Effect of seed age,stratification, and soaking on germination of wild asparagus (Asparagus acutifolius L.)

Wild asparagus (Asparagus acutifolius L.) is a widespread species found in all the Mediterranean areas. The spears are highly valued by consumers and owing to its frugality, this species is a feasible new crop with high income potential, especially for Mediterranean marginal areas. Currently, the cultivation of this species is limited because of its low and erratic seed germination that makes difficult the production of seedlings for plant propagation. In this research, non-after-ripened (1 month-old) and after-ripened seeds (dry stored at room temperature for 13 months) were exposed for 30 days in the dark to three moist stratification treatments: cold (5 °C), warm (23 °C) or no stratification; subsequently they were soaked for 12 h in warm water (35 °C) or not soaked. The effect of these pre-germination treatments on three germination parameters (germination percentage, time to 50% of final germination – T₅₀ – and germination pattern) was studied, as well as some possible seed dormancy forms involved therein. The 1-year dry storage period proved to be effective in after-ripened seeds by enhancing seed sensitivity to the subsequent pre-germination treatments. After-ripened seeds exhibited higher and more rapid germination compared to non-after-ripened seeds. Soaking, cold or warm moist stratification had similar single effect on non-after-ripened seeds (27% germination). With after-ripened seeds, only soaking or warm stratification were effective (47% germination) when singularly applied, while cold stratification did not improve germination. By combining stratification and soaking treatments, a higher germination for both non-after-ripened and after-ripened seed-lots was achieved. The highest germination was obtained when after-ripened seeds were stratified and soaked (76%), without any significant difference between cold or warm stratification. Single or combined application of moist stratification (regardless of the temperature used) and soaking resulted always in a faster germination compared to that of no-treated seeds and especially with after-ripened seeds (T₅₀ = 6 days). A non-deep type 1 physiological dormancy can be hypothesized for the seeds of this species. Low stratification temperature induce secondary dormancy in after-ripened seeds that can be removed by soaking them at 35 °C for 12 h.     

Influence of harvest time and after-ripening on the seed quality of eggplant

Eggplant cv. Emi and Tsakoniki were cultivated for seed in an unheated greenhouse and fruits were harvested at 25–65 days after anthesis (DAA) in order to determine the optimum harvest time. In addition, the effect of after-ripening on seed quality (i.e. seed size and germination) was examined by storing harvested fruit at 25 °C for 20 days prior to seed extraction. From the results, it was concluded that the optimum time of harvest for seed production is 55 DAA. Seeds extracted from fruits that were harvested at 25–35 DAA did not germinate, but when fruits harvested at the same age were stored for 20 days at 25 °C prior to seed extraction (i.e. seeds were after-ripened) germination was induced. Seeds extracted from fruits harvested at 45 DAA showed a high percent germination, which decreased after storage at 25 °C for 3 months. This decrease, however, was reduced by after-ripening prior to extraction. It is concluded that although eggplant is a non-climacteric species and fruit do not ripen after harvest, nevertheless seeds within the fruit continue to fill and mature after harvest; hence storage of prematurely harvested fruit prior to seed extraction permits the seeds of these fruits to after-ripen in situ and thereby increases seed size and germination. The implication of this result for eggplant seed production is discussed.     

Levels of physiological dormancy and methods for improving seed germination of four rose species

Low seed germination is a major problem in commercial rose propagation and breeding and is species-dependent. The present work selected four rose species previously un-examined to explore effective methods for improving seed germination and the relevant dormancy mechanism and its levels in seven experiments. The results showed that both pulp and achenes from the four rose shrubs had chemical substances that significantly inhibited seed germination with the inhibitory effect was more pronounced in pulp extract than of achenes. Single treatments of H₂SO₄ scarification, short-term cold stratification (<16 weeks) or warm stratification were less effective in breaking dormancy as indicated by lower germination index than their combinations. Comprehensive comparisons showed that among the six treatments the most effective for breaking dormancy was H₂SO₄ scarification followed by warm plus cold stratification, then H₂SO₄ scarification followed by cold stratification and finally warm plus cold stratification. Scarification with H₂SO₄ for 2–4 h ordinal followed by warm stratification at 20 °C for 4 weeks and cold stratification at 5 °C for 8 weeks was the best pretreatment for increasing seed germination percentage for Rosa multibracteata (81.4 ± 2.9%), Rosa hugonis (13.1 ± 6.0%), and Rosa filipes (62.7 ± 5.7%); and H₂SO₄ scarification for 4 h followed by cold stratification at 5 °C for 12 weeks was the best pretreatment for Rosa sericea (46.7 ± 8.7%). Our results suggest that these four species have only physiological dormancy caused by integrative roles of pulp, pericarp and embryo. The level of physiological dormancy was ranked as R. hugonis > R. sericea > R. filipes > R. multibracteata.     

