Exploring the Role of Calcium to Improve Chilling Tolerance in Hybrid Maize

Abiotic stresses, including chilling, impede the plant growth and development mainly by oxidative damage. In this study, seed priming with CaCl₂ was employed to reduce the damage caused by chilling stress in hybrid maize. Maize hybrid (Hycorn 8288) seeds were soaked in 50, 100 and 150 mg l⁻¹ (ppm) aerated solution of CaCl₂ for 24 h and dried. Treated and untreated seeds were sown at 27 °C (optimal temperature) and 15 °C (chilling stress) under controlled conditions. Seed priming with CaCl₂ significantly reduced the chilling damage and improved the germination rate, root and shoot length, and seedling fresh and dry weights. Activities of antioxidants, including catalase, superoxide dismutase and ascorbate peroxidase, were also improved. Soluble sugars and α-amylase concentrations determined as general metabolic indicators of stress were also increased by seed priming with CaCl₂. Priming also improved the performance of maize at optimal temperature. Maintenance of tissue water contents, reduction in membrane leakage and increase in antioxidant activities, and carbohydrate metabolism seemed to induce chilling tolerance by CaCl₂. Seed priming with 100 mg l⁻¹ CaCl₂ was the optimal concentration in improving the performance of hybrid maize both under optimal and stress conditions.     

Activation of Antioxidant System by KCl Improves the Chilling Tolerance in Hybrid Maize

As maize is a chilling-sensitive crop, low temperatures during the early stages of development can be injurious to crop growth and development. Prime mechanism behind chilling-induced damage is oxidative stress. This study was undertaken to improve the chilling tolerance in hybrid maize by seed priming with KCl. For priming, seeds of the maize hybrid Hycorn 8288 were soaked in 50, 100 and 150 mg l⁻¹ aerated solution of KCl for 24 h and then re-dried close to original weight. Primed and untreated seeds were sown at 27 °C (optimal temperature) and at 15 °C (chilling stress) under controlled conditions. Seed priming improved the performance of maize under both normal and stress conditions. It was found that the chilling tolerance in maize is well associated with the enhanced capacity of the anti-oxidative system. Priming with KCl significantly improved the chilling tolerance mainly by the activation of antioxidants including catalase, superoxide dismutase and ascorbate peroxidase enzymes. KCl treatments also improved the germination rate and time, root and shoot length, and fresh and dry weights of seedlings compared with control. Soluble sugars and α-amylase activity determined as general metabolic indicators of stress were also improved by seed priming with KCl. Other possible bases of chilling tolerance in maize included maintenance of high tissue water contents, reduced electrolyte leakage and carbohydrate metabolism. Seed treatment with 100 mg l⁻¹ KCl was the best treatment to improve the performance of hybrid maize both under normal and chilling stress conditions.     

Glycinebetaine Improves Chilling Tolerance in Hybrid Maize

Plant growth and development is hampered by various environmental stresses including chilling. We investigated the possibility of improving chilling tolerance in hybrid maize by glycinebetaine (GB) seed treatments. Maize hybrid (Hycorn 8288) seeds were soaked in 50, 100 and 150 mg l^?1 (p.p.m.) aerated solution of GB for 24 h and were dried back. Treated and untreated seeds were sown at 27 °C (optimal temperature) and at 15 °C (chilling stress) under controlled conditions. Germination and seedling growth was significantly hindered under chilling stress. Moreover, chilling stress significantly reduced the starch metabolism and relative water contents (RWC), and increased the membrane electrolyte leakage. However, activities of antioxidants (catalase, superoxide dismutase and ascorbate peroxidase) were increased under stress conditions. Seed treatments with GB improved the germination rate, root and shoot length, seedling fresh and dry weights, leaf and root scores, RWC, soluble sugars, α‐amylase activity and antioxidants significantly compared with untreated seeds under optimal and stress conditions. Induction of chilling tolerance was attributed to maintenance of high tissue water contents, reduced membrane electrolyte leakage, and higher antioxidant activities and carbohydrate metabolism. Seed treatment with 100 mg l^?1 GB was the best treatment for improving the performance of hybrid maize under normal and stress conditions compared with control and other levels used.     

