A Brief Review of a Nearly Half a Century Wheat Quality Breeding in Bulgaria

Wheat quality is a complex feature determined by the level of various indices and dependent on a number of factors. It is defined by different interactions involving glutenin and gliadin composition and abiotic stresses. The efforts of the wheat breeders are directed towards combining a high level of the indices in the new varieties with a stable expression of these indices in different years and environments.


Introduction
Wheat quality is a complex feature determined by the level of various indices and dependent on a number of factors. It is defined by different interactions involving glutenin and gliadin composition and abiotic stresses. The efforts of the wheat breeders are directed towards combining a high level of the indices in the new varieties with a stable expression of these indices in different years and environments.
The aim of this chapter is 1) to describe the glutenin and gliadin composition of Bulgarian winter bread wheat varieties, bred since the middle of 20 th century; 2) to asses the quality indices of wheat varieties; to compare the differences between wheat quality groups as well as the different period of creating the varieties; 3) to determine the level of influence of various environmental factors on the quality indices of wheat; to follow the response of common winter wheat varieties to various combinations of growing conditions; to study the ability of the varieties to realize their genetic potential for quality under certain environments.
The bread making characteristics of wheat flour are closely related to the elasticity and extensibility of the gluten proteins. The seed storage proteins are associated with agriculturally significant traits and they are used in a legal protection of cultivars (Knoblochova & Galova, 2000). Many studies have been made in order to investigate the genetic diversity of the initial material (Atanasova et al., 2009b;Bradova, 2008;Bushehri et al., 2006;Li et al., 2005;Tabasum et al., 2011;Tohver, 2007;Tsenov et al., 2009).
In this review eighty-nine cultivars developed at Dobrudzha Agricultural Institute (DAI) -General Toshevo, Bulgaria, during 1962Bulgaria, during -2010, and nine cultivars of the Institute of Plant and Genetic Resources (IPGR) -Sadovo, Bulgaria were investigated. Some of these cultivars were heterogeneous and their biotypes were considered as separate varieties when determining the ratio of high-and low-molecular weight glutenin and gliadin subunits and spectra. The allelic frequency in loci Glu-1, Glu-3, and Gli-1 was studied and the genetic variability in each allele was calculated. The percent of observed spectra was determined by decades.

Decade
Glu - 1 7 2+12 (6.9) c f a ( 6.9) I g f (6.9) 1 7+8 5+10 (6.9) c g a (6.9) f l b (6.9) 1 7+9 5+10 (6.9) f j c (6.9) b b a (3.45)  Table 2. Distribution of the most common spectra in decades In order to improve the quality of new varieties, a narrowing of the genetic diversity was observed especially after the mass penetration of the variety Bezostaya 1 in the breeding www.intechopen.com programs after the 80's. The direct usage as a parent in the hybridization or indirectly as a participant in the pedigree of other varieties, led to unification of the spectra of new varieties with that of Bezostaya 1. It is necessary to broaden the genetic basis by including alleles with good influence over the wheat quality. Such alleles are Glu-B1f (subunit 13+16), Glu-B1i (subunit 17+18), Glu-A3f, Glu-A3b.

Progress in development of quality parameters of Bulgarian wheat varieties
The breeding for wheat quality started in 1962 when the first contemporary wheat breeding program in the Dobrudzha Agricultural Institute was adopted. In the two breeding centers (DAI and IPGR) 26 high quality varieties were created till now which was 1/3 of the entire variety list. During 2006 and 2008 sixty nine varieties were tested for their quality parameters. The varieties belonged to different quality groups according to Bulgarian State Standard (BSS). Based on the level of indices sedimentation value, wet glutenin content and valorimeter, varieties from this investigation were divided in three groups (table 3).  Table 3. Grouping of varieties according to the level of sedimentation (sedim.), wet glutenin content (WGC) and valorimeter (val.) Some of the strong wheat varieties, according to BSS, failed to enter the first group in this investigation. Such varieties were: Demetra -with lower WGC; Preslav -with lower WGC and valorimeter; Dona -with lower sedimentation and WGC and Ludogorka and Momchil with lower levels for all three indices. A tendency in breeding of high quality varieties with low wet gluten content, even in comparison to medium and low-quality varieties, has been reported by Atanasova et al. (2010), Panayotov & Rachinsky (2002). One of the reasons for this is the use of Russian and Ukrainian sources in the breeding programs for wheat quality improvement. These sources have high quality of gluten but in lower amounts.

