplasm throughout the value chain. In this proof-of-principle study, the accuracy of Raman spectroscopy (RS), a non-invasive, non-destructive technique, in peanut phenotyping and identification is explored. We show that RS can be used for highly accurate peanut phenotyping via surface scans of peanut leaves and the resulting chemometric analysis: On average 94% accuracy in identification of peanut cultivars and breeding lines was achieved. Our results also suggest that RS can be used for highly accurate determination of nematode resistance and susceptibility of those breeding lines and cultivars. Specifically, nematode-resistant peanut cultivars can be identified with 92% accuracy, whereas susceptible breeding lines were identified with 81% accuracy. Finally, RS revealed substantial differences in biochemical composition between resistant and susceptible peanut cultivars. We found that resistant cultivars exhibit substantially higher carotenoid content compared to the susceptible breeding lines. The results of this study show that RS can be used for quick, accurate, and non-invasive identification of genotype, nematode resistance, and nutrient content. Armed with this knowledge, the peanut industry can utilize Raman spectroscopy for expedited breeding to increase yields, nutrition, and maintaining purity levels of cultivars following release.

Anthelmintic Drugs Resistance of Gastrointestinal Nematodes of Naturally Infected Goats in Haramaya, Ethiopia

Gastrointestinal parasites and their anthelmintic resistance are major constraints to goat production in Ethiopia. Experimental investigation by faecal egg count reduction test (FECRT) and larval cultures were used to assess the occurrence of anthelmintic resistance in naturally infected goats with gastrointestinal nematodes (GIN) in Haramaya, Ethiopia. One hundred goats with a minimum of 150 eggs per gram (EPG) count were selected and randomly divided into five groups; 20 goats in each group; four treated and one untreated group. The result of the faecal egg count reduction test percentage (FECRT%) and the lower 95% confidence limit showed the presence of anthelmintic resistance for all tested drugs except tetramisole. FECRT% and lower 95% confidence limit were 69.9% and 36.9 for albendazole, 84.3% and 66.1 for tetraclozan, 95.7% and 87.4 for tetramisole and 71.1% and 38.2 for ivermectin respectively. Trichostrongylus, Teladorsagia and Haemonchus showed anthelmintic resistance for tested drugs. Coproculture from different treatment group revealed Trichostrongylus (69.2% in ivermectin and 59.6% in albendazole) were the predominant nematode followed by Teladorsagia (21.9% in albendazole and 14.7% in ivermectin). In tetraclozan treatment group, Trichostrongylus (42%) and Teladorsagia (41.3%) were comparable, followed by Haemonchus (13%). In group treated with tetramisole, Teladorsagia (54.3%) were the most frequently detected nematode followed by Trichostrongylus (25.7%) and Haemonchus (11.4%). Therefore, this study demonstrated the presence of multi-drug resistant nematodes that may limit the productivity of goats. Moreover, further studies covering wider areas of Ethiopia and mechanisms of nematode resistance need to be studied in future.

Primary Metabolite Adjustments Associated With Pinewood Nematode Resistance in Pinus pinaster

The pinewood nematode (PWN) Bursaphelenchus xylophilus is the causal agent of the pine wilt disease (PWD) and represents one of the major threats to conifer forests. The detection of the PWN in Portugal, associated with Pinus pinaster, increased the concern of its spread to European forests. Despite its susceptibility to PWD, genetic variability found among P. pinaster populations has been associated with heritable PWD resistance. Understanding the mechanisms underlying tree resistance constitutes a valuable resource for breeding programs toward more resilient forest plantations. This study investigated changes in anatomy, chlorophyll a fluorescence (ChlF), and primary metabolism in susceptible and resistant P. pinaster half-sib plants, after PWN inoculation. Susceptible plants showed a general shutdown of central metabolism, osmolyte accumulation, photosynthetic inhibition, and a decrease in the plant water status. The ChlF transient rise (OJIP curve) revealed the appearance of L- and K-bands, indicators of environmental stress. In contrast, resistant plants revealed a regulated defense response and were able to restrict PWN migration and cellular damage. Furthermore, the accumulation of γ-aminobutyric acid (GABA) and succinate suggested a role of these metabolites in PWD resistance and the possible activation of the GABA shunt. Altogether, these results provide new insights to the role of primary metabolism in PWD resistance and in the selection of resistant phenotypes for disease mitigation.

