Sex dimorphism in dioecious Palmer amaranth (Amaranthus palmeri) in response to water stress

Main conclusion Phenological isolation can potentially reduce seed output and may be exploited as a novel tool for ecological management of dioecious weeds. Abstract Dioecious plants may benefit from a maximized outcrossing and optimal sex-specific resource allocation; however, this breeding system may also be exploited for weed management. Seed production in dioecious species is contingent upon the co-occurrence and co-flowering of the two genders and can be further disturbed by flowering asynchrony. We explored dimorphism in secondary sex characters in Amaranthus palmeri, and tested if reproductive synchrony can be affected by water stress. We have used seeds of A. palmeri from California, Kansas and Texas, and studied secondary sex characters under natural conditions and in response to water stress. Seeds of A. palmeri from California (CA) and Kansas (KS) were cordially provided by Dr. Anil Shrestha (California State University, Fresno, California) and Dr. Dallas E. Peterson (Kansas State University, Manhattan, Kansas), respectively. Seeds of a third population were collected from mature plants (about 30 plants) from a set-aside field in College Station, Texas. A. palmeri showed no sexual dimorphism with regard to the timing of emergence, plant height, and relative growth rate. While the initiation of flowering occurred earlier in males than females, females preceded males in timing of anthesis. Water stress delayed anthesis in males to a greater extent than females increasing the anthesis mismatch between the two sexes by seven days. Our data provide the first evidence of environment-controlled flowering asynchrony in A. palmeri. From a practical point of view, phenological isolation can potentially reduce seed output and may be exploited as a novel tool for ecological management of dioecious weeds.

Floral Biology and Pollination Efficiency in Yam (Dioscorea spp.)

Yam (Dioscorea spp.) is a monocotyledonous herbaceous vine cultivated for its starchy underground or aerial tubers in the tropics and subtropics. It is an allogamous and polyploid species that reproduces by both sexual and asexual mechanisms. However, many of the landrace cultivars, including most of the popular varieties, reproduce exclusively by vegetative propagation (planting the tubers). These varieties are either sterile or produce sparse and irregular flowering with high flower abortion rate, low fruit and seed set. Production of crossbreed seeds for genetic improvement and for maintaining genetic diversity in yams is, therefore, mainly achieved through natural or managed pollination. Flowering in yam is mostly dioecious and, in some instances, monoecious. Flowering asynchrony, sticky nature of the pollen grains, and cross incompatibility are among the challenges in making genetic progress in yam breeding. There are many limitations in basic and applied knowledge of yam flower biology and pollination. This paper, therefore, reviews the flowering biology, pollination, and methods of improving pollination efficiency in yam breeding programs.

The role of multiple reproductive barriers: strong post-pollination interactions govern cytotype isolation in a tetraploid–octoploid contact zone

Background and Aims Polyploidy is an important contributor to sympatric speciation and assortative mating is a key mechanism driving cytotype interactions in contact zones. While strong reproductive barriers can mediate the coexistence of different cytotypes in sympatry, positive frequency-dependent mating disadvantage ultimately drives the transition to single-ploidy populations. However, comprehensive estimates of reproductive isolation among cytotypes and across multiple barriers are rare. We quantify the strength of isolation across multiple reproductive stages in a tetraploid–octoploid contact zone to understand the potential for coexistence. Methods Assortative mating due to flowering asynchrony, pollinator behaviour, morphological overlap, self-fertilization and gametic competition between tetraploid and octoploid Gladiolus communis in a contact zone in the Western Iberian Peninsula were assessed in natural and experimental populations to quantify reproductive isolation (RI) between cytotypes. Key Results Tetraploids and octoploids have a high degree of overlap in flowering time and similar floral morphology, and are visited by generalist insects without cytotype foraging preferences, resulting in weak pre-pollination RI (from 0.00 to 0.21). In contrast, post-pollination isolation resulting from gametic selection was a strong barrier to inter-cytotype mating, with ploidy composition in stigmatic pollen loads determining the levels of RI (from 0.54 to 1.00). Between-cytotype cross-incompatibility was relatively high (RI from 0.54 to 0.63) as was isolation acquired through self-pollination (RI of 0.59 in tetraploids and 0.39 in octoploids). Conclusions Total RI was high for both tetraploids (from 0.90 to 1.00) and octoploids (from 0.78 to 0.98). Such high rates of assortative mating will enable cytotype coexistence in mixed-ploidy populations by weakening the impacts of minority cytotype exclusion. This study reveals the key role of gametic selection in cytotype siring success and highlights the importance of comprehensive estimates across multiple reproductive barriers to understand cytotype interactions at contact zones.

