Effect of cucumber stock on growth and propagation of Meloidogyneincognita and its relation with root exudates

Cucumber (Cucumis sativus L.) is a major vegetable grown in greenhouses with increasingly severe occurrence and damage of root-knot nematode due to continuous cropping. As there currently is no resistant cucumber variety to root-knot nematode, grafting has been the most effective way of improving the resistance of cucumber to root-knot nematode. However, the huge differences in root-knot nematode resistance among different varieties of cucumber stocks have posed significant challenges to grafting cucumber. To clarify the mechanism of the tolerance of grafted cucumber to root-knot nematode, two stocks with different resistances to root-knot nematode ‘Figleaf gourd’ (low sensitive) and ‘Tianzhen’ (high sensitive) and cucumber variety ‘Xintaimici’ were used to investigate the effects on Meloidogyne incognita growth and propagation by artificial inoculation. The study also determined the relationship between root exudates of stocks and the hatchability of M. incognit eggs. The results showed that at the start of M. incognita infection, the number of second-instars larvae of root-not nematode in the three varieties roots were significantly different, lowest in ‘Figleaf gourd’ and highest in ‘Xintaimici’. Although all the second-instars larvae in roots developed normally into adults, the total number of nematodes was highest in ‘Xintaimici’ and lowest in ‘Figleaf gourd’. The number of second-instars larvae was also highest in rhizosphere of ‘Xintaimici’ and lowest in ‘Figleaf gourd’. The characteristics and number of eggs in rhizosphere were the same as the second-instars larvae before secondary infection. Root exudates from cucumber and stocks had significant effects on the hatchability of M. incognita eggs, with ‘Xintaimici’ with the highest egg hatching rate followed by ‘Tianzhen’ and ‘Figleaf gourd’. The rates of egg hatching affected by root exudates of the three varieties obviously increased after inoculation with M. incognita, with ‘Xintaimici’ as the highest and ‘Figleaf gourd’ the lowest. Along with growth of cucumber, the enhancement effect of root exudates on egg hatching increased gradually. Based on the above results, root exudates of low susceptible cucumber stocks obviously inhibited M. incognita egg hatching and reduced M. incognita growth and propagation in both roots and rhizospheres. This was a possible mechanism of resistance of grafted cucumber to M. incognita.