Sweet potato genotypes CIP BRS Nuti and Canadense are resistant to Meloidogyne incognita, Meloidogyne javanica and Meloidogyne enterolobii

Sweet potato is a staple crop in Brazil presenting a smaller number of pathogens and diseases in comparison with other root and tuberous crops. Root knot nematodes are among the most serious sweet potato root pathogens. The impact of these pathogens also extends to following crops. Since in Brazil it is common to cultivate more than one crop per season this problem is rapidly disseminated. The aim of this study is to assess the resistance of two sweet potato clones and three commercial sweet potato genotypes to three different Meloidogyne species. Assays were performed under greenhouse conditions in two separate seasons. CIP BRS Nuti, one of the new clones and Canadense, one of the commercial genotypes were resistant to Meloidogyne incognita, M. javanica and M. enterolobii. This finding was obtained based on the reproduction factor smaller than 0,2 meaning that the initial population of 5,000 nematodes was reduced to less than 1,000 individuals after 90 days of inoculation. This data was also confirmed by the small number of eggs, egg masses and galls. Tomato and sweet potato cultivar Beauregard, known to be susceptible to the three nematode species were highly damaged by the pathogens. To our knowledge CIP BRS Nuti and Canadense are the first South American commercial cultivars with triple nematode resistance.

Genotyping of potato samples from the GenAgro ICG SB RAS collection using DNA markers of genes conferring resistance to phytopathogens

Wart (a disease caused by Synchytrium endobioticum) and golden cyst potato nematode (Globodera rostochiensis), which parasitize the roots of the host plant, cause significant damage to potato crop. Both of these disease factors are quarantined in the Russian Federation, and each registered variety is tested for resistance to their most common races and pathotypes. The main method of opposing such diseases is by the development of resistant varieties. An important step in this process is the selection of resistant genotypes from the population and the estimation of the resistance of hybrids obtained by crosses during the breeding process. Conducting a permanent phenotypic evaluation is associated with difficulties, for example, it is not always possible to work with pathogens, and phenotypic evaluation is very costly and time consuming. However, the use of DNA markers linked to resistance genes can significantly speed up and reduce the cost of the breeding process. The aim of the study was to screen the GenAgro potato collection of ICG SB RAS using known diagnostic PCR markers linked to golden potato cyst nematode and wart resistance. Genotyping was carried out on 73 potato samples using three DNA markers 57R, CP113, Gro1-4 associated with nematode resistance and one marker, NL25, associated with wart resistance. The genotyping data were compared with the data on the resistance of the collection samples. Only the 57R marker had a high level of correlation (Spearman R = 0.722008, p = 0.000000, p < 0.05) between resistance and the presence of a diagnostic fragment. The diagnostic efficiency of the 57R marker was 86.11 %. This marker can be successfully used for screening a collection, searching for resistant genotypes and marker-assisted selection. The other markers showed a low correlation between the presence of the DNA marker and resistance. The diagnostic efficiency of the CP113 marker was only 44.44 %. Spearman’s correlation coefficient (Spearman R = –0.109218, p = 0.361104, p < 0.05) did not show significant correlation between resistance and the DNA marker. The diagnostic efficiency of the NL25 marker was 61.11 %. No significant correlation was found between the NL25 marker and resistance (Spearman R = –0.017946, p = 0.881061, p < 0.05). The use of these markers for the search for resistant samples is not advisable.

Screening of Early Maturing Soybean Accessions for Resistance against HG Type 2.5.7 of Soybean Cyst Nematode, Heterodera glycines

Soybean cyst nematode (SCN; Heterodera glycines) is one of the devastating soybean pests worldwide, including the United States. Resistant cultivars combined with crop rotation are the primary methods for managing this nematode. SCN is known to have genetically diverse populations and can develop new virulent forms over time due to the continuous planting of cultivars derived from same source of resistance. Thus, identifying novel SCN resistant sources is of paramount importance for soybean breeding for nematode resistance. In this study, we screened 149 early maturity soybean [Glycine max (L.)] accessions for resistance to SCN HG type 2.5.7, which is one of the prevalent virulent SCN populations in North Dakota. SCN white females were extracted from individual plants of each accession after 35 days of growth in greenhouse conditions. The females were counted to determine a female index [FI = (average number of females on a tested accession/average number of females in Barnes, a susceptible soybean check) x 100]. The resistance response of each soybean accession was categorized as resistant, moderately resistant, moderately susceptible, and susceptible. Out of the soybean 149 accessions tested, only 13 were resistant in both runs of the experiments. The majority of screened soybean accessions were susceptible or moderately susceptible to the SCN HG type 2.5.7. The resistant soybean accessions identified in this study have the potential to be used in breeding SCN-resistant cultivars after further elucidation of the resistance genes or loci.