Improving the Performance of Wheat by Seed Priming Under Saline Conditions

Salinity is one of a major threat in harvesting good wheat stand on sustained basis. In this study, potential of seed priming techniques to improve the performance of wheat varieties (SARC‐1 and MH‐97) in a saline field was tested. For priming, wheat seeds were soaked in aerated solution of ascorbate (50 mg l^?1; ascorbate priming), salicylic acid (50 mg l^?1; salicylicate priming), kinetin (50 mg l^?1; kinetin priming) and CaCl₂ (50 mg l^?1; osmopriming) for 12 h. For comparison, seeds were also soaked in simple water (hydropriming); in addition, untreated seeds were also taken as control. Seed priming treatments substantially improved the stand establishment; osmopriming (with CaCl₂) was at the top however. Likewise maximum fertile tillers, grains per spike, 1000‐grain weight, grain yield and harvest index were observed in plants raised from seeds osmoprimed (with CaCl₂) followed by ascorbate priming in both the varieties tested. As an index of salinity tolerance, seed priming treatments also improved the leaf K⁺ contents with simultaneous decrease in Na⁺ concentration, osmopriming being the best treatment. Similarly, maximum total phenolic contents, total soluble proteins (TSP), α‐amylase and protease activities were observed in osmoprimed (with CaCl₂) seeds followed by ascorbate priming. Economic analysis also indicated that osmopriming is more viable with maximum net return and benefit‐to‐cost ratio. In conclusion, different seed priming treatments in wheat seeds improved the salinity tolerance nonetheless osmopriming (with CaCl₂) was the most effective treatments to get higher grain yield and net return in both wheat varieties whereas kinetin was the least effective.     

不同温度水杨酸引发对干旱胁迫下玉米种子发芽及幼苗生理特性的影响

为探究不同温度水杨酸(SA)引发对水分胁迫下玉米种子发芽和幼苗生长、生理特性的影响,以‘郑单958’、‘金甜808’和‘京科糯2000’为试验材料,设置5组处理(CK、5、10、15、20℃)研究干旱胁迫下幼苗生长表现。结果表明,水杨酸引发显著提高了玉米幼苗抗氧化酶活性,增加了渗透调节物质含量,降低了丙二醛(MDA)含量,缓解了水分胁迫对玉米生长的影响。其中,玉米发芽参数（发芽率、发芽势、发芽指数和活力指数）,‘郑单958’和‘金甜808’以15℃引发处理最高,较对照分别提高了16.67%、21.26%、17.69%、25.39%和10.88%、8.76%、10.02%、26.83%;而‘京科糯2000’以10℃引发处理最高,较对照提高了16.48%、10.73%、14.27%和32.00%。可见,种子引发增强了干旱胁迫下玉米种子的发芽能力,本研究结果可为种子引发在旱地玉米生产上的应用提供理论依据。     

多胺对玉米种子吸胀期间耐冷性和种子发芽能力的影响

以玉米耐寒自交系黄C和低温敏感自交系Mo17为材料, 研究了亚精胺(Spd)和精胺(Spm)引发对玉米种子吸胀中的耐冷性和种子发芽能力的影响。种子经0.25 mmol L^-1的Spd和Spm引发72 h后, 在5℃下低温吸胀不同时间(12、24、36和48 h)。结果表明, Spd和Spm引发提高了胁迫期间两自交系胚内过氧化物酶(POD)、过氧化氢酶(CAT)、超氧化物歧化酶(SOD)和抗坏血酸过氧化物酶(APX)活性, 以及可溶性蛋白质和脯氨酸(Pro)含量, 降低了胚渗出液的核苷酸含量, 同时显著提高发芽率, 并显著缩短平均发芽时间。低温吸胀48 h后, 与对照相比, Spd和Spm处理分别提高两自交系种子的平均发芽率18.5%和14.0%, 分别缩短平均发芽时间1.21 d和1.14 d。黄C在种子吸胀期间的耐冷性强于Mo17。总之, Spd和Spm处理能提高玉米种子吸胀期间的耐冷性, 提高低温胁迫下种子发芽能力。     