Methods to break seed dormancy in Cyclocarya paliurus (Batal)Iljinskaja

Cyclocarya paliurus is native to China and is the sole species in its genus. However, the seeds remain deeply dormant for 2 years in their natural environment. We tested different pretreatments of chemical scarification and exogenous application of gibberellic acid (GA₃) for efficacy in breaking dormancy and speeding germination. In contrast to scarified seeds, non-scarified seed did not germinate, indicating that C. paliurus seeds have hard, impermeable seed coat dormancy. Exogenous application of GA₃ significantly enhanced germination of scarified seeds. Compared with seeds stratified in sand with water, the germination of seeds stratified in sand moistened with 400 ppm GA₃ for 60 days was significantly increased and germination rate was over 90% after 120 days. Analysis of variance indicated that both GA₃ concentration and stratification medium had significant effects on seed germination and final germination percentage. Germination was higher for longer stratification periods, but no significant difference in germination was observed after 90 days. These results suggested that C. paliurus seeds exhibit both exogenous and endogenous dormancy. A combination of chemical scarification and exogenous application of GA₃ alleviated seed dormancy in a relatively short period of time.     

Effects of after-ripening,stratification and GA3 on dormancy release and on germination of wild asparagus (Asparagus acutifolius L.) seeds

Seeds of wild asparagus (Asparagus acutifolius L.) were treated and compared in this research to investigate seed dormancy class and level involved in this species. Four seed lots were compared: (i) freshly harvested seeds in 2007 (07Fr); (ii) freshly harvested seeds in 2008 (08Fr); (iii) after-ripened (AR) 2007 seeds dry stored in glass jars (ARg); (iv) AR 2007 seeds dry stored in paper bags (ARp). The 07Fr seeds were exposed to (1) chemical scarification combined with gibberellic acid (GA₃) levels (0, 200, 400, and 600 mg L⁻¹) and to (2) 28-day moist stratification at 5 and 23 °C, and two sequences of 5/23 °C combined with 0 and 400 GA₃ mg L⁻¹ levels, and (3) together to the 08Fr and AR seeds were exposed to 56-day moist stratification at 5, 23, or 5/23 °C. With the 08Fr and AR seed lots this last stratification treatment was combined with 0 or 800 GA₃ mg L⁻¹ levels. The dormancy depth of 08Fr (32% germination) was less than 07Fr seeds (2%). The latter after-ripened during dry storage and when stored in glass germinated more (47.5%) than in paper (12%). Stratification for 4 weeks was ineffective in improving germination of 07Fr seeds; when chemically scarified they did not germinate at all. The highest (nearly 70%) and the most rapid and uniform germination were observed for all the lots when they were warm stratified for 56 days. Warm stratification improved germination more than alternate temperature stratification, while cold stratification inhibited germination especially for the 08Fr and ARg lots, thus seeds seem not to have a morphological component to their dormancy. GA₃ only improved germination of 07Fr seeds, at a low rate. A. acutifolius seeds fit the characteristics of a non-deep physiological dormancy.     

