Primary Umbels Research Articles

DEVELOPMENTAL CONTROL OF SOME PHYSIOLOGICAL FACTORS ON REPRODUCTIVE BIOLOGY AND RUDIMENTARY EMBRYOS PHENOMENON IN CARROT SEEDS

This study was aimed to investigate delayed germination and immature embryos of carrot seeds; This research was implemented at vegetable field of College of Agricultural Engineering Sciences - University of Baghdad during two sequent seasons (fall and spring). The experiment was conducted using factorial within Randomized Complete Block Design arrangement with three factors and replicates (3X3X2). The aqueous barley sprouts extract (B0, B1) (0, 100 g.L-1) represented the first factor. Trehalose (T0, T1, T2) (0, 50, 75 mmole.L-1) represented the second factor. Calcium (C0, C1, C2) (0, 1, 2 ml.L-1) represented the third factor. Results showed the effectiveness of third order interaction treatment B1T2C1 in increasing germination speed and percent for the seeds of royal umbel (92, 97%); secondary umbel (90.67, 94.67%); and tertiary umbel (75.68, 86.33%). The mentioned treatment increased embryo length for the seeds of primary (royal) umbel (1628.3 µm), secondary umbel (1620.3 µm); and tertiary umbel (874.7 µm ). in compare with the lowest percents that found in B0T0C2 treatment.

Morpho-Biochemical characterization of Kalazeera (Bunium persicum Boiss. Fedts) germplasm grown in Global temperate ecologies

The present investigation explores the variability of Bunium persicum populations belonging to different regions. Variability among 74 genotypes for thirty-seven traits (29 quantitative and 8 qualitative) were studied to ascertain the population structure of the Bunium persicum. Among the agro-morphological traits, wide range of variability was recorded in tuber shape, tuber colour, seed shape, seed colour, growth habit, leaf shape, leaf colour, umbel shape, umbel colour, plant height (22.90–96.52 cm), primary branches plant−1 (1–6), umbel diameter of primary umbel (6.17 – 13.67 cm), number of primary umbels plant−1 (1–12), umbels plant−1 (8–40), seed yield per plant (0.55–13.10 g), essential oil content (3.2–9.3 %) etc. Significant and positive association was observed between number of seeds primary-1 umbel (r = 0.91), plant height (r = 0.65), number of seeds primary-1 umbel (0.52), number of seeds primary-1 umbel (0.43), number of seeds secondary-1 umbel (0.38) with number of umblets secondary-1 umbel. Cluster analysis classified the genotypes with different geographical origin into two major clusters and sub-clusters. Cluster-I comprises of 50 genotypes and cluster - II of 24 genotypes while the genotype SRS-KZ-189 from Kargil population was separated as an individual sub-group. Principal component (PC1) and (PC2) harbors accounted 20.2% and 14% of total variation. Variability of Kalazeera genotypes would facilitate the plant breeders to implement and design various crop improvement programme in future.

The impact of auxin on the vegetative and reproductive growth of carrot (Dacus carota L.)

Seed is a basic component of every crop species and quality seed is essential for farmers to achieve greater crop production and higher yields. Seed yield can be improved by using the growth hormones. Indole-3-butyric acid (IBA) IBAplays a vital role in reproductive and seed development of crop plant. An investigation is being conducted to determine effect of rooting hormone IBA on reproductive growth that leads to seed developement. Roots treated with three levels of IBA (500 ppm, 1000 ppm and 1500ppm) along with control in a 3 replication. Results showed that roots treated with IBA @ 1500 ppm had taken least number (28.4) of days to flowering with maximum plant height (34.3cm), number of leaves (15.3), leaves length (19.6 cm), number of secondary (10) and tertiary umbels (13.7), diameter of secondary (12.7 cm) and tertiary umbel (4.4), weight of secondary (5.1 g) and tertiary umbel (3.5), seed weight of secondary (4.4 g) and tertiary umbels (1.5 g) and biological weight of the plants (81.0 g) respectively. However, the diameter, weight and seed weight of primary umbel was good in IBA @ 1000 ppm. Thus it is recommended that IBA application at concentration of 1500 ppm can significantly improve growth of carrot seed plants, hence increasing production and seed quality