水杨酸对玉米种子萌发早期耐旱性的影响

为了探讨水杨酸(SA)引发对干旱胁迫下玉米种子生理生化特性的影响,以郑单958玉米品种为试验材料,在15℃黑暗下用0.1 mmol/L的SA引发处理36h,在15％的PEG-6000模拟干旱条件下吸胀不同时间(0,12,24,36,48 h),研究SA引发对干旱胁迫下玉米种胚、胚乳和种皮生理生化特性的影响.结果表明,干旱胁迫期间,种胚中CAT活性、胚乳中可溶性糖含量、种皮中可溶性蛋白含量增加.相对未引发种子,SA引发显著提高了种子CAT活性、可溶性糖含量、可溶性蛋白含量.因此,0.1 mmol/L SA引发处理可以提高玉米种子萌发早期的抗旱性.     

种子引发对碱胁迫下甜高粱种子萌发及幼苗生长的影响

为研究碱胁迫下种子引发对萌发及幼苗生长的影响,以甜高粱杂交种‘通甜1号’为试验材料,利用500 μmol/L γ-氨基丁酸(GABA)对种子进行引发处理。采用盆栽土培试验,将NaHCO₃:Na₂CO₃=5:1的混合碱胁迫液设3个水平(0、50、100 mmol/L)模拟碱胁迫,研究GABA种子引发处理对碱胁迫下高粱种子萌发状况及幼苗生长的影响。结果表明：随着碱胁迫强度增加,无论是经过引发处理的种子还是未经过引发处理的种子,其吸水量、萌发指数、出苗率和成苗率显著下降,幼苗生长受到限制,生物量积累降低。同等碱胁迫浓度下,经过引发处理的种子与未经过引发处理的种子相比,种子吸水量、萌发指数、胚的生长及幼苗叶面积均显著提高。低浓度碱胁迫条件下,经过引发处理的种子与未经过引发处理的种子相比,幼苗的出苗率和存活率较高、生长至第7天的株高和茎粗及总生物量均显著增加。试验表明,经过引发处理的种子可以不同程度地提高碱胁迫下甜高粱种子萌发指数,缓解碱胁迫对幼苗的不利条件,促进幼苗生长,提高耐碱性。     

Changes in Hormonal Balance: A Possible Mechanism of Pre‐Sowing Chilling‐Induced Salt Tolerance in Spring Wheat

There is a lack of knowledge about factors contributing to the chilling‐induced alleviatory effects on growth of plants under salt stress. Thus, the primary objective of the study was to determine whether chilling‐induced changes in endogenous hormones, ionic partitioning within shoots and roots and/or gaseous exchange characteristics is involved in salt tolerance of two genetically diverses of wheat crops. For this purpose, the seeds of two spring wheat (Triticum aestivum) cultivars, MH‐97 (salt intolerant) and Inqlab‐91 (salt tolerant) were chilled at 3°C for 2 weeks. The chilled, hydroprimed and non‐primed (control) seeds of the two wheat cultivars were sown in both Petri dishes in a growth room and in the field after treatment with 15 dS m^?1 NaCl salinity. Chilling was very effective in increasing germination rate and subsequent growth when compared with hydropriming and control under salt stress. Results from field experiments clearly indicated the efficacy of chilling over hydropriming in improving shoot dry biomass and grain yield in either cultivar, particularly under salt stress. This increase in growth and yield was related to increased net photosynthetic rate, greater potential to uptake and accumulate the beneficial mineral elements (K⁺ and Ca²⁺) in the roots and reduced uptake and accumulation of toxic mineral element (Na⁺) in the shoots of both wheat cultivars when grown under salt stress. Salt‐stressed plants of both wheat cultivars raised from chilled seed had greater concentrations of indoleacetic acid, abscisic acid, salicylic acid and spermine when compared with hydropriming and control. Therefore, induction of salt tolerance by pre‐sowing chilling treatment in wheat could be attributed to its beneficial effects on ionic homeostasis and hormonal balance. The results presented are also helpful to understand the chilling‐induced cross adaptation of plants in natural environments. Moreover, efficacy of pre‐sowing chilling treatment over hydropriming suggested its commercial utilization as a low risk priming treatment for better wheat crop production under stressful environments.     

