Annals of the Academy of Romanian Scientists

Series on Agriculture, Silviculture and Veterinary Medicine

Volume 15, Number 1/2026

ISSN 2344-2085

30

THE MODERN CHALLENGES AND OPPORTUNITIES FOR

IMPROVING THE GENETIC DIVERSITY OF TOMATOES

Milania MAKOVEI¹

Abstract. This article designated modern climatic and genetic factors as causes of the

intensification of genetic erosion in tomatoes (Solanum lycopersicum L). The possibility

of expanding the genetic diversity of tomatoes through the use of mutant genes in

breeding that control a wide range of economically valuable traits is being considered.

The potential of mutant forms as a source of resistance to abiotic stress factors (high and

low temperatures, drought) for use in breeding as donors is demonstrated. A description

is provided of the phenotypic expression of mutant genes controlling plant habit and

architecture, which determine the expression of various fruit traits, including resistance to

the most common diseases. The possibility of using certain mutant genes to expand the

range of recombinational variability in F₂populations and to obtain transgressive tomato

forms with a completely new combination of mutant marker and economically valuable

traits is demonstrated.

Keywords: Tomato (Solanum lycopersicum L.), climatic and genetic factors, mutant

genes, selection, genetic diversity

DOI

10.56082/annalsarsciagr.2026.1.30

1. Introduction

The tomato (Solanum lycopersicum L.) is one of the most widely cultivated

vegetable crops in the world (approximately 5 million hectares) [1]. Its high share

in the structure of gross vegetable production in various countries is due to its

ecological adaptability and the nutritional value of its fruits, which contain sugars,

organic acids, mineral salts, vitamin C, carotenoids, lycopene, fats, carbohydrates,

fiber, and others [22]. These qualities facilitate its use in both fresh and processed

forms.

However, global and local climate change on the one hand, and one-sided

breeding aimed at creating high-yielding, uniform, transportable tomato varieties

and hybrids that better meet general standards on the other, have led to the

intensification of its genetic erosion. Farmers and larger producers have also

contributed to this in their pursuit of high yields, they have ceased to grow local

varieties with superior flavor, leading to their loss as carriers of valuable traits

1

Doctor Habilitatus in Biological Sciences, Associate Professor, Leading Researcher Milania

MAKOVEI, Moldova State University, Institute of Genetics, Physiology and Plant Protection, 60,

Alexei Mateevici str., MD 2009, Chisinau. Republic of Moldova. ORCID: 0009-0009-5039-6270

E-mail: makoveimilania@gmail.com

The Modern Challenges and Opportunities for

Improving the Genetic Diversity of Tomatoes

31

characteristic of the ecological niche of the Republic of Moldova. The rapid

evolution of pathogens and pests has also contributed to this. All these factors,

identified as modern challenges (Figure 1), led to a deficit in the genetic diversity

f the tomatoes cultivated gene pool, a decrease in the adaptability of modern

varieties and hybrids, and their vulnerability to biotic, abiotic, and other stress

factors, which ultimately affected crop yields and, in particular, their quality and,

especially, the quality of the produce.

Figure 1. Climatic and genetic factors increasing tomato erosion and opportunities to improve its

genetic diversity

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Milania Makovei

The increasing deficit of tomato genetic diversity indicates that the search for

opportunities to improve and expand it is becoming a strategic direction for

modern research. This requires a reorientation of fundamental research and

applied breeding toward the search for, identification of, and incorporation into

the breeding process of sources of new germplasm with higher genetic diversity.

These may include wild and semi-cultivated tomato varieties, landraces, as well as

hybrid populations artificially created with their participation.

Of particular interest in this regard are spontaneously occurring and artificially

induced mutations [22, 17, 19]. The availability of a large number of easily

identifiable tomato mutant marker genes it possible to address a wide and diverse

range of research questions. These include, first and foremost, genome mapping

[18]; localization of quantitative traits [3]; identification of the characteristics of

the heterosis effect [8]; study of recombinational variability in F₂-F₃hybrid

populations [9, 11, 16]; study of biochemical and physiological processes of plant

development [6, 18]; and others. There are examples of their effective use in

practical breeding to obtain new varieties with a beneficial combination of

economically valuable traits [9, 10, 16].

