The expert consultation on the use of crop wild relatives for pre-breeding in potato was a workshop organized by the Global Crop Diversity Trust in collaboration with CIP and took place from the 22nd – 24th of February 2012.

1. Reproductive behavior and germplasm classification
of wild potato populations: relevance in germplasm
conservation and breeding
Elsa L. Camadro
Laboratorio de Genética
Instituto Nacional de Tecnología Agropecuaria
Universidad Nacional de Mar del Plata
Consejo Nacional de Investigaciones Científicas y Técnicas
Argentina

2. Premises of the presentation
The knowledge of the reproductive biology of wild potatoes
and its consequences in the functioning of natural populations
is of utmost importance to understand the morphological and
molecular variability encountered in the group
The choice of genetic materials and methodological approches
used to classify wild germplasm has direct consequences in:
population sampling
ex situ conservation of germplasm (gene frequencies)
breeding

3. Plant classifications in the XXth and XXIth centuries
Artificial binomial system developed
by von Linneus in the XVIIIth
based in the use of “holotypes”
(single physical examples or illustrations of organisms known
to have been used when the species or lower-ranked taxon
were formally described)
with the more recent aid of biochemical and molecular tools

4. Species Concept
based on
reproductive relations morphological phenotypes
and morphological discontinuities (uni- and biparental organisms)
(biparental organisms)
Biological species Taxonomic species
The Biological species can coincide (or not) with the Taxonomic species
If the two uses of the term are not distinguished,
the confusion is perpetuated

5. Genus Solanum
~1,000-2,000 species
(herbs or shrubs)
≥110 ≤235 wild and
cultivated tuber-
bearing species
Section Petota (Tuberarium)
Subsection Potatoe (Hyperbasarthrum)
Spooner y Hijmans 2001

6. Species concept in subsection
Hyperbasarthrum (actually Potatoe)
Early XXth century
Narrow taxonomic unit, with little phenotypic variability
(Bitter, Juzepczuk, Bukasov)
Mid XXth century
Profound revision of tuber-bearing species due
to great phenotypic variability encountered
(Hawkes 1963)
Late XXth and early XXIth centuries
New revisions (Hawkes 1990; Spooner´s group)

7. Taxonomic revisions
(last 20 years)
Mainly based on:
Herbarium materials and samples of living plantas,
with more recent application of molecular tools to
accessions with previously assigned specific categories
No. of tuber-bearing species:
Hawkes (1990): 227
Spooner and Hijmans (2001): 203
Spooner and Salas (2006): 189
Spooner (2009): converging around 110

8. Main features of wild and cultivated potatoes
Form polyploid series
(2n=2x, 3x, 4x, 5x, 6x; x=12)
Can reproduce:
•sexually (by seeds)
•asexually (by stolons and tubers)

9. Posses one multiallelic S-locus conferring
gametophytic SI
diploids obligate outcrossers
polyploids -allogamous (can self-pollinate by
competitive S-alleles interaction)
-autogamous (self-pollinate)
S7 S1 S2
S4
1st Third
S1 S2 S1 S2
Self-compatible Self-incompatible

10. -continues-
Present scarce genome differentiation
All species share a common genome (A),
and four derived genomes (B, C, D, E)
Under genetic control, can produce:
•2n pollen and/or 2n eggs
Gametophytes with sporophytic chromosome numbers
•Haploids
Sporophytes with gametophytic chromosome numbers
In nature, are isolated by external and/or
internal hybridization barriers
The internal barriers are genetically controlled
and can be incomplete
Camadro et al. 2004

11. General Observations
The breeding system provides for:
 maintenance of superior genotypes in stable environments
 evolution of new genotypic combinations in changing
environments
 overlapping of generations (parental, hybrids, BCs)
 The morphological phenotypic differences among taxa
are not of great magnitude
Hybridization and gene flow within and between
ploidy levels and generations produce very complex
patterns of morphological variation

12. Potato accessions
Samples of natural populations ex situ conserved as:
original collections or multiplications of original collections
Purposes
Conservation of samples of natural variability of a species
and of genes for breeding and other applied purposes
P1 P2 P3
xxxx xx x x x x x x
xxxx xx x x x x x x
xxxx x x x x x x x
x x x x x x
Passport information for potato accessions:
Collection date, locality, latitude, longitude and altitude a.s.l.