Growing season climate affects phenological development, seed yield and seed quality of dill (Anethum graveolens)

Dill seed production was investigated over two seasons, comprising a spring growing cycle (SGC) and an autumn growing cycle (AGC). The effects of growing cycle on phenological traits, yield and quality of dill seeds formed on different umbels of the mother plant were investigated. Significant differences were noted in the flowering period, seed yield and quality parameters. The SGC resulted in a shorter time from sowing to bolting and flowering initiation compared with the AGC. Plant height, number of umbels/plant, number of umbelets/ umbel, umbel diameter, umbel length and seed weight/plant increased in the AGC. In contrast, decreased germination at 20/30°C and at 13°C, and increased mean germination time at 20/30°C in AGC indicated lower seed quality compared with SGC. Primary umbels produced the best yield and higher quality seeds, followed by the secondary umbels while tertiary umbels gave poor yield and quality seeds in both SGC and AGC. In conclusion, AGC was advisable for higher seed yield, but SGC resulted in higher seed quality compared with the AGC. This highlights the need to select a suitable growing cycle to guarantee high seed yield and quality for each seed production environment.

Impacts of high temperature on embryonic growth and seed germination of dill (Anethum graveolens)

Temperature is the main exogenous factor that determines the growth, development and productivity of agricultural plants, including seed germination. In this work, we studied the thermosensitivity of heterogeneous dill seeds (Anethum graveolens). The study aimed to study the short-term (1-5 days) effect of high temperature (40°C) on the growth of the embryo and germination of dill seeds formed on different umbels of the mother plant. The growth of the embryo had a significant effect on seed germination (r = 0.976; P < 0.001). Seeds collected from primary umbels have a more developed embryo and can overcome the effects of thermal stress. We also found that the duration of heat exposure at 40°C, leading to a decrease in viability, can vary from 1-5 days for seeds from primary umbels, to 1-2 days for seeds from secondary umbels, which, in our opinion, is due to the heteromorphism. The influence of the place of seed formation on the mother plant and the high temperature during germination is critical for embryo growth and dill seeds’ germination.

Effect of plant density and fertilizer doses on seed yield and its attributes in carrot

Plant density per unit area is expected to exert influence on the number of primary and secondary umbels. In some experiments contribution of primary umbels has been reported up to 90% of total seed yield. Nitrogen, phosphorous and potassium being the major plant nutrients are required by the crop for higher and quality yields, and carrot is no exception to this. Further, interaction between planting density and the major nutrients (NPK) is expected to have profound impact on seed yield and quality. Thus, the present investigation was undertaken to work out the optimum combination of planting density and fertilizers level for quality seed production of carrot. The results of the investigation revealed that plant spacing of 45 x 30 cm and 150% RD NPK, alone as well as in combination with each other favoured the seed yield and its contributing characters viz. plant height, days to flower initiation, days to 50% flowering, number of umbels per plant, and seed yield per plant and per hectare. The highest seed yield obtained for this interaction was 995.27 kg ha−1.

Multivariate analysis of morphological diversity among closely related Daucus species and subspecies in Tunisia

