Luciano Pecetti

Biodiversity in a germplasm collection of durum wheat

SummaryOver 7,600 durum wheat accessions belonging to 22 country gene pools were evaluated in Syria, during the seasons 1985–86 through 1987–88 under semi-arid Mediterranean climatic conditions. Data on seven agronomic traits are presented to assess the distinctiveness and the phenotypic diversity of these pools. Univariate statistical analysis revealed differences among materials of diverse origins for all traits. Mean phenotypic diversity within countries was highest in the germplasm from India, lowest in that from Bulgaria. In a canonical variate analysis, the first three canonical variables explained 77.7% of the total variance. A cluster analysis was performed to supplement the generated information by the canonical analysis. The multivariate analyses evidenced the distinctiveness of the Ethiopian germplasm. The gene pools from Syria and Jordan, closely resembling each other, appeared separate from all others. A certain peculiarity was also shown by the germplasms from Greece, Morocco and France, while the remaining countries clustered into four groups. The results of the present evaluation could provide useful information for breeding activities, germplasm collection, and establishment of ‘core’ collections. Evidence is presented that environment played a major role in creating the overall variation for the considered traits, although germplasm exchange seemed also an important factor.

Climatic adaptation in subterranean clover populations

SummaryLong-term persistence and, hence, agronomic success as a pasture of the annual species subterranean clover depend primarily on seed yield and seed survival over seasons. In natural populations, plant characteristics influencing seed setting and formation of seed reserves in the soil are expected to be ‘adjusted’ to the prevailing environmental conditions of the sites of origin. Knowledge on plant/environment relationships may provide information on adaptive strategies of persistence, and guidelines for selecting adapted varieties to specific conditions. On pure lines from a number of populations such relationships were assessed for flowering time, seed yield, burr fertility, individual seed weight, initial hardseededness, and rate of hardseededness breakdown over summer. Flowering time decreased on decreasing annual rainfall, i.e., on shortening the growing season, as adaptive response to the need of producing adequate seed before the onset of the dry season. Individual seed weight decreased on decreasing rainfall, and increasing temperatures. Hard-seed maintenance over summer was higher in populations from hot and dry environments, where the marked effect of temperature on hardseededness breakdown exerts a strong selective pressure. Within-population variation, assessed on flowering time, was particularly wide, with early genotypes occurring even in populations from long-season environments. The adaptive relevance of maintaining high levels of within-population polymorphism to cope with unpredictable climatic fluctuations is discussed. Number of constituent lines as a measure of the population structure, and intra-population variation were both influenced by altitude and rainfall, tending to decrease as the climatic selective pressure becomes severe, under both low-rainfall, hot conditions and high-elevation, cold-prone environments.

Geographic variation in tetraploid wheat (Triticum turgidum spp. turgidum convar. durum) landraces from two provinces in Ethiopia

There is considerable wealth of genetical and morphological variation in tetraploid wheat collected from Ethiopia by past expeditions. Several authors have speculated on the reasons for this concentration of diversity so far removed from the centre of origin of wheats in West Asia. The present study reports results of evaluation carried out on material collected in the early 1970s from Ethiopia. The landraces from the two provinces Shewa and Tigray were found to be distinctly different. This divergence was attributed to the differences in environmental conditions between them. Wide differentiation among landraces within each province was also present. The Ethiopian farmers practice of growing composite cultivars in the field has resulted in bulk samples of Ethiopian landraces containing several agrotypes. The proportion of total variance due to differences among agrotypes within landraces was by far the greatest found in this study, followed in most cases by the variation among landrace populations within provinces which exceeded, in turn, the variation between province gene pools. The optimal strategy for further germplasm collections and implications for improvement and conservation in locally-based community gene banks are discussed.

Agronomic value and plant type of Italian durum wheat cultivars from different eras of breeding

