Results are reported of late blight resistance in S. tuberosum ssp. an
digena (adg) and its use in breeding. Tests were carried out on materi
al of the gene bank in Gross Lusewitz (GLKS). Seedlings were cultivate
d under glass cover in a 6-years test period. To examine tuber resista
nce to Phytophthora infestans the following test was set up: 2-5 tuber
s per idiotype, up to 8 idiotypes per accession and year of test were
taken and 1274 different accessions were examined with an average numb
er of 23 idiotypes and 59 tubers from each. Inoculation was made by fr
esh deep cuts to the pith and by subsequent immersion in a solution of
zoospores, 6-9 x 10(4) ml-1 with a mixture of the pathotypes (1.2.3.4
.5.7.10.11, 1.2.3.4.7.8.10 and 1.2.3.4) at a temperature of 16-18-degr
ees-C and at an air humidity of >90%. Evaluation of the presence of ae
rial mycelium and browning after 7 days allowed the calculation of a r
esistance score (B(K)): grade 9 (highly resistant) to grade 1 (highly
susceptible). The mean values derived from the accessions (Fig. 1) rev
ealed that a medium level of susceptibility is dominating and that the
y rarely exceed average levels of cultivars. Approximately 1% of the a
ccessions contained greater-than-or-equal-to 25% of idiotypes with B(K
) greater-than-or-equal-to 6 and these may be interesting for breeding
purposes. Table 1 shows the analysis of accessions with the most favo
urable mean values. Geographic evaluation did not yield indications fo
r a more purposeful search for. sources of resistance, since detailed
reports on find-spots were missing (Table 2). Combination tests with P
hytophthora-resistant genes of adg for crosses of adg with S. demissum
(dms) and S. stoloniferum (sto) proved to be more useful as they part
ly showed good heritable resistance to haulm and tuber infection of P.
infestans (Table 3). The problem of the possible role of unknown r-ge
nes is discussed. Only a few crosses with ssp. tuberosum (tbr) generat
ed a progeny with sufficient resistance. Selection from such progeny o
ver several years resulted after the second year in rejections, mainly
because of susceptibility for viruses, too small tubers and lack of f
lowering (Table 4). Results of varietal research of the former German
Democratic Republic proved that with the use of suitable parents in br
eeding for nematode resistance, Phytophthora susceptibility from adg c
ould be balanced off (Table 5). The cultivar Auralia is a good example
of the importance of adg in achieving a high level of resistance to l
ate blight.