Effect of pre-incubation humidity and temperature treatment on the in vitro germination of avocado pollen grains

Optimum in vitro germination of pollen grain of the avocado cultivars Fuerte, Nabal, Ettinger, Bacon and Zutano occurred at 25 °C. However, there were significant differences between cultivars in percentage germination and relative humidity (RH) requirements for optimum pollen grain growth. The most sensitive cultivar to relative humidity was Fuerte, in which the germination of pollen grain rose from 11.4%, at 40% RH, to about 50%, after one hour at 100% RH. The germination% of Nabal pollen grain was already high at 40% RH and was not increased by higher relative humidity. Increased relative humidity also helped to sustain the viability of avocado pollen. At 30 °C and 5% RH the pollen grains of Fuerte quickly lost its ability to germinate, at 40% RH for 1 hour, germination was reduced spectacularly compared to pollen kept in saturated with moisture environment where it was not affected the first 24 hours. The effects of temperature and relative humidity on fruit-set and yield of avocado are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of nitrogen nutrition on yield and growth of an everbearing strawberry cultivar (cv. Evie II)

Strawberry plants are relatively unresponsive to nitrogen (N) fertilization. Supraoptimal N application also results in excessive vegetative growth, which competes to reproductive growth. Two strawberry field experiments were conducted for two consecutive years using fertigation to investigate the effect of different nitrogen (N) application rates on yield and growth of an everbearing strawberry (cv. Evie II). N was injected weekly into the drip irrigation system at 0, 0.5, 1, 3, and 6 kg N/ha/week the first year and 0, 1, 2, and 3 kg N/ha/week the next year. Fruit yield and fruit number were not affected the first year, but were increased the second year due to N application. However, there was no effect of N nutrition on average berry weight for both years. It was concluded that N fertilization may increase yield and fruit number, but average berry weight remains unaffected.     

Agronomic Assessment of Nitrogen Use Efficiency in Spring Wheat and Interrelations with Leaf Greenness Under Field Conditions

Four spring wheat genotypes (Triticum aestivum L.) were grown without (N0 = 0 kg N ha^?1) and under ample (N1 = 250 kg ha^?1) nitrogen (N) fertilizer in field experiments in two seasons. The aim was to assess genotypic variation in N use efficiency (NUE) components and N-related indices during grain filling thus to identify superior wheat genotypes. Leaf chlorophyll (SPAD) readings at crucial growth stages were employed to help differentiate genotypes. Interrelations between yield and N-related indices with SPAD, where also assessed to explain possible pathways of improving NUE early in the growing season. Results showed that genotypic effects on NUE were mostly evident in 2000, a year with drier preanthesis and wetter postanthesis than the normal periods. ‘Toronit’ almost always had the highest biomass yield (BY) and grain yield (GY). Except in 1999 under N0, ‘L94491? showed the highest % grain N concentration (GNC). Genotypes affected SPAD at almost all stages and N fertilization delayed leaf senescence for all genotypes and growth seasons. Correlations between SPAD at different growth stages and GY, N biomass yield at maturity (NBYM) and GNC were significant (P≤ 0.001), positive and strong/very strong (>r = 0.7). N translocation efficiency (NTE) was inversely related to PANU (~r = ? 0.77, P≤ 0.001), suggesting that N after anthesis is being preferentially transported to the ears to meet the N demand of the growing grains. It is concluded that there is still a large potential for increased NUE by improved N recirculation, use of fast and inexpensive crop N monitoring tools and high yielding, N uptake efficient genotypes.

Abbreviations: NUE, Nitrogen use efficiency; SPAD, Minolta SPAD-502 chlorophyll meter, NHI, nitrogen harvest index; HI, Harvest index; NTE, N translocation efficiency from vegetative plant parts to grain; DMTE, dry matter translocation efficiency; CPAY, contribution of pre-anthesis assimilates to yield; PANU, Post-anthesis N uptake, d.a.s., days after sowing, N0, zero (0) kg ha^?1 applied N fertilizer, N1, 250 kg ha^?1 applied N fertilizer.     

