D. G. Roupakias

Cat3, a third gene locus coding for a tissue-specific catalase in maize: Genetics, intracellular location, and some biochemical properties

SummaryA new and unique catalase isozyme, CAT-3, has been found in Zea mays. It is encoded in the Cat3 nuclear structural gene which is distinct from the two previously described catalase structural genes, Cat1 and Cat2. The Cat3 gene is both tissue- and time-dependent in its expression, being expressed primarily in young leaves and in the pericarp of nearly mature kernels. Cell fractionation experiments, utilizing epicotyl (coleoptile+primary leaf) and mesocotyl cells, suggest that CAT-3 is associated with the mitochrondria where it may play a role in the alternate oxidase pathway. CAT-3 was purified and characterized with respect to some of its biochemical properties. While CAT-3 differs in some of its properties from CAT-1 and CAT-2, it is similar to these and to other catalases in most respects.

Chromosomal location of the catalase structural genes in Zea mays using B-A translocations.

SummaryB-A translocations have been used to map the catalase genes, Cat1, Cat2, and Cat3 of Zea mays. Cat1 was found to be on the short arm of chromosome 5, 9.1 map units from brittle endosperm (bt1). Cat2 was located on chromosome 1S, while Cat3 was located on the distal half of chromosome 1L. There was no linkage between Cat2 and Cat3. The significance of mapping the catalase structural genes is discussed.

Interspecific hybridization between Vicia faba (L.) and Vicia narbonensis (L.): Early pod growth and embryo-sac development

SummaryFertilized embryo-sac development and pod growth was studied in one Vicia faba cultivar, one Vicia narbonensis population and their reciprocal crosses. The initial development of endosperm and embryo was at least four days faster in V. narbonensis than in V. faba. Pods and ovules developed also faster in V. narbonensis than in V. faba. The growth rate of the hybrid pods followed the growth rate of the mother species, but was slower than that of the pods from selfed flowers. In the cross V. narbonensis × V. faba the ovules stopped growing 9 days after pollination, while in the reciprocal cross they stopped growing 15 days after pollination. Hybrid embryo-sacs from V. faba × V. narbonensis were aborted before they reached the stage of 256 endosperm nuclei or 200 embryo cells. Selfed V. faba embryo-sacs reached this stage in less than 9 days after pollination. In the reciprocal cross the embryo-sacs were aborted before they reached the stage of 128 endosperm nuclei or 80 embryo cells. Selfed V. narbonensis embryo-sacs reached this stage at the 4th day after pollination. Given that at these stages the embryo has less than 200 cells it was concluded that an in-ovule embryo culture technique should be developed to obtain hybrid plants.

Anther Culture Response of Barley Genotypes to Cold Pretreatments and Culture Media

The embryoid formation and plant regeneration in anther cultures of three barley (Hordeum vulgare L.) cultivars (Niki, Karina, Thermi), one F1 hybrid (Niki × Thermi), two F2 populations (Niki × Thermi, Niki × Karina), and two F3 populations (Niki × Thermi, Niki × Karina) were investigated in two solid induction media after cold pretreatment for 14 and 28 days at 4°C . The media used (N6 and FHG) differed in their composition and source of energy (maltose in FHG vs. sucrose in N6). Embryoid frequency and green plant regeneration depended on both the induction medium composition and cold pretreatment. The combination of the FHG induction medium with 28-day-long cold pretreatment was the most efficient in haploid embryoid formation and green plant production. In addition, the green plant production was genotype-dependent. Cv. Thermi and F1 hybrid Niki × Thermi exhibited the highest frequency of green plant production. The parent with high or even moderate frequency of embryoid formation in anther culture could lead to the effective production of green plants from the F1 hybrid or the F2 generation for breeding purposes.

Adaptability to organic farming of lentil ( Lens culinaris Medik.) varieties developed from conventional breeding programmes

The development of organic agriculture has raised the demand for crop varieties well-adapted to organic farming systems. Most of the varieties presently cultivated in organic agriculture were developed from conventional breeding programmes. The objective of the present work was to study the adaptability to organic farming systems of lentil ( Lens culinaris Medik.) varieties developed from conventional breeding programmes. Twenty varieties were evaluated over five environments under organic and conventional farming systems from 2005 to 2007. Genotype×system interactions (GSI) for grain yield were significantly different in four out of the five environments and GSI explained 0·03–0·17 of the variance. Spearmans rank correlation index of the 20 varieties between the conventional and organic system ranged from 0·27 to 0·93 in the five environments. Direct selection of the top five varieties in organic systems resulted in significantly higher grain yields than indirect selection in one out of the five environments. However, among the top five varieties, the highest yielding varieties under conventional farming systems were not always the highest yielding varieties under organic farming systems. These results indicate that the demands of organic agriculture for yield performance could be only partially satisfied by varieties developed under conventional breeding programmes.

Comparative efficiency of honeycomb and conventional pedigree methods of selection for yield and fiber quality in cotton (Gossypium spp.)

