Selection for fast germination in rapeseed (Brassica napus L. and B. Campestris L.)

Summary Eleven populations of Brassica napus L. and twelve populations of B. campestris L. were subjected to three cycles of selection for fast germination at 2°C and at 25°C. The seeds from the selected populations, and unselected control populations grown in the same environment as the selected populations, were examined for germination behaviour at 2°C and 25°C, and for growth behaviour at 10°C. The populations in both species responded differently in terms of germination behaviour to selection for fast germination. In most of the populations that did respond positively to selection, selection practised at 2°C was superior to selection at 25°C in improving percent germination at 2°C, and was as good as the selection at 25°C in improving germination rate at the higher temperature. Selection for fast germination had no effect on growth characteristics of B. napus and B. campestris populations grown at 10°C. Thus, selection for fast germination at one low temperature may lead to improvement in germination characteristics over a range of temperatures, but will not necessarily lead to improved growth performance of the selected populations.     

In vitro pollen germination and tube growth of tomato (Lycopersicon esculentum Mill.) and its relation with plant growth

Summary In vitro pollen germination at 10°C, 14°C and 22°C of four groups of two pure line tomato varieties was compared with their plant growth at 19°C D/10°C N under controlled environmental conditions. Generally, pollen germination was slow at 10°C but after 6 h the percentage of germination was similar to that at 22°C. Maximum germination was obtained at 14°C already after 4 h. The longest pollen tubes occurred at 22°C. The two varieties within each group differed significantly from each other for percentage of pollen germination. For one group, this difference was greater at 10°C than at 22°C. The varieties in two groups also differed significantly for pollen tube growth. These differences in pollen tube growth rate were greater at 22°C than at 10°C. There was no clear relationship between pollen germination, pollen tube growth and plant growth in any of the four pairs of varieties. The results are discussed with regard to the possibility of pollen selection at low temperature in order to improve the efficiency of breeding for growth at low temperature.     

Genetic variation for seed dormancy in Cuphea laminuligera and Cuphea lanceolata

Summary Various Cuphea species are adapted to temperate climates and characterized by caprylic, capric, and lauric acid-rich seed oils. These fatty acids are solely commercially available from palm kernel and coconut oils; thus, there is considerable interest in Cuphea as an alternative source of these fatty acids. Cuphea is a genus of undomesticated species characterized by seed dormancy and seed shedding. Our goal is to eliminate these domestication barriers in a few species with agronomic potential. Our objective was to survey existing Cuphea laminuligera and C. lanceolata germplasm for genetic variation for seed dormancy (germination percentage after a certain seed storage period). Recurrent half-sib family selection was practiced in various open-pollinated and synthetic populations. Half-sib family seed were evaluated for germination percentages at 26° C after various seed storage periods. There was significant genetic variation among families in every population. Additive genetic variance, half-sib family-mean heritability, and expected selection response magnitudes depended on the length of the seed storage period within a given population. Estimates of these parameters were significantly greater for longer seed storage periods within a population. Heritability estimates ranged from 0.00 to 0.79. Expected half-sib family selection responses ranged from 0.0 to 23.9%. Our study demonstrated there is substantial genetic variation for seed dormancy in C. laminuligera and C. lanceolata.     

Low temperature seed germination of Lycopersicon species evaluated by survival analysis

Summary Low temperature germination responses were evaluated for 18 high altitude accessions representing five wild Lycopersicon species and 19 accessions of L. esculentum which have reputed ability to germinate in the cold. Survival analysis indicated that one accession of L. chilense germinates better at 10°C than PI 120256, the fastest-germinating L. esculentum genotype, and that PI 120256 germinates as well as PI 126435 (L. peruvianum). Additional wild ecotypes exhibiting rapid germination at 10°C were identified from L. peruvianum and L. hirsutum. These ecotypes may possess genetic potential for introgressing cold germination ability into L. esculentum cultivars.     