The genus Daucus includes about 20–25 species worldwide. Northern Africa represents a major center of diversity of Daucus, with Tunisia thought to contain 11 species and seven subspecies. The greatest taxonomic problems, however, and the greatest economic importance relative to immediate use in breeding, is in a group of species and subspecies in the Daucus carota L. clade, all containing 2n = 18 chromosomes. We assessed morphological diversity from a Daucus L. germplasm collection of nine individuals each from 45 accessions (405 individuals in total), at the National Gene Bank of Tunisia, of the following wild and one cultivated members of this clade: D. carota subsp. capillifolius (Gilli) Arbizu, D. carota subsp. carota, D. carota subsp. gummifer (Syme) Hook. f., D. carota subsp. sativus (Hoffm.) Arcangeli (cultivated), D. sahariensis Murb., and putative hybrids of D. carota subsp. carota and subsp. capillifolius. A prior study showed the effectiveness of fruit characters to identify several species and subspecies in the collection, but distinction between some closely related D. carota subspecies was difficult. In order to resolve the taxonomic classification, we tested 32 quantitative and qualitative morphological characters from leaves, stems and flowers on a field collection of 45 accessions corresponding to the different species/subspecies. The Shannon–Weaver diversity (H’) index was used to study the phenotypic diversity. The estimated H’ ranged from monomorphic for umbel type, position of involucral bracts on primary umbel, anther color, and symmetry of peripheral flowers to highly polymorphic for other traits. The highest (0.98) and the lowest (0.26) H’ values were recorded for flowering pattern within plants and foliage coverage. Multivariate analyses of principal components and dendrograms of all data and canonical discriminate analysis of the quantitative data supported the subdivision of the Daucus collection into five groups with various degrees of distinctness: (1) D. sahariensis, (2) D. carota subsp. capillifolius, (3) D. carota subsp. carota, very similar to (4) D. carota subsp. gummifer, and (5) D. carota subsp. sativus intergrading with putative hybrids between D. carota subsp. capillifolius and D. carota subsp. carota. Individual character state distribution plots provide useful characters and insights into taxonomic problems in the D. carota clade that we here discuss in reference to ongoing molecular studies in Daucus.

Effect of plant density and foliar nutrient application on seed yield and quality in Asiatic carrot (Daucus carota)

A field experiment was conducted to study effect of plant density and foliar spray of nutrients on carrot (Daucus carota L.) seed yield and quality during winter season of 2012-13 and 2013-14. Plant height, days to 50% flowering, number of umbels/plant, number of seeds/umbel, seed yield/umbel, percentage contribution of different order umbel to total seed yield, seed yield/plant, seed yield/ha, 1 000 seed (mericarp) weight, germination (%) and vigour index were recorded. Significant highest average plant height, earliness in days to 50% flowering and seed yield/ha (12.9 q) were observed in high plant density (13 plants/m2). More number of secondary (11.6) and tertiary umbels (30.1) and higher seed yield/plant (25.2g) were recorded in low plant density (4 plants/m2). Per cent contribution of primary umbel to total seed yield was maximum (41.76%) in 13 plants/m2 and minimum (16.89%) in 4 plants/m2. But an increasing trend in contribution percentage to total seed yield by secondary and tertiary umbels was recorded from 13 plants/m2 to 4 plants/m2.Seeds from primary and secondary umbels recorded high quality in plant density of 5 plants/m2 and 4 plants/m2 respectively.Comparative reduction in pooled seed vigour was observed in 7 plants/m2 and 13 plants/m2. Foliar spray of 0.1% MgSO4at 30 and 60 days after transplanting (DAT) increase the seed quality. Both seed yield and qualityincrease was observed in 0.1% borax spray at 30 and 60 DAT.

Influence of Different Maturity Stages on Fruit Yield and Essential Oil Content of Some Apiaceae Family Plants A: Anise (Pimpinella anisum, L.)

This study investigated the effects of harvesting at different plant maturation stages on the fruit and essential oil yield as well as its compositions of anise. It was carried out at El- Baramoon Research Farm, Mansoura Horticulture Research Station, HRI, ARC, Egypt, during the winter seasons of 2013/2014 and 2014/2015. The plants were harvested at eight different fruit development stages and determinations were made of the yields of fruit , germination percentage the thousand fruit weight (seed index), the essential oil percentage and its constituents. The obtained results indicated that high yield and quality of anise fruits were obtained when fruits harvested at stage 4 (the primary umbel was matured completely).The highest essential oil percentage was higher in stage 1 (the primary umbel was at the beginning of waxy stage.). However, this high percentage of essential oil did not produce the maximum oil yield per plant in stage1 was associated with low fruit yield. Essential oil yield per plant with high Trans-Anethole content reached their maximum when fruits harvested at stage 4. Generally, it could be recommended that to obtain the maximum fruit yield and quality as well as high essential oil yield with high Trans-Anethole content, anise fruits should be harvested at stage 4 (The primary umbel was matured completely).