A comprehensive approach to evaluating and identifying sources of new

germplasm, combined with the use of classical breeding methods alongside

gametic technologies, can also contribute to improving the genetic diversity of the

tomato. According to Pfahler (1982), the male gametophyte of the tomato is more

sensitive to environmental conditions and changes than the female gametophyte,

which is covered by thick layers of somatic tissues [15]. This has been confirmed

in the works of other authors who use male gametophyte traits as criteria for

evaluating and selecting genotypes resistant to adverse environmental factors, not

only in tomatoes but also in other agricultural crops [4, 5, 12]. High sensitivity

and the presence of a large amount of pollen allow for the rapid testing of

extensive collections and the identification of genotypes resistant to one or several

stress factors at once [10].

Hybridization plays a key role in expanding genetic diversity as one of the most

important methods of classical breeding. It allows us to harness heredity as the

greatest force that drives morphological development. Interspecific and

intergeneric crosses are particularly effective in this regard, facilitating the

production of plant forms with entirely new combinations of valuable traits [22].

The combined use of classical breeding and pollen analysis methods allows for

working with large hybrid populations using a streamlined approach and

identifying genotypes that combine economically valuable traits with resistance to

various abiotic stress factors [10].

Farmers can also contribute to expanding the genetic diversity of tomatoes by

selecting, under production conditions, the most valuable varieties that are less

susceptible to current local challenges, differ in fruit characteristics, and possess

The Modern Challenges and Opportunities for

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33

high flavor qualities. Selection, conservation, and active cultivation of these

varieties represent one potential approach to enriching the gene pool of local

varieties with ecotypes capable of realizing their genetically determined

productivity potential under the conditions of the Republic of Moldova.

As we can see, there are quite a few opportunities to overcome the negative

impact of climatic and genetic factors on the intensification of tomato erosion.

Proper organization and their combined use will allow for the intensification of

the search, identification, and selection of the most valuable genotypes that

combine economically valuable traits with resistance to abiotic and biotic stress

factors, thereby contributing to the expansion of tomato genetic diversity.

The aim of the research was to comprehensively study the genetic potential of

mutant marker genes of tomato for their effective use in practical breeding,

improving varietal diversity and replenishing collections with genes controlling a

wide range of economically valuable traits

2. Materials and Methods

The experimental material consisted of 125 mutant tomato lines carrying 187 mutant

marker genes, more than 50% of which are of practical value for addressing current

challenges in practical breeding.

2.1. Phenotypic expression of mutant genes.

The nature of expression and the degree of phenotypic expression of the mutant genes

were determined in accordance with the tomato gene nomenclature [22, 20].

Studied the nature and characteristics of the expression of marker genes controlling

plant habit, architecture, and fruit traits (shape, color, taste).

2.2. Screening of mutant tomato lines for resistance to abiotic stress factors.

Testing for resistance to abiotic stress factors (high and low temperatures, drought) was

conducted based on male gametophyte (pollen) traits using artificially simulated stress

conditions in vitro [10]. Fresh pollen collected from the flowers of each mutant sample

served as a control, it was germinated on an artificial nutrient medium (15% sucrose

and 0.006% boric acid) under in vitro conditions (3 hours) at a temperature of 25°C.

Pollen viability-germination (p, %) and pollen tube length (l, µm) were determined.

Resistance to high (45°C) and low (6°C) temperatures, as well as drought (simulated by

high sucrose concentration), was assessed based on the ability of pollen from

experimental samples to germinate (pollen germination resistance), and the ability of

germinated grains to form pollen tubes (resistance based on tube length) of a length

sufficient for fertilization (three pollen grain diameters) [7] under the influence of these

stressors. For each sample and in each experimental treatment, 500 pollen grains were

evaluated in 3 replicates. Pollen preparations were examined under a microscope (Zeiss

model, 7×20). The resistance of each genotype was determined by the ratio of the

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Milania Makovei

indices of the studied pollen traits in the experimental variants (E) to the control (C),

expressed as a percentage (%).

2.3. The expression of morpho biological and economically valuable traits in

homozygous and heterozygous offspring.

