Mapping a Reniform Nematode (Rotylenchulus reniformis ) Resistance Locus Introgressed From Gossypium Aridum Into Upland Cotton (G. hirsutum ).

In recent years the reniform nematode (Rotylenchulus reniformis) has been expanding its geographic distribution in the U.S. as well as increasing its numbers in affected fields, and together with root-knot nematode, they cause the greatest losses due to pathogens in U.S. cotton.  In this association mapping study, a tri-species hybrid, (G. arboreum × bridging line G 371 -G. hirsutum × G aridum-), was crossed with MD51ne (G. hirsutum) and progeny from the cross was used to identify and map SSR markers associated with reniform nematode resistance.  Seventy-six progeny (the 50 most resistant and 26 most susceptible) plants were genotyped with 104 markers.  Twenty-five markers were associated with a resistance locus that we designated Ren^ari and two markers, BNL 3279_132 and BNL 2662_090, mapped within 1 cM of Ren^ari.  The validity of these markers was also tested on the entire progeny population and resistant individuals of the next generation.  Because the SSR fragments associated with resistance were found in G. aridum and the bridging line G 371, G. aridum is the likely source of this resistance; this resistance is simply inherited, possibly controlled by a single dominant gene.  Another source of reniform nematode resistance appears to be the diploid accession employed in the initial cross, G. arboreum A2-190.  The markers identified in the present study provide valuable tools for breeders and geneticists developing new lines and cultivars, especially in light of the difficulty assessing nematode resistance using reniform nematode screens.