Abstract
Soil-borne pathogenic fungi (SBPF) and root-knot nematodes (RKN) co-exist in the rhizosphere and are major pathogens causing root diseases in cucurbits. Current knowledge on soil-borne pathogens of cucurbit crops grown under protected cultivation, their host-pathogen interactions, and mechanisms of resistance has been reviewed. Plant resistance is an effective and sustainable method to control soil-borne diseases and the available resistant cultivars and rootstocks to key soil-borne pathogens are reported. The importance of proper pathogen diagnosis in the right choice of cultivar or rootstock is highlighted because of the specificity in the response of the cucurbit crops to fungal and nematode species and races. Plants protect themselves through common mechanisms of resistance against SBPF and RKN including hardening of their cell walls, pathogenesis-related (PR) proteins, and production of antimicrobial molecules. The activity of some enzymes, such as peroxidases and phenylalanine lyase, is increased after pathogen infection and is higher on SBPF and RKN resistant than susceptible cucurbits. Plant hormones such as salicylic acid, jasmonic acid, and ethylene are involved in the response of cucurbits to SBPF. Most mechanisms of resistance to RKN affect post-infection development of the nematode, which results in a delay or disruption of the life cycle. Traditional and biotechnological tools used for breeding for resistance in cucurbits are described. Grafting is an effective non-host resistance method to control primarily Fusarium wilt but not to control RKN. However, new rootstocks with resistance to both pathogens have been developed recently and their effects on fruit quality and yield stability need additional studies. The impact of grafting on yield in pathogen-infested soils is discussed.
Highlights
The botanical family Cucurbitaceae includes several economically important vegetable crops cultivated worldwide in a variety of climates and environmental conditions
The purpose of this review was to examine current knowledge on plant resistance to pathogens co-existing in the rhizosphere of selected cucurbit crops, the mechanisms involved, and traditional and biotechnological tools used for breeding for resistance with special emphasis on progress of grafting
The importance of markers in breeding, when they are highly associated with a trait of interest, is their use as tools to perform marker-assisted selection breeding (MAS) or to be incorporated into resistant gene introgression programs by taking into account that the markers are often plant germplasm-dependent [123,124] and that, occasionally, it will need more than one marker to detect a gene
Summary
The botanical family Cucurbitaceae includes several economically important vegetable crops cultivated worldwide in a variety of climates and environmental conditions. Numerous pathogens are associated with cucurbitaceous crops even though those causing disease in the root system are primarily soil-borne pathogenic fungi (SBPF) and plant-parasitic nematodes (PPN). These pathogens share the same habitat in the rhizosphere, disrupt the vascular system of the host plant, and interfere with physiological processes involved in water and nutrient uptake.
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