Grafting and Paladin Pic-21 for Nematode and Weed Management in Vegetable Production

Biochemical and nanotechnological approaches to combat phytoparasitic nematodes

The foundation of most food production systems underpinning global food security is the careful management of soil resources. Embedded in the concept of soil health is the impact of diverse soil-borne pests and pathogens, and phytoparasitic nematodes represent a particular challenge. Root-knot nematodes and cyst nematodes are severe threats to agriculture, accounting for annual yield losses of US$157 billion. The control of soil-borne phytoparasitic nematodes conventionally relies on the use of chemical nematicides, which can have adverse effects on the environment and human health due to their persistence in soil, plants, and water. Nematode-resistant plants offer a promising alternative, but genetic resistance is species-dependent, limited to a few crops, and breeding and deploying resistant cultivars often takes years. Novel approaches for the control of phytoparasitic nematodes are therefore required, those that specifically target these parasites in the ground whilst minimizing the impact on the environment, agricultural ecosystems, and human health. In addition to the development of next-generation, environmentally safer nematicides, promising biochemical strategies include the combination of RNA interference (RNAi) with nanomaterials that ensure the targeted delivery and controlled release of double-stranded RNA. Genome sequencing has identified more than 75 genes in root knot and cyst nematodes that have been targeted with RNAi so far. But despite encouraging results, the delivery of dsRNA to nematodes in the soil remains inefficient. In this review article, we describe the state-of-the-art RNAi approaches targeting phytoparasitic nematodes and consider the potential benefits of nanotechnology to improve dsRNA delivery.

Grafting for managing vegetable crop pests

Nematode and disease resistant rootstocks have been developed for many vegetable crops including tomato, eggplant, melon, watermelon, and cucumber and are being utilized by an increasing number of growers. Grafting commercially desirable vegetable scions on nematode and disease resistant rootstocks has been significantly stimulated by the need for an alternative to banned soil fumigation with methyl bromide, which had been the primary method for managing soil-borne nematodes, diseases, and weeds. Rootstocks resistant to root-knot nematodes (Meloidogyne spp.) and diseases including Fusarium wilt, Fusarium crown and root rot, Verticillium wilt, bacterial wilt, Southern blight, and sudden wilt have been developed and many are available commercially. New technologies such as transcriptomics, identification of differentially expressed genes, transgene rootstocks, and RNAi silencing are being used in the development of vegetable rootstocks which are resistant to pests, salt tolerant, and heat and cold tolerant. Overall, grafting has proven to be a successful and environmentally safe method for managing root-knot nematodes and soil-borne diseases by reducing infection, disease development, and inoculum build-up in the soil, which is especially important for growth of healthy subsequent crops. © 2021 Society of Chemical Industry.

How rootstock/scion combinations affect watermelon fruit quality after harvest?

Grafting of vegetable seedlings is a unique horticultural technology, practiced for more than five decades, aiming to overcome problems associated with intensive cultivation on limited arable land. Grafting can protect vegetables against soil-borne diseases and nematodes; against abiotic stresses such as high or low temperatures, salinity, drought or excessive soil-water content; and against elevated soil concentrations of heavy metals and organic pollutants. Watermelon is one of the most popular vegetables to be grafted, and more than 90% of the plants worldwide are commercially grafted. This mini review aims to summarize the latest available information about the effects of rootstock/scion combinations with respect to enhancing or impairing watermelon fruit-quality. A better understand of the influence of rootstock/scion compatibility or incompatibility on fruit-quality parameters will facilitate decision-making by growers and direct breeding programs to produce high-quality grafted fruits in a cost-effective manner. © 2020 Society of Chemical Industry.

A sulfur-containing volatile emitted by potato-associated bacteria confers protection against late blight through direct anti-oomycete activity

Plant diseases are a major cause for yield losses and new strategies to control them without harming the environment are urgently needed. Plant-associated bacteria contribute to their host’s health in diverse ways, among which the emission of disease-inhibiting volatile organic compounds (VOCs). We have previously reported that VOCs emitted by potato-associated bacteria caused strong in vitro growth inhibition of the late blight causing agent Phytophthora infestans. This work focuses on sulfur-containing VOCs (sVOCs) and demonstrates the high in planta protective potential of S-methyl methane thiosulfonate (MMTS), which fully prevented late blight disease in potato leaves and plantlets without phytotoxic effects, in contrast to other sVOCs. Short exposure times were sufficient to protect plants against infection. We further showed that MMTS’s protective activity was not mediated by the plant immune system but lied in its anti-oomycete activity. Using quantitative proteomics, we determined that different sVOCs caused specific proteome changes in P. infestans, indicating perturbations in sulfur metabolism, protein translation and redox balance. This work brings new perspectives for plant protection against the devastating Irish Famine pathogen, while opening new research avenues on the role of sVOCs in the interaction between plants and their microbiome.

Plant Volatiles Reduce the Viability of the Root-Knot Nematode Meloidogyne incognita Either Directly or When Retained in Water

Volatile organic compounds (VOC) produced by green residues for the management of plant-parasitic nematodes are poorly studied for oilseed plants and some Brassica spp. To investigate the activity of VOC in vitro and as biofumigants, dry and aqueous macerates of broccoli (Brassica oleracea var. italica) shoots and sunflower (Helianthus annuus) seed were used against the root-knot nematode Meloidogyne incognita. VOC produced by sunflower seed caused higher mortality of M. incognita second-stage juveniles (J₂) than VOC produced by broccoli shoots but both plant species were equally effective in decreasing the infectivity and reproduction of this nematode. The number of galls and eggs produced by the nematode in tomato roots was reduced by 89 and 95%, respectively, on average, at the highest concentrations of broccoli and sunflower seed macerates tested as biofumigants. When nematodes were placed in water exposed to broccoli VOC, J₂ immobility increased and the number of galls and eggs produced by the nematode in tomato roots decreased 80 and 96%, respectively. Water exposed to sunflower seed VOC had no effect on the viability of the nematode. Gas chromatography was used to identify five and six chemical groups in broccoli and in sunflower seed macerates, respectively, but only alcohols, sulfurated VOC, and terpenes were detected in the water exposed to these plant macerates. Sulfurated VOC from the water exposed to broccoli macerates were found to be involved in its activity against M. incognita. The purified VOC dimethyl disulfide (DMDS) and 3-pentanol were tested directly against J₂ and showed a lethal concentration of 176 and 918 µg/ml (ppm), respectively, whereas dimethyl sulfide had no effect against M. incognita. Furthermore, DMDS and 3-pentanol retained in water killed J₂ and reduced gall formation and the number of eggs of M. incognita on tomato roots. Both these plant species produced toxic VOC to M. incognita, whereas only VOC retained in water exposed to broccoli had activity against M. incognita.