Divergent full-sib recurrent selection for germination at low temperature in a maize population

Summary Four cycles of divergent full-sib recurrent selection for the ability to germinate at low temperature were conducted in a maize (Zea mays L.) F₂ population. The selection criterion was the high (H) or the low (L) value in algebraic terms of the difference (DG) between germination percentage at 9.5°C (G9.5) detected 19 days after sowing and germination percentage at 25°C (G 25) seven days after sowing; both traits were evaluated in a controlled environment (germinator). Direct and correlated responses estimated during the course of selection were in accordance with those evaluated at the end. Selection for H led to populations with higher DG values, while the reverse was noted for L; differences between H and L populations increased in successive selection cycles, though divergence tended to level off. Selection for H also resulted in higher G 9.5 (day 19), shorter germination time and more flinty kernels, while selection for L led to responses in the opposite direction as well as to a lower G 9.5 detected 37 days after sowing (i.e. at the end of germination). In contrast, responses were negligible for G 25 and varied erratically from one cycle to another for kernel weight.Abbreviations DG (G 9.5–G 25) - FS full sib - GI germination index - G 9.5 germination percentage at 9.5°C - G 25 germination percentage at 25°C - H high DG value in algebraic terms - KT kernel type - KW kernel weight - L low DG value in algebraic terms     

Reproductive compatibility studies between wild and cultivated strawberries (Fragaria × ananassa) to obtain “bridge species” for breeding programmes

The Fragaria genus has become relevant due to worldwide economic importance of the octoploid hybrid F. × ananassa. Interspecific hybridizations are widely employed in breeding programmes to introduce useful characteristics from wild species to cultivated varieties, although many reproductive barriers prevent gene flow between species. Hybrid genotypes that can act as a bridge between related wild species and cultivated strawberry could be useful to overcome those barriers. The aim of this work was to obtain interspecific hybrids of Fragaria and to analyse possible reproductive barriers. In the Banco de Germoplasma de Frutilla‐UNT, crossings were carried out among wild species of Fragaria with different ploidy levels and cultivated strawberry. To confirm hybrid condition of genotypes obtained, histological techniques and microsatellite markers were used. When wild species were crossed with cultivated strawberry in both directions, there was low production of achenes, while in crosses between wild species of Fragaria genus, achene production was very high. The percentage of germination of achenes was high when crossed species had the same ploidy level, and very low or null when they presented different ploidy levels. Although pre‐zygotic incompatibility associated to the degree of domestication and postzygotic barriers related to different ploidy levels of the progenitors were detected, new hybrid genotypes of Fragaria were obtained. These new hybrids could be used as “bridge species” in breeding programmes, since preliminary results showed no incompatibility barriers when they were crossed with Duchesnea indica.     

Enhanced pollen grain embryogenesis and plant regeneration in anther cultures of Brassica juncea cv. PR-45

Summary Pollen grain embryogenesis in anther cultures of Brassica juncea cv. PR-45 was considerably enhanced by treating the donor plants with 4 mll^-1 (v/v) of ethrel or delayed sowing of the donor plants, the latter treatment being superior. The anthers derived from plants sown about two months after the normal sowing period showed 18% androgenesis as compared to 3.5% in the control.Pollen grain embryos normally showed very poor germination (10%) on B₅ or B₅ containing GA₃. However, ABA or cold treatment promoted normal germination of these embryos. Exposure of the embryos to 4°C for 6 days, which proved to be the best treatment, induced 66% germination of the embryos.     

Techniques for collecting,handling germinating,and storing of pollen of the filbert (Corylus spp.)

Summary Temperature and humidity immediately before dehiscence were important in maintaining viability and germination of filbert pollen. Air temperatures at or above 23°C during dehiscence and pollen storage resulted in nonviability after 8–24 h. Cut branches bearing elongating catkins when exposed to temperatures of 18°±2°C during dehiscence yielded viable pollen. Manganese and boron added to the medium did not significantly increase germination, while 10–100 p.p.m. boron appeared to inhibit it. Storage tests indicated that filbert pollen viability may be maintained at 92% relative humidity and –18°C for at least 12 months.Also published as Tech. Paper No. 2305, Oregon Agricultural Experiment Station.     

