Heterosis and mixing effects in barley under drought stress

Yield stability is one of the main breeding objectives in breeding for stress environments, such as the semi‐arid areas of Syria. The objectives of this study were to measure the effects of heterogeneity and heterozygosity on yield and yield stability by comparing doubled haploid lines (DHL) in mixed vs. pure stand (influence of heterogeneity) and F₂ populations vs. corresponding DHL mixtures (influence of heterozygosity). Six barley lines from two gene pools (LR = landraces, EL = experimental lines) were used to produce nine crosses (two LR × LR, three EL × EL, four LR × EL). The F₂ generation and eight DHL per cross were produced from each cross. The six parental DHL, nine F₂ populations, nine 8‐line mixtures and 72 DHL in pure stands were tested in five environments under drought stress in north Syria. The mean superiority of F₂ populations over DHL mixtures for yield traits across environments and cross combinations ranged between 7.5 and 10%. The effect of heterogeneity was small throughout. For grain yield, harvest index, 1000‐grain weight and plant height significant interactions between heterozygosity levels and environments were observed. The effect of heterozygosity for grain yield increased substantially from ‐1.2% in the highest‐yielding environment to 45.6% in the most stressful environment. Interactions between levels of heterozygosity and cross combinations were significant for most traits. F₂ populations were considerably more stable than DHL in pure stands, yet not as stable as DHL mixtures. It is concluded that heterozygosity is more important than heterogeneity in breeding for improved yield and yield stability under drought stress.     

Evaluation of Chlorophyll Content and Fluorescence Parameters as Indicators of Drought Tolerance in Barley

Drought is a major abiotic stress that severely affects food production worldwide. Agronomic and physiological traits associated with drought tolerance are suitable indicators for selection of drought tolerance genotypes to reduce the impact of water deficit on crop yield in breeding program. The objective of this study was to identify indicators related to drought tolerance through analysis of photosynthetic traits in barley （Hordeum vulgare L.）. These traits included chlorophyll content, initial fluorescence （Fo）, maximum primary yield of photochemistry of photosystem Ⅱ （Fv /Fo） and maximum quantum yield of photosystem Ⅱ （Fv/Fm）. Four genotypes （Tadmor, Arta, Morocco9-75 and WI2291） variable in drought tolerance were used to investigate the correlation between these traits and drought tolerance. The results reflected that all of these traits were affected negatively in the four genotypes at different levels of post-anthesis drought stress, but the decrease in drought tolerant genotypes was much less than that of drought sensitive genotypes. The results further revealed that the components of the photosynthetic apparatus could be damaged significantly in drought sensitive genotypes, while drought tolerant genotypes were relatively less affected. On the other hand, the values of chlorophyll content, Fo, Fv/Fo and Fv/Fm in drought tolerance genotypes were significantly higher than those in drought sensitive genotypes under drought stress. It was concluded that chlorophyll content, Fo, Fv/Fo and Fv/Fm could be considered as reliable indicators in screening barley germplasm for drought tolerance.     

Breeding for yield stability in unpredictable environments: single traits,interaction between traits,and architecture of genotypes

Summary Attempts to identify individual traits to use as an indirect measure for grain yield have shown some degree of success in environments where crop yields are affected by no stress or only by predictable stresses. However, analytical breeding has been largely unsuccessful in the case of a) stressful environments characterized by low yields due to high variability in the frequency, timing, duration and severity of a number of climatic stresses, and b) breeding programs where the major objective is greater yield stability defined as a reduction in the frequency of crop failures. Experimental evidence suggests that, when environmental variability is high due to unpredictable differences in frequency, timing and severity of various climatic stresses, each time different combinations of several traits are likely to confer drought resistance. Interaction among traits in determining overall crop response to variable stresses is expected to occasionally enhance the importance of a specific trait in a specific stress situation. In this context it becomes difficult to consider drought resistance as a character with its own identity in terms of inheritance.Assessment and verification of traits based on the use of isogenic lines tends to oversimplify the interactions between traits, as the approach provides information on the effect of a specific trait only in a specific genetic background.At the population level of organisation, the dilemma between selection for individual traits and specific combinations of traits can be translated into the dilemma between selection for individual genotypes and specific combinations of genotypes. The evidence that natural selection under stress conditions has not been able to identify either a single trait or a single genotype with a given adapted architecture of traits, is discussed in relation to germplasm development philosophies to stabilize yield in unpredictably stressed environments.     

The Presence of Granular Excretory Ducts in the Rabbit Zygomatic Gland

The proximal and interlobular ducts of rabbit zygomatic glands show a particular morphological feature consisting of numerous secretory granules localized in the apical cytoplasm of the cells. It is suggested that there is a similarity between these ducts and the granular ducts of submandibular glands in rodents.     

Diversity for Disease Resistance in Barley Landraces from Syria and Jordan

A number of barley landraces collected in Syria and Jordan were evaluated for resistance to yellow rust, powdery mildew, scald and covered smut by inoculating single-head progenies with local pathogen strains during two years of field tests. A large diversity in resistance was observed for each pathogen both between populations of different collection sites as well as between head progenies within collection sites. The level of resistance varied from absolute and partial resistant types up to highly susceptible lines. No consistent association between the environmental conditions of the collection site and the level of resistance of the landrace-lines could be found.     