Effects of cultivar,orchard elevation,and storage on fruit quality characters of sweet cherry (Prunus avium L.)

Fruit quality characters were analysed in the sweet cherry cultivars, Burlat, Van, Tragana and Mpakirtzeika, harvested from low (39–59 m), medium (216 m) or high (490–546 m) elevation sites. The effects of storage for 2 or 4 days at 2 °C and 1 day at 20 °C on the fruit antioxidant contents were also evaluated. Tragana and Mpakirtzeika had greater fruit fresh weight (FW) and total soluble solid content compared to Van and Burlat, the latter being the most red colored. Tragana and Burlat had greater total phenolic content and total antioxidant capacity, measured by DPPH extinction, compared to Mpakirtzeika and Van (mean values 204.4 mg vs. 103.7 mg gallic acid equivalent 100 g⁻¹ FW, and 176.1 mg vs. 79.3 mg ascorbic acid equivalent 100 g⁻¹ FW, respectively). The geographic elevation had a marked influence on the cherry antioxidant content in all studied cultivars, apart from Van, with high elevation orchards producing cherries with greater contents of antioxidant compounds compared to lower elevation orchards. Changes in the antioxidant contents during storage were depended on the cultivar and some times on the orchard elevation. Total antioxidant capacity was significantly correlated with total phenolic content in Tragana, Burlat and Mpakirtzeika, but not in Van; nevertheless this was not the case during storage.     

Influence of nitrogen nutrition on nitrate levels of strawberry leaf blades and petioles

Hydroponic and field experiments were conducted to assess the optimum nitrogen (N) levels in strawberry leaves for the appropriate management of its N nutrition under field or protected cultivation. Unlike the common view that leaf petiole is the right plant organ to sample for strawberries, the study showed that the leaf blade, of the most recently fully expanded leaf, is more responsive and therefore a better indicator of the N supply changes in the strawberry plant. This was attributed to the distinctive characteristic of strawberry plants to accumulate high concentrations of nitrates in leaf blades when there is luxury consumption of N.     

Effect of propagation material on some quality attributes of strawberry fruit (Fragaria x ananassa, var. Selva)

In the Mediterranean region, cold-stored plants (summer planting system) are used as the main strawberry planting material (plant establishing period July–August). However, recently fresh plants (winter planting system) have also started being used for strawberry production (plant establishing period October–November). As the plantations originated from cold-stored or fresh plants differ in plant growth and yield, some differences in fruit quality have also been expected; therefore, the objective of the current study was to compare fruit quality of plants originated from different propagation material. Cold-stored plants were well developed before the beginning of the spring harvest, while fresh plants continued growth concomitantly with fruiting. The harvesting period of cold-stored plants lasted 4–6 weeks (second week of April–second half of May). Fresh plants produced fewer and larger fruits than cold-stored plants, but for a longer harvest period, which lasted throughout all summer. Differences in soluble solids and dry matter content between the fruits from cold-stored and fresh plants were observed in the first three sampling dates in both years of the experiment. In some sampling dates, significant differences in anthocyanin, titratable acidity and ascorbic acid content, were observed between fruits of plants originated from different propagation material.     

Effects of NaCl stress on red raspberry (Rubus idaeus L. ‘Autumn Bliss’)

The increasing interest in the cultivation of red raspberry (Rubus idaeus L.) in warmer climates and in the mild-Southern parts of Europe requires better understanding of the salinity effects especially in the primocane-fruiting type cultivars. The aim of this work was to study the response of the ‘Autumn Bliss’ primocane-fruiting cultivar in elevated NaCl concentrations.     

