Effect of Citrullus amarus accessions on the population dynamics of Meloidogyne incognita and M. java']javanica and watermelon yield

The aims of this study were to determine i) the effect of grafted watermelon cv. Sugar Baby onto C. amarus accessions BGV0005164 and BGV0005167 on M. incognita and M. javanica population growth estimated by means of the values of maximum reproduction rate, maximum nematode density and equilibrium density in pot experiments; ii) the effect of increasing nematode densities on plant productivity in pot experiments; and iii) the effect of repeated cultivation of watermelon cv. Sugar Baby grafted onto both C. amarus accessions and onto C. lanatus 'Robusta' during two seasons in a plastic greenhouse on M. incognita reproduction, disease severity, crop yield and selection for nematode virulence. In pot experiments, the values of maximum reproduction rate, maximum nematode density and equilibrium density of M. incognita were 37 %, 72 % and 68 % lower in watermelon grafted onto BGV0005164 than in ungrafted, and 28 %, 76 % and 77 % lower when grafted onto BGV0005167. Regarding M. javanica, the values of maximum reproduction rate, maximum nematode density and equilibrium density in watermelon grafted onto BGV0005164 were 88 %, 65 % and 14 % lower than in ungrafted, and 80 %, 76 % and 33 % lower when grafted onto BGV0005167. Dry shoot weight of ungrafted and grafted watermelon inoculated with a range of nematode densities between 0 and 1200 s-stage juveniles per 100 cm 3 of soil was not affected, irrespective of the nematode isolate. In the plastic greenhouse experiment, M. incognita reproduced less in grafted than in ungrafted watermelon. Disease severity was higher in ungrafted than in grafted watermelon. The level of resistance of both C. amarus accessions was not affected after two-year cultivation, but it decreased from moderately resistant in 2017 to slightly resistant in rootstock `Robusta' Watermelon grafted yielded between 2.9 and 5.6 kg more per plant than the ungrafted in 2017, and between 2.0 and 2.7 kg more per plant in 2018. In conclusion, C. amarus accessions BGV0005164 and BGV0005167 performed as poorer hosts to M. incognita and M. javanica. Watermelon grafted onto these C. amarus accessions improved fruit yield when they were cultivated in nematode infested soils without affecting its level of resistance to M. incognita after two consecutive crops.