GENETIC DETERMINATION, VARIABILITY AND RELATIONSHIPS BETWEEN (1®3), (1®4) ß-D-GLUCAN CONTENT AND OTHER AGRONOMIC TRAITS IN SPRING BARLEY

Andrzej Bichoński, Magdalena Gut

ABSTRACT

The aim of the present work was to determine the variability and genetic determination of β-glucan content in the wort of spring barley as well as other significant traits, such as: yield, 1000 kernel weight, earliness, plant height and resistance to lodging and powdery mildew. Also the phenotype correlations between the analysed traits were examined. The objects of the investigation were spring barley strains of F₆ – F₇ generation evaluated in 2000-2002 in three locations. With the exception of 1000 kernel weight, genotypes were differentiated in relation to all the traits investigated. Nearing and high values CV(p) and CV(g) suggest that the variability of the barley examined forms with regard to this trait results from both genetic and environmental determinations. The barley strains examined could be a starting point for the cultivation of spring barley oriented both at decreased and increased β-glucan content while a high coefficient o

Key words: (1→3), (1→4) β-D-glucans, barley, genetic determinations, correlations..

INTRODUCTION

(1®3), (1®4) β-D-glucans are an important component in barley endosperm and aleurone cell wall [2,3]. High viscosity causes adverse effect of these components on the recovery of malt extract, makes wort filtration difficult, and may also lead to haze formation in beer [5,9]. Besides its negative effects on brewing quality, a high β-glucan content in cell walls of the endosperm makes the access of hydrolases to their substrates in the endosperm cells difficult and so retards the transfer of carbohydrate to the embryo, resulting in slower germination [18]. On the other hand, β -glucans have a positive influence on human health – they reduce serum cholesterol, increase mineral and vitamin availability and modulate gluco-regulation in diabetics [8,13]. Thus barley breeding must be conducted in two separate ways – for the decreased β-glucan content – for brewing industry and for nutrition.

In most countries of the world, brewery barley is dominating in breeding, thus the majority of research into β-glucans concern the influence of these compounds on the brewing quality of barley [15,11]. Also the influence of environment and agronomic practices upon β-glucan content in grain is examined [10,18]. However, there are no reports concerning the variability and relationships between the level of β-glucan content in grain and other agronomic traits. In breeding oriented both at a decreased and an increased β-glucan content, this question proves to be extremely essential, as high requirements of the market concerning the varieties introduced for breeding require these varieties to offer a complexity of positive traits.

Therefore, the aim of the present work is to determine the variability and genetic determination of β-glucan content against the background of other significant traits, such as: grain yield, 1000 kernel weight, earliness, plant height and the resistance to lodging and powdery mildew. Also the phenotype correlations between the traits analysed were examined here, as it is known from practice that information of this kind is extremely helpful in the selection.

MATERIAL AND METHODS

The objects of the research were spring barley strains of F₆ – F₇ generation investigated between 2000-2002 in three locations, i.e. in breeding stations of Bąków, Polanowice and Modzurów. The set and number of the genotypes examined were changing in the years according to the principles accepted for breeding experiments, yet the same in all the points each year. In 2000 77 strains and in 2001 and 2002 140 forms were tested. In all the locations, the strains were grown on the 10 m² plots, with a standard level of fertilisation of 70, 100 and 150 kgˇha^-1 of N, P, K, respectively. Experiments were carried out in randomized block design with four replications.

During the vegetation, the earliness was marked defined as the number of days from 1^st day of May to heading, also the plant height was measured and resistance to lodging and to powdery mildew were estimated. For both traits the 9-1 score was adopted, where 9 meant full resistance, and 1 – complete lodging or powdery mildew attack. After the harvest, the yield from a plot was calculated to tˇha^-1 with 15% of moisture, and the 1000 kernel weight was determined.

Malting was carried out in the micro-malt of the Cracow Plant Breeding and Acclimatization Institute at 12°C, after the grains had reached 45% of moisture in the samples of 500 g of each strain. The process took 7 days together with water absorption by the grains. The wort was obtained with standard methods and the β-glucan content was evaluated with the fluorimetric method [1,6,7] in Tecator apparatus.

