CROP SCIENCE ▶▶▶


of a variety and its sources of resistance, then try not to grow those with similar traits in con- secutive rotations. “Initially, it’s likely that a grower won’t necessarily be able to grow a re- sistant variety in every rotation (for marketing reasons). So alternating resistant and non-re- sistant varieties in combination with other control methods will be vital. Another require- ment is growers willing to trial new varieties, and feed information back to breeders about how it responds on farm,” she adds. “This will help monitor for any potential break down of resistance or shift in populations.”


What is PCN resistance? To use varietal resistance to potato cyst nema- tode effectively, it is vital to understand how a variety will behave when planted into infested soil. To screen for PCN resistance, candidate va- rieties are inoculated with pure populations of PCN of known pathotype. Their multiplication is compared with the multiplication on the susceptible genotype (typically Desiree). The degree of multiplication (relative susceptibili- ty) is used to assign a resistance score on a 1-9 scale. For example, a score of 3 would mean that PCN multiplication would be 50% of the susceptible control, while a score of 4 would have 25%. A 1 means highly susceptible and will aid significant multiplication of PCN in the soil, a 4 has some useful resistance and can re- duce pest numbers, while a 9 is highly resist- ant and can dramatically reduce populations.


What about tolerance? There is considerable variation between pota- to varieties’ tolerance to PCN. This can be


Differences between varieties for resistance and tolerance to potato cyst nematodes


tolerance variety (resistance G. Pallida/G. rostochiensis*) very tolerant tolerant


moderate intolerant


Camel (9**/9**), Cara (2/9), Performer (8/4) and Royal (3/9)


Arsenal (9/6) Brook (2/9) Eurostar (9**/9**), Lanorma (5/9), Markies (2/9) and Marvel (5/8) Cabaret (2/9), Divaa (5/3), Harmony (4/4), Maris Piper (2/9), Rock (9**/9**) and Rooster (2/2)


Estima (2/2), Innovator (8/2), Maris Peer (2/2), Nadine (3/9), Panther (8/2), Pentland Dell (2/2), Ramos (4/8) and Sante (4/9)


* resistance on a scale of 1-9, with 9 being most resistant. ** based on breeder data only – treat with caution Resistance rating source: AHDB.


An important requirement for a succesfull introduction of double resistance, is growers willing to trial new varieties, and feed information back to breeders about how it responds on farm.


defined as the ability to produce a similar yield compared with a PCN-free soil. Independent data on varietal tolerance is limited, so the in- dustry relies on breeder and anecdotal


evidence to predict how a variety might per- form in the presence of PCN. A variety can have both resistance and tolerance, one or the other, or neither (see table).


Consider before planting PCN resistant varieties


• Globodera pallida populations are geneti- cally diverse and plant resistance to the species polygenic, so a variety’s resistance performance is likely to vary depending on the pathotypes of the nematodes present in the soil.


• High resistance to G. rostochiensis (Ro1) is more reliable. Other species pathotypes do exist in Europe, but not in the UK so far.


• A thorough soil-sampling regime to es tab- lish pest numbers and species is advisable to target the right varieties in the right place.


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• Although varieties with strong resistance are available, don’t rule out those with par- tial resistance. Those can be very useful in preventing multiplication in low Pi (initial population) situations, when combined with a nematicide.


• Tolerance can be influenced by many fac- tors including soil type, planting date, seed size and depth and nutrient availability. This is particularly true in high pH soils, where phosphorus uptake drops and re- duces tolerance.


▶ FUTURE FARMING | 22 February 2019


• Where PCN is a problem, avoid anything that delays crop development, particularly herbicide damage and diseases such as rhizoctonia. Such factors can reduce plant tolerance to the pest.


• PCN reduces green leaf area, so varieties with large haulms are preferred where weed burden is high for maximum crop- weed competition.


• Note that PCN damage can be exacerbated where verticillium wilt is present.


PHOTO: PENN COMMUNICATIE


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