Abstract
Four rotation sequences consisting of ungrafted tomato cv. Durinta – melon cv. Paloma or tomato grafted onto the resistant rootstock ‘Aligator’ – melon grafted onto the resistant Cucumis metuliferus accession BGV11135, and in reverse order, were conducted from 2015 to 2017 in a plastic greenhouse infested or not with Meloidogyne incognita to determine the plant tolerance (T), the minimum relative crop yield (m) and fruit quality. The relationship between M. incognita densities in soil at transplanting (Pi) of each crop and the crop yield was assessed and T and m were estimated by the Seinhorst’s damage model. In addition, the volume and the number of nuclei of single giant cells and the number of giant cells, its volume and the number of nuclei per feeding site in susceptible tomato and melon were compared to those in the resistant tomato and C. metuliferus 15 days after nematode inoculation in pot test. The relationship between the Pi and the relative crop yield fitted the Seinhorst’s damage model in both ungrafted and grafted tomato and melon, but not for all years and cropping seasons. The estimated T for ungrafted and grafted tomato did not differ but m was lower in the former (34%) than the latter (67%). Sodium concentration in fruits from ungrafted but not from grafted tomato increased with nematode densities in spring 2015 and 2016. The estimated ungrafted melon T did not differ from the grafted melon cultivated in spring, but it did when it was cultivated in summer. The relative crop yield of ungrafted melon was lower (2%) than the grafted cultivated in spring (62%) and summer (20%). Sodium concentration in melon fruits from ungrafted plants increased with nematode densities. No variations in fruit quality from grafted melon cultivated in spring were found, although less dry matter and soluble solid content at highest nematode densities were registered when it was cultivated in summer. Lower number of giant cells per feeding site was observed in both susceptible tomato germplasms compared to the resistant ones but they were more voluminous and held higher number of nuclei per giant cell and per feeding site.
Highlights
Tomato (Solanum lycopersicum) and melon (Cucumis melo) are two of the major horticultural crops worldwide with annual productions of 5.163.466 and 655.677 tonnes in 2017, respectively (FAOSTAT, 2017)
Grafted and ungrafted tomato cultivated in spring in non-infested plots yielded 4.1 and 3.9 kg plant−1 on average, respectively, and 2.2 and 2.0 kg plant−1 when cultivated in summer
In spring 2017, m- and T-values for ungrafted tomato cultivated in a population densities (Pi) range from 0 to 2174 J2 250 cm−3 of soil were 0.27 ± 0.26 and 32 ± 25 J2 250 cm−3 of soil, respectively, (Figure 1A) and did not differ from those estimated in spring 2016
Summary
Tomato (Solanum lycopersicum) and melon (Cucumis melo) are two of the major horticultural crops worldwide with annual productions of 5.163.466 and 655.677 tonnes in 2017, respectively (FAOSTAT, 2017). Root-knot nematodes (RKN), Meloidogyne spp., are one of the most important limiting soil borne pathogens for vegetable production (Hallmann and Meressa, 2018). Among the more than 100 RKN species described, M. arenaria, M. incognita, M. javanica and M. hapla are the most damaging species, which are worldwide distributed, have a wide range of host plants and reproduce by parthenogenesis (Jones et al, 2013), allowing an exponential increase of nematode densities at the end of the crop from low densities at planting (Greco and Di Vito, 2009). The infective second-stage juvenile (J2) moves between the soil particles and penetrates the host plant roots near to the elongation zone. The J2 moves intercellularly to the root tip, turns after the casparian strips, enter into the vascular cylinder to establish a feeding site and becomes sedentary. The embryogenesis leads to the J1 that molts inside the egg and becomes J2 until hatching occurs
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