Some consequences of pollen storage in the raspberry (Rubus idaeus L.)

Summary Raspberry pollen was stored at 5°C and –13°C for six months and then tested for its ability to induce pyrene set and the production of viable seedlings, and for its effect upon the segregation of a major gene s. Only pollen stored at –13°C gave a pyrene set and germination percentage adequate to produce sufficient seedlings for a breeding programme. It is suggested that tests of pollen viability in the raspberry should include studies of pollen germination, and the effect of this pollen on pyrene set and seed germination. Possible causes of the loss of viability in the pollen stored at 5°C are discussed.     

Embryo rescue,for the production of F1 hybrids,in English rose

Summary The ability to recover embryos from achenes resulting from two sexual crosses of English rose varieties was investigated. Functional germination of recovered (rescued) embryos was considerably higher than for seed material when germinated conventionally. This technique also enabled the germination process to be fully controlled, and the aseptic techniques employed, avoided death of the germinating embryo due to fungal or bacterial infection. Seedlings, produced from recovered embryos, were successfully transferred to glasshouse conditions and matured to flowering plants. Many such plants exhibited combined floral characteristics of the two parent lines. The effects of media type, carbohydrate source and specifically the growth regulator BAP on the germination of recovered embryos was also assessed. The low percentage germination observed for achenes as used in this study, was due to both physical and chemical restrictions on the embryo. It is now therefore possible, to use embryo rescue techniques on English roses to recover flowering plants, of potential commercial value, that would normally be lost after sexual crossing.Abbreviations BAP 6-benzylaminopurine     

Variation among Andean races of maize for cold tolerance during heterotrophic and early autotrophic growth

Cold in the initial growth stages is an important stressfactor for maize grown in regions with a temperate climate,particularly in case of early sowing. Sources of tolerancehave been identified in adapted genotypes, but promisinggenes for cold tolerance should also be found in materialdeveloped under the lower-temperature margins of the cropdistribution. This research was conducted in order to testAndean maize accessions for cold tolerance expressed duringboth the heterotrophic and early autotrophic growth stages.Experiments were conducted in controlled environments tostudy cold tolerance traits (germination %, germinationindex and plant growth rate) at continuous 10^°C (heterotrophic growth) and at varying 10–16^°C (autotrophic growth). An experiment was also performed inthe field with early sowing (both heterotrophic and autotrophic growth). In each experiment, a control trialwas conducted in more favourable conditions (i.e. continuous25^°C in a controlled environment or late planting inthe field) so that cold tolerance traits could also beexamined as the ratio between the stress and the controltrial. None of the accessions was superior for all coldtolerance traits. However, several Andean maize accessionsoutperformed the US Corn-belt hybrid checks for one or moretraits, both in heterotrophic and autotrophic growth. Overall, BOZM 855, PMS 636, Poblacion D, Poblacion E andBOZM 696 were the best accessions, suggesting that they canbe a promising source of genes for improving cold toleranceof adapted maize genotypes.     

Genetic differences in growth within and between Lycopersicon species

Summary Growth analyses were carried out on 88 accessions of five Lycopersicon species. Experiments were conducted in a climate room at 19/14° C day/night temperature which was irradiated at 20 W/m² for eight hours per day. Large differences in plant weights between wild species and the cultivated tomato were observed from 44 to 84 days after sowing. The increase in plant dry weight could be described by a second order polynomial function. When compared at a standardized plant weight of one gram, the relative growth rates (RGR) of the wild and cultivated accessions ranged from 5.3 to 11.8% and 8.5 to 12.2% per day respectively, limiting the use of wild species as sources for strong growth. When expressed at plant weights of one and three g large differences in decrease of the RGR were observed within L. esculentum. The modern hybrid tomato cultivars were among the fastest growing genotypes, with a relatively slow decrease in RGR.     