The morphological, biological, and economically valuable traits, including yield and

fruit quality, were assessed in accordance with UPOV recommendations (Solanum

lycopersicum L.) [21] and standard methods [14]. Hybridization was carried out

according to schemes specifically developed by us. More than 50 F₁hybrid

combinations were obtained. The nature of expression and the degree of phenotypic

expression of traits controlled by mutant genes in the F₁and F₂progeny populations

were determined following the gene nomenclature [22]. Statistical analysis of the raw

data was performed using the computer software programs Excel and Statistica 7.

3. Results and Discussions

The success of breeding new tomato lines, varieties, and hybrids depends directly on

the availability of thoroughly studied donor plants with the desired traits in collections.

However, concepts for organizing such collections remain undeveloped, a situation

observed not only in local collections but also in global ones [23]. According to the

author, of the one million samples collected in global collections, less than 1% have

phenotypic characteristics. This creates enormous difficulties for breeders, as they must

repeatedly review large amounts of material in search of sources of the desired traits.

Consequently, a comprehensive study of available genetic resources not only for

immediate use but also for supplementing existing and creating new trait collections –

is a top priority. In this regard, we conducted an assessment of the genetic potential of

mutant tomato forms, aimed at identifying genes that control a wide range of traits at

different stages of ontogenesis, including resistance to abiotic and biotic stress factors,

for the subsequent expansion of existing and creation of new traits collections.

3.1. The potential of mutant tomato varieties for resistance to abiotic stress factors,

as determined by male gametophyte (pollen) characteristics.

Testing of an extensive collection of materials revealed significant heterogeneity among

mutant forms in terms of the level and type of pollen resistance to high and low

temperatures and drought.

First and foremost, marked differences were observed between genotypes within the

collection regarding indicators of traits characterizing the quality of freshly collected

pollen (control). Depending on their genotypic characteristics, the “viability-

germination” trait varied widely (from 1.5% to 78.2%). Regarding the ability of

germinated pollen grains to form pollen tubes of a certain length under in vitro

conditions, the variation among them was even greater (from 11 µm to 150 µm). This

The Modern Challenges and Opportunities for

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35

indicates that the same plant cultivation conditions had different effects on pollen

quality, highlighting the genotype-specific characteristics of each.

The differences between mutant forms were more pronounced in terms of their pollen’s

response to high and low temperatures and drought. Pollen response was inconsistent,

even within a single genotype, as measured by two different traits:

“pollen germination resistance” and “resistance to pollen tube length”. The genotype-

specific response of pollen to the effects of various factors, both individually and in

combination, allowed for their classification into groups based on the type and level of

resistance of each genotype to a specific stress factor (Figure 2).

Figure 2. Characteristics of mutant tomato forms by type and level of resistance to high and low

temperatures and drought

Twenty-two mutant forms were identified whose pollen germinated rapidly and with

high efficiency (54.6%–97.8%), while also forming long pollen tubes (58 µm–150 µm)

under the influence of all three negative factors. This indicates the high resilience of

their male gametes, which are capable of germinating and forming long pollen tubes

under conditions that significantly from optimal ones.

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Milania Makovei

In contrast, another group of mutant forms (26 genotypes) exhibited pollen that was

highly sensitive to all three stress factors. Both pollen germination rates and pollen tube

lengths were very low in this group, ranging from 0.4% to 9.7% and 1.0 µm to 20.4

µm, respectively. They were classified into the group of unstable genotypes (Figure 2).

The third, fourth, and fifth groups comprised mutant forms (28 genotypes) whose

pollen exhibited high resistance to only one of the stress factors studied, but was highly

sensitive to the other two. Conversely, mutant forms (Group 6) were identified whose

pollen germinated well, simultaneously forming very long pollen tubes under the

influence of high temperature and drought, but exhibited high sensitivity to the low-

temperature factor. A similar pollen response is also characteristic of the mutant forms

distributed in groups 7 and 8 (Figure 2).

This is undoubtedly a unique gene pool of particular value for use as a source of

resistance to abiotic stress factors in the male gametophyte during the breeding of new

tomato varieties and hybrids, as well as for expanding existing genetic collections and

establishing new trait-based genetic collections.

