- Marketable
yield: Up to 1990 the
marketable grades were 40 to 80 mm but since 1991 they have been 45 to 85 mm. Yields are presented as
percentages of the yields of the control varieties, Pentland Dell for maincrop and second early varieties
and Home Guard for first early varieties. For maincrop and second early varieties, mean yields are presented
from two trials per year conducted in Northern Ireland over a minimum of three years. For first early
varieties yields at an early lift, normally mid-end June, are presented in the tables together with
yields at maturity.
- Tuber number
and size: Varieties producing a large number of tubers will have a high figure on a 1-9
scale,
each point on the scale being an increment of 50,000 tubers/ha giving an increase from 200,000 tubers/ha
for 2 to 500,000 tubers/ha for 8 on the scale. Varieties with greater proportions of their marketable
yields in the 65 - 85 mm grade (60 - 80 mm pre-1991) compared with the 45 - 65 mm grade (40 - 60 mm
pre-1991) will have high figures on a 1-9 scale.
- Defects
and
damage: Low production of defects, namely cracked, green, mechanically damaged during handling
at harvest, misshapen, slug or wireworm damaged tubers, is indicated by a high figure on a 1-9 scale.
Varieties with good resistance to damage as assessed in controlled tests will have a high figure on
a 1-9 scale.
- Foliage maturity: Varieties
whose foliage
matures and senesces early are given a high figure on a 1-9 scale.
Consumer
quality
- Dry matter: Dry matter is presented
as a percentage figure.
- Freedom
from disintegration: Varieties which disintegrate when cooked will have a high figure on a 1-9
scale.
- Mealiness: Varieties which are mealy when cooked
will have a high figure on a 1-9 scale.
- Cooked flesh colour:
When cooked, flesh colour is described as white (W), cream (C), light yellow (LY) or yellow (Y).
- Freedom
from after-cooking blackening: Varieties which show little tendency to blacken after cooking
will have a high figure on a 1-9 scale.
- Freedom from enzymic
browning: Varieties in which a brown colour does not develop on the surface of peeled potatoes
before cooking will have a high figure on a 1-9 scale.
- Crisp
colour: Varieties which have a light colour after crisping will have a high figure on a 1-9 scale.
Diseases
and pests
Good resistance to disease, including viruses, is indicated
by a high figure
on a 1-9 scale. For some varieties, resistance to dry rot has been determined separately for Fusarium
coeruleum (F.c.) and Fusarium sambucinum (F.s.). Resistances to potato cyst
eelworm, Globodera rostochiensis and Globodera pallida,
are usually presented as S (susceptible), PR (partially resistant) and R (resistant) but, more recently,
a numerical 1-9 scale has been introduced for new varieties similar to that for fungal and viral diseases.
This information on diseases and pests mainly summarises results of tests conducted during the two preliminary
years of evaluation for National List purposes in the United Kingdom. Resistance scores on some varieties
have been based on tests conducted by the National Institute of Agricultural Botany, Cambridge.