Compatibility and incompatibility in witloof-chicory (Cichorium intybus L.). 1. The influence of temperature and plant age on pollen germination and seed production

Summary For the production of inbred lines and F₁ hybrids in witloof-chicory information is wanted on characteristics such as the incompatibility system. These characteristics can only be studied properly if the influence of temperature and physiological status of the plant on pollen germination and seed production is known. Investigations were carried out with 9 self-incompatible (SI) and 6 self-compatible (SC) clones in glasshouses of the IVT phytotron at constant temperatures of 10, 14, 17, 20, 23 and 26°C. In general, in vivo pollen germination percentages were rather low after self pollination with an optimum for germination around 17–20°C. No seeds were formed at the lowest temperature (10°C) while seed production for SC clones was usually (rather) good at higher temperatures. At 26°C seed production in some clones decreased. Both pollen germination and seed production decreased at the end of the flowering period. There was a rather positive relationship at e.g. 17 and 20°C between pollen germination after selfing and seed production. When no pollen germination was observed, no seed formation occurred. When pollen grains did germinate, seed development would not necessarily occur in all cases. So this relationship only enables negative mass selection for SC.     

Ecotype differentiation of Ribes rubrum in Norway

Summary Clones of Ribes spp. from 6 regions in Norway and from Denmark, together with a commercial variety, had shown differences in phenological and morphological characters. However, some crossing between wild and cultivated material was suspected to have occurred. A cluster analysis was performed in order to regroup the clones. The results for both vegetative and generative characters showed that most of the clones had a common origin. Some differentiation had occurred between wild and cultivated types and also between northern and southern types (north and south of 61° N resp.). These may be considered to be different ecotypes. The pattern is compared with that of other species.     

The breeding systems and some interspecific relations of a number of African Trifolium spp.

The breeding systems of 12 species and varieties of Trifolium from Africa were investigated. One annual and the three perennial species were allogamous and self-incompatible, the other annuals were autogamous.The effect of temperature on pollen germination and growth was variable. In some species high temperatures (30°C) adversely affected pollen germination and low temperatures (20°C) in others. A high humidity (93–98% R.H.) was essential for good pollen germination and growth.Approach grafts indicated that these species were closely related, however, this method of grafting may not be as reliable as the cleft graft for assessing species relations. From hybridization attempts between seven species, it appears that some interspecific hybrids may be possible within this group.     

Interspecific hybridization in the genus Gossypium through embryo culture

Summary With embryo rescue and culture techniques interspecific hybrids have been obtained amongst diploid cultivated (Gossypium arboreum, G. herbaceum) and wild species (G. stocksii, G. anomalum) of cotton. The early abscission of the young bolls was prevented by repeated application of growth regulators followed by the culture of immature hybrid embryos (15 days after pollination). The best growth and development were obtained on modified Murashige and Skoog's medium with supplements. The plants were stouter when the cultures were first incubated in the dark for 15–25 days, followed by exposure to light. The hybrid plants transferred to soil developed further and matured, and were more or less intermediate between their respective parents.     

Low temperature storage of pistachio pollen

Summary Pollen from four male pistachio (Pistacia vera L.) clones was stored at –196°C and –20°C for up to 12 months and tested for ability to germinate in vitro following a period of hydration at high humidity. Germination of fresh pollen was high (>80%) for each clone. At –196°C, pollen of cv. Peters survived freezing, storage and thawing with no loss of germinability; pollen of the other three clones had sharp declines in germination possibly attributable to cellular lesions incurred during freezing or thawing. When the relative humidity of the –20°C storage environment was maintained at or near 33%, Peters pollen had high rate of germination through 12 months storage. Without control of relative humidity, Peters pollen germination was high at 4 months, but declined at 12 months. Germination requirements became more exacting for pollen stored at –20°C for 12 months at suboptimal humidity conditions. Pollen of the other three clones did not tolerate storage at –20°C as well as Peters pollen regardless of the storage humidity environment.     