3.2. Genetic diversity of mutant genes that determine the growth habit and

architecture of tomato plants.

Plant habit is a key indicator for any variety or hybrid, determining its intended use and

agronomic suitability.

An evaluation and analysis of the potential of mutant forms based on the phenotypic

expression of genes affecting plant habit revealed a high degree of diversity, but only a

few of them have practical value.

This diversity is mainly related to plant size, which is controlled by the genes bls, d, dd,

dmp, dmd, sd, ssp, sp, sp⁺and sp^±. Morphological differences between them are

determined both by the intensity of lateral shoot formation (ls) and the degree of their

branching (atn, bu, br, cg, bip).

A special group within the collection consists of forms with mutant genes ssp, br, com,

sd, d, dd and bls, which increase the plant’s compactness. They exhibit a distinctive

phenotype caused by mutational changes in the genome (Figure 3). These are compact

varieties with short internodes the plants are stunted in growth. Twenty-four forms have

been identified, which are grouped by a series of mutant genes exhibiting similar

phenotypic manifestations.

The clear phenotypic expression of mutant marker genes under various growing

conditions (open field, greenhouse) made it possible to include some of them in

hybridizations (Mo 113, Mo 443, Mo 500, Mo 504, Mo 632, Mo 755, and Mo 791).

Crossbreeding them with lines from our own breeding program and known

The Modern Challenges and Opportunities for

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37

Figure 3. Some varieties of mutant tomato plants with a bush-type growth habit

varieties (L111, L1185, Fakel, Zagadka, Barnaulsky Konservny) and subsequent

analysis of heterozygous F₁progeny and segregating F₂populations demonstrated

the effectiveness of their use. Eleven F₂populations from different hybrid

combinations were analyzed. High recombination and transgressive variability

was established for marker traits. The pronounced phenotypic expression of traits

such as compactness, dwarfism, limited growth, and leaf surface characteristics

allowed for the evaluation of extensive hybrid populations at early stages of

ontogenesis (in the seedling phase). This made it possible to accelerate the

research by conducting it on small plots and to identify a wide variety of forms

with genetically determined traits.

The targeted use of some of these has made it possible to accelerate the breeding

process and, in a short period of time, create more than 20 lines and a number of

ornamental varieties – Prichindel, Cireaska, MiracolMak, Dimetra and Ilika.

These are intended for cultivation on balconies, loggias, and terraces, and are

homologated in the Republic of Moldova [2].

At the same time, the collection was found to contain genes controlling

indeterminate (sp⁺), determinate (sp), and superdeterminate (ssp) plant growth

types. Of particular interest are plant varieties with a semi-determinate (sp^±)

growth type (Mo 147, Mo 341, Mo 432, Mo 446, Mo 544, Mo 620, Mo 723, La

1159, La 2529, La 2921, La 3179), which are widely sought after in breeding for

heterosis to create early-maturing F₁tomato hybrids.

Such a high degree of diversity among mutant genes that control plant growth

patterns opens up broad opportunities for their versatile use in breeding to develop

tomato varieties and hybrids intended for cultivation both in the field and in

greenhouses.

However, a significant factor reducing the efficiency of tomato cultivation in

protected ground conditions is the excessive formation of lateral shoots, the

removal of which requires considerable labor and financial costs. The creation of

varieties and hybrids with low suckering potential, short internodes, and a longer

fruiting period may help solve this problem.

This is possible by incorporating the ls (lateral suppressor) and br (brachytic)

genes into the breeding program. However, their direct use is complicated by their

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Milania Makovei

linkage to traits of the reproductive system (small fruit size, partial sterility). We

were able to partially overcome these difficulties using a specially designed

crossing scheme that included mutant lines (Mo 341, Mo 835, Mo 443, La 2529,

La 3179), semi-mutant forms (111, 11069, 1751), and cultivated-type lines (L28,

L186, L187, L828, L556). Analysis of F₁hybrids showed 100% dominance of the

tillering ability of the cultivated parental forms in all combinations. In contrast, in

the segregating F₂populations, high recombination variability was observed for

the ls and br genes, confirming the conclusions of other authors regarding the role

of mutant genes in activating genetic recombination and broadening the spectrum

of intrapopulation variability, which facilitates the selection of new forms with

beneficial combinations of economically valuable traits in the F₂–F₃generations

[22, 9, 16].