Penyimpanan Serbuk Sari Jagung dan Potensinya untuk Produksi Benih Hibrida

Production of maize hybrid seed is hindered by relatively poor production by the male line pollen; short live of the pollen which was ascribed to desiccation and dehydration sensitive and flowering asynchrony between male and female lines. The aims of this study were to enhance production and viability of male line pollen and also to determine the suitable storage condition for maintaining pollen viability in order to be used for production of hybrid seed. The research consisted of two experiments. The first experiment was arranged in split plot randomized block design with NPK dosages as main plot (0, 300, 600, 900 kg ha-1) and application of boron as sub-plot (0, 1.5, 3, 4.5, 6 kg ha-1), replicated three times. The second experiment used randomized block design with two factors, i.e. storage temperature (-196 oC and -20 oC) and storage period (0, 1, 2, 3, 4 weeks). The result showed that NPK 900 kg ha-1 increased the number of spike per tassel from 9.3 to 10.7. Application of NPK 600 kg ha-1 or boron 1.5 kg ha-1 improved pollen viability. Combination of NPK 900 kg ha-1 and boron 6 kg ha-1 resulted in the highest pollen viability of 95.3%. Pollen after being stored for four weeks either in -196 ºC or -20 ºC was possible to be used for seed production with 20% seed set.<br /><br />Keywords: boron, freezer, liquid nitrogen, NPK dosage, pollen viability <br /><br />

Influence of geographic distance and genetic dissimilarity among clones on flowering synchrony in a Teak (Tectona grandis Linn. f) clonal seed orchard

Influence of genetic dissimilarity among teak (Tectona grandis Linn. f.) clones on flowering synchrony was studied in a Clonal Seed Orchard (CSO) of teak in Karnataka, Southern India. Flowering phenology was monitored for all the 24 teak clones of the CSO and flowering synchrony between clones was assessed adopting a novel ‘overlap index’. Genetic dissimilarity among these clones was assessed adopting DNA based ISSR (Inter Simple Sequence Repeats) analysis. Large variation in the time of ‘flower initiation’ and of ‘peak flowering initiation’ was observed among the clones belonging to diverse sources, suggesting large asynchronous flowering. Cluster analysis based on ISSR marker indicated that the clones originating from a same source clustered together and there was a clear segregation based on their origin. Correlation analysis revealed a significant negative association between the average Jaccards’s dissimilarity index between pairs of clones and average peak flowering overlap index. Clones from geographically diverse regions had high genetic dissimilarity and also showed high flowering asynchrony within them.

Effect of increased UV-B radiation on the anthocyanin content of maize ( Zea mays L.) leaves

The level of UV-B radiation reaching the surface of the earth is increasing due to the thinning of the ozone layer in the stratosphere over recent decades. This has numerous negative effects on living organisms.Some of the Hungarian inbred maize lines examined under the climatic conditions in Chile exhibited an unusually high proportion of pollen mortality, flowering asynchrony and barrenness. The evidence suggests that this can be attributed to the approx. 30% greater UV-B radiation in Chile.The investigation of this problem within the framework of abiotic stress breeding programmes is extremely important in the light of the global rise in UV-B radiation, which may make it necessary to elaborate a selection programme to develop inbred lines with better tolerance of this type of radiation.In the course of the experiment the same ten inbred lines, having different maturity dates and genetic backgrounds, were tested for five years in Chile and Hungary. The tests focussed on anthocyanin, a flavonoid derivative involved in the absorption of damaging UV-B radiation.Averaged over years and varieties, the total anthocyanin content in the leaf samples was significantly higher in Chile than in Hungary. This was presumably a response at the metabolic level to the negative stress represented by higher UV-B radiation.In the five early-maturing flint lines the anthocyanin contents were more than 45% greater than those recorded in Hungary. This suggests that these genotypes, originating from northern regions, were not sufficiently adapted to the higher radiation level. In these samples higher UV-B caused a sharp rise in the quantity of anthocyanin, which absorbs the dangerous radiation. In late-maturing genotypes the initial content of the protective compound anthocyanin was higher at both locations, so in these types the high radiation level was not a problem and did not cause any substantial change.Similar conclusions were drawn from the results of fluorescence imaging. The F440/F690 ratio indicative of the stress level was higher in late lines with a high anthocyanin content, good tolerance and good adaptability.