Increasing embryogenesis and doubling efficiency by immediate colchicine treatment of isolated microspores in spring Brassica napus

The effect of colchicine on induction of embryogenesis andchromosome doubling during microspore culture was evaluated in twoF₁ hybrids of spring oilseed rape (Brassica napus L.). Immediatecolchicine treatment of isolated microspores with the concentrations 50 and500 mg/L for 15 h stimulated embryogenesis and produced largeamounts of healthy-looking embryos. These normal embryos germinatedwell at 24 ^°C after being transferred to solid regeneration mediumand an initial period of low temperature (2 ^°C) for 10 days, andcould directly and rapidly regenerate vigorous plants. A high doublingefficiency of 83–91% was obtained from 500 mg/L colchicinetreatment for 15 h with low frequency of polyploid and chimeric plants.The present experiment showed that a treatment duration of 30 h revealedless positive effects on embryogenesis and doubling efficiency, especially athigher colchicine concentration (1000 mg/L). Poor embryogenesis andembryo germination were observed from ordinary microspore culturewithout change of induction medium and colchicine treatment, and severalsubcultures were required for induction of secondary embryogenesis andplant regeneration.     

Embryo rescue in Rosa hybrida L.

Summary Two crosses between Rosa hybrida L. cultivars, that fail to produce progenies by conventional means, were carried out. In one of them, total hip abscision occured seven weeks after pollination; in the other one, only 2% of the fertilized hips remained on the plants after eleven weeks. Four- and five-week-old fertilized ovules were isolated in the first cross and six-week-old embryos in the second. The ovules were cultured on six media which differed in their mineral salt and sucrose concentrations while the embryos were cultured on only one of these media and eventually cold treated for one month at 4° C before being placed in a culture room set at 23° C. The embryos that had been isolated in ovulo when they were still not visible under a binocular lens developed atypically. The embryos isolated in ovulo when they were heart-shaped and on average 0.27 mm long performed in ovulo germination on some media and/or enlargement on all of them after two weeks; after another two week culture, once isolated from the ovule, all of them germinated. The cultured isolated embryos, that were exposed to cold, enlarged and germinated more rapidly when placed at 23° C than those not exposed to cold. Furthermore, the plantlets resulting from untreated embryo germination were characterized by large cotyledons which were only partially green. These results are discussed in regard to embryogenesis, precocious germination and dormancy.     

Interspecific hybridization between sunflower and wild perennial Helianthus species via embryo rescue

Interspecific crosses were made between the cultivated sunflower inbred line HA89 and accessions of five wild perennial Helianthus species (H. giganteus L., H. laevigatus T. & G., H. resinosus Small, H. pauciflorus Nutt. and H. decapetalus L.) resistant to broomrape ( Orobanche cernua Loefl.). Using the genetic male-sterile isogenic version of that line as female, successful reciprocal crosses were also obtained with all these wild species except with H. decapetalus. Five-day-old hybrid embryos were excised and cultured in vitro. In all cases, few mature plants were obtained from embryos in early developmental stages (early heart and globular) but up to 28% mature plants were obtained from embryos in later stages of development. Very immature embryos were difficult to excise without damage. Hybrid embryos and mature plants were obtained from all five wild species. Interspecific hybrid embryos from different wild species showed distinct developmental potentials, the proportion of hybrid embryos in different developmental stages varying among species. Differences in the proportion of hybrid embryos at the several developmental stages were also obtained for the reciprocal crosses (cultivated × wild), which showed higher proportion of fully developed embryos. Hybrids involving H. giganteus and cultivated sunflower were difficult to obtain without the use of embryo culture. Embryo culture proved to be an useful tool to overcome post-zygotic hybrid incompatibility in different Helianthus spp., and facilitated interspecific transfer of resistance to O. cernua. This revised version was published online in July 2006 with corrections to the Cover Date.     

