Identification of Four Populations of Meloidogyne incognita in Georgia, United States, Capable of Parasitizing Tomato-Bearing Mi-1.2 Gene

Abstract

Meloidogyne incognita, the southern root-knot nematode (RKN), is the most predominant plant-parasitic nematode species of tomato and causes significant yield loss. The Mi-1.2 gene confers resistance in tomatoes to M. incognita; however, virulent RKN populations capable of parasitizing resistant tomato cultivars have been reported from different regions in the world. Four naturally occurring virulent populations of M. incognita were found in vegetable fields from four counties in Georgia with no history of tomato cultivation of the Mi gene. Two consecutive greenhouse trials showed that all four virulent RKN populations reproduced on tomato cultivars, including Amelia, Skyway, and Myrtle, with the Mi-1 gene, while an avirulent population of M. incognita race 3 was unable to overcome host resistance. Virulent RKN populations varied in reproduction among resistant cultivars, with Ma6 population having the greatest reproduction potential. No difference in penetration potential of the virulent (Ma6) and avirulent populations was found on susceptible and resistant tomato cultivars. However, virulent Ma6 population females were successful at egg-laying, whereas avirulent female development was arrested in the resistant cultivars. The virulent Ma6 population also induced feeding sites in the roots of resistant cultivars, whereas the avirulent population did not. To our knowledge, this is the first report of resistance-breaking populations of M. incognita in Georgia and the second state in the United States after California.

Successional effects of cover cropping and deep tillage on suppression of plant‐parasitic nematodes and soilborne fungal pathogens

“…PPNs recovered from soil were identified to the genus level based on morphological features 46,47 and counted using an inverted microscope (ZEISS Axio Vert.A1, Oberkochen, Germany) at 10‐40× magnification. Identification of stubby‐root and root‐knot nematodes to the species level was conducted by species‐specific PCR described in Hajihassani et al 48,49 …”

“…45 PPNs recovered from soil were identified to the genus level based on morphological features 46,47 and counted using an inverted microscope (ZEISS Axio Vert.A1, Oberkochen, Germany) at 10-40× magnification. Identification of stubby-root and root-knot nematodes to the species level was conducted by species-specific PCR described in Hajihassani et al 48,49 2.4 Assessment of soilborne fungal pathogens Fields were naturally infested with Athelia rolfsii, Rhizoctonia solani, and Sclerotinia sclerotiorum. Initial incidence of southern blight on tomato (A. rolfsii), damping-off of tomato, squash, and cabbage (R. solani), and Sclerotinia rot of cabbage (S. sclerotiorum) were identified at the beginning of field trial by collecting symptomatic plants from the field and having specimens examined and confirmed by Jason Brock at the University of Georgia Plant Disease Clinic (Tifton, GA).…”

Phased chromosome-scale genome assembly of an asexual, allopolyploid root-knot nematode reveals complex subgenomic structure

“…A widely investigated example is acquisition of ability to reproduce on tomato with the resistance gene Mi-1, which confers effective resistance to MIG species and is widely deployed for nematode management in tomato [32]. Many independent studies have identified MIG populations that are able to break Mi-mediated resistance; these include both field isolates and greenhouse selections of isofemale lines [33,34]. However, efforts to decipher the genetic mechanisms for these phenotypic variants have not so far been successful due in part to the lack of tractable genetics and limitations in genome assemblies.…”

Tomato Mi-gene Resistance-Breaking Populations of Meloidogyne Show Variable Reproduction on Susceptible and Resistant Crop Cultivars

“…However, the occurrence of Meloidogyne populations that can reproduce on resistant cultivars has been reported from tomato-growing areas worldwide, and the frequency of resistance breaking appears to be increasing ( Sikora et al, 1973 ; Netscher, 1977 ; Berthou et al, 1989 ; Prot, 1984 ; Eddaoudi et al, 1997 ; Ornat et al, 2001 ; Djian-Caporalino et al, 2011 ). In the USA, the occurrence of resistance-breaking populations of M. incognita was initially reported from California ( Kaloshian et al, 1996 ) and recently also from Georgia ( Hajihassani et al, 2022 ). While the appearance of resistance-breaking populations has been linked to repeated exposure to resistant tomatoes ( Netscher, 1977 ; Viglierchio, 1978 ; Castagnone-Sereno et al, 1993 ; Noling, 2000 ; Meher et al, 2009 ), such populations have also been isolated in fields with no history of resistant tomato crops ( Riggs and Winstead, 1959 ; Kaloshian et al, 1996 ; Eddaoudi et al, 1997 ; Ornat et al, 2001 ; Tzortzakakis et al, 2005 ; Hajihassani et al, 2022 ).…”

“…In the USA, the occurrence of resistance-breaking populations of M. incognita was initially reported from California ( Kaloshian et al, 1996 ) and recently also from Georgia ( Hajihassani et al, 2022 ). While the appearance of resistance-breaking populations has been linked to repeated exposure to resistant tomatoes ( Netscher, 1977 ; Viglierchio, 1978 ; Castagnone-Sereno et al, 1993 ; Noling, 2000 ; Meher et al, 2009 ), such populations have also been isolated in fields with no history of resistant tomato crops ( Riggs and Winstead, 1959 ; Kaloshian et al, 1996 ; Eddaoudi et al, 1997 ; Ornat et al, 2001 ; Tzortzakakis et al, 2005 ; Hajihassani et al, 2022 ). Hajihassani et al, (2022) reported differences in the degree of virulence between resistance-breaking populations on the same resistant tomato cultivar, but others ( Castagnone-Sereno et al, 1994 ) reported no differences between different resistance-breaking populations.…”