Selection of Barley Lines for Drought Tolerance in Low-Rainfall Areas

An experiment was conducted at five locations in Jordan (Khanasri, annual rainfall 150 mm; Ramtha, 225 mm; Muwaqar, 150 mm; Rabba, 350 mm; Ghweer, 250 mm) during the 1996/1997 growing season, to evaluate the yield performance and some agronomic traits of 84 barley breeding lines and three long‐term checks (Zanbaka, Arta and Klaxon) for drought tolerance. An α‐lattice design with two replications and six incomplete blocks for each replication was used. Genotype 6 (WI2291/Tadmor) was found to be superior in grain yield, especially compared to the best check (Arta) at the two wettest locations (Rabba and Ghweer). Genotype 21 (Mo.B1337/WI2291/5/Emir/Sb//CM67/3/F8‐HB‐854‐23/121//148‐221/4/CI 08887/CI05761) out‐yielded the best check (Arta) at the driest location (Khanasri), while genotype 61 (Salmas/Arabia Aswad) produced a higher grain yield than the best check (Zanbaka) at Ramtha. The correlations amongst grain yield, biological yield, straw yield, plant height and harvest index were always significant and positive regardless of the location. The correlations amongst days to heading, days to maturity and grain yield were significant at the two driest locations only. This suggests that different phonologies are required to maximize grain yield in wet and dry environments. Also, the relationship between grain yield and the length of grain‐filling period was positive in the wettest location (Rabba), negative in the driest (Khanasri) and not significant at the two intermediate locations. These results emphasize the importance of selection in the target environment and the need to develop early‐maturing genotypes as a way of withstanding drought and high temperatures during the grain‐filling period. A high and negative correlation coefficient was found between the drought susceptibility index and grain yield at the driest site, whereas at the wettest site the correlation coefficient was lower and in some cases positive, indicating the existence of traits that are desirable under drought and undesirable under favourable conditions.     

Decentralized-participatory plant breeding: an example of demand driven research

It is widely recognized that conventional plant breeding has been more beneficial to farmers in high-potential environments or those who can profitably modify their environment to suit new cultivars, than to the poorest farmers who cannot afford to modify their environment through the application of additional inputs and cannot risk the replacement of their traditional, well known and reliable varieties. As a consequence, low yields, crop failures, malnutrition, famine, and eventually poverty still affect a large proportion of humanity. Participatory plant breeding (PPB) is seen by several scientists as a way to overcome the limitations of conventional breeding by offering farmers the possibility to choose, in their own environment, which varieties suit better their needs and conditions. PPB exploits the potential gains of breeding for specific adaptation through decentralized selection, defined as selection in the target environment, and is the ultimate conceptual consequence of a positive interpretation of genotype × environment interactions. The paper describes a model of PPB developed by The International Center for Agricultural Research in the Dry Areas and used successfully in several countries in West Asia and North Africa. Genetic variability is generated by breeders, selection is conducted jointly by breeders, farmers, and extension specialists in a number of target environments, and the best selections are used in further cycles of recombination and selection. Technically, the process is similar to conventional breeding, with three main differences. Testing and selection take place on-farm rather than on-station, key decisions are taken jointly by farmers and the breeder, and the process can be independently implemented at a large number of locations. The model also incorporates seed production. Farmers handle the initial phases, multiplying promising breeding material in village-based seed production systems. The PPB model is flexible; it can generate populations, pure lines, and eventually mixtures of pure lines in self-pollinated crops; as well as hybrids, populations, and synthetics in cross-pollinated crops. PPB has several advantages. New varieties reach the release phase much faster than in conventional breeding, and are better suited to farmers’ needs and willingness to invest in inputs and management. Release and seed multiplication activities concentrate on varieties known to be farmer-acceptable. These advantages are particularly relevant to developing countries where large investments in plant breeding have not yielded returns, and many “improved” varieties developed through conventional breeding are not adopted by farmers. PPB also ensures that biodiversity is maintained or increased because different varieties are selected at different locations. In addition to the economical benefits, participatory research has a number of psychological, moral, and ethical benefits, which are the consequence of a progressive empowerment of the farmers’ communities; these benefits affect sectors of their life beyond the agricultural aspects. In conclusion, PPB, as a case of demand driven research, gives voice to farmers, including those who have been traditionally the most marginalized such as the women, and elevates local knowledge to the role of science.     

Consequences of a decentralized participatory barley breeding programme on changes in SSR allele frequency and diversity in one cycle of selection

Changes in allele type, allele frequency and genetic diversity because of selection by individual farmers and breeders were assessed using simple sequence repeats (SSRs) during one cycle of selection in a decentralized participatory barley breeding programme. Selection by both breeders and farmers resulted in the loss of a number of alleles in the majority of the locations, with more alleles lost in the heterogeneous breeding materials than in the fixed genotypes, indicating selection against undesirable traits uncovered in the heterogeneous breeding materials that are presumably linked to SSR alleles. After selection, significant allelic frequency changes were observed at several loci in both the germplasm groups. As the selection was conducted independently in each location, an allele had a chance of being selected in more than one location, and therefore considering the whole study area the allelic composition and diversity of the original genetic materials was maintained after the selection. The study showed the importance of decentralized participatory plant breeding in maintaining genetic diversity that helps stabilize and sustain production in unpredictable production conditions.