Adaptation,Agronomic Potential,and Current Perspectives of Quinoa Under Mediterranean Conditions: Case Studies from the Lowlands of Central Greece

Quinoa was cultivated for 7000 years by indigenous people of the Andes, but in recent decades it is gaining international attention because of its tolerance to abiotic stresses, the wide genetic variability, and its high nutritional value. Greece was among the European countries and in the Mediterranean basin, the first European country, which since 1995 was involved in the “American and European Test of Quinoa” organized by the Food and Agriculture Organization and the Quinoa Project “CIP-DANIDA.” The experiments (1995–2004) were conducted in the lowlands of Central Greece (Larissa region). The first experiments focused on the adaptation of quinoa varieties to warm and dry climatic conditions and to the effect of plant density on seed yield (SY). Drought, low relative humidity, high temperatures (>32 °C), and long days (during anthesis) were considered unfavorable for seed production. Moreover, crusting and drying up of the soil surface had a negative effect on the proportion (60–70%) of emerged seedlings. The best sowing density is considered to be 25 plants m^?2. Considering the effect of sowing date on SY and quality, it was found that early sowing in March is more suitable (in areas where frost avoidance is ensured), whereas latest (May) sowing was unsuitable and resulted in poor germination. The evaluation of 25 quinoa varieties showed that only 8 (six European and two Latin American) varieties produced seeds, whereas the rest 17 produced only panicles and flowers. Dry matter quality of the produced stems was analyzed for protein and fiber content. Dry stems of the plants remained after seed harvest contained high percentage of fibers (45%). The eight most promising varieties were also evaluated for their yielding potential and their seed composition under contrasting soil properties. Compared to neutral soil conditions, SY in the saline–sodic soil was decreased up to 45%. Mineral and protein content in seeds was higher in the varieties originated from Latin America. SY for some varieties exceeded 1000–1500 kg ha^?1, and seeds were rich in protein (15–18.5%) and minerals content. On a breeding program started in 2002, 23 families have been created using mass selection procedures for the creation of new varieties from plants survived in the saline–sodic soils. These selections had to be evaluated in dense sowing in typical SY experiments, but experimentation was discontinued in the absence of financial support. Farmers’ knowledge gaps on cultivation techniques, the distances from the European markets, and the absence of incentives are probably considered the major obstacles to date for crop’s expansion in Greece. Research should focus on the evaluation of promising genetic material in different agroecological zones including higher altitudes.

Abbreviations: AETQ, American and European Test of Quinoa; FAO, Food and Agriculture Organization; SY, seed yield; a.s.l., above sea level; N, neutral soil; S-S. saline–sodic soil; B, branched plant types; UN-B, unbranched plant types.     

Germplasm diversity and genetic relationships among walnut (Juglans regia L.) cultivars and Greek local selections revealed by Inter-Simple Sequence Repeat (ISSR) markers

Inter-Simple Sequence Repeat (ISSR) markers were used for the assessment of genetic diversity among walnut (Juglans regia L.) selections from Greek native populations in comparison to internationally cultivated walnut genotypes. Similarity coefficient values from 0.13 to 0.93 (with an average of 0.48) were found among the 56 accessions examined, which indicated the presence of a high degree of genetic variability. Most international cultivars were grouped together while most Greek native populations could not be placed into a distinct group. The Greek native population genotypes were found more diverse than the international cultivars. The mean similarity coefficient values for the former and latter were 0.44 and 0.56, respectively. In the cultivar group, two subgroups were distinguished; one consisted of genotypes involving ‘Payne’ and the other ‘Franquette’ in their pedigrees. Some cultivars and populations could not be grouped according to their pedigrees or collection area. Analysis of molecular variance (AMOVA) revealed that a larger part of the genetic variation exists among Greek walnut populations within a collection region (89%) than among the regions (11%). The pairwise regional PhiPT values indicated that the most geographically distant regions are the most genetically differentiated. The high variability existing in the Greek germplasm in combination with their valuable agro-morphological traits suggested that it would be beneficial to utilize this native germplasm pool in walnut breeding programs and germplasm management activities to maximize genetic diversity in cultivated walnut.