Chronica - Acta Horticulturae

Pepper seed production.
bacterium tumefaciens that resulted in the
creation of transformed tomato lines with heavy
metal tolerance. At the Virus Immunity
Laboratory, the most promising lines with high
biological value are tested for Tomato mosaic
virus (ToMV) and Cucumber mosaic virus (CMV)
resistance. A large part of the tomato breeding
materials for fresh consumption and processing
are assessed for their chemico-technological
and sensory properties at the Vegetable Fruit
Quality and Processing Laboratories. The genetic
diversity of the exploited materials of tomato
is characterized and identified at the Molecular
Genetics Lab using molecular markers.
The aims of a joint program with the
Cytogenetics Laboratory are to incorporate a
male-sterile gene in valuable breeding lines and
cultivars as well as to investigate the expression
of dominance and recessiveness responsible for
fertility and sterility in hybrids and backcross
progenies. Incomplete dominance and lethality
were expressed in some of the homozygous
genotypes. To prevent flower abortion in winter
and early spring, some substances that influence
earliness and yield were licensed from the
Physiology Laboratory.
A comprehensive system of soil and substrate
analysis was elaborated at the Plant Nutrition
Laboratory in order to diagnose soil and substrates
nutrient status. Monitoring nutrient needs of
tomato grown as soil and soil-less culture is carried
out in order to recommend the optimal
norms for fertilization. Relationships are established
between the nutrient levels and the quality of
the production. In collaboration with the Plant
Protection Unit the impact of vesicular mycorrhizae
(VAM) fungi is being investigated on the
growth, development, and productivity of tomato
as well as the use of biological agents against
soil-borne pathogens and root-knot nematodes
as an alternative to methyl bromide as a treatment
for soil disinfection in greenhouses.
Biomethods are being improved by searching
for new biological agents. Several entomopathogenic
fungi (Aschersonia sp., Verticillium
lecanii), parasites (Encarsia formosa, Aphidius
matricariae, A. ervi) and predators (Phytoseiulus
persimilis, Macrolophus costalis, M. nubilis, and
Amblyseius sp., Orius niger) are used as bioregulators
to ameliorate the density of economically
important pests on tomato: Trialeurodes
vaporariorum, Myzus persicae, Aphis nasturtii,
A. gossypii, Thrips tabaci, and Frankliniella occidentalis.
The antagonistic activity of Trichoderma
sp., Gliocladium and Enterobacter cloaceae
is investigated. Procedures are elaborated
for control of soil-borne and aerogenic fungal
pathogens.
Pepper Program
In the course of over 70 years, a great diversity
of genetic materials has been created and maintained,
mainly based on unique local forms,
typical for the region of Bulgaria. They were
improved by the methods of conventional breeding.
Some of these local cultivars, due to their
valuable characteristics, are still in production
and are also initial materials for creation of new
cultivars, responding to contemporary requirements.
At present, the pepper breeding team
disposes with a valuable collection of over 500
local and introduced accessions.
Contemporary breeding program is focused on
the creation of green and red fruited types as
well as pepper for grinding (paprika). The breeding
program for “green pepper” and “red
pepper” emphasizes the creation of lines and
cultivars with high biological value (mainly on
ascorbic acid content, over 120 mg per 100 g
for green and over 200 mg for red) as well as on
good sensory properties. The desired characteristics
for fresh consumption are crispness, succulence,
freshness and non-pungency and for
processing (for baked, canned, and for juices)
are easy peeling, fleshy pericarp and intensive
red color. Attention is paid also to variable
nuances of green (light yellow to dark green)
and red (light orange to dark red) colors and to
various shapes: oblate, edged, bell, blocky, conical
tapered, kapia, and slender type.
The objectives of the paprika breeding program
is earliness and uniformity in ripeness as well as
enhancement of quality and quantity of total
pigments and their long storage. Red pepper
lines with over 300 ASTA units are now established.
One of the breeding directions is to
search or create forms with stable pigment content
after frost.
At the Plant Tissue Culture Laboratory, procedures
are optimised for obtaining haploids in anther
culture, derived from local cultivars of
Capsicum annuum. These procedures will be
used for species conservation, maintenance,
and creation of homozygous lines. Also effective
procedures for micropropagation, callusogenesis,
organogenesis, and regeneration of valuable
forms, lines, cultivars and F1 hybrids are
developed.
The investigations at the Virus Immunity
Laboratory are focused on strain variability of
the most spread viruses on pepper in Bulgaria:
Tobacco mosaic virus (TMV) and Cucumber
mosaic virus (CMV). Recently Pepper mild
mottle virus (PMMV) and Eggplant mottle dwarf
virus (EMDV) were discovered in greenhouse
pepper during a collaborative programme with
the Plant Virology Institute in Torino, Italy. One
of the aims of the team is to introduce TMV
resistance in several traditional pepper cultivars.
Breeding lines and hybrids have been created,
resistant to Verticillium dahliae and Phytophthora
capsici, thanks to a joint programme
with Plant Protection Unit. An important aim of
the breeding team is to create male sterile analogues
of the most spread commercial pepper
cultivars in order to be used in a hybrid programme.
The requirements of new pepper cultivars
to environmental factors are investigated
with the Agrotechnology Unit in order to assess
their suitability for different growing regions.
Cucumber Program
The cucumber breeding program deals with all
types of cucumber species such as long
European type, American slicers, mini and
pickling cucumbers. A great number of F1
hybrids of top performance have been created,
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