Seed scientists and other plant biologists are interested in the measurement of germination because seeds from different individuals, populations, seed lots and treatments can differ in germination percentages, rate (speed) and uniformity. Mean time to germination (MGT) is a measure of the rate and time-spread of germination; however, there is a problem with using this method to calculate germination rate. MGT does not show the time from the start of imbibition to a specific germination percentage. MGT has been used to compare specific pairs or groups of means and to evaluate seed vigour. However, it is not the real time to mean germination but just an index of germination speed. Using MGT is not correct for ANOVA, post-ANOVA or the other comparison tests, because it does not show time to a specific germination percentage. Thus, we recommend that t50 be used instead of MGT. The t50 has all benefits of MGT, but it does not have the problems of MGT in treatment comparisons.

-Abutilon theophrasti and Barnyardgrass (Echinochloa crus-galli) are major weeds that affect cropping systems worldwide. Laboratory and greenhouse studies were conducted to determine the effects of temperature, pH, water and salinity stress, and planting depth on seed germination and seedling emergence of Velvetleaf and Barnyardgrass. For Velvetleaf, the base, optimum and ceiling germination temperatures were estimated as 5, 35 and 48 o C, respectively. Seed germination was sensitive to drought stress and completely inhibited by a potential of -0.6 MPa, but it was tolerant to salinity. Salinity stress up to 45 mM had no effect on the germination of Velvetleaf, but germination decreased with increasing salt concentration. Drought and salinity levels for 50% inhibition of maximum germination were -0.3 MPa and 110 mM, respectively. Seed germination of Velvetleaf was tolerant to a wide range of pH levels. For Barnyardgrass, the base, optimum and ceiling germination temperatures were estimated as 5, 38 and 45 o C, respectively. Seed germination was tolerant to drought stress and completely inhibited by a potential of -1.0 MPa. Salinity stress up to 250 mM had no effect on seed germination. Drought and salinity levels for 50% inhibition of maximum germination were -0.5 MPa and 307 mM, respectively. A high percentage of seed germination was observed at pH=5 and decreased to 61.5% at acidic medium (pH 4) and to 11% at alkaline medium (pH 9). Maximum seedling emergence of Velvetleaf and Barnyardgrass occurred when the seeds were placed on the surface of the soil or at a depth of 1 cm.Keywords: pH, planting depth, seed germination, temperature, weed.RESUMO -Abutilon theophrasti e Echinochloa crus-galli são as principais plantas daninhas que afetam os sistemas de cultivo em muitas partes do mundo. Estudos em laboratório e em casa de vegetação foram conduzidos para determinar os efeitos da temperatura, pH da água e estresse salino e da profundidade de semeadura na germinação e na emergência das plântulas de A. theophrasti e E. crus-galli. Para A. theophrasti, as temperaturas de base, ótima e de teto de germinação foram estimadas em 5, 35 e 48 o C, respectivamente. A germinação das sementes foi sensível ao estresse hídrico e inibida completamente por um potencial de -0,6 MPa, mas foi tolerante à salinidade. Estresse salino de até 45 mM não teve nenhum efeito sobre a germinação de A. theophrasti, porém esta diminuiu com o aumento da concentração salina. Os níveis de seca e de salinidade para 50% de inibição da germinação máxima foram de -0,3 MPa e 110 mM, respectivamente. A germinação das sementes de A. theophrasti foi tolerante a uma vasta gama de níveis de pH. Para E. crus-galli, as temperaturas de base, ótima e de teto de germinação foram estimadas em 5, 38 e 45 o C, respectivamente. A germinação das sementes foi tolerante ao estresse hídrico e inibida completamente a um potencial de -1,0 MPa. Estresse salino de até 250 mM não teve efeito sobre a germinação das sementes. Os níveis de seca e de salinidade para 50% ...

