Search for sources of genetic resistance to Meloidogyne enterolobii in tomato and in wild Solanum (section Lycopersicon) accessions

Resumo

Meloidogyne enterolobii (syn. M. mayaguensis) is an emerging plant pathogen capable of inducing root galls and yield reduction in a wide range of host species. This pathogen has also been reported as a global threat for tomato (Solanum lycopersicum L.) crop production mainly due to its ability to overcome the Meloidogyne resistance meditated by the Mi-1 gene. Despite the potential importance of this nematode, sources of resistance to M. enterolobii are not yet available for breeding purposes. The main objective of the present work was to evaluate a large Solanum (section Lycopersicon) germplasm (comprising nine species and one botanic variety) aiming to identify useful sources of resistance to M. enterolobii. In the first screening assay, 101 accessions and the susceptible standard S. lycopersicum ‘Santa Cruz’ were inoculated and evaluated under controlled (greenhouse) conditions. Twenty-day-old seedlings were inoculated with a suspension of M. enterolobii eggs (710 eggs per plant) and maintained in expanded 128-cell polystyrene trays during the entire course of the experiment. The phenotypic criteria used for evaluation (done at 45 days after inoculation) were the number of root galls, gall index, number of eggs, and the reproduction factor. Twenty accessions with promising resistant reaction to M. enterolobii in the first screening test were selected and employed in a subsequent assay. Plants of the 20 selected accessions were cultivated in 400 cm3 pots filled with sterile soil. Inoculation procedures were identical to the first assay, but with higher inoculum pressure (3,300 eggs per plant). Three accessions with superior tolerance levels to M. enterolobii were identified viz. S. lycopersicum ‘Yoshimatsu’, S. lycopersicum ‘CNPH 1246’ and S. pimpinelifolium CGO 7650 (= CNPH 1195). These accessions were re-evaluated against a distinct M. enterolobii population as well as against two other root-knot nematode species (M. javanica and one M. incognita race 1). Under higher inoculum pressure, ‘Yoshimatsu’ was found to be resistant to M. javanica and M. incognita race 1, but susceptible to a M. enterolobii from guava. The other two sources displayed susceptibility to all three nematodes. The results indicated additional germplasm screening since no source of stable genetic resistance to M. enterolobii was found so far.