Durum wheat has been subjected to intense breeding in Italy due to its local economic importance. Four groups of Italian cultivars representative of different breeding eras were compared in northern Syria for yield potential and morphophysiological features at a moderately favourable site, and drought tolerance at a stressful site. Group 1 included indigenous landraces; Group 2 comprised genotypes selected from exotic landraces (released in 1920s–1930s); Group 3 included genotypes selected from crosses or mutagenesis involving Group 2 materials (1950s–1960s); Group 4 comprised genotypes selected from crosses between CIMMYT and Group 2 materials (from 1970s). Under moderately favourable conditions, a yield increase of 1.03 t ha–1 was observed from Group 1 through Group 4, corresponding to a genetic gain of about 0.017 t ha–1 per year. Such increase was only partly accounted for by a parallel increase in spike fertility and seed weight. Plant stature decreased dramatically from Group 1 to Group 4; a remarkable reduction of height was already attained in Group 3, before the introduction of dwarfing genes from bread wheat. Earliness of heading and grain filling duration increased consistently across breeding phases, the length of crop cycle remaining almost unaltered. No significant improvement of drought tolerance resulted from the breeding activity, suggesting the need to put more emphasis on selection for real stress tolerance rather than escape. Overall variation for morphophysiological traits, assessed by a principal components analysis, highlighted the great diversity among the Group 1 cultivars, while variation within Groups 3 and 4 was lower. Indigenous landraces, little used in the breeding history, as well as novel, unexploited exotic germplasm sources could contribute to broaden the crop genetic base in the region.

Yield vs. morphophysiological trait-based criteria for selection of durum wheat in a semi-arid Mediterranean region (northern Syria)

Abstract The value of germplasm-specific and general indexes of selection based on morphophysiological traits was assessed as an alternative to conventional yield-based selection for grain yield improvement of durum wheat in a semi-arid Mediterranean region. General indexes were developed from the evaluation of a collection of 503 landrace accessions. Specific indexes were also defined for each of the durum wheat types mediterraneum typicum and syriacum as well as for a third germplasm group including mostly Mediterranean material pertaining to neither of these types. Indexes included two or three traits among the following: displacement from optimal heading date (difference in absolute value of days from the mean heading date of three control cultivars), early growth vigour, kernels per spike and kernel weight, the two yield components being alternative to each other. The efficiency of selection criteria was assessed in another set of 64 entries in terms of predicted yield responses and actual yield gains over target environments other than that of selection. Each of the three environments acted by turns as the selection environment and the remaining two as the target environments. These environments allowed for the assessment of selection criteria over a wide range of seasonal rainfall and mean yield levels. Large genotype×environment interaction was observed for yield and early vigour. Ranking of selection indexes for predicted and actual yield responses were fairly consistent, indicating an advantage of general indexes. The best among them, including heading displacement and kernels per spike, was, on the average, 20% and 11% more efficient than yield-based selection in terms of predicted and actual responses, respectively. The advantage of this index was the consequence of the absence of covariation and the moderate to high values of genetic correlation with yield over target environments, heritability and ratio of genotypic to genotype×environment interaction variance of its component traits.

Performance of durum wheat landraces in a Mediterranean environment (eastern Sicily)

SummaryThe evaluation aimed at identifying landrace genotypes adapted to the rather unfavourable growing conditions of durum wheat in Sicily, to be used as parental material in a breeding programme. The trial was carried out in three seasons experiencing varying climatic conditions, and included 75 landraces, 25 of which were selected under severe drought in Syria. Wide differences were observed for most traits among genotypes and seasons of evaluation. Yields of the best performing entries identified in each season never significantly differed from that of the best check variety. The top-yielding landraces were consistently better than the remaining entries for the three yield components, viz. number of spikes per plant, number of kernels per spike and mean kernel weight. In the driest season they were also significantly earlier in heading, confirming the importance of earliness under drought. An analytical breeding approach relying on an array of morpho-physiological traits as selection criteria did not seem appropriate for the given environment, as the variable stress level enhanced the importance of specific traits under specific situations. The genotypic response was largely season-specific. Nonetheless, five landraces were in the best group in all seasons. The selection made in Syria also appeared somewhat effective in Sicily, particularly in the less favourable seasons.

Developing a tall durum wheat plant type for semi-arid, Mediterranean cereal–livestock farming systems

Abstract Durum wheat cropping in semi-arid areas of West Asia and North Africa is frequently integrated into a cereal–livestock farming system. The wheat straw, mostly used for feeding animals, represents an important commodity, its average sale price per unit weight being not less than 40% of that of grain in three recently surveyed areas. There is uncertainty whether the widespread, short-statured wheat plant type could be economically preferable in these environments relative to a tall type, especially when considering straw yield. Within the Mediterranean durum wheat gene pool, mediterraneum typicum germplasm possesses a markedly tall stature, implying high straw yield. In a first phase of evaluation under prevailing conditions of northern Syria, 13 entries characterized by early heading and good agronomic performance were identified from a collection of about 2000 Tunisian and Algerian accessions. In a second phase reported here, these entries were evaluated in relation to two widely grown adapted cultivars, i.e., the semi-dwarf variety ‘Cham 1’ and the local landrace ‘Haurani’, across four environments of northern Syria diversified for rainfall and soil characteristics. In an economic assessment, the straw value was expressed in terms of grain-equivalent, defining an economic yield as: grain yield +(0.40× straw yield ) . Compared with the control cultivars, the mediterraneum typicum entries were taller but tended to later heading with a similar grain filling duration. However, a few entries as early as the controls were also found. Almost all exotic entries outperformed ‘Haurani’ for economic yield. Two entries showed significantly higher (P 12%) and aerial biomass across environments than ‘Cham 1’, owing to higher straw yield and similar grain yield. They compensated for the relatively lower spike fertility by heavier kernels. Genotype×environment interactions were generally limited for yield-related traits. Straw yield was closely associated with plant height (r=0.76, P