Promotion by 5-aminolevulenic acid of pepper seed germination and seedling emergence under low-temperature stress

The effects of incorporating 5-aminolevulenic acid (ALA) into the priming solution on low-temperature germination and emergence percentage performance of red pepper (Capsicum annuum cv. Sena) seeds before and after seed storage were investigated. Seeds were primed in 3% KNO₃ solution for 6 days at 25 °C in darkness containing 0 ppm, 1 ppm, 10 ppm, 25 ppm, 50 ppm or 100 ppm ALA. Following priming, seeds were either immediately subjected to germination and emergence tests at 15 °C or stored at 4 °C or 25 °C for 1 month after which they were subjected to germination and emergence tests at 15 °C. Priming pepper seeds in the presence of ALA improved final germination percentage (FGP) and germination rate (MGT) at 15 °C compared to non-primed seeds. The highest FGP was obtained from seeds primed in the presence of 25 ppm and higher ALA concentrations while the highest MGT was obtained from seeds primed in KNO₃ supplemented with 10 ppm ALA. Emergence percentages were the highest for the seeds primed in the presence of 25 ppm ALA and 50 ppm ALA while non-primed seeds had the lowest emergence percentage. Highest emergence rates (MET) and heaviest seedlings were also obtained from seeds primed in KNO₃ supplemented with 50 ppm ALA. Although all priming treatments improved germination and emergence performance of pepper seeds at 15 °C following 1 month of storage under two different temperatures, inclusion of 25 ppm and 50 ppm ALA into the priming solution resulted in higher germination and emergence percentages and faster germination and emergence compared to seeds primed in KNO₃ only and non-primed seeds. These results indicate that priming seeds in 25 ppm and 50 ppm ALA incorporated into the KNO₃ solution can be used as an effective method to improve low-temperature performance of red pepper seeds and that these seeds can be stored for 1 month at 4 °C or 25 °C and still exhibit improved germination and emergence performance at 15 °C.     

Seed dormancy and germination of Michelia yunnanensis (Magnoliaceae)

Michelia yunnanensis Franch. is a Chinese endemic ornamental shrub with potential for greater utilization as a landscape and medicinal plant if propagation was less difficult. Seed development and breaking of seed dormancy were investigated to improve propagation of M. yunnanensis. No fresh seeds germinated when tested at the time of dispersal. Newly matured seeds of M. yunnanensis contained differentiated linear underdeveloped embryos that were physiologically dormant. The embryo/seed length ratio of M. yunnanensis was 0.15. Warm stratification did not break seed dormancy. Dormancy was broken by cold stratification at 4 °C but not by flowing water or nitrate. Embryos developed grew inside seeds during cold stratification at 4 °C. In newly harvested dormant seeds, embryos were 0.94 mm long and increased in length 139% before radicle emergence (germination). GA₃ substituted for cold stratification to break dormancy in seeds of M. yunnanensis incubated at 25 °C or 20/25 °C. Mature M. yunnanensis seeds exhibited intermediate complex morphophysiological dormancy. Optimal germination of non-dormant seed in terms of both germination percentage and rate occurred at 20/25 °C.     

Temperatures affecting embryo development and seed germination of Christmas rose (Helleborus niger) after sowing

Embryo development followed by seed germination was investigated in seeds of Christmas rose (Helleborus niger) held under different temperature conditions. The seeds had a heart-shaped embryo when dispersed from parent plants. That embryo developed rapidly to the torpedo stage at 25 °C, after which no further development occurred. When seeds with a torpedo-stage embryo were held at 15 °C, the embryos developed to the cotyledon stage, but no further germination occurred. Similar phenomena in the course of embryo development were observed in seeds held in a non-heated polyethylene house, in which the embryos developed to the torpedo stage at 20 °C or more, while further development to the cotyledon stage was attained only at temperatures of 15 °C or less. Seeds with a cotyledon-stage embryo rarely germinated until they were treated at 4 °C for more than 8 weeks. These results suggest that seeds of H. niger have a deep, simple morphophysiological dormancy caused by the combination of rudimentary embryos and a physiological dormancy that can be broken by cycles of warming and chilling.     

Germination of Passiflora mollissima (Kunth) L.H.Bailey, Passiflora tricuspis Mast. and Passiflora nov sp. seeds

Passiflora mollissima, Passiflora tricuspis and Passiflora nov sp. are three passion fruit species occurring in Bolivia. Germination percentages and rates were determined for 11 different treatments. Per species, germination of 100 seeds was monitored every 3 days, during 90 days. Germination started after 9 days and 50% of final germination was reached within a month or less. Successful, recommended methods for P. mollissima are removing the basal point of seeds (27% germination) or removing the basal point in combination with pre-soaking seeds for 48 h in 50 ppm GA₃ (18%). Pre-soaking seeds for 24 h in 400 ppm GA₃ (42%) and removal of the basal point in combination with pre-soaking seeds for 48 h in 50 ppm GA₃ (36%) are suggested methods to improve germination of P. nov sp. Removing the apical point of P. tricuspis seeds resulted in maximal germination (57%). No unique treatment gave satisfactory results for the three species tested. Exogenous dormancy, probably a combination of mechanical and chemical dormancy is present in the three species studied. Presence of physical dormancy was found in P. mollissima.     

