The objectives to investigate the relationship between elevated ammonium and glutamine levels in grape leaves exhibiting Pinot Leaf Curl and to compare the levels of putrescine in symptomatic and asymptomatic leaves were completed. Ammonium and glutamine varied widely among leaf samples and in many instances leaves with symptoms showed elevated levels of these metabolites compared to leaves without symptoms. However, examples where the levels of glutamine and ammonia were nearly equal were found and in some cases symptom leaves actually exhibited lower levels of these compounds than non-symptom leaves.
While the levels of ammonia and glutamine are certainly of interest in assessing the nitrogen status of grapevine leaves, they do not show promise as markers or indicators of Pinot Leaf Curl. On the other hand, the diamine putrescine (1,4-diaminobutane) was found to be elevated in 12 of 14 cases studied in this project, and in the other two the levels were the same in symptom and non-symptom leaves. Therefore, unlike glutamine and ammonia, no examples were found where putrescine was higher in non-symptom leaves than in symptom leaves.
Since putrescine has been implicated as a toxic metabolite leading to leaf chlorosis and necrosis in potassium deficiency and Spring Fever this research suggests the possibility that it also plays a role in Pinot Leaf Curl. However, given the range of putrescine observed in symptom and non-symptom leaves from various Pinot varieties and clones from different sites, its presence remains correlative relative to symptoms and a causal role remains to be established.
The success of this research lies in the fact that prior to this study we had only anecdotal evidence that Pinot Leaf Curl is a nitrogen-related disorder. The differences seen in all of the nitrogen metabolites studied in this project, especially putrescine, give some support to that idea and may suggest management practices that could be tried in an attempt to ameliorate the disorder.