Level of indices Varieties
Wheat varieties, belonging to second group by BSS, in this investigation showed level of indices for the first group. With higher level of all three indices were varieties Bozhana and Stoyana. With higher sedimentation and valorimeter were Slaveya and Venka 1. Varieties Galateya, Prostor, Zagore had higher WGC and valorimeter value. Some varieties from third www.intechopen.com  1962-1972 1973-1983 1984-1994 1995-2005 1962-1972 1973-1983 1984-1994 1995- 5 1962-1972 1973-1983 1984-1994 1995-2005 >2005 Ov er a l l  1962-1972 1973-1983 1984-1994 1995-2005 1962 -1972 1973-1983 1984-1994 1995-2005 >2005 Do ugh stability y = 0,2899x + 1,0675 R2 = 0,457  1962-1972 1973-1983 1984-1994 1995-2005 1962-1972 1973-1983 1984 -1994 1995-2005  As a result of breeding a progress was determined in almost all the indices defining end-use quality in wheat. The breeding periods were divided into decades as follows : 1962-1972; 1973-1983; 1984-1994; 1995-2005 and after 2005. The average values of the whole group of sixty-nine wheat varieties and that of the high-quality group were compared. The most strongly modification was observed for the indices: dough stability, where the enlargement was 24% for the entire group and 60% for the quality group; sedimentation value -26%for whole group and 44% for quality group (figure 2). For the indices valorimeter and loaf volume a high level had been reached which changed very slowly through the years. The group of quality wheat varieties had greater progress compared to the all varieties regardless of the quality index and its behavior. It was valid even to the indices for which the breeding progress was not statistically proven.

Evaluation of genotype, environment and their interaction for quality parameters of Bulgarian varieties
The complex nature of wheat quality is determined by the level of various indices and dependent on a number of factors. One of the problems of breeding for quality is not only achieving a high level of the indices in the new varieties, but also achieving a stable expression of these indices in different years and environments (Atanasova et al., 2008;Johansson et al., 2001;Williams et al., 2008). It is valuable for breeding to determine the nature and direction of the effects of different genetic and environmental factors on the specific quality indices (Hristov et al., 2010;Panozzo & Eagles, 2000;Tsenov et al., 2004), and to study the performance of the varieties under changeable growing conditions. This would allow predicting to some degree their response to certain combinations of environmental factors Drezner et al., 2006;Yong et al., 2004). The variation of the quality indices when growing each individual variety under different environments is always helpful both for the distribution of the new varieties and for their improvement in breeding programs (Gomez-Becera et al., 2010). The data on the variation of winter wheat quality is contradictable with regard to the level of genotype effect (Gomez-Beccera et al., 2010;Williams et al., 2008). In breeding there is always the question whether the high quality of a given variety under favorable environments is a prerequisite for the realization of its high-quality potential under unfavorable environments, too, or is it and impediment for its stability (Hristov et al., 2010;Tsenov et al., 2004).
Sixteen Bulgarian winter wheat varieties from first and second quality group according to BSS were tested at two locations: Dobrudzha Agricultural Institute -General Toshevo (DAI) and Institute of Agriculture and Seed Science, Obraztsov Chiflik, Rouse (OCH) during 2004-2007. The expression of 5 grain quality indices which give information about various quality aspects was analyzed: test weight (kg) (BSS 7971-2:2000), sedimentation value of flour (ml) (Pumpyanskii, 1971), wet gluten content in grain (%) (BSS 13375-88), valorimeric value (valorimeter, conditional units) (BSS 16759-88), and loaf volume, determined according to the methods adopted at the DAI laboratory.
The effect of the location was highest on wet gluten content and valorimeric value (table 4). The traits test weight and loaf volume were affected most by the year conditions. The distribution of the varieties into groups according to their quality had highest influence on the expression of sedimentation. The independent influence of the genotype on the variation of most of the investigated indices was lowest. Atanasova et al. (2008) and Zhang et al. www.intechopen.com (2005) have found out that the genotype had higher effect on the expression of sedimentation, while Drezner et al. (2006Drezner et al. ( , 2007, Panozzo and Eagles (2000), Tsenov et al. (2004) have proved that the environment has greater effect on the quality indices of wheat. Among the various combinations between the factors, the interaction quality group x genotype had the highest effect on almost all investigated traits. The exception was wet gluten content, which was affected most by the interaction location x year. Hristov et al. (2010), Mladenov et al. (2001), Williams et al. (2008) have found out that in spite of the significant effect of the interaction genotype x environment on the expression of the quality parameters of wheat, this effect was less significant than the independent influences of the genotype and the location.  The growing conditions at DAI were more favorable for expressing genetic potential of wheat varieties as it is revealed by mean values of the indices (table 5). It is logical to expect higher values for the indices of the varieties from the first quality group. The results from the variance analysis were once again confirmed; the values for wet gluten content were not significant and there were no considerable differences between the two quality groups.
It is difficult in breeding for wheat quality to develop varieties with high quality indices, which remain stable under various growing conditions (Atanasova et al., 2008;Johansson et al., 2001;Williams et al., 2008). According to Finlay & Wilkinson (1963), Sudaric et al. (2006) genotypes with coefficient of regression (b i ) under 0.7 were considered unresponsive to changeable environments; with b i between 0.7 and 1.3 had average stability; and >1.3 were considered responsive to good environments. Most of the varieties involved in this investigation have moderate stability for all the indices with some exceptions (  Table 5.