不同处理方法对莼菜种子发芽的影响

以当年采收的莼菜种子为材料，运用低温、激素、热水浸泡、不同发芽温度以及光照时间等
对莼菜种子进行处理，分析不同处理方法对其发芽率和发芽势的影响。结果表明：4 ℃低温处理对提高莼
菜种子发芽率有较好的效果，莼菜种子4 ℃水藏后用500 mg·L^-1 GA₃ 溶液浸泡6 h+40 ℃水浸泡50 min
对打破莼菜种子休眠有较好的作用；发芽温度以25 ℃最好，20 ℃条件下种子发芽周期较长，30 ℃条件下
种子发芽孔处易滋生白毛腐烂；种子在部分光照条件下发芽率较高，全黑暗条件下几乎不发芽。     

Effect of set-size and storage temperature on bolting,bulbing and seed yield in two onion cultivars

The effects of three set-sizes (12.5, 17.5 and 22.5 mm in diameter) and seven storage temperatures (0, 5, 10, 15, 20, 25 and 30 °C) on bolting, bulbing and seed yield in two onion (Allium cepa L.) cultivars ‘Hygro’ and ‘Delta’ were investigated. The incidence of bolting increased linearly with set-size and curvi-linearly with decreasing storage temperature. Time to inflorescence emergence and floret opening showed a curvi-linear response to storage temperature with the earliest inflorescence emergence and floret opening occurring at 5 °C and the latest at 30 °C for ‘Hygro’ and at 25 °C for ‘Delta’. Seed yield per umbel also showed a curvi-linear response to storage temperature with the lowest seed yield occurring at 30 °C for ‘Hygro’ and at 25 °C for ‘Delta’ and the highest seed yield at 5 °C. For a seed crop, storage of large sets (22.5 mm) of these cultivars at 5 °C for 120 days appeared to be optimum with 5–12% higher seed yield per umbel than that of 90 days storage. Bulb yield showed a curvi-linear response to storage temperature with the highest bulb yield occurring at 25 °C and the lowest at 5 °C.     

Interspecific variations in seed germination of Corylopsis

This study was initiated to investigate the differences in germination percentages and rates between Corylopsis coreana Uyeki and Corylopsis sinensis var. calvescens Rehder & E.H. Wilson following a warm stratification (WS) and cold stratification (CS), and to study the effect of different WS temperatures interacting with different durations of CS. Warm stratification at 10 °C, 15 °C, 20 °C, and 25 °C was given for 1 month (1 M 10 °C, 15 °C, 20 °C, and 25 °C WS) followed by 0 M, 1 M, 2 M, and 3 M of CS at 5 °C (0 M, 1 M, 2 M, 3 M CS) and seeds were germinated in an air conditioned greenhouse maintained at 18.5 °C/18 °C. On average, less than 1% of C. coreana seeds germinated when sown without any WS and CS or with 1 M 15 °C, 20 °C, and 25 °C WS without CS treatment. However, 26% C. coreana seeds germinated after 1 M 10 °C WS without any CS treatment. Germination was not affected by WS temperatures when followed by 2 M 5 °C CS. It is concluded that C. coreana exhibited low seed germination at 10 °C and that this temperature could be considered the upper limit of CS for C. coreana. Only 2 M CS was required for more than 90% seeds to germinate. However, C. sinensis var. calvescens required longer than 3 M CS for more than 29% seeds to germinate. This clearly shows that there is an interspecific variation in optimum dormancy-breaking requirements.     