Storage of avocado pollen

Summary Avocado pollen was stored at a range of temperatures and relative humidities (RH) for up to one year and the pollen was tested for viability in vivo.Pollen stored for one month was capable of germination on the stigma and penetrating the ovule when stored at 4°C with <1,23,55 and 75% r.h. and at -196°C with 0% r.h. Most pollen samples stored at 25 and -15°C at a range of r.h. would germinate on the stigma but none would penetrate the ovule.After one year of storage, pollen at 4°C and <1 and 23% r.h. would germinate on the stigma but would not penetrate the ovule. There was no germination of pollen stored at 4°C and 55 and 75% r.h. Only pollen stored at -196°C and 0% r.h. would penetrate the ovule, but thawing and refreezing once during the year destroyed the viability.     

Analysis of differences in growth of cucumber genotypes under low light conditions in relation to night temperature

Summary Growth of four breeding lines and two cultivars of slicing cucumber with different growth at low temperature and light intensity was analysed in relation to night temperature. Plants were grown from 17 days after sowing at 20°C day temperature and 20, 15 or 10°C night temperature (NT), a light intensity of 24 W/m² visible radiation and a daylength of 8 hours. Data from six successive harvests, ending 47 days after sowing, were analysed according to a MANOVA procedure.RGR, NAR, LAR, SLA and LWR generally decreased with time. Ln W and RGR were largely similar at 20 and 15°C NT, but reduced at 10°C NT. LAR and SLA decreased at each lower NT, whereas LWR increased. NAR was only marginally affected by NT. Significant genotypic differences occurred for 1n W, LAR, SLA, LWR, stem length and percentage of dry matter in leaves and stems at all NT's and for RGR and NAR only at 20°C. Genotypic differences for 1n W could not be explained by differences for RGR, but by differences for initial plant weight.Significant genotype × night temperature interactions were present for LWR. Breeding lines increased LWR in response to lower NT, while that of cultivars remained fairly constant. Implications for breeding are discussed.Abbreviations and definitions L plant length - LA leaf area - W dry weight of the shoot - RGR relative growth rate (the increase in W per unit of time and unit of W) - NAR net assimilation rate (the increase in W per unit of time and unit of LA) - LAR leaf area ratio (the leaf area at time t per unit of W) - SLA specific leaf area (the leaf area at time t per unit of leaf weight) - LWR leaf weight ratio (the leaf weight at time t per unit of W) - RGR NAR × LAR - LAR SLA × LWR - MANOVA multivariate analysis of variance     

Difference of optimum germination temperature of seeds of intact and dehusked japonica rice during seed development

The effects of incubation temperature on germination of intact and dehusked japonica rice that had been harvested every 5 days from 10 days after anthesis (DAA) to 70 DAA were surveyed. At 30 ^°C incubation, the germination percentage of intact seeds at 25 DAA exceeded that of dehusked seeds. This tendency persisted until 65 DAA, when around 95% of both intact and dehusked seeds germinated. Germination percentages of intact seeds incubated at 20 ^°C were lower than seeds incubated at 30 ^°C for all DAA. However, germination percentages of dehusked seeds incubated at 20 ^°C were consistently higher than at 30 ^°C. Germination percentages of intact and dehusked seeds were similar at 20 ^°C incubation. Germination of intact seeds under 34/11 ^°C (16/8 h) was higher than at 30 ^°C. In contrast, germination of dehusked seeds under 34/11 ^°C (16/8 h) was lower than at 30°C. Inhibitory effects of removing husk on germination were observed from 15 to 70 DAA. Almost all of the intact seeds at 45 DAA germinated when imbibed 35, 30 and 25 ^°C, and germination percentages decreased with decreasing incubation temperatures from 20 to 15 ^°C. By contrast, germination percentage of dehusked seeds was highest in 20 ^°C incubation temperature; further increase or decrease of incubation temperature reduced germination percentage. The optimum germination temperature of intact and dehusked seeds of japonica rice differs during seed formation, such that the extent of germination inhibition by husk removal depends on the incubation temperature.     

Reduction of micro-environmental variation in a selection field of rye

Summary With mass selection it is impossible to adjust single plant performance for variation in purely private growing conditions (including instability of development). This was demonstrated by using the character initial kernel weight when honeycomb selection is applied. Further, it was investigated whether reduction for variation for kernel size, depth of sowing and orientation of the kernel at sowing results in reduced phenotypic variation for the mature plant characters on which the selection is based. The conclusion is that with mass selection it is very rewarding to apply a precision drill and to use sieved seed when sowing a selection field. The orientation of the kernel may be neglected.     