Annual shoot growth in different populations of Lonicera involucrata collected in North America and grown in Norway

Summary Seeds were collected from shrubs and brushwood of Lonicera involucrata (Rich.) Banks ex K. Spreng. in coastal Oregon (44–45° N) and interior British Columbia (54–55° N). The annual shoot growth of the resulting half-sib families and populations was studied in Ås, Norway (60° N). The move of these locally adapted types to a new environment revealed the great genetic variation within and between provenances. The start and duration of the growing period were mainly determined by latitude, while the growth rate varied more between provenances than within. Different statistical approaches are discussed.     

Differential cold sensitivity of pollen grain germination in two Prunus species

Summary Pollen grains from selected cutivars of almond [Prunus dulcis (Mill.) D. A. Webb] and peach (Prunus persica Batsch L.) were exposed to a range of temperatures between 1°C and 34°C on a thermogradient plate. Pollen germination at temperatures below 9°C was conspicuously greater in almond than peach. Miximal germination percentages were attained at about 16°C (almond) and 23°C (peach). The two species did not differ in their capacity for pollen tube elongation over a broad range of temperatures. Maximal pollen tube elongation occurred at temperatures 5°C to 8°C higher than maximal pollen germination. Species affiliation appeared to be of much greater consequence than chilling requirement or bloom date of the sporophyte in predicting gametophytic response to temperature.     

Impact of natural and human selection on the frequency of the F1 hybrid between cultivated and wild pearl millet (Pennisetum glaucum (L.) R. Br.)

In the Sahel, pearl millet yields are affected by the proportion of hybrid phenotype plants resulting from genetic mixing between domesticated and wild forms. Man counteracts this mixing by applying a production method, the efficiency of which is quantified in this study. Under experimental conditions, cultivated and wild pearl millet were hybridised in order to obtain cultivated pearl millet seeds including a known proportion of F1 hybrids tagged by two different allozymes. These seeds were sown in the field and the cultivation was conducted following practices common in the Sahel. The evolution of the survival rate of plants and the frequency of hybrids were followed over several stages during the season: sowing, germinating, emergence, thinning, flowering and maturing of the seeds. Owing to plant mortality in the experiment, the average tendency was a hybrid frequency that decreased steadily in the first part of the growing season from 42% during germination, to 37% at emergence. It then fell to 17% after the thinning of the plantlets by the farmer. At the end of the cycle, after thinning, only 11% of mature plants were hybrids. Thus, under the combined pressures of natural and human selection, the frequency of hybrids in the field declined drastically. In interaction with natural pressure, the farmer's practices of selection of seeds, sowing in pockets and thinning have the combined effect of heavily selecting the cultivated genotype and limiting without completely preventing the introgression of wild pearl millet genes into the cultivated genome. This revised version was published online in July 2006 with corrections to the Cover Date.     

Gene cloning of ZmMYB59 transcription factor in maize and its expression during seed germination in response to deep‐sowing and exogenous hormones

Discovering the key genes responsible for deep‐sowing germination is very meaningful to cultivate maize varieties with strong germination ability in soil. In this study, ZmMYB59 gene whose functions remain unknown was successfully cloned. Subcellular localization showed that ZmMYB59 was localized in the nucleus. By analysing cis‐acting elements of its promoter sequence, many elements of MYB binding domain responsive to hormones (particularly gibberellin, GA) were found. On this basis, ZmMYB59 expression in different sowing depths, germination stages, tissues and treatments was analysed by real‐time PCR. ZmMYB59 expression levels in embryos or seedlings were significantly decreased with the increase in sowing depth at 2 days or 4 days after sowing (DAS). Further analysis showed that its expression in mesocotyls was also significantly downregulated with the increase in sowing depth at both 6 DAS and 8 DAS. Similarly, seed soaking with 10^‐5 M GA₃ inhibited ZmMYB59 expression in mesocotyls at 3 DAS. These results suggest that ZmMYB59 may play a negative regulatory role in seed germination in deep soil and the regulation is involved in GA signalling pathway.