Manipulation of Plant Spacing and Steckling Size to Increase Growth and Seed Yield in Carrot (Daucus Carota L.) Under Temperate Conditions of Kashmir

An experiment was conducted at Urban Technology Park, Division of Vegetable Science, SKUAST-Kashmir during 2013-2014. Four levels of spacing and four steckling sizes in carrot were used giving rise to sixteen treatment combinations. Widest spacing (60 cm x 75 cm) recorded maximum plant height number of branches plant-1, number of secondary umbels plant-1, number of tertiary umbels plant-1, seed yield per primary umbel, secondary umbel and tertiary umbel and seed yield plant-1. However highest seed yield, number of secondary and tertiary umbels were recorded in closest spacing of 60 cm × 30 cm. Extra-large steckling size (150-175 g) recorded highest plant height, number of branches plant-1, number of secondary and tertiary umbels, seed yield per primary, secondary and tertiary umbel, seed yield.

Optimization Coriander Production for Fruit and Essential Oil A: Determination of Best Fruit Maturity Stage

This study was carried out at El- Baramoon Research Farm, Mansoura Horticulture Research Station, HRI, ARC, Egypt, during the two winter growing seasons of 2012/2013 and 2013/2014, to determine the optimum time of harvest coriander fruits for maximum viable fruit yield and oil percentage. Coriander fruits were harvested at seven different maturity stages. In this investigation, it has been found that the maximum yield and quality of coriander fruits in terms of fruit yield, thousand fruit weight (seed index) and germination percentage were reached its maximum at the third stage (the secondary umbels colour was changed). Moreover, essential oil percentage was higher in the early harvesting stages and was high at the first maturity stage (the primary umbel was at the beginning of waxy stage). In addition, essential oil yield / plant with high linalool content reached their maximum when fruits harvested at the third stage. Generally, it could be recommended that to obtain the maximum fruit yield and quality as well as high essential oil yield with high linalool content, coriander fruits should be harvested at the third maturity stage of fruit development.

Lectotype Designation for Seven Species Names in the <I>Daucus guttatus</I> Complex (Apiaceae) from the Central and Eastern Mediterranean Basin

Abstract The Daucus guttatus complex includes two to four species growing from central and northern Italy to the Middle East. They are characterized by being typically annuals up to 50 cm high; with primary umbels up to 7 cm in diameter with fewer than 25(35) rays; discolored umbels frequent, bearing one to several dark colored umbellules which form different color patterns; and mericarps relatively small, ca. 2.0–4.5 mm. The taxonomy of this complicated group has not been satisfactorily resolved to date and is the focus of current research. Seven names of species belonging to the D. guttatus complex occurring in the central and eastern Mediterranean basin are typified here: Daucus guttatus, Daucus bicolor, Daucus involucratus, Daucus setulosus, Daucus broteri, Daucus hirsutus, and Daucus speciosus. Historical data are reported to justify lectotype and/or epitype selection, and selected morphological and distributional data are used to facilitate identification. The resulting typifications will enable pro...

Biochemical and physiological analysis in carrot seeds from different orders of umbels

In carrot seed production, harvesting of the umbels is generally staggered, or sometimes the whole plant is harvested with the umbels at different stages of maturation; in that case, there is a risk of harvesting immature seeds and of losses due to natural dehiscent, or to physiological deterioration as a result of unfavourable environmental factors. The present study aimed to evaluate the physiological and biochemical changes related to the maturation of 'Planalto' carrot seeds from diferent umbels. The samples were collected 120 days after anthesis, with the primary, secondary and tertiary umbels being harvested separately. Seeds were analysed for germination, first count and germination rate, at temperatures of 25 °C (optimum) to 35 °C (adverse), as well as for emergence in the greenhouse and the emergence rate. Analyses were also carried out of the enzymes peroxidase (POX), ascorbate peroxidase (APX), catalase (CAT) and superoxide dismutase (SOD), and of the total protein. Seeds obtained from the primary and secondary umbels displayed a higher rate of germination than from the tertiary umbels, with the seeds from the primary umbels showing high activity for peroxidase, catalase and superoxide dismutase, and low activity for the enzyme ascorbate peroxidase.