13. Information unavaible or lacking
In situ sampling
No. and spatial distribution of sampled plants at collection site
No. harvested fruits or tubers/sampled plant
No. sampled plants/population
How the seed sample (accession) is formed
If seedlings are sampled, their spatial distribution
Are accessions representative samples of
the natural genetic variability at the sampling site?
Ex situ seed/tuber multiplication
Effective no. of parental plants
No. harvested fruits or tubers/plant
No. harvested seeds/fruit
How the seed sample (accession) is formed
Discarding unwanted contamination/crossing
Has genetic drift being avoided?

14. Current classification approaches are based on
the Taxonomic species concept
not taken into consideration:
Natural populations of sexual reproducing allogamous plants
are expected to exhibit morphological and genetic variation
(one plant=one genotype)
Morphological and genetic variation can occur within and
between populations of the same taxonomic species
Natural populations can consist of uni- and biparental plants,
with overlapping of generations
Breeding relations within and among spontaneous populations
provide for hybridization and introgression among ploidy levels
and generations, creating complex patterns of variation

15. Camadro et al. 2012

16. Pre-zygotic hybridization barriers

17. Prevention of fertilization due to abnormalities in
Pollen tube growth
Pollen germination
Estigma
1/3
1st Third 1er Tercio
2do2/3
Tercio
3 3/3
er
Tercio
ovary
Gametophytic SI Cross Incompatibility
Bilateral (CI)
Unilateral or Bilateral
Camadro y Peloquin 1981

18. Compatible Incompatible

19. Post-zygotic barriers

20. Inviability of embryo and/or endosperm in the
F1 hybrid seed due to abnormal embryo and/or
endosperm development/abortion
Hybrid sterility (principally male sterility)
Inviability or weakness of F2 and advanced
segregating generations
Camadro et al. 2004

21. Inviability of F1 hybrid seed
endosperm Genetic causes
(EBN)
Abortion
Endosperm abortion
embryo
Genetic causes
(cannot be circumvented)

22. 2x 1NBE cmm x 2x 1NBE cmm, 15 DDP 4x 2NBE acl x 2x 1NBE cmm, 9 DDP
2x 2NBE grl x 4x 4NBE grl, 9 DDP 4x 2NBE acl x 2x 2NBE grl, 11DDP
Masuelli y Camadro (1997)

23. Hybrid Male Sterility

24. Male sterility and cytological abnormalities
Interspecific artificial hybrids
Diploids: S. tuberosum (tbr) x S. chacoense (chc),
tbr x S.gourlayi (grl),
tbr x S. spegazzinii (spg)
(Santini et al. 2000)
Tetraploids: grl x tbr and tbr x grl
(Larrosa et al. 2005)
Spontaneous hybrids
grl-S. infundibuliforme
(Larrosa et al. 2005)

25. Species of hybrid origin
 S. ruiz-lealli
(Raimondi et al. 2000; Marfil et al. 2009)
“Species”
S. okadae
(Camadro et al. 2007; Bottini et al. 2008)
S. chacoense
(Bottini et al. 2009; Larrosa et al. 2010;
Poulsen et al. 2011)

26. “tetrad” type sterility
tbr x grl tbr x chc
Interspecific 2x (artificial) F1 hybrids
Santini et al. (2000)

27. N
S. x ruiz-lealli
2x species of hybrid origin)
E E
Raimondi et al. 2005

28. Erazzú and Camadro 2008

29. polen
Fertile and sterile pollen in spontaneous and artificial hybrids and
populations with specific category
Larrosa et al. 2010

