False erosion

False erosion is due to error. The most frequent cause is an inadequate testing of a new cultivar, which is mistakenly believed to be resistant to a parasite. With expanding cultivation, this parasite becomes seriously damaging, and it is wrongly postulated that the resistance has broken down. It is so much easier to blame nature than to admit to one's own incompetence.

Good examples of false erosion have occurred with mosaic virus of sugarcane. This savage disease was controlled so effectively with horizontal resistance that it all but disappeared. The cane scientists tended to forget about it, and new cultivars would sometimes be released to farmers with an unrecognised susceptibility to mosaic.

Perhaps the best example of a false erosion was that of grape rootstocks to Phylloxera, already discussed (see 5.9.1).

A false erosion can also occur when a susceptible cultivar is used as a standard during an extended breeding program. As the breeding population as a whole gains resistance, the standard becomes relatively more susceptible. This can give a false impression of a loss of horizontal resistance in the standard cultivar.

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