Occurrence of a new race of Meloidogyne enterolobii and avirulent M. incognita populations parasitizing cotton in western Bahia state, Brazil

Meloidogyne incognita is the root-knot nematode (RKN) species globally known to infect cotton plants, and the resistant cultivar IMA 5801B2RF has recently been released in Brazil for its control. In 2019, the first infection by M. enterolobii on resistant cotton was reported in Minas Gerais state, Brazil. In 2021, in our previous survey, this nematode species was detected again in Brazil in the municipality of Sao Desiderio, western Bahia state on the same resistant cotton cultivar. In a continuous study, we have surveyed cotton fields from six municipalities in Bahia state, in areas supposedly cultivated with the resistant cotton; all the six populations from three different geographical origins were M. incognita, but M. enterolobii was not found again, confirming its restricted occurrence in western Bahia state. The RKN identifications were based on biochemical and molecular approaches and revealed the phenotype alpha-esterase Est En2 for M. enterolobii and Est I2 for M. incognita and typical SCAR patterns of these species, confirming the enzymatic identification. In soil and root analysis we detected second-stage juveniles (J2) of M. incognita in 21 samples (50% of occurrence) and Rotylenchulus reniformis in 13 samples (31%) extract from soil and roots and identified using taxonomic approaches. A bioassay with the resistant cotton cultivar in greenhouse conditions revealed a high reproduction of M. enterolobii (RF = 12.8) but did not allow reproduction of the field populations of M. incognita (RF < 1.0), showing that these populations of M. incognita were not virulent to this resistant cotton. There may have been an incorrect identification in the field cultivar and/or seed mixture in on-farm seed production. Our study provided the first report of a natural infection of a new race of M. enterolobii on cotton and highlighted the absence of virulent M. incognita populations on cotton in western Bahia state, Brazil.

Automated summary

This study reported the natural infection of M. enterolobii on cotton in Brazil and highlighted the absence of virulent M. incognita populations on cotton in western Bahia state.