30. Tetrad stage in spontaneous and artificial hybrids
and populations with specific category
Larrosa et al. 2010

31. P MI MII AI
MII AI AII MII
AII AII TI TII
Meiosis in spontaneous and artificial hybrids
and populations with specific category
Larrosa et al. 2010

32. Bolivia Argentina
a b
a
S. okadae (2x)
Accessions from Germplasm Potato Bank,
INTA, Argentina
Argentina Camadro et al. 2007

33. S. kurtzianum (2x)
OKA 872 OKA 5026 OKA 6003
OKA 6144 OKA 4505 OKA 6125
Accessions from Germplasm Potato Bank, INTA, Argentina
Bedogni & Camadro 2009

34. Evaluation of morphological characters
(quanti- and qualitative) and molecular markers (SSR)
Accessions from:
 S. kurtzianum, Catamarca, La Rioja and
Mendoza
Sympatric “species”:
•S. chacoense (chc),
•S. spegazzinii (spg)
“outliers”
•S. oplocense (opl) y S. maglia (mag)
Genetic distances among sympatric accessions
with different specific statuts
was smaller than among allopatric accessions
with the same specific status
Bedogni & Camadro 2009

35. Accessions of S. kurtzianum (ktz) S. chacoense (chc), S.
spegazzinii (spg), S. maglia (mag) and S. oplocense (opl)
opl
C OKA 6147
C OL 4943
C OKA 6144
M SCl 4505
R OKA 6003
R OKA 6125
M ClM 872
C OKA 6141
C OKA 5026
M mag
R OKA 6113
C OKA 6107
0.00 0.22 0.45 0.67 0.90
SM Coefficient
 = chc  = ktz  = spg
C=Catamarca, M=Mendoza, R=La Rioja
Nuclear SSR markers
Bedogni & Camadro 2009

36. UPGMA phenogram of accessions of S. kurtzianum (ktz),
S. chacoense (chc), S. spegazzinii (spg), S. maglia (mag) and
S. tuberosum ssp. tuberosum (tbr)
M ClM 872
M mag
M SCl 4505
R OKA 6125
C OKA 6144
R OKA 6003
R OKA 6113
tbr
C OKA 6147
C OKA 6107
C OKA 6141
C OL 4943
C OKA 5026
0.00 1.60 3.21 4.81 6.42
Euclidean Distance Coefficient
 = chc  = ktz  = spg
C=Catamarca , M= Mendoza, R= La Rioja
Morphological Qualitative Traits
Bedogni & Camadro 2009

37. UPGMA phenogram of accesssions of S. kurtzianum (ktz),
S. chacoense (chc), S. spegazzinii (spg), S. maglia (mag) and
S. tuberosum ssp. tuberosum (tbr)
tbr
C OKA 6107
C OKA 6147
M mag
R OKA 6003
C OKA 5026
C OL 4943
M SCl 4505
C OKA 6144
R OKA 6113
R OKA 6125
M ClM 872
C OKA 6141
0.00 2.02 4.05 6.07 8.09
Euclidian Distance Coefficient
Morphological Quantitative Traits
Caracteres Morfológicos Cuantitativos
Bedogni & Camadro 2009

38. To fully exploit in breeding the genetic variability
of the wild potato germplasm
Screen various accessions (if available),
(particularly if the “species” has wide geographic or environmental distribution)
Take into consideration:
macro- and micro-environments of the originally sampled sites
type of original samples (botanical seed, seedlings, tubers)
Screen 15-25 plants/accession for allogamous “species”
(one plant= one genotype) and ≥10 plants for autogamous “species”
(there could be homozygosity for different gene combinations)
Use incomplete diallele crossing designs
(keeping tract of individual genotypic combinations. Breeding barriers
can be incomplete, hybrids are very frequent and there are
nuclear-cytoplasmic interactions)
Conclude with respect to a given accession, not a species
(do not extrapolate results).

39. Thank you

40. Gametofitos
Gametos ♂
polinización
Polen germinando
Situaciones
estructurales Óvulo maduro
y fisiológicas
Fecundación
Gameto ♀
Formación
Semillas viables Saco embrionario