The complex nature of the expression of the traits “internode length” and “number

of lateral shoots per stem” in F₂inbred populations necessitated their

classification into a cluster complex based on breeding value in combination with

other traits (flower structure, fruit weight, shape, and color). This allowed us to

identify more than 50 recombinant forms with a completely new combination of

mutant marker and economically valuable traits. Some of them (23 lines) already

demonstrate stable expression of traits in the F₃–F₄generations. Eight of these

have a semi-determinate growth habit and are characterized by early fruit ripening

(94…109 days). Most of these lines are distinguished by weak tillering ability,

short internodes, and uniform inflorescences, including in fruit color, shape, and

weight. Some genotype variants with different levels of tillering ability are clearly

shown in Figure 4.

Figure 4. Varieties of tomato genotypes based on the pattern of lateral shoot (stepson) formation

and internode length: 1 – plants with short internodes but intense lateral shoot formation; 2 – short

internodes, single reduced lateral shoots; 3 – short internodes and absence of lateral shoots; 4 –

long internodes and absence of lateral shoots

The Modern Challenges and Opportunities for

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The rich genetic potential of the collection of tomato mutant forms, particularly in

terms of genes influencing plant habit and architecture, and the potential for their

effective use in breeding to develop varieties and hybrids with novel and

beneficial combinations of economically valuable traits demonstrates the potential

for their use in creating trait collections and expanding genetic diversity.

3.3. Mutant genes controlling various fruit traits and their significance for

expanding the genetic diversity of tomatoes.

Genes controlling fruit traits (color, taste, shape, fruit weight, fruit surface

structure, pericarp thickness, number of seed chambers, etc.) play a special role in

enriching the tomato’s cultivated gene pool.

An assessment of the potential of mutant forms based on the nature of their

expression and the degree of phenotypic expression of the genes they carry

revealed a high degree of diversity, including unique combinations of genes that

influence different fruit traits.

A total of 32 gene carriers controlling unusual fruit coloration were identified:

Abg, dg, gs, gf, r, t, y, sh, o, B, Del. Marked differences between mutant forms

carrying the same genes were established based on the nature of expression and

the intensity of coloration in the ripening fruit, depending on their combination

with other genes within the same genome (Figure 5).

Figure 5. Characteristics of fruit coloration in the mutant tomato lines Mo 922, Mo 120, and Mo

632, which carry the t (tangerine) gene, under different combinations of this gene with other genes

in their genomes

Fruit coloration is determined by several genes, with the R-red flesh being

dominant over the r-yellow, the Y-yellow skin over the y-colorless, and the P-

smooth, shiny, hairless skin over the p-dull, hairy surface. The recessive t gene is

responsible for orange fruit color. Most mutants in the collection (93 forms) carry

the dominant RTY genes and have red flesh and yellow skin. Mutants with the

double recessive genotype rrtt have orange-colored fruits. The homozygous

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Milania Makovei

genotypes RRTT, rrTT, and RRtt have red, yellow, and orange fruits, respectively.

Fruit color is also influenced by the B gene. Some authors believe that the B, B^c,

and B^oggenes, which control lycopene and β-carotene content, simultaneously

influence the color, taste, and marketability of the fruit [22, 9]. The B gene causes

an increased β-carotene content in the fruit only in the presence of the dominant R

gene. Therefore, the RRTTBB genotype produces β-orange or pink fruits, whereas

the RRTTB⁺B⁺genotype produces red ones. Yellow-fruited tomatoes have the

genotype rrTTB⁺B⁺. In some mutant forms, the yellow flesh of the fruit may be

determined by recessive atat genes.

Mutant forms carrying the hp, hp-1 and Ip genes have also been described and

isolated, these are of interest for the development of varieties characterized by

high levels of carotenoids, ascorbic acid (vitamin C), and dry matter. According to

available information [13], genes of the high pigment series increase the content

of lycopene in fruits by 35–45%, β-carotene by 80–90%, and vitamin C by 20–

50%, making their use essential in tomato breeding for taste qualities.