Chemical priming with urea and KNO<Subscript>3</Subscript> enhances maize hybrids (<Emphasis Type="Italic">Zea mays</Emphasis> L.) seed viability under abiotic stress

Seed priming is a method to improve germination and seedling establishment under stress conditions. The effect of seed priming in chemical solutions such as urea and KNO₃, on protein and proline content, germination, and seedling growth responses of four maize (Zea mays L.) hybrids under drought and salt stress conditions was studied in a controlled environment in 2010. Treatments included stress type and intensity at five levels: moderate drought (MD), severe drought (SD), moderate salt (MS), severe salt (SS), and control (C1, without stress), three seed priming types including water (C2, as control), KNO₃, and urea (as chemical priming), and four maize hybrids including Maxima, SC704, Zola, and 307. The results showed that the highest germination percentage (Ger %), germination rate (GR), seedling length (SL), radical length (RL), and seedling to radical length ratio (S/R) were achieved in no stress treatments and most proline content in SD treatment. Urea priming led to more Ger%, GR, and SL compared to other primers and treatment under KNO₃ priming resulted in higher RL compared to other primers. Chemical priming had no effect on S/R and proline content. Also, in terms of most traits, no difference was found among the four hybrids. Results showed that salt stress could affect GR and RL more than the drought stress. Drought stress affected germination percentage and S/R more than the salt stress. Both stresses decreased all measured parameters, except protein and proline content which were increased remarkably, and more under drought compared to salt stress. Based on proline content, hybrid 304 appeared to be more resistant to stress than other hybrids. Generally, KNO₃ and urea alleviated effects of both stresses and led to increased germination and seedling growth as well as the root length. Therefore, priming could be recommended for enhancing maize growth responses under stressful conditions.     

Effects of Thermal and Salt Treatments during Imbibition on Germination and Seedling Growth of Sorghum at 42/19 °C

This investigation tested the influence of thermal treatment of seeds at various stages of imbibition on the germination percentage, speed and growth response of seeds and seedlings. Seeds of sorghum (Sorghum bicolor L Moench) were treated in 2, 4 or 6 g NaCl l^?1 solutions and exposed for 2 h to 45 °C during the first, second or third days of imbibition. Thereafter, the seeds were dried and germinated at 42/19 °C (day/night temperature). Salt treatments did not improve the final germination percentage but increased germination speed over untreated seeds. The higher the salt concentration used, the greater the dry weights of plumules and radicles. Thermal treatment on the third day of imbibition yielded higher germination percentages than untreated seeds, while thermal treatment on the second day gave faster germination. Both the second and third day thermal treatments gave superior germination indices and higher plumule‐to‐radicle ratios. It is concluded that thermal treatment may assist in acclimating seeds to heat stress.     