Rapid seedlings regeneration from seeds and vegetative propagation with sucker and rhizome of Eremospatha macrocarpa (Mann & Wendl.) Wendl and Laccosperma secundiflorum (P. Beauv.) Kuntze

To develop efficient seedling production methods for Laccosperma secundiflorum and Eremospatha macrocarpa, a study was conducted to examine regeneration using offsets combined with several physical and chemical treatments of seeds. Offsets categorized into small, medium and large diameters, were planted in three conditions: shaded and open nursery, and greenhouse. We tested sucker from E. macrocarpa, and sucker and rhizome from L. secundiflorum. For both species, high viability percentage (ranging from 55% to 100%) were observed for small and medium suckers planted in shaded nursery and greenhouse, against less than 49% for sucker planted in open nursery. The mean seedling emergence times were estimated to 84, 77 and 75 days after planting (DAP) for small, medium and large sucker of L. secundiflorum, respectively under open nursery condition, and 76, 75, 95 DAP for small, medium and large suckers of the same species, respectively in shaded condition. Greenhouse has a significant positive effect on E. macrocarpa seedlings emergence time. For this species, the mean seedling emergence times were estimated to 43 DAP for small sucker and 76, 93 DAP for medium and large suckers. No seedling was obtained from rhizome planted in all the growing conditions tested. Concerning seed dormancy breaking, germination percentages and rates were determined for 13 treatments. The best treatments were pre-soaking unscarified seeds for 4 days in 1.01 g l⁻¹ and 0.10 g l⁻¹ KNO₃, with 79% and 68% of germination, respectively and in 3.46 × 10⁻³ g l⁻¹ GA₃ for 68% of germination. These methods are suggested to improve germination of L. secundiflorum seeds. Successful and recommended methods for E. macrocarpa are pre-soaking scarified seeds in 3.46 × 10⁻³ g l⁻¹ and 3.46 × 10⁻⁴ g l⁻¹ GA₃, 96% and 94% of germination, respectively. Dormancy, probably a combination of mechanical and chemical dormancy, is present in the two species.     

Dormancy and germination of Areca triandra seeds

The dormancy mechanisms of Areca triandra Roxb. Ex Buch-Ham seeds were studied by treating the intact or mechanically scarified seeds with scarification, chemical soaking and stratification. The results indicate that the seeds have exogenous and endogenous dormancy. The exogenous dormancy is imposed by the pericarp and it is the major limiting factor for germination. It can be broken by mechanical scarification, but not by chemical scarification in 98% H₂SO₄ for 30 min. Chemical treatments (soaking for 24 h in 100–200 mg/L GA₃, 0.2% KNO₃ and 0.1–0.3% NaNO₂, and for 12 h in 10% H₂O₂ or 20 min or 12 h in 15% H₂O₂) and stratifications, especially, cold stratifications for 30–120 days, broke the endogenous dormancy and significantly hastened germination of mechanically scarified seeds, although they did not increase the germination percentages.     

Dormancy and germination in Rosa multibracteata Hemsl. & E. H. Wilson

Most of the achenes produced by Rosa multibracteata Hemsl. & E. H Wilson are dormant on maturity and require pretreatment to stimulate germination. To investigate the mechanism of dormancy and to develop effective methods of improving germination, roles of the pericarp, testa, and embryo of R. multibracteata in regulating dormancy were studied by investigating the effect of different pretreatments on germination. The effects of temperature and water stress were also tested with achenes treated by warm plus cold stratification. In freshly harvested achenes, pericarps are permeable and the embryo fully developed, which eliminates the possibility of physical, morphological, or morphophysiological dormancy. Germination percentage remained low (<5%) despite softening the pericarp or even removing it fully. However, fully removing the testa improved germination significantly (39%), indicating the possible presence of germination inhibitors in the testa. Dry storage, scarification with sulphuric acid (H₂SO₄), and warm stratification proved ineffective by themselves but when combined with cold stratification, improved germination and shortened the cold stratification period needed to break dormancy. Dry storage for 68 weeks followed by cold stratification for 16 or 24 weeks resulted in maximum germination (72–79%) among all the treatments. In achenes scarified with H₂SO₄, germination increased with an increase in the duration of cold stratification. Neither gibberellic acid (GA₃) nor ‘smoke water’ (water through which smoke had been bubbled for 2 h) had any positive effect on germination even on seeds that had been mechanically scarified or stratified. Both high temperature and water stress lowered germination in achenes treated with warm plus cold stratification. Our results suggest that R. multibracteata achenes have an intermediate physiological dormancy, and that dry storage for 68 weeks followed by cold stratification for 16 or 24 weeks is the best method for propagating R. multibracteata from seed.     