The results obtained were worked out statistically. For all the traits examined the two variance analyses were carried out, where total variability was divided into the following elements: environmental content (P), where as environment the combination of locality and year were assumed, genetic differences between the genotypes (G) and genotype-environment interaction (G x P). The latter element was used as the denominator for the F test during the verification of the hypotheses concerning the main elements. The coefficients of genotype determination of the traits (H), which are equivalent to heritability coefficient (h²), were marked from the mean square values for genotypes and genotype-environment interaction, according to the following formula:

H = (m₁ - m₂)/m₁

where:

H – the coefficient of genetic determination,
m₁ and m₂ – mean squares for genotype and genotype-environment interaction, respectively [4].

The coefficients of genotype (CVg%) and phenotype (CVp%) variability which characterise the variability between the objects examined were computed following the formula by Węgrzyn and Bichoński [16]. These coefficients were used for the estimation of genotype-environment interaction, while it was assumed that if the mean square for the genotype-environment interaction is solely determined by random reasons, CV is lower or equal to 5%, whilst the presence of this interaction increases the values of this coefficient [17].

RESULTS AND DISCUSSION

The analysis of variance presented in Table 1 indicated a highly significant differentiation of environments and genotypes with regard to all the traits examined. The exception was 1000 kernel weight. The highest variability was observed in β-glucan content – the variability of other investigated traits was much lower, whilst the lowest value of CV was observed for 1000 kernel weight and earliness. The high variability of β-glucan content is confirmed by the coefficients of phenotypic and genotypic variability (Table 2). The high and nearing values of CV(p) and CV(g) suggest that variation in β-glucan content is controlled by both genetic and environmental factors. This is also indicated by a high mean square for the genotype-environmental interaction. Thus the earlier observations made by Narasinhalu et al. [12] and Perez-Vendrell et al. [14] as well as the latest findings made by Zangh at al. [19] are confirmed. However, th e results obtained are contradictory to the data of Ram and Verma [16], according to whom the environment does not have any significant influence on β-glucan content in grain.

The data contained in Tables 1 and 2 suggest also clearly that the examined traits may be a starting point for the spring barley breeding directed both at decreased and increased β-glucan contents. A high coefficient of genetic determination of this trait (H = 0.85) allows to expect also an effective selection.

Some problems can be encountered with the combination of the required level of β-glucan content with other functional traits: for example low β-glucan content with high yield or/and high 1000 grain weight – characters very important for brewery industry. Although 1000 kernel weight, earliness and resistance to powdery mildew were characterised by a high level of genetic determination, and the yield, plant height and resistance to lodging showed a medium level of genetic determination, the variability of these traits was rather low. It can be therefore supposed that it would be difficult to obtain the strains combining extreme values of the favourable traits. Such a supposition can be confirmed by the coefficients of the phenotype correlations between the traits analysed presented in Table 3.

β-glucan content was significantly correlated with all the traits examined with the exception of the resistance to powdery mildew and plant height (r = -0.08 and -0.09, respectively), whilst the majority of these correlations proved to be adverse to the selection of brewery barleys; and so the selection of the forms for brewing industry, which demands the variations with low β-glucan content, but, at the same time, high-yielding and with large grains will be made difficult by the positive correlation of this feature with yield and 1000 kernel weight. It will be also difficult to obtain early forms, but it may be expected that they will be resistant to lodging (negative correlation between β-glucan content and the number of days to heading and resistance to lodging).

The selection of the forms with high nutritional value should thus be easier, as, with the exception of the resistance to lodging, all the correlations observed are favourable to this direction. The data presented in Table 3 concerning the relationships between all the examined traits indicate, however, a number of adverse relationships, for example yield and 1000 kernel weight is related in this way to earliness and resistance to lodging, so it can be supposed that obtaining the form combining the demanded level of β-glucan content with other favourable traits will not be an easy task.

CONCLUSIONS

1. The nearing and high values of the coefficient of phenotype CV(p) and genotype CV(g) variability suggest that the variability of the barley forms examined with respect to this trait results both form genetic and environmental determinations.

2. A high coefficient of the genetic determination of β-glucan content (H = 0.85) allows to expect an effective selection.

3. The selection of brewery barleys with a decreased β-glucan content and a high level of other traits may turn out to be difficult because of a number of adverse relationships between them.

4. The selection of the forms with high nutritional value should be much easier as with the exception of the resistance to lodging, all the observed correlations are favourable to this direction.

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