The gs gene also imparts a distinctive coloration to the fruit. Tomatoes with this

gene have a striped surface on both green and ripe fruit. The gs gene is easily

transmitted, especially to large-fruited plants from its carriers. The coloration of

the radial stripes on ripe fruits varies: golden on pink fruits; pink-red on orange

fruits; and yellow or orange on red fruits (Figure 6).

Figure 6. Expression patterns of traits controlled by the gs gene.

The presence of the Del and sh genes in the tomato genome gives the fruit flesh a

reddish-orange color, which is associated with a decrease in lycopene content and

an increase in β-carotene.

Varieties with the Abg and gf genes, which influence the chlorophyll content in

the fruit, have higher levels of lycopene and β-carotene. This gives them a dark

hue, the intensity of which depends on their interaction with other genes (Fig. 7).

A number of other genes may also influence fruit color, but those whose

combination can ensure high levels of vitamin C, β-carotene (provitamin A), and,

overall, high processing and taste qualities of the fruit are of particular value for

breeding. Of the genotypes shown in Figures 6 and 7, five are the result of our

own breeding program using the gs, Del, and gf genes in crosses.

The Modern Challenges and Opportunities for

Improving the Genetic Diversity of Tomatoes

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Figure 7. Characteristics of trait expression in genotypes with the Del, sh, Abg and gf genes

The appearance of the fruit is most appealing when the fruit ripens simultaneously

and uniformly across its entire surface. Mutant forms with the u gene, which is

recessive to the U gene that controls the presence of a green spot at the base of

the fruit, exhibit uniform coloring. Sometimes the green spot remains even on

ripe fruits, which leads to a decrease in product quality. The proportion of

mutant tomato forms with a green spot at the base of the fruit in the collection is

quite high, at 53.6%.

One of the most important characteristics that largely determines the direction

and intended use of the product is the shape of the fruit. In contrast to the

commonly accepted round fruit shape, the mutant collection includes genotypes

with flat, ellipsoidal, pear-shaped, heart-shaped, oval, cylindrical, and other

shapes. The high diversity of the collection is due to the presence of forms with

different fruit surfaces (ranging from smooth to highly ribbed) (Figure 8). In

some forms, the fruit surface is smooth, but the apical part is elongated into a

more or less pointed tip. The nature of the manifestation and the degree of

phenotypic expression of these and a number of other traits are controlled by the

presence in the collection of a large number of the genes O^l, o, obl, el, f, bk, n

and n-2.

Figure 8. Varieties of mutations in the shape and surface of the fruit with the n, n-2, bk, el and f

genes

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Milania Makovei

Mutant genes rin, nor and alc are of particular value for breeding, as their

presence in the tomato genome prevents fruit overripening (Figure 9). These

genes contribute to increased total yield and affect the viscosity of fruit juice,

which is twice as high in varieties and hybrids containing these genes compared

to conventional ones, ensuring high marketability [9].

By using them in crosses with inbred lines with high combinatorial potential, we

were able to obtain more than 24 combinations of F₁hybrids.

Figure 9. Phenotypic expression of traits controlled by the nor, rin and alc genes

Most of these exhibited high heterosis in terms of yield and fruit quality. Some

(F₁Ingstar and F₁Rozamak) successfully passed state testing and were

homologated in the Republic of Moldova [2]. A number of others are currently

undergoing competitive testing. However, to improve the efficiency of breeding

F₁heterotic hybrids involving these genes, it is recommended to use earlier-

maturing varieties and lines with high taste qualities and large fruits as one of

the parental forms (preferably the maternal parent).The intermediate inheritance

of these traits by F₁hybrids balances the negative influence of the parent with

mutant genes. In such combinations, the first-generation offspring typically

exhibit heterosis in terms of overall productivity and fruit quality.

The genes that control the degree of pubescence in various parts of the tomato

plant including the fruits namely W^om, Ln, p, Vi confer exceptional ornamental

value and special significance on the plants.