Heat treatment and harvest date interact in their effect on superficial scald of ‘Granny Smith’ apple

A study was made of the effect of hot water dips (HWD) at temperatures of 42, 44, 46 and 48 °C (HWD 42 °C, HWD 44 °C, HWD 46 °C and HWD 48 °C, respectively) for 3 min on development of superficial scald and the concentration of α-farnesene and conjugated trienols (CT), CT₂₅₉, CT₂₆₉, CT₂₈₁, as well as OD₂₀₀ on Granny Smith apple fruits harvested on three dates and stored 125 days in air at 2 °C. HWD 48 °C efficiently decreased surface scald in the second and third harvest. α-Farnesene and CT were measured spectrophotometrically and by HPLC. No clear relationship of OD₂₀₀ and scald development was observed. Correlation of scald index and OD₂₀₀ at the end of storage was negative for the second harvest date. There was no significant correlation between the scald index and CT₂₅₉. Scald index was positively correlated with CT₂₆₉ after 80 days for the second and third harvest and at the end of storage for the second harvest. CT₂₈₁ was spectrophotometrically detectable only at the end of the storage, for the third harvest date, in control, HWD 42 °C, and HWD 44 °C. HWD 42 °C had significantly higher CT₂₈₁ compared to HWD 44 °C and control. HPLC analysis of control samples revealed presence of CT₂₈₁ in all three harvest dates, and presence of at least two components, as was the case of CT₂₅₉ and CT₂₆₉. The ratio of these two components was different for all three CT species. Fruit maturity was an important factor determining the response of fruit to heat and occurrence of superficial scald. The results indicate that a successful treatment using HWD to control superficial scald may be obtained after further research and that there are still some questions on the role of different CT's in scald biochemistry that should be addressed in future research.     

Changes in antioxidants and fruit quality in hot water-treated ‘Hom Thong’ banana fruit during storage

The effects of hot water treatment on antioxidants and fruit quality were investigated in banana fruit of cv. Gros Michel (Musa acuminata, AAA Group, locally called cv. Hom Thong) by immersing fruits in hot water (50 °C) for 10 min, before storage at 25 °C for 10 days or 14 °C for the first 8 days followed by storage at 25 °C for the second 8 days until ripening. Quality parameters including peel color and pulp firmness indicated that hot water treatment helped to delay banana fruit ripening at both storage conditions. Hot water treatment decreased the levels of hydrogen peroxide (H₂O₂) and malonydialdehyde (MDA) during storage at 25 °C. Glutathione (GSH and GSSG) contents and the ratio of GSH/GSSG during fruit approaching ripening were significantly induced in hot water-treated fruits while ascorbic acid (AA) contents were slightly increased. In addition, the combined treatment increased free phenolics and flavonoids during storage. Results suggest that hot water treatment has led to an induction of antioxidants in banana fruits as indicated by an increase of antioxidants and a decrease of H₂O₂ during ripening, and all of which result in a delayed ripening of banana fruit.     

Seed-coat anatomy and proanthocyanidins contribute to the dormancy of Rubus seed

Rubus seed has a deep double dormancy that restricts germination due to seed coat structure and chemical composition. Improved germination of diverse Rubus species required for breeding improved blackberry and raspberry cultivars is partly dependent on the seed coat structure. This study evaluated the seed coat structure of three species with thin (R. hoffmeisterianus Kunth & C. D. Bouché), medium (R. occidentalis L.) and thick (R. caesius L.) seed coats. The three species exhibited distinctive seed-coat cell composition. The very thin testa (0.086 mm) of R. hoffmeisterianus had little exotesta (surface) reticulation; with the meso- and endotesta composed of sclereids of homogenous shape and size. R. occidentalis had a thick testa (0.175 mm) and a highly reticulate exotesta; the meso- and endotesta were composed of several diverse types of sclereids. R. caesius had the thickest seed coat (0.185 mm) but only moderate exotesta reticulation; the meso- and endotesta were composed of large, irregular, loosely arranged sclereids. R. occidentalis, a medium size seed, was the most heavily lignified with seed-coat thickness similar to R. caesius, the largest seed. Proanthocyanidins (PAs) from dry seed of six Rubus species were extracted and quantified by high performance liquid chromatography. R. hoffmeisterianus, a thin only slightly hard seed, had half the PA (0.45 μg/seed) of R. occidentalis with a thick, extremely-hard seed coat and diverse sclereids (1.07 μg/seed). PA content and sclereid composition both appear contribute to seed coat hardness and resulting seed dormancy. The effectiveness of sulfuric acid for Rubus seed scarification is likely due to degradation of PAs in the testa.     