Zinc seed priming improves salt resistance in maize

Salt stress is a major yield‐limiting factor in crops by reducing nutrient uptake and plant growth. Under salt stress, decreased water and nutrient uptake results in nutrient imbalance in plants. In addition, at high pH in saline conditions, solubility of minerals is also reduced leading to low availability of certain nutrients. Perspectives to overcome these limitations by Zn seed priming were studied with maize plants exposed to NaCl as salt stress. Maize seeds were primed for 24 hr in deionized water and 4 mm ZnSO₄·7H₂O solution (ZnP) and subsequently air‐dried at room temperature before further use. The DTZ (diphenylthiocarbazone) staining method was used for showing Zn²⁺ localization in the seeds. Zn²⁺ and other nutrient concentrations in unprimed, water and ZnP seeds and maize plants were analysed by inductively coupled plasma mass spectroscopy (ICP‐MS). Maize plants (cv. Sun star L.) were grown for 3 weeks in complete nutrient solution with or without salt stress (100 mm NaCl) under glasshouse conditions. Seed Zn²⁺ contents were increased after ZnP treatment by 600%. In maize seeds, most of the primed Zn²⁺ accumulated in the outer tissues (particularly, aleurone layer) of maize seed. Zn priming decreased the injurious effects of salt stress on plant growth. Under salt stress conditions, biomass production of plants from ZnP treatments was 25% higher compared to water priming treatment. Zn seed priming also improved mineral nutrient status of plants grown in both control and salt stress conditions. Plants from ZnP treatments also showed higher accumulation of Na⁺ in the shoots. This offers perspectives for using Zn seed priming for improving early seedling development and plant nutrient status of maize under salt stress conditions.     

Seed priming improves germination in saline conditions for Chenopodium quinoa and Amaranthus caudatus

Seed priming has proved to be an effective method in imparting stress tolerance to plants using natural and/or synthetic compounds to treat the seeds before germination. The present work aimed to evaluate the effectiveness of priming treatments in seeds of Chenopodium quinoa and Amaranthus caudatus to improve germination under NaCl. Species‐specific protocols for seed hydropriming and osmopriming were established by germinating seeds under different water potentials and creating seed imbibition curves. Primed seeds were then germinated under different concentrations of NaCl, and the effect of priming was analysed based on the parameters, such as final germination percentage (FGP), germination index (GI) and mean germination time (MGT). Seed hydropriming and osmopriming caused significant improvements in germination velocity and uniformity, reflected in high FGP, high GI and reduced MGT under salinity. C. quinoa had a higher tolerance to salinity than A. caudatus during seed germination. Improved germination in salinity resulted from osmopriming seeds with solutions of low water potential for A. caudatus, while for C. quinoa, this effect was achieved from hydropriming and osmopriming seeds with solutions of high water potential. Primed tolerance to moderate salinity was achieved for A. caudatus, and for both species, the salinity threshold for germination to occur was slightly broadened.     

种子引发对水分胁迫下水稻发芽及幼苗生理性状的影响

不同基因型稻种经水引发及聚乙二醇(PEG)渗透胁迫引发处理均能降低稻种丙二醛(MDA)含量,促进可溶性总糖(SS)降解,加快稻种内部糖代谢进程,提高相溶性溶质脯氨酸(Pro)及可溶性蛋白质(SP)含量,也有利于提高苯丙氨酸解氨酶(PAL)、超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性,引发效果较明显。且适度PEG引发稻种的效果明显好于水引发,杂交籼稻在PEG浓度为20%的条件下引发效果最优,而常规粳型水稻在PEG浓度为10%~15%的引发条件下效果较好,但超出最高PEG引发浓度的阈值,会对稻种产生危害,影响其正常萌发。引发处理后的稻种对不同程度水分胁迫程度的响应表明,适当强度的引发处理利于激发稻种物质代谢、利于各水稻品种的萌发、幼苗形态指标及保护性酶等生理指标的显著提高,而严重的水分胁迫均不利于稻种萌发;表明引发处理虽能提高水分胁迫条件下种子活力,但稻种激发自身对外界萌发环境的协调能力有限,且不同品种间存在明显差异,籼稻优于粳稻。     

Hermetically Sealed Storage of Cereal Seeds and its Influence on Vigour and Germination

Investigations of the influence of hermetic cereal seed storage on germination were carried out in the laboratory of the Faculty of Agriculture in Osijek (Croatia) over 5 years (1992–96). Seeds of four species (winter wheat, winter barley, spring oat, and maize) were stored in hermetic glass containers at an air temperature of 20 °C and a relative humidity of 65 %. The moisture level in stored seeds was 13 %. After 5 years, statistically highly significant associations (P < 0.01) were found between storage longevity (five researched years) and seed germination of the four cereals. Germination of all investigated cereals was high (between 97.25 % for maize and 93 % for winter wheat) after harvest. The germination level decreased for all cereals, on average by 38 %, over the 5 years of storage. The highest germination values were found for wheat seeds (84.75 %) and the lowest germination values for maize seeds (36.0 %). The results showed that germination of all investigated cereals seeds was negatively correlated with storage longevity. The differences in germination found amongst the cereals were statistically highly significant (P < 0.01).     

