5 September 1997

RESISTANT BEET ON HORIZON

SUGAR beet which resist beet cyst nematode attack are fast approaching commercial availability. Once on the market they could allow tighter rotations and cropping of formerly infested land.

Three such varieties are already on the official variety list in France. Further lines for the UK are expected soon.

Evasion, Nemakill and Mercure are the first fruits of a programme run by breeder Hilleshog, now operating as Novartis Seeds.

Beet cyst nematode (Hetero-dera schachtii) is found in almost all beet-growing areas, but is particularly frequent where beet or other host crops have been grown for long periods, often in close rotation.

Symptoms are usually first noticed when patches of stunted plants appear and wilt before those in the surrounding less infested area. Infested plants have small tap roots, with many laterals, on which the nematodes can be seen as small, white cysts.

The pest occurs when host crops, which include all brassicas and beet species, are grown too close together. A three-year rotation is the minimum required, but five years is preferable, particularly on light mineral or organic soils.

Once infection strikes profitable beet production is impossible at anything less than once in eight years.

Novartis Seeds believes it can help growers combat the problem by using varieties which have had genetic resistance to the pest added from wild beet species.

Resistance is based on a hypersensitivity reaction in which the larva within the root becomes surrounded by necrotic tissue so it cannot complete its life cycle.

At Novartis Seeds breeding facility in Landskrona, Sweden, molecular markers have been identified which are linked to the nematode resistance gene. This has eased screening.

Samples are taken from very young plants, four to six weeks old. A quick molecular test is run in the lab and the results analysed the same day. The lab can use this method to analyse up to 10,000 samples per week. This has accelerated breeding, leading to the faster introduction of resistant varieties.

The first two experimental varieties, HM 1091 and HM 1092, were tested by Comite Technique Permanent de la Selection (CTPS) in France in 1992. The small number of cysts on the roots indicated very high resistance.

In 1993 and 1994 improved versions of the two varieties were tested by CTPS. Analysis of soil samples taken at harvest indicated a decrease of about 75% in the nematode population in comparison with the control variety, Carat, which showed an increase of 35% in the nematode population.

Further breeding work is under way to eliminate wild beet characters which affect juice purity and root characters, including multiple crown and tumour formation.n

Sugar beet growers could adopt more flexible rotations if new varieties from Novartis Seeds meet claims for cyst nematode resistance.

BEET NEMATODES

&#8226 Rotation problem on light mineral/organic soils in particular.

&#8226 Genetic resistance from wild beet could help.

&#8226 Trials of new varieties well under way.