Screening Capsicum species of different origins for high temperature tolerance by in vitro pollen germination and pollen tube length

Successful fruit set depends on several reproductive processes including pollen germination and tube growth processes. An experiment was conducted to determine the effects of temperature on pollen germination characteristics and to identify species/genotypic differences in Capsicum using the cumulative temperature response index (CTRI) concept. Pollen was collected from plants of seven genotypes from five Capsicum species, adapted to various parts of the world and grown outdoors in large pots. The pollen was subjected to in vitro temperatures ranging from 15 to 50 °C at 5 °C intervals. Pollen germination and tube lengths were recorded for all species after 24 h of incubation at the respective treatments. Species/genotypes differed significantly for in vitro pollen germination percentage and pollen tube length with mean values of 78% and 734 μm, respectively. The mean cardinal temperatures (T_min, T_opt, and T_max) averaged over genotypes, were 15.2, 30.7, and 41.8 °C for pollen germination and 12.2, 31.2, and 40.4 °C for pollen tube growth. The CTRI of each species/genotype calculated as the sum of eight relative individual stress response values, such as maximum pollen germination, maximum pollen tube length; T_min, T_opt, and T_max temperatures of pollen germination, and pollen tube lengths, identified species tolerance to high temperatures. Capsicum annum cv. Mex Serrano from Mexico was identified as tolerant, C. chacoense cv. 1312 and C. spp. cv. Cobanero from Argentina and Guatemala, respectively as intermediate and C. frutescens cv. Early Spring Giant from China, C. annum cv. Long Green from South Korea, C. spp. cv. NM89C130 and C. pubescens cv. 90002 from Guatemala as sensitive to high temperatures. The tolerant species/genotypes can be used in breeding programs to develop new genotypes that can withstand high temperature conditions both in the present climate and particularly in a future warmer climate.     

Induction of bulb maturity of Ornithogalum thyrsoides

The influence of bulb maturity at bulb harvest on growth and flowering response of Ornithogalum thyrsoides Jacq. ‘Chesapeake Starlight’ was investigated. Experiments were designed to determine if bulb maturity can be induced by bulb storage temperatures and whether bulb maturity can be evaluated by flowering responses. Bulbs with all senesced leaves at harvest were considered “mature” or with emerging young leaves and re-growing young roots were considered “immature”. Bulbs were potted after 0, 3, and 6 weeks of 30 °C or 2 weeks of 10 °C given either in the middle or at the end of 6 weeks of 30 °C. Mature bulbs, as compared to immature bulbs, took longer for leaves to emerge when control bulbs that did not receive any temperature treatment after harvest were planted upon harvest. Leaf emergence of the immature bulbs was significantly earlier than that of the mature bulbs. Mature bulbs which received 30 °C for 3 weeks (30 °C/3 week) flowered 31 days faster than immature bulbs and all bulbs flowered. Leaf emergence and flowering of mature and immature bulbs that received 30 °C/6 weeks or 2 weeks of 10 °C in the middle of 6 weeks of 30 °C (30 °C/2 weeks–10 °C/2 week–30 °C/3 weeks) did not differ from each other. Maturity can be induced by storing immature bulbs at 30 °C/6 weeks. Maturity, as evaluated by flowering percentage and days from leaf emergence to flowering, can be induced in O. thyrsoides. Immature bulbs can, therefore, be harvested for later forcing as long as bulbs are treated with 30 °C/6 weeks. It is proposed that maturity can be correlated with the speed of flowering and bulbs can be harvested at immature physiological state for forcing. Postharvest high-temperature treatment can be used to force immature bulbs that were harvested before the senescence of the leaves.