Relationship Between Growth, Secondary Metabolism, and Resistance of Apple

Abstract

The paper shows that N‐induced vigorous shoot growth increases susceptibility of apple trees to Venturia inaequalis. This is due to a weakened defence in infected leaves of the high N cultures showing large lesions with excessive sporulation, whereas infected leaves from the low N cultures exhibited successful defence with only small chlorotic lesions and no sporulation. This might be explained by biosynthesis of phenylpropanoids in the young leaves of the resistant trees. A negative correlation between shoot growth of apple trees and the concentration of phenolic compounds in young leaves was found. Studies on in vitro shoot cultures revealed that the availability of sugars for the phenylpropanoid pathway is a strong regulatory factor. The ratio of sucrose and nitrogen in the medium influenced the total level of secondary products in the in vitro grown plantlets. Moreover, the relative deficiency of sugars was responsible for a metabolic block mainly at the level of glucosyl transferase and concomitant aglycone accumulation.

Differential gene expression in leaves of a scab susceptible and a resistant apple cultivar upon Venturia inaequalis inoculation

“…In contrast, the susceptible cultivar Golden Delicious expressed a thaumatin-like clone upon V. inaequalis infection which goes in line with the results on the protein level observed by Gau et al (2004). In addition, the pathogen-induced up-regulation of a F3'5'H gene which is assumed to be responsible for 3 0 -hydroxylation of flavonoids in Golden Delicious fits in the accumulation of catechins often observed in infected apple leaves (Mayr et al 1997;Leser and Treutter 2005;Treutter and Feucht 1990;Picinelli et al 1995;Rühmann et al 2002). These results give new insights into the response of apples, which are resistant or susceptible to the scab fungus and may help to understand mechanisms of basal defence and cultivar-specific resistance.…”

Significance of flavonoids in plant resistance: a review

“…It was further shown that the inhibition of the enzyme phenylalanine-ammonia-lyase led to severe scab symptoms on the leaves of a resistant cultivar (Mayr et al 1997). Environmental conditions (N-fertilisation) favouring the growth of apple trees inhibited their flavonoid biosynthesis and increased the susceptibility to pathogen (Rühmann et al 2002;Rühmann and Treutter 2003;Leser and Treutter 2005). A transient inhibition of the flavanone 3-hydroxylase (FHT) in apple leaves by a treatment with the dioxygenase inhibitor Prohexadione-Ca r induced several changes in their flavonoid composition.…”

Phenolic compounds of apple cultivars resistant or susceptible toVenturia inaequalis

“…For this reason, the development of scab-resistant varieties appears as the best means of control. It is known that many plants species are resistant to certain diseases naturally (Rühmann et al, 2002). The resistance genes of resistant apple genotypes possibly act as regulatory genes of phenol synthesis (Michalek et al, 1999).…”