APHID TOLERANCE OF DIFFERENT HOP GENOTYPES: FIRST ATTEMPTS TO DEVELOP A SIMPLE BIOTEST FOR HOP BREEDING BY THE USE OF PHORODON HUMULI

Abstract

A keystone of future pest management in hops is the breeding of cultivars (cvs.) that are tolerant or resistant to Phorodon humuli infestation. During 2006 and 2007 first attempts were made for the development of a biotest concerning the aphid susceptibility of different hop genotypes. We chose for these tests the susceptible cvs. 'Hallertauer Magnum' (HM) and 'Herkules' (HS), the aphid-tolerant or -resistant cvs. 'Spalter Select' (SE) and 'Boadicea' (BO), and two apparently resistant genotypes from our germplasm - the male accession 38 and the wild hop Jena 49. Aphid cages were mounted to leaves taken from potted greenhouse plants of these six genotypes, and each cage was equipped with an aphid larva with known day of birth. The leaves (12 replications per genotype) were stored in a climate chamber, and the 72 cages opened three times a week to count and remove all newborn larvae. The mother aphids stayed in their cages until the death of the last aphid marked the end of a series. Altogether eight series were conducted. The cumulative alive offspring of one aphid was highest on HM, with an overall mean number of 66.2 larvae, and lowest on 38, with 14.9 larvae. However, overall means of the other cvs. were not significantly lower - 59.7 on HS, 59.6 on SE and 57.6 on BO. The maximum number of larvae produced by one aphid was 115 on HM. The lifespan of the aphids was longest on HM, with an overall mean of 39.8 days, and shortest on 38, with 24.4 days. The other genotypes produced similar lifespans from 31.7 to 34.3 days. The record holder survived on HM for 69 days. These results, especially concerning the aphid-tolerant cvs. BO and SE, demonstrate that for the development of a practical, simple aphid biotest there is still a long way to go.