Influence of gamma irradiation on pollen viability, germination ability, and fruit and seed-set of pumpkin and winter squash

The influence of irradiation dose (50, 100, 200 and 300 Gray), irradiation time (July 9th, 11th, 15th, 21st and 28th) and pollen age (0th and 1st days) on the pollen viability, germination ability and fruit and seed-setwere investigated in pumpkin (Cucurbita moschata Duchesne ex Poir.) and winter squash (Cucurbita maxima Duchesne ex Lam.). Along with increasing of irradiation dose, irradiation period and pollen age, pollen viability, germinability and fruit and seed-set decreased, significantly. Irradiated and nonirradiated pollens maintained their viability for 1 - 4 days and 4 - 7 days, respectively. Non-irradiated pollens of winter squash were germinated for 2 days and produced the highest germination rate (22.6 and 22.9%) on July 9th and 11th, respectively. Moreover, irradiated pollens were germinated for 2 days at 50 Gray (1.1 - 8.5%) and for one day at 100 Gray (0.6 - 10.4%). On July 9, the fruit-set rate ranged from75.0% (at 50 Gray) to 63.0% (at 100 Gray) by pollination with 0th day pollens in winter squash. Pollination with irradiated pollens at 50 Gray and 100 Gray gave both seeded and seedless fruits depending on irradiation periods. All fruits obtained from pollinations with non-irradiated pollens were seeded. Although irradiated pollens at 200 Gray and 300 Gray were not germinated in medium, they gave fruit more or less, but fruits were seedless. The highest fruit-set rates were determined 75.0% (57SI21) inwinter squash and 26.3 (55BA01) in pumpkin, pollination with 0th day old pollens. In all irradiation times, the percentage of fruit and seed-set of pumpkin was lower than that of winter squash

Some characters of the pollen of spring and summer flowering common oak (Quercus robur L.)

Summer flowering of the common oak is a natural rarity, considering the large area of the species natural distribution. This phenomenon can be classified as an ancestral (atavistic) property. Pollen morphological and physiological characters from spring flowering male inflorescences collected over the period 2004 - 2007 and summer flowering male inflorescences collected in 1999 were compared. The analysis included the pollen of a tree with frequent summer flowering and a control tree with spring flowering only. The size and form of summer pollen differed from the spring flowering pollen. The germination percentage and germination energy depended on the pollen growing medium (0, 5, 10, 15, 20, 25% sucrose solution), year of collection (2004 - 2007), temperature (+5°C and -20°C) and storage period (1 to 24 months). The study results are significant for the explanation of common oak phylogenetic development, and they contribute to the knowledge of pollen characters under the effects of different factors.Projekat ministarstva br. 17302

Functional Androdioecy in Critically Endangered Gymnocladus assamicus (Leguminosae) in the Eastern Himalayan Region of Northeast India

Gymnocladus assamicus is a critically endangered tree species endemic to Northeast India, and shows sexual dimorphism with male and hermaphrodite flowers on separate trees. We studied phenology, reproductive biology and mating system of the species. The flowers are small, tubular, odorless and last for about 96 hours. Pollen grains in both morphs were viable and capable of fertilization leading to fruit and seed set. Scanning electron micrographs revealed morphologically similar pollen in both male and hermaphrodite flowers. The fruit set in open pollinated flowers was 43.61 percent, while controlled autogamous and geitonogamous pollinations yielded 76.81 and 65.58 percent fruit set respectively. Xenogamous pollinations between male and hermaphrodite flowers resulted in 56.85 percent fruit set and pollinations between hermaphrodite flowers yielded 67.90 percent fruit set. This indicates a functionally androdioecious mating system and pollination limited fruit set in G. assamicus. Phylogenetic analyses of Gymnocladus and the sister genus Gleditsia are needed to assess if the androdioecious mating system in G. assamicus evolved from dioecy as a result of selection for hermaphrodites for reproductive assurance during colonization of pollination limited high altitude ecosystems

Evaluating the combined effects of climate change parameters on growth and physiology of Theobroma cacao L.

Climate change scenarios predict increases in the atmospheric carbon dioxide concentration [CO2] leading to global warming and changes in rainfall patterns in tropical regions. This will potentially impact the sustainability of cacao production and the livelihoods of millions of smallholder cacao farmers. Through a series of experiments, carried out under controlled environment facilities (growth cabinets and greenhouses), this research aimed to examine the interactive effects of elevated [CO2], temperature and water deficit on the growth and physiology of juvenile and mature plants of different cacao genotypes. Elevated [CO2] improved photosynthesis and growth parameters in cacao plants. However, the enhancement of growth was more evident in seedlings than matures trees. In seedlings, elevated [CO2] shifted the optimal temperature of photosynthesis by 2.5°C under warming conditions, suggesting potentially increased resilience of cacao to increased temperatures under higher [CO2] when air humidity and soil water is not limited. However, above 36/27°C (day/night) the compensatory effect of elevated [CO2] diminished. The negative effect of increased temperatures on growth and leaf area in juvenile and mature cacao plants, as well as on aspects of reproductive development (pollen viability and fertilisation success), pod growth and pod and bean biomass, were alleviated by elevated [CO2]. However, the apparent susceptibility of some genotypes to increases in temperature seemed to regulate the extent to which elevated [CO2] alleviated the negative impacts of temperature. Under the water-limited treatment, the compensatory effect of elevated [CO2] on photosynthesis and growth of seedlings was still observed but at a lower magnitude. However, temperature increases above 36/27°C exacerbated the adverse effect of water deficit. Genotypic variation in response to the different climate parameters demonstrated the potential for breeding cacao to cope with future scenarios. The results have shown that the impact of climate parameters on cacao are dynamic and interactive in nature, and the effect of a single climate variable may be modulated by others when they occur in combination