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II. Evaluation of Cultivated Wheat

II. Evaluation of Cultivated Wheat

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EVALUATION OF GENETIC RESOURCES IN CEREALS



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Pullman, Washington, U.S.A., and estimated yellow berry content of the

grain produced. Porceddu and Scarascia-Mugnozza (1983) carried out

similar studies for ascertaining variability in landraces of durum wheat

from Algeria, Ethiopia, and Italy and found that there was clear separation

between Ethiopian and Italian material, but Italian landraces were more

variable among themselves than Ethiopian ones and material from Algeria

was more variable than both the other two. Hence, differences among

landrace populations from the same country were highly significant for all

1 1 characters studied, except kernel weight and spike density. Using

multivariate analysis also, Kosina ( 1980) evaluated structure and caryopsis quality of some hybrids of spring wheat.

Ehdaie and Waines (1989) described genetic variability in T. aestiuum

from Iran. They concluded that local landraces, such as those found in

Iran, could be improved by selection for shorter genotypes with fewer

tillers per plant, but with larger and heavier grains. Morphological and

physiological variability in T. aestiuum collected from Afghanistan was

also reported comprehensively by Tani and Sakamoto (1987).

There are traits, such as resistance to diseases and tolerances to certain

types of soils, for which variability can only be observed at particular sites.

Such traits are economically important and every effort must be made to

record and document them by carrying out evaluation at sites where the

incidence of that particular stress is the greatest, such as the so-called

disease “hot spots.” For example, for screening against resistance to

Septoria tritici (leaf blotch), ICARDA uses a humid and high-rainfall site

located on the Mediterranean coast in Syria in addition to artificial inoculation. For experiments on tolerance to salinity, a drought-affected site on

the shores of salt lake Jabboul in northern Syria is used. Jana et al. (1983)

evaluated 3000 durum wheat accessions from various countries at this site,

and 10 lines were found to be highly tolerant to combined stresses of

salinity and drought. However, it is known that salinity is highly variable in

the field and if experiments do not comprise several replicates, laboratory

confirmation with tests such as chlorophyll influorescence (Smillie and

Nott, 1982) may be used to help identify salt-tolerant lines.

Selected bread wheat and barley plants from landraces grown in Nepal

and Pakistan were examined and variability for certain qualitative traits

described by Witcombe (1975). Barley from Nepal was found to be more

variable than barley from Pakistan, whereas in the case of wheat the

reverse was true. Murphy and Witcombe (198 I ) further analyzed landraces

of wheat from northern India by growing single plants under glasshouse

conditions in Wales, U.K. Multivariate analysis of data on quantitative

traits was used to distinguish between introduced material and indigenous

germplasm on the basis of means recorded on single plants. This data



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analysis method was used to detect modern varieties so they could be

excluded from genebanks as genetic resources. However, variability studies based on observations of quantitative traits on single plants in a controlled environment are inconclusive and should be verified by field studies

before an inference is drawn.

Damania et al. (1985) evaluated populations of wheat and barley landraces from Nepal (Triticum aestivum and Hordeum vulgare L.) and the

Yemen Arab Republic (T. turgidum L. and H . distichum L.) for morphological variability and days-to-heading under field conditions using sufficiently large samples. Observations were recorded for 18 characters on 50

randomly selected plants from each landrace. There were significant differences in variability among regions in the Yemen and river valleys in

Nepal, as well as among landraces in the same regions or river valleys. It

was concluded that landrace variability within primary or secondary centers of diversity could not be fully evaluated without growing the plant

material in the field under conditions similar to the original habitat, although an initial impression of the extent of variability can be obtained

through the application of polyacrylamide gel electrophoresis (PAGE) of

seed proteins (Damania et a / ., 1983). Variability in high-molecular-weight

glutenin subunits in landraces of hexaploid wheats from Afghanistan was

also evaluated by Lagudah et al. (1987) using PAGE. The variability

seemed to be independent of the altitude and geographical location of the

collection site.

A world collection of bread wheat (T. aestivum L.) maintained by the

USDA was systematically analyzed for protein and lysine content by

Vogel et al. (1973). Lewontin (1974) has expounded the advantages of

electrophoretic surveys of proteins as measures of genetic diversity and

reviewed the technical limitations and conceptual opportunities offered

to plant biologists using this technique. Wheats can also be evaluated

for quality and study of genomes and genotypes with the use of PAGE

(Konarev et al., 1979). Kobrehel and Gautier (1973) studied peroxidase

patterns of primitive and modern wheats by PAGE and found that

brownness in macaronis can be associated with the compositions of the

peroxidases. Damania (1985) demonstrated the usefulness of this technique in evaluating landraces of hexaploid wheats and their possible utilization in improving the bread-making quality of modern varieties.