The phenotypic expression of these genes is observed from the cotyledon leaf to

the mature fruit, which is covered with a light fluff down (Figure 10). Mature

fruits have a beautiful, presentable appearance and excellent taste, due to their

high content of dry matter, sugars, and vitamin C. The fruits are intensely red

with dense flesh, multi-chambered, and have seeds that form only in the apical

portion of the fruit. As the fruit grows and develops, the pubescence on it

decreases and becomes slightly visible in mature fruit (Figure 10).

Carriers of the W^omand Ln genes (Mo 835 and Mo 341) have been incorporated

into the breeding program. Direct and reciprocal hybrids (16 combinations) were

obtained from crosses with homozygous lines (L8/234, L33/241, L1033) and

The Modern Challenges and Opportunities for

Improving the Genetic Diversity of Tomatoes

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cultivated-type lines (L187, L556, L828) with high combinatorial ability, which

are currently undergoing genetic and biochemical studies for their effective use

in practical breeding and replenishment of collections with useful genes.

Figure 10. The nature of fetal phenotypic expression at different stages of development,

controlled by the Ln and W^omgenes

A high degree of heterogeneity was observed among the mutant forms, as

evidenced by fruit weight, pericarp thickness, and the number of seed chambers.

Fruit weight is a complex polygenic trait that varies depending on environmental

conditions [22]. Significant differences in fruit weight were observed among the

mutant forms: 24.6% of the forms had large and very large fruits (100…300 g);

very small fruits (0.4…20 g) were observed in 17.8%; the remaining 57.6% of

mutant tomato forms had fruit weights ranging from 30 to 100 grams.

Pericarp thickness and the number of seed chambers are traits that directly

determine fruit quality and marketability. The collection describes a large

number of mutant genes controlling pericarp thickness, shape and seed chamber

structure – Gr, bs, bs-2, el, ck, fie, Ip, lo, loc, Ol, ptb, ss, and others. The

phenotypic expression of some of these is shown in Figure 11.

Figure 11. Some varieties classified by characteristics such as number, shape, color, and structure

of the seed chambers, which are controlled by the Lc, Ip, lo, loc, O^l,bs-2 genes

3.4. Genetic sources of resistance to certain diseases.

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Milania Makovei

The presence of genes controlling resistance to pathogens may help address

problems associated with the rapid evolution of pathogens. From the total number

of tomato mutant forms studied, 14 genotypes were identified that carry genes

controlling resistance to Mi – Meloidogyne incognita; Tm, Tm^2a, Tm-2 – to

Tomato mosaic virus; F – to Fusarium; Ve – to Verticillium; Cf, Cf-2, Cf-3, Cf-4

to Cladosporium. The genomes of these mutant forms contain, in various

combinations, genes that simultaneously control resistance to a particular

pathogen, different fruit traits, and plant growth type (primarily indeterminate and

semi-determinate). They can be used to enrich working and long-term collections

with valuable genes.

Сonclusions

(1). It is shown that the genetic potential of mutant forms, which carry a large

number of marker genes controlling important economically valuable traits in

tomatoes, represents a unique source of new germplasm for enhancing genetic

diversity through the creation of new breeding materials, lines, varieties, and

hybrids of tomato, as well as for supplementing existing and creating new trait

collections.

(2). A high degree of heterogeneity was observed among mutant tomato lines in

terms of resistance to abiotic stress factors (high and low temperatures, drought).

Genotypes with different levels and types of resistance, as determined by

characteristics of the male gametophyte of the tomato, have been identified; under

conditions of climate change, these are of particular value for use in breeding

programs as sources of resistance.

3). It was found that mutant genes, when combined with cultivated tomato lines,

stimulate genetic recombination processes, leading to an expansion of the

spectrum of intrapopulation transgressive variation and the emergence of new

forms with unique combinations of mutant marker and economically traits,

thereby contributing to the enrichment of the tomato crop gene pool and the

expansion of its genetic diversity.

Acknowledgments

The research was carried of the Proiect in the field of science and innovation

25.80012.5107.15SE, “Genetic diversity of mutant marker genes of tomato

(Solanum lycopersicum L.) as a source of new germplasm for the creation of

varieties and heterotic hybrids capable of realizing the productivity potential

under climate change”, financed by the National Research and Development

Agency.

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Improving the Genetic Diversity of Tomatoes

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urilor%20de%20plante%20al%20RM%202025%20final.pdf

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