种子沙引发对转基因抗虫棉耐盐性的影响

 以转基因抗虫棉花品种中棉所41和浙905为材料,以其遗传背景品种中棉所23为对照,研究了种子沙引发处理对转基因抗虫棉品种在0%、1.0%和1.5% NaCl浓度下的萌发率、出土率和幼苗生长特性的影响。结果表明,沙引发处理对转基因抗虫棉品种在盐胁迫下的种子萌发和幼苗生长具有明显的效果,但对于非转基因棉品种的效果不明显。幼苗子叶、茎秆和根的超氧化物歧化酶（SOD）活性、过氧化物酶（POD）活性和丙二醛（MDA）含量测定结果表明,沙引发处理使棉花幼苗的子叶和根部维持了较高的SOD与POD活性,但显著减少幼苗体内MDA的积累,说明沙引发有助于促进棉花在逆境下幼苗生长发育和抗逆性的提高。     

Effect of High Temperature on Seedling Growth and Photosynthesis of Tropical Maize Genotypes

Genotypic variability in relation to growth and photosynthetic CO₂ assimilation rate (P_n) is well known for maize (Zea mays L.) under heat stress conditions. This study was, however, initiated to test whether genotypic growth variation is related to variations in individual leaf size, leaf extension rate (LER), and photosynthesis of the single leaf at high temperature. Six tropical maize genotypes selected from the International Maize and Wheat Improvement Centre (CIMMYT) with contrasting growth responses were grown for 9 days after emergence (DAE) in the first and for 15 DAE in the second experiment at 25/22 °C and 42/30 °C. High temperature caused a marked decrease in the growth parameters, and the genotypes showed high growth variations irrespective of temperature levels. Interestingly, genotypes did not follow a similar ranking in relation to biomass production between 9 DAE (heterotrophic growth phase) and 15 DAE (autotrophic growth phase) at 25/22 °C, but the pattern was similar at 42/30 °C. Total leaf area and daytime LER of leaves 2 (l₂), 3 (l₃), and 4 (l₄) showed a tight correlation with biomass production at both temperatures, while the LER of the youngest leaf (l₄) at night also showed the same correlation at 42/30 °C. A significant relationship between the areas l₂ and l₃ and biomass was observed only at high temperature and not at 25/22 °C. The P_n decreased markedly at high temperature and genotypic variability was pronounced. The genotypes maintained a similar ranking of P_n measured from l₂ at 8 DAE and from l₃ at 13 DAE under unfavourable conditions only and not at 25 °C. Of the six genotypes, F250 outperformed the others in relation to growth and P_n activity. A tight correlation between photosynthesis of different leaves and growth was detected at high temperature but not at the optimal temperature for growth. It is concluded that the areas l₂ or l₃, daytime LER and P_n, all measured at high temperature stress conditions, can be regarded as good indicators of the thermo‐tolerance of tropical maize genotypes at the seedling stage.     

Germination Responses of Cañahua (Chenopodium pallidicaule Aellen) to Temperature and Sowing Depth: A Crop Growing Under Extreme Conditions