Mean values of the investigated traits according to different factors of variation
The valorimeric value is an index which determines gluten quality and which correlates strongly with end-use quality. Most of the investigated varieties possess moderate stability (b i from 0.7 to 1.3) with regard to this trait. Varieties Milena and Aglika (b i = 1.00 and b i = 1.25, respectively) from first quality group were an evidence that high values of the traits can be observed in stable genotypes, too (Hristov et al., 2010;Mladenov et al., 2001;Sudaric et al., 2006) and that stability is not necessarily related to low mean values, as previously stated (Becker and Leon, 1988). The ecovalence values of the individual varieties for this trait were very high, which brings forth the strong effect of the environment. The variation expressed through the ecovalence was much lower in the wheat varieties from the second group in comparison to the varieties from the first group (56.8 and 99.6, respectively) (table 6).
A number of researchers have found out that the varieties with lower quality potential are considerably more stable, especially under stress Tsenov et al., 2004). The values of the regression coefficient of the separate groups are quite indicative in this respect. The regression coefficient in the first group was above 1.0. This means that that the varieties from this group realized their quality potential under conditions more favorable for its formation. Therefore the W i values of variety Zlatina, which is a quality variety, were several times higher than the mean values for this group. On the other hand, varieties like Aglika, Milena and Preslav demonstrated considerably lower variation of their quality indices in comparison to the other varieties from the group. It can be suggested that such stability is due to the fact that the absolute values of the indices in this case were low. These data once again prove that when comparing the response of the varieties to the environment www.intechopen.com with regard to their quality, conclusions should be made very carefully. The results for the individual varieties and their indices are not unidirectional and therefore when selecting a variety for mass production it is necessary to consider the purpose for its cultivation, the potential of the given variety and its ability to realize this potential with stability and adequacy.  Table 6. Stability parameters of varieties from different quality groups When compare the mean values of varieties with their stability it can be seen that for the conditions of DAI varieties Demetra, Zlatina, Aglika differ from the total group with higher levels of the indices ( figure 3). For the other location (OCH) these varieties were Demetra, Enola, Aglika. The most poorly performing variety for the two locations was Prelom.