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.     

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.     

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.     

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.     

The effect of germination temperature on seed dormancy in Croatian-grown winter wheats

The expression of seed dormancy related to germination temperature was studied in 25 wheat genotypes grown in the field at two locations near Zagreb and ?upanja in Croatia during 2008/2009 growing season. Germination tests were conducted at 15, 20 and 25?°C at harvest maturity (Time 1) as well as after 10?days (Time 2) and 15?months (Time 3) of seed after-ripening at room temperature, respectively. Significant (P?<?0.05) differences among locations (L), temperatures (T) and genotypes (G) as well as significant L?×?T, G?×?L, G?×?T and G?×?L?×?T interactions were observed for weighted germination index (WGI) at both Time 1 and Time 2. At Time 3 significant differences among genotypes for germination percentage were found only at the early stages of germination. The 25 wheat genotypes responded with decreasing WGI mean values (increasing dormancy) as temperature changed from 15 to 25?°C. The rate of dormancy increase with higher germination temperature varied among genotypes. Some genotypes, having similar values of WGI at 15?°C, significantly differed from each other at 25?°C and vice versa. This indicates that the range of germination temperatures included in the present study is useful when testing genotypes for their temperature-dependent dormancy potential. The number of genotypes with WGI values significantly different from the mean, as a measure of the power of germination test to detect differences in dormancy level among genotypes, as well as heritability estimates for WGIs were the highest at Time 1 for 15?°C and at Time 2 for 20?°C.     

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.     

Mass selection of wheat for grain filling without transient photosynthesis

Summary Post-anthesis chemical desiccation of wheat (Triticum aestivum L.) plants in the field eliminates transtent photosynthesis by killing all green tissues, thus revealing the plant's capacity for grain filling from stored stem reserves, as the case is for post-anthesis stress such as drought or leaf diseases. This study was conducted to investigate whether mass selection for large kernels under chemical desiccation would lead to the improve ment of grain filling in the absence of transient photosynthesis.Six crosses of common spring wheat were subjected to three cycles of mass selection from F₂ through F₁ when selection was performed for large kernels by sieving grains from plants that were erther chemically desiccated after anthesis, or not (controls). The resulting 36 bulks (six crosses by three selection cycles by two selection environments) were compared with their respective F₂ base populations, when tested with and without chemical desiccation.Selection for large kernels under potential conditions (without chemical desiccation) did not improve kernel weight under potnetial conditions, evidently because these materials were lacking in genetic variation for kernel weight under potential conditions. In four of the crosses, 3rd cycle selection for large kernels under potential conditions decreased kernel weight under chemical desiccation. On the other hand, selection for large kernels under chemical desiccation was effective in improving kernel weight and test weight under chemical desiccation, depending on the cross and the selection cycle, with no genetic shift in mean days to heading or mean plant height. Selection for large kernels under chemical desiccation was also effective in some cases in increasing kernel weight under potential conditions. The results are interpreted to show that selection under potential conditions and under chemical desiccation operate on two different sources for grain filling, namely transient photosynthesis and stem reserve utilization, respectively. In order to expose genetic variability for stem reserve utilization to selection pressure, transient photosynthesis must be eliminated, as done by chemical desiccation in this study.     

A non-destructive selection method for faster growth at suboptimal temperature in common bean (Phaseolus vulgaris)

Summary A non-destructive method has been developed to select common bean (Phaseolus vulgaris L.) plants whose growth is less effected at a suboptimal temperature. Shoot weight was determined at a suboptimal (14°C) and optimal temperature (20°C), 38 days after sowing and accessions identified with a significantly lower than average weight reduction at 14°C compared to their weight at 20°C. Weight of primary leaves and of the shoot was correlated with seed weight at both temperatures, but no correlation was found between shoot weight reduction at 14°C and seed weight.     