The effectiveness of honeycomb pedigree selection (HPS) as compared to conventional pedigree selection (CPS) was studied in one intraspecific (G. hirsutum L. × G. hirsutum L.) cross population (population I) and one interspecific (G. hirsutum L. × G. barbadense L.) cross population (population II). Combined selection for yield and lint quality traits was applied for four cycles at two locations for population I and atone location for population II. Finally, the best F6 lines derived by each method, together with the unselected population derived by single seed descent (SSD) and three check cultivars, were tested in comparative experiments, separately for each cross, at the same locations. In both populations the analysis of variance indicated significant differences among the groups of the material tested for seed cotton yield, mean boll weight, micronaire reading, staple length, and uniformity ratio. No significant differences were found with respect to plant height, lint percentage, and fiber strength in population I and with respect to lint percentage and fiber strength in population II. In population I, on the basis of mean seed cottonyield and number of superior lines derived by each method as compared to the check varieties and the unselected SSD population, HPS-lines were superior to CPS-lines for seedcotton yield, fiber length and boll weight. HPS-lines, however, did not differ significantly in seedcotton yield from the best check cultivar Eva. Finally, the material derived by CPS was earlier in maturity than the material derived by HPS and SSD. Also in population II, on the basis of mean seedcotton yield and number of superior lines derived by each method as compared to the unselected SSD population, HPS-lines were superior to CPS-lines. No significant differences, however, were identified between the material of the two methods for lint quality traits. It was concluded that in both populations HPS was more effective than CPS in identifying lines with high yielding ability and good lint quality. This superiority of HPS is attributed, at least partially, to its effectiveness in early generation selection.

Heterosis in Cotton

Heterosis is a term used to describe the phenomenon in which the performance of an F1, produced by the crossing of two homozygous but genetically different individuals, is superior to that of the best parent. Since the time Shull (1914) introduced the term heterosis, breeders have made wide use of this phenomenon, and the list of crops in which heterosis has led to economic gains is ever-increasing (Sinha and Khanna 1975). In addition, the remarkable improvement in yield of maize during the 20th century has largely resulted from utilization of heterotic F1 hybrids (Eberhart 1979). Thus, while plant breeders have been utilizing heterosis for the improvement of crop productivity, the biological basis of heterosis remains unknown. There are, at present, two major theories suggested to explain the genetic basis of heterosis, the dominance and the overdominance hypotheses. In the past, geneticists and breeders found it difficult to approach the dominance vs. overdominance controversy experimentally. Tsaftaris (1995) reviewed the work pertaining to heterosis using molecular analysis and concluded that, in maize, overdominace is the main genetic basis of heterosis. Later, however, Stuber (1995) suggested that the overdominance observed in maize was probably pseudooverdominance (i.e., nearby loci at which alleles having dominant or partially dominant advantageous effects are in repulsion-phase linkage).

Embryo rescue inVicia faba andVicia narbonensis

Embryo rescue in twoVicia faba L. cultivars (‘Polycarpe’ and ‘A-107’) and oneV. narbonensis L. population (A-202) was studied under a 22 ± 2°C/ 16 ± 1° day/night temperature regime. Very young ovules (1.0–1.8 mm long) cultured, in-ovule, on five liquid media remained green for a longer period of time on modified B5, modified Murashige and Skoog and modified Beasley and Ting media than on modified Phillips and Collins and modified Bourgin and Nitsch media. However, no embryo growth or embryo germination was observed. In-ovule culture of older ovules, 6 and 8 days forV. narbonensis and 10 and 14 days forV. faba, on modified B5 liquid medium allowed 6-day-oldV. narbonensis and 14-day-oldV. faba embryos to be rescued. Finally, culture of whole pods of the two species resulted in the rescue of even younger embryos. Thus, plantlets were obtained from as young as 4-day-oldV. narbonensis pods and 11-day-oldV. faba pods.

Plant density affects the reliability of using F1 and F2 yield to predict F3 yield in barley

Prediction of F3 population yield on the basis of the parental lines, the F1, and the F2 generation yield at low and high plant density was studied in barley (Hordeum vulgare L.). Six F1 crosses together with the 7 parental cultivars were evaluated under high plant density with adjacent check plots and under low plant density in a honeycomb design. In the following year, the 6 F2 populations together with the 7 parental lines were also evaluated at high plant density with adjacent check plots. In addition, the 6 F2s together with a check (cv. Athinaida) were evaluated at low plant density in a honeycomb design. During the third year, the 6 unselected F3 populations together with cv. Athinaida were evaluated under commercial cropping conditions in a randomised complete block design with 4 replications at 2 locations. It was found that yield performance of the F3 population could not be predicted by the mid-parental value (MPV). Similarly, the F3 population yield was not effectively predicted from the yield of the F1 ,F 2 ,o r F 1 + F2 generations when they were evaluated under high plant density. In contrast, the F3 population yield was predicted effectively from the yield of the F1 ,F 2 ,o r F 1 + F2 generations when they were evaluated at low plant density. The best results were obtained when the mean yield of the F1 and F2 generations was taken into consideration. It was concluded that low plant density increases the reliability of using F1 and F2 yield per plant in predicting the yield of the F3 populations in barley under crop environment.

Breeding barriers between Gossypium spp. and species of the Malvaceae family

Cotton breeders have long recognised the importance of alien germplasm from the Malvaceae family, especially the cultivated species, as sources of genes for cotton improvement. An understanding of the biological nature of the incompatibility systems that prevent hybridisation and/or seed development is necessary for the successful hybridisation and introgression between cotton and cultivated Malvaceae species (Hibiscus cannabinus and Abelmoschus esculentus). The objectives of the present study were to determine the reasons for reproductive isolation between Malvaceae species. The current study utilised two alien Malvaceae species and established that pollen–pistil incompatibilities are the primary reasons that hybrids with Gossypium hirsutum are not obtained. The alien pollen tubes showed major inhibition of growth in cotton pistils and seldom grew beyond the stigma. Only pollen tubes of A. esculentus grew into the ovary of cotton.