PEAR SCAB: EPIDEMIOLOGY, CONTROL AND RESISTANCE OF VENTURIA PIRINA TO FUNGICIDES

In 1962 scab was found for the first time in pear orchards in Israel.
Since then it has caused losses in cv.
Spadona, the principal pear cultivar in Israel, and infected also cv.
Gentile.
It has not been found on cv.
Coscia even in heavily scab-infected Spadona orchards.

Five races of V. pirina were identified, four from cultivated pears (Pyrus communis) and one (race 5) from the wild pear P. syriaca. Race 2 is the incitant of scab in orchards of cv.
Spadona and Gentile.
Races 1,3 and 4 infect pear cultivars which have no agricultural value, and race 5 infects the wild pear only.

Failures in pear scab control were primarily caused by inadequate control measures.
But in 1975–1976, heavy losses occurred because of benomyl-resistance.
Since 1977, benzimidazole fungicides have not been used for pear scab control.
The benomyl-resistant isolates are stable and competitive with the benomyl-sensitive wild type isolated.
After 10 years of not using benzimidazole fungicides, the proportion of the resistant isolates in V. pirina populations stayed consistant.

Genetic studies revealed that benomyl resistance is controlled by a single gene.
Great variation has been found among the resistant isolates.
Four levels of resistance were distinguished and designated as Ben^LR, Ben^MR, Ben^HR, and Ben^VHR according to their growth on media containing, 0, 0.5, 5 and 50 ug/ml benomyl.
The negatively correlated cross-resistance (NCCR) to diethofencarb (NPC) of Ben^VHR confirmed that Ben^HR and Ben^VHR are differed alleles.
The benomyl resistance level is governed by five allelic mutations at a single locus.

V International Symposium on Pear Growing

E. Shabi

https://doi.org/10.17660/ActaHortic.1989.256.23