Can varietal resistance to blight be useful in potatoes?

UK - May 06, 2005

Unlike cereals where disease sensitivity rankings are significant, potato disease rankings play little part in the selection of varieties or in the fight against blight.  But some interesting trials indicate that growers can usefully employ this information to prioritise their spraying regimes and to plan a more robust blight programme, according to Dow AgroSciences.

"When choosing a potato variety, the key to selection has to be closely linked with the end market and the customers' specifications.  Secondary to this comes agronomic features together with the quality defects or diseases that are most troublesome for the farms' particular growing conditions, husbandry and storage facilities.  Growers do not appear to consider blight disease ratings high in their list of key varietal features.  But some interesting field work last year hints that different varieties do demonstrate their intrinsic blight resistance and that these differences could be exploited to prioritise which field to spray first, particularly if the weather has delayed application and interfered with planned spray intervals.  This information should not be used to cut back on fungicides on the more resistant varieties but to indicate where a more robust approach is needed," explains John Sellars, Marketing Specialist for Dow AgroSciences.

The trials looked at eight different potato varieties, representing different types, different market outlets and different sensitivity ratings for foliage and tuber blight.  The varieties in the trial were Estima, Hermes, King Edward, Maris Peer, Maris Piper, Pentland Dell, Russet Burbank and Saturna.  All need to be protected from blight as both yield and quality are paramount, whatever market you are going for," says Mr Sellars.     

"Disease progression in the crop of Pentland Dell, which has a rating of 6 for foliage blight in the 1-9 rating scheme, was the slowest and least severe of all the varieties tested.  Foliar blight developed much more slowly and green leaf was maintained for longer.  The next best response at slowing disease progression was seen in crops of Maris Peer and Estima, which have blight ratings of 4.  The varieties with the lowest rating for foliage blight, Russet Burbank and King Edward (with only a 3 rating) showed they were the most sensitive in the trials and the least effective at preventing blight development." 

"With potato blight being such a devastating disease, causing severe loss of yields and quality, it is important that the crop is protected throughout its growing period.  There are no commercially available potato varieties that offer complete resistance, but foliar blight could be controlled more effectively by a robust spray programme applied at shorter spray intervals on varieties that are more susceptible to foliar blight.  Independent trials indicate that the most effective fungicide programme starts early with one or two systemic or curative treatments or a strong protectant such as Dithane NT, followed by Electis (zoxium and mancozeb) alternating with Ranman TP (cyazofamid plus adjuvant) from early main canopy right up until desiccation.  Straight cymoxanil could be added as necessary for kickback activity.  Foliage blight resistance is not always related to tuber blight resistance, but a robust fungicide programme incorporating products with known zoospore activity, such as Electis and Ranman, will give high levels of control of both foliar and tuber blight in all varieties," concludes John.