Effect of Storage and Umbel Orders on Seed Quality of European Carrot Cultivar Solan Rachna under Cold Desert Conditions of Himachal Pradesh

These investigations were carried out to study the effect of umbel orders and storage on seed quality of European carrot cv. Solan Rachna produced and stored in cold desert conditions at RHRSS, Tabo, Lahaul and Spiti, HP during 2008–2012. Significant differences among seeds of different umbel orders were observed with respect to 1000-seed weight, seedling length and seed vigour index-I. Heaviest seeds were produced on primary umbels with 1000-seed weight of 1.53 g followed by secondary umbel seeds (1.49 g), mixed seed lot (1.42 g) and tertiary umbel seeds (1.19 g). Germination showed a progressive decrease with increasing umbel order. The longest seedlings (10.60 cm) were observed in primary umbel seeds. Similarly, the most vigorous seeds were borne on primary umbels. Storage period affected physiological traits like germination, seedling length and seed vigour. The highest germination (68.67%) was observed in the fresh seeds and lowest (30.33%) in oldest seeds. The longest seedlings were produced by the fresh seed and the length decreased with the storage period of the seed lot. Seed Vigour Index-I decreased with storage period of the seeds. Interaction of umbel order and storage period of carrot seed significantly affected physiological quality. The longest seedlings (11.71 cm) were produced by the youngest seeds of primary umbel, whereas the shortest seedlings were produced by the mixed lot seed stored for three years. Seedling length decreased significantly with increasing storage period within umbel orders. Primary umbel order seeds had least germination reduction with increasing storage period. Vigour deterioration was more pronounced in seeds of inferior umbel orders.

First Report of Umbel Browning and Stem Necrosis Caused by Diaporthe angelicae on Carrot in France.

In 2011, carrot (Daucus carota L.) seed production occurred on 2,900 ha, which accounts for approximately 25% of the area devoted to the production of vegetable fine seeds. Since 2007, symptoms of umbel browning have been regularly observed in carrot production areas located in the central region. Initially, triangular necrotic lesions appeared on carrot umbels that later spread to the entire umbels and often progressed to the stems. Diseased umbels became dried prematurely, compromising seed development. The loss in seed production was estimated at approximately 8% of the harvested carrot umbels during the cropping seasons of spring and summer 2007 and 2008 in France. In collaboration with seed companies, diseased carrot stems were collected from seven fields of seed production (eight plants per field) and a fungus was isolated from the tissue. The cultures were grown on malt (2%) agar (1.5%) medium and incubated for 2 weeks at 22°C in darkness. Young fungal colonies were white and a brownish green pigmentation developed when the colonies became older. The same color was observed from the top and on the reverse of the colonies. To induce sporulation, isolates were grown on water agar (1.5%) medium in the presence of carrot stem fragments for 1 week at 22°C in darkness, followed by 1 week at 22°C in white light under a 16-h photoperiod. Pycnidia were produced on stem fragments and contained alpha and beta conidia typical of the genus Diaporthe (2). Alternatively, pycnidia were also obtained on malt agar medium after 2 weeks of culture at 25°C in white light under a 12-h photoperiod. The size of alpha and beta conidia was 6.3 ± 0.5 × 2.3 ± 0.4 μm and 23.3 ± 1.8 × 0.9 ± 0.2 μm, respectively (n = 170). In order to confirm the identification at the genus level and determine the species, DNA was extracted from the mycelium of three representative isolates and the ITS regions of the ribosomal DNA were amplified using universal primers (1). The sequences of the amplified products (GenBank Accession Nos. KF240772 to KF240774) were 100% identical with the ITS sequence of a Diaporthe angelicae isolate deposited in the NCBI database (CBS 111592 isolate, KC343027). To confirm pathogenicity, the three isolates of D. angelicae were inoculated on carrot umbels in the greenhouse. A total of nine plants were inoculated (three plants per isolate). Using a micropipette, 10 μl of a conidial suspension containing alpha and beta conidia (105 conidia mL-1) were deposited at the base of the primary umbel and two secondary umbels, which were wounded before inoculation using a scalpel blade. Seven inoculated plants developed triangular, necrotic lesions that were typical umbel browning. D. angelicae was re-isolated on malt agar medium from the inoculated diseased carrot umbels. To our knowledge, this is the first report of D. angelicae in carrot cultivated for seed production in France. The disease resembles the lesions described in the Netherlands in 1951 on carrot inflorescence caused by Phomopsis dauci (3). In future experiments, it would be crucial to precisely determine if D. angelicae could be transmitted to the seeds.

