Plant-parasitic nematodes are costly burdens of crop production. Ubiquitous in nature, phytoparasitic nematodes are associated with nearly every important agricultural crop and represent a signiicant constraint on global food security. Root-knot nematodes (Meloidogyne spp.) cyst nematodes (Heterodera and Globodera spp.) and lesion nematodes (Pratylenchus spp.) rank at the top of list of the most economically and scientiically important species due to their intricate relationship with the host plants, wide host range, and the level of damage ensued by infection. Limitations on the use of chemical pesticides have brought increasing interest in studies on alternative methods of nematode control. Among these strategies of nonchemical nematode management is the identiication and implementation of host resistance. In addition, nematode genes involved in parasitism represent key targets for the development of control through gene silencing methods such as RNA interference. Recently, transcriptome proiling analyses has been used to distinguish nematode resistant and susceptible genotypes and identify the speciic molecular components and pathways triggered during the plant immune response to nematode invasion. This summary highlights the importance of plant-parasitic nematodes in agriculture and the molecular events involved in plant-nematode interactions.

'Criollo de Morelos 334' (CM334) is one of the most promising sources of resistance to Phytophthora capsici in pepper. This Mexican accession is distantly related to bell pepper and its resistance displays a complex inheritance. The QTLs involved in resistance to P. capsici were previously mapped. In order to transfer the resistance factors from CM334 into a bell pepper genetic background, a modified, recurrent breeding scheme was initiated. The breeding population was divided into three sub-populations which were screened by distinct phenotypic tests of increasing severity. The plants from the first sub-population were screened with low-severity tests and backcrossed to the susceptible bell pepper; the plants from the second and third sub-populations were screened by more severe resistance tests and crossed with the plants from the first and second sub-populations, respectively. In this study, the phenotypic data for the three sub-populations during five screening/intermating cycles were analysed. In parallel, the changes in allelic frequencies at molecular markers linked to the resistance QTLs were reported. The resistance phenotype and allelic frequencies strongly depended on the sub-population and screening severity. Regarding allelic frequency changes across the selection cycles, a loss of resistant QTL alleles was observed in the first sub-population, particularly for the low-effect QTLs, whereas a better conservation of the resistant QTL alleles was observed in the two other sub-populations. The same trend was observed in the phenotypic data with an increasing resistance level from the first to the third sub-populations. The changes in the allelic frequencies of loci not linked to resistance QTLs and for horticultural traits across the breeding process indicated that the recovery of the recipient parent genome was not significantly affected by the selection for resistance.

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Fungal, bacterial and viral diseases are economic foliar diseases that cause yield losses, between 40 and 100%, in commonly grown dry bean cultivars in the world. Development of disease resistance genotypes is a complex interaction between genetic and environmental factors. This study focused on determining the natural infection of disease-causing pathogens of angular leaf spot, powdery mildew, bacterial blight and bean common mosaic virus in different agro-ecologies in relation to grain yield. Diversity of 211 bean genotypes were tested at two different disease hot spots areas under incomplete block design, with two replications for two cropping seasons in Tanzania. Diseases severity was significantly different (p<0.001) for genotypes and their interactions with the environment and season. Higher disease severity was observed at Lyamungo site than Selian site. Effects of genotypes by environment were observed with maximum yield of 2170 kg/ha to low yield of 398 kg/ha with the grand mean of 1151.54 kg/ha. High annual rainfall and relative humidity contributed to disease development among the tested environment. Five genotypes (FEB 189, A774, NUA 16, KG 71-4 and DOR 766) expressed trait of resistance to above diseases and are advised to be incorporated in breeding programs for enhancing dry bean productivity.

Genome-wide association studies (GWAS) have been utilized to detect genetic variations related to several agronomic traits and disease resistance in common bean. However, its application in the powdery mildew (PM) disease to identify candidate genes and their location in the common bean genome has not been fully addressed. Single-nucleotide polymorphism (SNP) genotyping with a BeadChip containing 5398 SNPs was used to detect genetic variations related to PM disease resistance in a panel of 211 genotypes grown under two field conditions for two consecutive years. Significant SNPs identified on chromosomes Pv04 and Pv10 were repeatable, ensuring the phenotypic data’s reliability and the causal relationship. A cluster of resistance genes was revealed on the Pv04 of the common bean genome, coiled-coil-nucleotide-binding site–leucine-rich repeat (CC-NBS-LRR, CNL), and Toll/interleukin-1 receptor-nucleotide-binding site–leucine-rich repeat type (TIR-NBS-LRR, TNL)-like resistance genes were identified. Furthermore, two resistance genes, Phavu_010G1320001g and Phavu_010G136800g, were also identified on Pv10. Further sequence analysis showed that these genes were homologs to the disease-resistance protein (RLM1A-like) and the putative disease-resistance protein (At4g11170.1) in Arabidopsis. Significant SNPs related to two LRR receptor-like kinases (RLK) were only identified on Pv11 in 2018. Many genes encoding the auxin-responsive protein, TIFY10A protein, growth-regulating factor five-like, ubiquitin-like protein, and cell wall RBR3-like protein related to PM disease resistance were identified nearby significant SNPs. These results suggested that the resistance to PM pathogen involves a network of many genes constitutively co-expressed.

Each year, plant-parasitic nematodes (PPNs) cause over $100 billion in damages to crops [1]. The most scientifically and economically essential PPNS include cyst nematodes (Heterodera and Globodera spp.) root-lesion nematodes (Pratylenchus spp.); the burrowing nematode Radopholus similes; Ditylenchus dipsaci, and root-knot nematodes (Meloidogyne spp.) which ranks number one [2]. The use of chemical pesticides typically maintains nematode control; however, the overuse of such chemical agents has resulted in a negative environmental impact Sande D, et al. [3] thus, alternative methods of nematode control which are

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Five healthy, vigorous cultivars of sweet potato [Ipomoea batatas (L.) Lam] were cultivated under rootknot nematode Meloidogyne incognita challenge to distinguish levels of resistance to infection. Roots and soil samples were collected 84 days' post-infection and evaluated for specific host responses to nematode infection by visual screening analysis and quantitative assessments of symptoms of infection. Resistant control cultivar Nugget showed the highest degree of resistance manifested in lower necrosis and galling, high fresh root weights and low nematode and egg counts. Necrosis and galling scores were highest in susceptible cultivars Georgia Jet and DMO1 where extensive root cracking was observed in Georgia Jet, and storage root development was severely restricted in DMO1 which also produced the highest egg counts. TUO2 and Whatley Loretan were considered intermediately resistant based on egg counts and necrosis and galling. Our results suggest that genotypic differences between cultivars were apparent in multiple host responses to root-knot nematode infection. We have also provided initial evidence to support the identification of newly developed sweet potato cultivars with intermediate resistance to root-knot nematodes.