Variety
Projection to the ordinate of the two-dimensional matrix genotype x character, regardless of the direction, determines the stability of the varieties (Yan et al., 2007). For the conditions of DAI as most stable and exceeding the mean level were varieties Aglika, Sadovo 1, Preslav, Demetra. Varieties Milena and Preslav had most stable reaction at OCH location as they had almost null projection to the ordinate. Under the same conditions with high variability stand out varieties Enola and Pliska. variation of quality indices of studied varieties in the two locations (Stoeva et al., 2006). There was a similar component structure of the factors which mainly influence the variation of the quality over locations. About 65% of the total variation of the two-dimensional matrix variety x character for each location is for first and second PC. The biggest part is for PC1 (table 7).

Breeding of wheat quality in Bulgaria -Steps, drawbacks, prospects
Breeding of new varieties with good quality has always been on the attention of the breeding programs in Bulgaria (Boyadjieva et al., 1999;Panayotov et al., 1994;Rachinski, 1966;). Combining high yield and quality in wheat is a challenge for the contemporary breeding as it is connected with many obstacles with different nature (Baenziger et al., 2001;Dencic et al., 2007;Eagles et al., 2002;Trethowan et al., 2001). Analysis of wheat quality begins with studying the initial material (Tsenov et al., 2010c). When foreign samples are received they are study for three years for a set of quality indices. Those with high levels are included in hybridization programs especially if they show high yield potential, stress tolerance, disease resistance. The basic foreign parent components for hybridization are from breeding centers with traditions and excellent achievements in breeding for wheat quality (table 9).
The quality of Bulgarian wheat varieties is based on the widespread use of variety Bezostaya 1 and other Russian and Ukraine sources (Panayotov & Kostov, 2007;Todorov et al., 1998;Tsenov et al., 2010b). During the last years samples with different origin are widely used as they possess high level of productivity combined with high end-used quality. The quality analysis during the breeding process is made according the scheme described in the table 10.
The beginning of quality analysis of the breeding lines is in the screening nursery. The main tests in this unit are sedimentation value of the flour and grain protein content. Quality index of each line and quality standard varieties is calculated by these two parameters. These indices are defined as they possess high and positive correlation with the main parameters, connected with the strength of flour and dough (Bona et al., 2003, Dacheva & Boydjieva, 2002  In the next trial units (PYT, CYT) the analysis extend and cover almost all aspects of quality of grain, flour, dough and bread. Along with this an analysis is made to determine the allelic diversity of the lines. At least three year data from CYT, which is the last level of screening of breeding materials, are needed in order to be able to assign each line in the following quality group: A -strong wheat; B -medium and C -wheat with soft endosperm (figure 4).
In the yield trails of Executive Agency of Variety Testing, Field Inspection and Seed Control (EAVTFIS) the candidate-varieties are also testing in these three groups at least 2 or 3 years. Each group has specific standards for comparison.

Fig. 4. Bread-making quality groups
The evaluation and selection for quality is associated with many difficulties from different nature. They can be determined as follows: 5. Samples with high combining ability for quality are limited. 6. Complex genetics suggests a special selection procedure (Tsenov & Stoeva, 1998). 7. The selection in the early hybrid populations is not effective because of fading forming process and restricted amount of grain for analysis. 8. There is a lack of breeding indices for parallel selection for quality and yield potential and other parameters.

Conclusions
As a result of a nearly half a century breeding in Dobrudzha Agricultural Institute 26 varieties from the first quality group are created. This is nearly one third of the entire variety list. The massive usage of variety Bezostaya 1 in the breeding programs direct or indirect narrowed the genetic diversity of the materials and to some extent unified their glutenin and gliadin spectra. The efforts to include foreign initial materials in hybridization, with alleles with good influence over the wheat quality, will probably be rewarded in the near future.
A breeding progress is determined for almost all the indices, defining end-use quality in wheat. The group of high quality wheat varieties has greater progress compared to all varieties irrespective of the indices.
Different factors influence on the wheat quality and on the expression of different indices. The knowledge of the nature and direction of the effect of these factors is valuable for predicting to some extend the performance of wheat varieties in certain growing conditions. Most of the Bulgarian varieties show moderate stability at different environments. But the results for the individual varieties and their indices are not unidirectional and therefore when selecting a variety for mass production it is necessary to consider the purpose for its cultivation, the potential of the given variety and its ability to realize this potential with stability and adequacy.