Intercropping of Medicinal and Spice crops under different Agroforestry tree species in Punjab

Performance of five medicinal and spice crops viz. Fenugreek, Fennel, Celery and Dillseed was investigated as sole crops and as intercrops with block plantations of Poplar, Dek, Toon, Gmelina, Maharukh and Eucalypt spaced at 6 x 3.5 m at the age of two and three years during 2006-2007 and 2007-2008, respectively in the Research Farm of Department of Forestry and Natural Resources, Punjab Agricultural University, Ludhiana, Punjab. Eucalypt trees recorded the maximum height, whereas the mean gain in DBH was maximum in Maharukh. Crown spread was more of Dek than rest of the tree species after three years of tree growth. All the crops performed better as sole crops than intercrops. Increase in age of trees from two to three years resulted in significant decline in growth and yield contributing characters like plant height, number of primary branches, umbels and umbellets per plant in Fennel, Celery, Dillseed, and number of pods, seeds/pod and pod length of Fenugreek crop. The seed yield of Fenugreek and Fennel was higher under Gmelina, whereas Dillseed recorded highest yield under Poplar trees during both the years. The production of Celery was higher under Poplar and Toon at the age of two and three years, respectively. All the crops recorded the highest reduction in seed yield when grown with Eucalypt than other trees during 3rd year of tree growth. Celery gave the highest returns followed by Fennel and Dillseed in second year of tree growth, while Dillseed, Fenugreek and Fennel remained more remunerative in the subsequent year.

Effect of umbel position on dill (Anethum graveolens L.) plants growing in field stands on selected seed stalk features

Abstract Research was carried out on the effect of the umbel position on the ‘Amat’ dill (Anethum graveolens L.) plant on selected features of the seed stalk in the years 2002-2004. Commercial seeds of the species were sown on a small production field and grown for the purpose of producing seeds. Out of the field plant stands, three hundred plants were randomly selected. The following morphological features were then measured in respect to the seed stalk architecture in these plants: the length of the seed stalk, number of branches with primary, secondary and tertiary umbels, length of branches with primary umbels, as well as the main and primary umbel diameters. In addition, seed yield per plant, the weight of 1000 seeds, germination capacity, seed length and width, seed embryo and endosperm lengths for seeds from the main and primary umbels were also calculated and measured. Additionally, the main and primary umbels were divided into three parts: external, middle and internal, and seeds from each were examined separately. The position of the umbel on the seed stalk did not affect the number of branches with primary, secondary, and tertiary umbels on the dill plant and had no effect on its seed stalk architecture. There was no significant difference within the position of the main and primary umbels on the seed stalk grown in field stands. The diameter of the main umbel was the same as the primary one. The lower its position on the seed stalk, the lower the seed yield and germination capacity. The best seeds, in terms of their 1000 seed weight, came from the external part of the main umbel. The different localisation of seeds within the three designated parts of the main umbel had no effect on seed length or width or on their endosperm and embryo lengths. The recorded seed embryo length from the internal part of the primary umbel was smaller than its values from the two other parts of that umbel.