Laboratory and greenhouse experiments were conducted to determine the effects of drought and salinity stress, temperature, pH and planting depth on yellow sweet clover (Melilotus officinalis) germination and emergence. Base, optimum and ceiling germination temperatures were estimated as 0, 18.47 and 34.60 o C, respectively. Seed germination was sensitive to drought stress and completely inhibited at a potential of -1 MPa, but it was tolerant to salinity. Salinity stress up to 90 mM had no effect over the M. officinalis seed germination, but the germination decreased by increasing the salt concentration. The drought and salinity required for 50% inhibition of maximum germination were 207 mM and -0.49 MPa, respectively. High percentage of seed germination (>92%) was observed at pH = 5-6 and decreased to 80% at acidic medium (pH 4) and to 42% at alkaline medium (pH 9) pH. Maximum seedling emergence occurred when the seeds were placed at 2 cm depth and decreased when increasing the depth of planting; no seed emerged from depths of 10 cm.RESUMO -Experimentos de laboratório e de casa-de-vegetação foram conduzidos para determinar os efeitos dos estresses de seca, salinidade, temperatura, pH e a profundidade de plantio sobre a germinação e a emergência do trevo amarelo doce (Melilotus officinalis). Temperaturas base, ótima e teto para germinação de M. officinalis foram estimados em 0, 18 e 34 o C, respectivamente. A germinação das sementes mostrou-se sensível ao estresse hídrico e foi totalmente inibida nos potenciais de -1 MPa. A germinação de M. officinalis foi tolerante à salinidade. Estresse salino até 90 mM não tiveram efeito sobre a germinação de sementes de M. officinalis, mas a germinação decresceu com o aumento da concentração de sal. A seca e a salinidade necessária para inibição de 50% de germinação máxima foi de 207 mm e -0,49 MPa, respectivamente. Alta porcentagem de germinação (>92%) foi observada em pH = 5-6 e desceu para 80% em condições ácidas (pH 4) e para 42% sob condições alcalinas (pH 9). Emergência máxima ocorreu quando as sementes foram posicionadas na profundidade de 2 cm e diminuiu com o aumento da profundidade de plantio. Nenhuma semente emergiu quando a profundidade de semeadura foi de 10 cm.Palavras-chave: germinação; pH; estresses abióticos, profundidade do solo, temperatura, estresse hídrico.

BackgroundExposing imbibed seeds to high temperatures may lead to either thermo-inhibition of germination or thermo-dormancy responses. In thermo-inhibition, seed germination is inhibited but quickly resumed when temperatures are lowered. Upon prolonged exposure to elevated temperatures, thermo-dormancy may be induced and seeds are not able to germinate even at optimal temperatures. In order to explore underlying physiological and molecular aspects of thermo-induced secondary dormancy, we have investigated the physiological responses of tomato seeds to elevated temperatures and the molecular mechanisms that could explain the performance of tomato seeds at elevated temperature.ResultsIn order to investigate how tomato seeds respond to high temperature we used two distinct tomato accessions: Solanum lycopersicum (cv. Moneymaker) (MM) and Solanum pimpinellifolium accession CGN14498 (PI). MM seeds did not germinate under high temperature conditions while seeds of PI reached a maximum germination of 80%. Despite the high germination percentage of PI, germinated seeds did not produce healthy seedling at 37 °C. By using a candidate gene approach we have tested if similar molecular pathways (abscisic acid (ABA) and gibberellic acid (GA)) present in lettuce and Arabidopsis, are regulating thermo-inhibition and thermo-dormancy responses in tomato. We showed that the ABA biosynthesis pathway genes NCED1 and NCED9 were upregulated whereas two of the GA-biosynthesis regulators (GA3ox1 and GA20ox1) were downregulated in tomato thermo-dormant seeds at elevated temperature. To identify novel regulators of tomato seed performance under high temperature, we screened a Recombinant Inbred Line (RIL) population derived from a cross between the two tomato accessions MM and PI for thermo-inhibition and dormancy induction. Several QTLs were detected, particularly for thermo-dormancy, which may be caused by new regulators of thermo-inhibition and thermo-dormancy in tomato.ConclusionsNone of the genes studied in this research were co-locating with the detected QTLs. The new QTLs discovered in this study will therefore be useful to further elucidate the molecular mechanisms underlying the responses of tomato seeds to high temperature and eventually lead to identification of the causal genes regulating these responses.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1455-6) contains supplementary material, which is available to authorized users.

-Studies were conducted to estimate parameters and relationships associated with sub-processes in soil seed banks of oilseed rape in Gorgan, Iran. After one month of burial, seed viability decreased to 39%, with a slope of 2.03% per day, and subsequently decreased with a lower slope of 0.01 until 365 days following burial in the soil. Germinability remained at its highest value in autumn and winter and decreased from spring to the last month of summer. Non-dormant seeds of volunteer oilseed rape did not germinate at temperatures lower than 3.