However, predictions on good or poor gluten quality based solely on

presence or absence of certain bands in an electrophoretic gel may not be

conclusive. It has been pointed out that the band with relative mobility

(Rm) 45 and the band of Rm 42, which were indicators for good pasta and

bread-making qualities in durum and bread wheat, respectively, were

merely genetic markers, whereas other proteins (low-molecular-weight

glutenins) were responsible for gluten viscoelasticity (Pogna et al., 1988).



EVALUATION OF GENETIC RESOURCES IN CEREALS



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Information on the genetic variability of a sample is extremely useful

and the eventual objective of every evaluator should be to describe the

variation on the basis of a list of differences between and within samples in

the sequence of nucleotides in the deoxyribonucleic acid (Erskine and

Williams, 1980). At present, the study of storage protein (prolamins) variants by electrophoresis is the most convenient and rapid method available

for detecting genetic differences at the DNA level in a cereal collection

(Damania et al., 1983). Documentation of data derived from electrophoretic studies of storage proteins in cereal genetic resources has been

reviewed by Konarev et al. (1979).

However, it may be argued that heterogeneity in storage proteins alone

is of little value to the breeders or genetic conservationists because its

correlation with any single agronomic character is obscure. Nevertheless,

these markers can perhaps monitor the relative genetic diversity with a

greater degree of accuracy (Brown, 1978; Damania, 1983) than field studies

with an inadequate number of traits. A prescreening procedure for identification of the ploidy levels and chromosomal aberrations, such as deletions with the use of electrophoresis, has been described by Damania

(1985). This technique can also be used as a tool for elimination of duplicate germplasm stocks (Damania and Somaroo, 1988).



Ill. EVALUATION OF CULTIVATED BARLEY

Barley is one of the most dependable cereal crops in harsh environments. It is grown in semiarid areas as well as in cold, short-season areas.

Local varieties and landraces of barleys occupy nearly 80% of the cultivated areas in West Asia and North Africa and these should be collected

before they are lost.

Ward (1962), in one of the early efforts to characterize a large number of

germplasm samples, evaluated 6200 lines from the USDA world collection

of barleys and recorded observations on seven qualitative characters. He

concluded that only a very small portion of the potential genetic diversity

in barley was represented in the collection. Farmers still rely on barley

landraces that have a stable performance in the dry areas and rarely

outyield modern homogeneous varieties (Ceccarelli et al., 1987). The

variability within these landraces is large and compares well with that

within populations of its wild relative, Hordeum spontaneum, growing in

the same region (Jana and Pietrzak, 1988). Variability for agronomic traits

in landraces of barley has been evaluated by several workers. De Pace et

al. (1978) crossed a set of six old Italian wheat varieties (female parents)

with five breeding lines from the International Wheat and Maize Improve-



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ment Center (CIMMYT). The F3 progenies were grown in the field and

variability for flag-leaf size, heading, and maturity time was recorded on

single plants. It was concluded that utilization of genetic resources distant

from the present varieties is advantageous as it permits breakage of linkage

groups.

The Cereal Improvement Program at ICARDA collected barley landraces from 33 locations in the drier regions of Syria and Jordan (Weltzien,

1982a). On subsequent evaluation it was found that some samples from

Syria had a definite cold requirement to induce flowering (Weltzien,

1982b), indicating that under local conditions this trait may contribute to

yield stability by preventing winterkill of early-planted material. Information of this kind is valuable for a crop improvement program, not only by

showing which characteristics contribute to adaptation but also by indicating the degree of plasticity present in the indigenous landraces for which

varietal improvement may be undertaken.

Tolbert et al. (1979) carried out a diversity analysis on the USDA world

collection of barleys and Ceccarelli et al. (1987)evaluated genetic diversity

of barley landraces from Syria and Jordan for agronomic, morphological,

and quality traits. Considerable diversity was observed between as well as

within collection sites. Single-plant progenies were identified with larger

yields and more desirable expression of agronomic characters than the

original landraces. On the other hand, Murphy and Witcombe (1986) performed discriminant and reciprocal averaging analysis on single plants of

covered and naked barleys from the Himalaya and confirmed their difference in a multivariate way.

Sixteen populations of two-rowed barleys from the Yeman Arab Republic were screened for loose smut (Ustilago nuda) disease and found to

be highly resistant when compared to the six-rowed barley landraces from

Nepal (Damania and Porceddu, 1981). Incidence of diseases varies depending on climatic factors and inferences made of natural infestation in a

single season should be avoided as they can be misleading. In another

screening of landrace material, van Leur et al. (1989) tested 280 barley

lines collected from different sites in Syria and Jordan. Large variability in

response to four disease-yellow rust, scald, powdery mildew, and

covered smut-was observed. No consistent association between the

environmental conditions of the collection site and the level of resistance

of the landrace lines could be found.

Variation of flavonoids between barley lines was studied and found to be

greatest in the Near East (Afghanistan and Iran) and Ethiopia (Frost et al.,

1975). Allard et al. (1970) reviewed some studies on enzyme variability in a

world collection of barleys and reported on the geographical distribution of

different enzyme variants and factors responsible for the development and

maintenance of the observed variability in the samples.



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