Heterogeneity of carrot seeds depending on their position on the mother plant

Abstract The period of vegetation and flowering of carrot usually is very long, and the flowers are formed in different parts of the mother plants. This leads to the formation of seeds with different qualities. Often heterogeneity is of a maternal type, which depends on the position of the umbels on the mother plants. The main goal of the present study was to investigate the quality differences in carrot seeds from different parts of the mother plant. The seedstalks from ‘Nantski’, a typical Bulgarian cultivar, were grown by the conventional method for seed production technology. In botanical maturity the seeds from the primary, secondary and tertiary umbels were extracted separately. The seed yield from umbels, dry weight of the seeds, seed size, length, width and thickness, weight per seed, 1000 seed weight, germination energy (first count), germination capacity (final count), mean germination time, uniformity of germination, fresh weight of seedlings, length of radicle, length of hypocotyls and vigour indexes were investigated. The contents of raw protein, sugar, lipids and the basic calorific values were also analysed. The germination was the highest for the seeds from primary umbels, followed by the ones from secondary umbels and lowest for those from the tertiary umbels. The difference between the highest and the lowest value was 6.30%. These results suggest that it is better to harvest the carrot seeds depending on their position on the plant and divide them into separate lots with different qualities.

The effect of plant density on seed yield and quality of carrot (Daucus carota L.)

The hypothesis that by increasing carrot (Daucus carota) plant density the contribution to seed yield by the primary umbels would increase, and that therefore both seed yield and seed quality would increase, was examined in two experiments in different years in Canterbury. A radial trial design provided plant densities from 2 to 84 plants/m2 and from 4 to 100 plants/m2 in experiments one and two respectively. Seed yield increased with increasing plant density in both experiments, and at the highest density the primary umbels contributed 90% (experiment one) and 60% (experiment two) of the seed yield. In both experiments seeds from the primary umbels had a greater thousand seed weight and higher germination than those from the other order umbels, and for the second experiment they also had higher seed vigour. The quality of seeds from the primary umbels was consistently higher than that of seeds from the secondary umbels across all plant densities, and for the latter, both germination and seed vigour declined as plant density increased. These results therefore support the hypothesis, and densities higher than the 20 plants/m2 currently used commercially have the potential to increase both seed yield and quality. Keywords: seed production, primary umbels, germination, vigour, plants/m2

Germinação e vigor de sementes de cenoura sob condições de altas temperaturas

Em decorrência do desenvolvimento de cultivares tolerantes ao calor e com resistência às principais doenças de folhagem, o cultivo de cenoura vem expandindo-se também para outras regiões, como Norte e Nordeste. Altas temperaturas por ocasião da semeadura podem reduzir a germinação de sementes de cenoura e comprometer o estabelecimento da cultura. Avaliou-se o efeito de altas temperaturas na germinação e no vigor de sementes de cenoura de diversas cultivares comercializadas no Brasil bem como em progênies de meio-irmãos de uma polulação de cenoura 'Brasília'. Sementes da cv. Brasília foram colocadas para germinar em temperaturas constantes de 20; 24; 28; 32 e 36ºC por um período de 14 dias. Sementes provenientes de umbelas primárias e secundárias de 120 progênies de meio-irmãos de uma população de cenoura 'Brasília' foram também avaliadas quanto à viabilidade (germinação a 20ºC) e temperaturas elevadas (35ºC), vigor (primeira contagem de germinação) e massa de 100 sementes. Finalmente, sementes de 28 lotes comerciais de cenoura foram avaliadas quanto à germinação a 20 e 35ºC. Houve decréscimo na germinação à medida que a temperatura aumentou, sendo que a 36ºC apenas 27% das sementes germinaram. O teste de germinação a 20ºC mostrou que existem variações entre os lotes comerciais, e que, em condições de alta temperatura (35ºC), a germinação foi bastante reduzida para a maioria deles. As progênies de meio-irmãos apresentaram-se com alta germinação e vigor a 20ºC. Entretanto, à temperatura de 35ºC, somente algumas progênies apresentaram germinação superior a 60%. Em adição, as sementes provenientes das umbelas primárias germinaram melhor a 35ºC que aquelas provenientes das umbelas secundárias. Para a obtenção de melhor estande no campo, principalmente em condições adversas de altas temperaturas, a seleção e desenvolvimento de cultivares mais tolerantes, bem como a utilização de sementes provenientes de umbelas primárias seria altamente recomendado.