The behaviour of populations of potato‐root eelworm (Heterodera rostochiensis Woll.) towards some resistant tuberous and other Solanum species

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Abstract
SUMMARY: Forty‐seven British populations of potato‐root eelworm (Heterodera rostochiensis) were tested for ability to form cysts on plants with resistance derived from Solanum tuberosum ssp. andigena, S. multidissectum, S. vernei, S. sanctae‐rosae, S. famatinae and S. × juzepczukii, and on S. nigrum, S. sarachoides and Nicotiana spp.The potato variety Arran Banner was used as the standard susceptible host and the number of cysts formed on the resistant plants in pot tests was expressed as a percentage of those formed on Arran Banner or assessed visually from the cysts observed on the outside root mat. Cyst production on andigena hybrids ranged from less than 1% of those on Arran Banner to slightly over 100%. About half of the populations produced 10% or less, and populations of this type, against which andigena resistance would be effective, were especially common in south‐east England and Northern Ireland. Cyst production on famatinae hybrids, a race of S. nigrum from East Germany, S. miniatum and S. sarachoides, resembled that on andigena hybrids. Cyst production on multidissectum hybrids varied less and only a few populations produced less than 10% and none less than 3% of the number on Arran Banner. S. vernei was highly resistant to all but about 5% of populations and a race of S. nigrum from Rothamsted was resistant to all tested.In selection experiments the proportion of females able to complete development increased when andigena hybrids, S. vernei or S. nigrum, were grown repeatedly in the same inoculum. Increase on S. vernei was slow, the pattern of increase on andigena hybrids suggested recessive inheritance but this could not be confirmed and increase on S. nigrum was more rapid, suggesting that the genetic mechanisms concerned in plant resistance and those concerned in the production of resistance‐breaking nematode biotypes differ for the three types of plant.The tests revealed much variability between populations of potato‐root eelworm from different localities despite the fact that they have undergone much selection on one type of host plant, cultivated Solanum tuberosum ssp. tuberosum. No cysts were seen on Nicotiana spp. Nevertheless, H. tabacum may prove to be little more than a recognizable biotype of H. rostochiensis.