Preservation of the urediniospores of Phakopsora euvitis, the causal agent of grape leaf rust

Abstract

Grape leaf rust, caused by Phakopsora euvitis, is an important disease causing considerable damage to vineyards in tropical regions. This study compared different temperatures and dormancy-reversion procedures for the preservation of P. euvitis urediniospores. Urediniospores from inoculated Vitis labrusca cv. Niagara Rosada vine leaves were collected, dehydrated, and compared with non-dehydrated leaves. Both groups of urediniospores were stored at −80 °C, −20 °C, 5 °C, and 25 °C. Urediniospore viability was evaluated by in vitro germination, whereas the severity of grape leaf rust was assessed by inoculation on leaves of ‘Niagara Rosada’ potted plants, performed immediately prior to storage and after 15, 30, 60, 90, 120 and 150 days. The viability of non-dehydrated urediniospores stored at 25 °C was low, while dehydrated urediniospores retained viability up to day 30. Dehydrated urediniospores stored at −80 °C had the best viability values during the 150-day experimental period. Independently of storage conditions, urediniospores germinated in vitro induced symptoms of disease in vine leaves. The severity of the disease had a strong positive correlation with the percentage of preserved urediniospores that germinated (r = 0.88). Combining dehydration and storage at low temperatures is essential to maintain the viability of urediniospores for at least 150 days.