Cañahua (Chenopodium pallidicaule) is grown in the Altiplano of Bolivia and Peru, between 3810 and 4200 m a.s.l. Rural indigenous households have cultivated the cañahua as a subsistence crop for millennia. The seeds have a high content and quality of protein. We studied the relation between the following: (i) temperature and seed germination and (ii) the effect of temperature and sowing depth on seedling emergence of five cultivars and one landrace. Three experiments were conducted as follows: (i) seeds of a cultivar were germinated in Petri dishes at six temperatures (3, 5, 10, 14, 20 and 24 °C), (ii) sown at five depths (0, 5, 10, 25 and 50 mm) in a mixed peat soil substrate at three temperatures and (iii) one landrace (Lasta) and 5 cultivars (Lasta and Saihua growth habit) were sown in 6 depth (0, 5, 10, 25, 35 and 50 mm) in a sandy loam at two temperatures (5 and 15 °C). Temperature had significantly effect on the germination percentages of the plants (P < 0.001). Seeds germinated at the lowest temperature (3 °C). The estimated base temperature was close to 0 °C. A polynomial function described well the relation between time to 50% germination (t₅₀) and temperature in the interval from 3 to 24 °C resulting in a linear relationship between germination rate and temperature. Shallow sowing depth (5–25 mm) resulted in 80% germination at 15 °C. There were significant differences of emergence in relationship to burial depth (P < 0.001). Only few seedlings emerged when seeds were sown at 50 mm depth. We did not find significant differences in emergence of seedlings between Lasta and Saihua at 15 °C. Nevertheless, at 5 °C, seedlings of cañahua belonging to the Lasta growth habit form did have higher germination rate as were shown for the Kullaca cultivar and the Umacutama landrace. This may be attributed to larger seed size of these cultivars.     

Inheritance of Seed Dormancy in Lisianthus (Eustoma grandiflorum)

The genetics of chill-related seed dormancy, exhibited by a lisianthus (Eustoma grandiflorum) genotype native to North America, was investigated. Less than 1 % of the seeds germinated by direct hydration at 20°C, while full germination (98%) was attained by chilling imbibed seeds, for at least 11 days, at 3°C, before transferring them to 20°C. The inheritance of seed dormancy was analyzed in F₁, BC₁, and F₂, populations, derived from mating between a normal non-chill-requiring genotype (P₁) and the above chill-requiring genotype (P₂). F₁ seeds, of both reciprocals, and BC₁ (P₁) seeds were all non-dormant. The proportion of seed dormancy in F₂ and BC, (P₂) was 0.06 and 0.68, respectively. The inheritance model proposed includes six diallelic loci with cumulative effects, in which the presence of at least nine ‘dormancy-conferring’ alleles is necessary for inducing phenotypic seed dormancy. Possible implications of inherent seed dormancy on the utilization of native lisianthus germplasm for breeding are discussed.     

Influence of Soil Temperature on Seedling Emergence and Early Growth of Peanut Cultivars in Field Conditions

Peanut or groundnut (Arachis hypogaea L.) sown in early spring often has poor seed germination and seedling development. The influence of soil temperature on seedling emergence and early growth of six peanut cultivars (Florida MDR98, Southern Runner, Georgia Green, SunOleic 97R, Florunner and C‐99R) was studied in natural field soil profiles in temperature‐gradient greenhouses. We evaluated the influence of a range of soil temperatures by sowing at eight dates between January 2001 and May 2002 in Gainesville, Florida. On each sowing date, two additional temperature treatments (ambient and ambient +4.5 °C air temperature) were evaluated by sowing on either end of each greenhouse and applying differential heating. In total, 16 different soil temperature treatments were evaluated. Each treatment was replicated four times in four different greenhouses. Mean soil temperature from sowing to final emergence in different treatments ranged from 15 to 32 °C. Sowing date, temperature treatment and cultivar had significant effect on seedling emergence and development (V₂ stage). For all cultivars, the lowest germination was observed at the earliest sowing date (coolest soil temperature). Among cultivars, Florida MDR98 was the most sensitive to reduced (cool) temperature with the lowest germination and smallest seedling size at 21 days after sowing, followed by Southern Runner. Georgia Green was the most cold‐tolerant with the highest germination, followed by SunOleic 97R. There were no significant differences among cultivars for base temperature, which averaged 11.7 and 9.8 °C for rate of emergence and rate of development to V₂ stage respectively. These results imply that cultivar choice and/or genetic improvement of peanut for cold tolerance during emergence and seedling development in regions where cooler soil temperatures persist and/or regions where early sowing is desirable.