Evaluation of chilling sensitivity in different rice varieties. Relationship between screening procedures applied during germination and vegetative growth

Summary Rice varieties were screened for chilling tolerance during germination and vegetative growth using different techniques. The effects of temperature during germination were investigated from 10 to 25°C. The screening was most effective at 10°C. Time of data collection has to be considered in order to discriminate slow germinating from chilling sensitive varieties. Chilling survival tests (10°C) applied at the 2-leaf stage revealed that different chilling durations brought complementary results: the longer treatments allowed to identify the most tolerant varieties, while shorter treatments allowed to distinguish intermediate from most sensitive rices. Results of chilling tests applied at the 2- and the 8-leaf stages showed a high correlation. Low-temperature electrolyte leakage and low-temperature fluorescence were also highly correlated to each other and to survival tests applied at the same development stage. By contrast, weak correlations were observed between low-temperature germination and plantlet chilling survival. It is concluded that low-temperature electrolyte leakage and low-temperature fluorescence are good indicators of chilling tolerance during the vegetative growth. The possibility to use a chilling screening procedure applied at this stage in order to predict the chilling tolerance at other development stages is discussed.     

Pedigree selection for Gibberella ear rot resistance in maize

The pedigree method is often used for developing inbred lines in maize (Zea mays L.). This study was conducted to assess the effectiveness of pedigree selection for improving resistance to Gibberella ear rot in four maize populations. Selection was based on the severity of ear rot symptoms after inoculation with macroconidial suspensions of Fusarium graminearum (Schwabe) into the silk channel (for two populations) and into the developing kernels (for two other populations). Samples of the selfed families (S₁ to S₅), recovered from remnant seed from the selection programs, were evaluated for disease resistance during three years, using inoculation and evaluation protocols similar to those used during selection. Among-family selection was effective in both of the populations selected after silk inoculation and in one of the populations selected after kernel inoculation. Responses to selection were more evident in later than in earlier generations for both types of inoculation. Changes in the estimated genetic gain over generations were consistent with changes in the variances among families, which tended to increase in early generations and to decrease in later generations. Selection after kernel inoculation seemed to have been more effective than selection after silk inoculation in developing families with more stable resistance. Based on the results obtained here, it seems that responses to family selection could be accelerated without increasing operational costs by increasing selection intensity in later generations and inoculating fewer plants per family.     

Partial control of chromosome elimination by temperature in immature embryos of Hordeum vulgare L. x H. bulbosum L.

Summary Embryos derived from Hordeum vulgare L. x H. bulbosum L. were subjected in vivo to a range of temperatures, and the proportions of hybrid plants which retain both parental sets of chromosomes were determined. Elimination of the H. bulbosum genome was significantly increased at temperatures greater than 20°C and resulted in fewer hybrid plants compared with temperatures below 17.5°C. Embryos were also allowed to develop in situ at 15°C and then transferred to 26°C for 8, 16 or 24h during the first 7 days after pollination. A period of 16 h at 26°C (equivalent to at least one complete mitotic cycle) at 2–5 days after pollination was found to be sufficient to increase chromosome elimination significantly above the levels obtained at a constant 15°C. At this stage (2–5 days after pollination at 15°C) the mean embryonic cell number was 2.3–223.     

The yield stability of CIMMYT'S maize germplasm

Summary Relationships between whole-plant and germination NaCl tolerance and two in vitro measures of NaCl tolerance were evaluated in lucerne (Medicago sativa L.). No significant correlations were observed between relative NaCl tolerance of non-regenerating callus cultures, herbage regrowth, seed or pollen germination, and pollen tube growth. Simulated selection using indirect measures of NaCl tolerance produced small expected gains in relative NaCl tolerance during herbage regrowth and seed germination. These gains were less than 30% of those expected with direct selection for regrowth or germination tolerance. Selection based on the apparent NaCl tolerance of callus tissue or male gamephytes would appear unproductive. Direct selection for NaCl tolerance both at germination and during mature plant regrowth would appear to be necessary to rapidly develop lucerne populations with field-relevant levels of tolerance to NaCl stress.Approved by the Arizona Agric. Expt. Stn. as Journal Series no. 5015.