Diversity and geographic distribution of stem solidness and environmental stress tolerance in a collection of durum wheat landraces from Turkey

Variation and geographic distribution of stem solidness and environmental stress tolerance were assessed under dryland conditions in a collection of 2420 durum wheat landrace morphotypes collected in 28 administrative provinces of Turkey. The former trait is known to confer resistance to wheat stem sawfly – a serious pest insect in West Asia and North Africa. Both characters were scored on a visual five-level scale. Score mean values and frequency distributions in the different provinces were significantly different for both traits according to analysis of variance and chi-square test, respectively. Two groups of provinces emerged with high frequency of solid-stemmed, and hollow-stemmed accessions, respectively. The former could be of interest in durum wheat breeding against the sawfly. The group of solid-stemmed province germplasms was collected at lower altitude than the other, being also different on average for higher temperatures and evapotranspiration, and shorter growing season at sites of origin. Overall frequency of morphotypes tolerant to stress conditions prevailing in the evaluation site was rather low (10%). This low frequency may be due to low adaptation of materials in this harsher environment than those of origin where rainfall is usually higher and temperatures markedly lower. Nonetheless, differences among provinces in frequency distribution of stress tolerant morphotypes were evidenced. The relatively more tolerant gene pools originated either along the western coast or in the southern part of the country, along the ‘Fertile Crescent’. The least tolerant province germplasms originated either in the North along the Black Sea or in the highlands of the eastern Anatolian Plateau. Germplasm from provinces Malatya and Izmir combined good levels of both stem solidness and stress tolerance.

Diversity and geographic distribution of adaptive traits in Triticum turgidum L. (durum group) wheat landraces from Turkey

SummaryA collection of 2,420 accessions derived from single-spike population samples of durum wheat landraces collected in 1984 from 172 sites in 28 provinces in Turkey was evaluated for nine adaptive traits at the ICARDA research station at Tel Hadya, near Aleppo, Syria. Differentiation of these accessions among provinces was found for number of days to heading, maturity, grain-filling days, as well as for plant height, peduncle length, number of spikelets per spike, spike length, awn length, and kernel weight. The first three canonical variables accounted for 90% of the total variance. Canonical analysis also revealed significant correlations to province mean temperatures, altitude, latitude, and length of the growing season, but not with total seasonal rainfall. Eight distinct groups of provinces were identified by cluster analysis. These clusters had both geographical orientation to eastern and western Turkey and to agroecological zonation for clusters having both eastern and western provinces. Accessions were found with high kernel weight, early heading and maturity, and awnless spikes which could be utilized in crop improvement programs targeted at either favorable or stressed environments.

Geographic variation for spike and grain characteristics in durum wheat germplasm adapted to dryland conditions

SummaryA set of 109 durum wheat accessions, selected from a world collection for their adaptation to dry environments, were further evaluated under moisture-limiting conditions. The entries were subdivided into 9 gene pools based on their country of origin. Data are presented to assess the phenotypic variation and distinctiveness of these pools for some spike and grain features. Analysis of variance revealed highly significant differences among materials of diverse origin for all traits except protein content. Within-country variation was generally wide as regards spike length and 1000-kernel weight. The Ethiopian germplasm presented a remarkable variability and distinctiveness. Entries with interesting values for breeding purposes were detected in most country gene pools. In general, selection of germplasm adapted to harsh environments did not result in a loss of variability for the considered traits, with the possible exception of protein content. Ethiopian entries presented the highest number of significant pairwise character correlations. The two most important traits in a discriminant analysis by country of origin were spike density and 1000-kernel weight. Diversity among gene pools was further assessed by a canonical analysis. The first three canonical variables explained 90% of the total variance. The gene pools of Ethiopia, Greece, Egypt and Jordan appeared clearly distinct from the other germplasm subsets studied. Geographically distinct patterns emerging from this study could be the result of the combined effect of natural and human selection.