D. Gray

Some effects of umbel order and harvest date on carrot seed variability and seedling performance

SummaryThere were no effects of umbel order or date of seed harvest on the coefficient of variation (CV) of carrot seed weight. Seed grading reduced the CV from 31% to 22% compared with ungraded seeds and the effects were similar for all treatments. The CV of embryo length was lower in seeds from primary (P) than secondary (S) umbels and it declined with a delay in harvest, the reduction being greater for seeds from S umbels. Seed grading had no effect on the CV of the embryo length of ऩ seeds but it reduced the CV of S seeds, particularly at the early harvest. Fewer seedlings emerged and emergence was later from early-harvested and S umbel seeds than from late-harvested’ and ऩ umbel seeds, and the last two sources also produced larger seedlings than the first two, even after allowing for differences in seed weight. The CV of seedling weight decreased with a delay in harvest and was lower from seeds from ऩ than from S umbels, particularly at the early harvest. In general, grading improved the emergence ch...

Seed quality in carrots: the effects of seed crop plant density, harvest date and seed grading on seed and seedling variability

SummaryCarrot seeds (Chantenay types) harvested 44–61 days after anthesis (early harvest) had higher coefficients of variation (CVs) of embryo length and subsequent seedling weight than those of seeds harvested 70–92 days after anthesis (late harvest). Seed grading after harvesting the seed crop reduced the CVs of some of the early harvested seed crops. Seed crops grown at high plant density (80 plants m—2) compared with low density (10 plants m-2) produced seed with lower CVs but the effects were small. Averaged over three experiments the CVs of seedling weight from early- and late-harvested seeds were 53% and 43%, respectively. For high- and low-density crops the corresponding figures were 49% and 47% and for ungraded and graded seeds 50% and 45%. The CV of seedling weight and the ‘spread’ of seedling emergence times were closely related to the CV of embryo length but not to the CV of seed weight. This suggests that, in addition to estimates of viability determined by standard tests, a measurement of th...

Studies on carrot seed production: effects of plant density on yield and components of yield

SummaryThe yield of carrot seed (Chantenay types) increased by about 50%-55% with an increase in plant density from 10 to 80’plants m-2 in two experiments but in another there was no effect of density. The percentage of the yield contributed by the primary umbel was, on average, 25% and 62% for the low and high density crops, respectively. Increasing the plant density from 10 to 80 plants m-2 reduced the number of seeds per plant, largely because of fewer umbels, per plant. At anthesis, or soon after, seeds from primary umbels and low-density crops “were heavier, than those from secondary umbels and high-density crops. These differences were maintained throughout growth and, in . one year, were intensified by the shorter period of seed growth in the high-density crop. The lower mean seed weight in 1979 compared with 1980 was associated with a shorter period of seed growth and higher temperature after anthesis.

Scale-up studies for osmotic priming and drying of carrot seeds

Carrot seeds (Daucus carota) were primed in polyethylene glycol solution of −0·7 MPa osmotic potential for 7 to 10 d at 15 °C on filter paper and in either a bubble column of 0·5 1 or a stirred bioreactor of 51 at a seed concentration of 100 g l−1. In the bubble column, air was used and in the stirred bioreactor, both air and “enriched air” (75% O2/25% N2). Dissolved oxygen profiles and oxygen uptake rates as a function of time were measured and calculated respectively. The use of enriched air ensured that the dissolved oxygen concentration was generally greater than 100% of saturation with respect to air and gave an enhanced maximum oxygen uptake rate of 600 λl O2g−1 h−1 compared to 400 λl O2g−1 h−1 in the case of air. Compared with untreated seeds, priming by any of the methods did not influence the percentage germination but the mean germination times were reduced from about 4 to 1 d. With enriched air the treatment time was least and the spread of germination times was most reduced. Drying of seeds, following priming, also had no influence on the percentage germination but increased the mean germination times by 0·6 to 0·9 d whether cabinet drying for 48 h or fluidized bed drying for 4·5 h was used. Thus, large scale priming with enriched air followed by fluidized bed drying produces primed seeds, ready for storage, of the same quality as seeds treated in the laboratory by filter paper priming and cabinet drying but in some 3 d less.

The effects of seed-crop plant density, transplant size, harvest date and seed grading on leek (Allium porrum L.) seed quality

SummaryIn three years’ experiments the percentage seedling emergence from seed compost in glasshouse tests was between 83% and 91%, when averaged over all treatments. Crops grown at 97 plants m−2 produced seed of higher viability and, for 1983- and 1984-seed 6% to 7% higher percentage seedling emergence in the field than seed from crops grown at 11 plants m−2. There were no effects of steckling transplant size or variability on the subsequent performance of the seed. Seed-crop harvest date, over the range from c. 45–90 days after flowering, had little effect on percentage seed germination and seedling emergence except in 1982 where early harvesting reduced seedling emergence in the field. There were no consistent or large effects of seed-crop harvest date on the coefficient of variation (CV) of seed, seedling or mature plant weight. Large seed (2. 00–2.24 mm) increased seedling emergence in the field by 13% compared with ungraded seed and by 21% compared with the smallest size grade (1.60–1.80 mm). Seed g...

Priming and pre-germination of parsnip (Pastinaca sativa L.) seed

SummarySeedling emergence and growth responses to priming seeds in polyethylene glycol solutions, to germinating them before sowing and to a combined priming and pre-germination treatment were examined in the field and growth rooms using several stocks of seed. Priming or priming and pre-germinating seeds of a slowly germinating stock improved the percentage seedling emergence compared with untreated and pre-germinated seeds. In rapidly germinating stocks all three seed treatments showed similar levels of emergence which were higher than those of untreated seeds. Both priming and pre-germinating seeds reduced the mean emergence time and, in general, the effect of the combined treatment was greater than either treatment alone. Priming alone generally had no effect on the spread of emergence time or on seedling or plant weight variability, but pre-germinating seeds increased variability, particularly in a slowly germinating stock. Priming seeds before pre-germinating them reduced this variability.

Improving seedling establishment by a dibber drill

SummaryEight experiments with onion, three with leek and three with lettuce over the period 1991–1993 examined the influence of dibber and coulter drills on seedling establishment. In some of the experiments Alcosorb was applied to cover the seeds in the dibbed holes and Soiltex was applied as a band to the soil above the line of seeds. Additionally, seeds of differing quality and primed seeds were used. The dibber drill gave more uniform depth of sowing and spacing between seed positions than the coulter drills and it improved seedling emergence, substantially, where a soil cap or crust formed after sowing, and sometimes gave earlier and more uniform seedling emergence. It appeared that part of the improvement could be ascribed to better water supply to the seed associated with compaction of the soil around the seed and, indeed, there were benefits from using a seed press wheel sited immediately behind the point of seed delivery with the coulter drill. The use of Soiltex reduced impedance to shoot growth...

Hearting and Mature Head Characteristics of Lettuce (Lactuca Sativa L.) as Affected by Shading at Different Periods During Growth

SummaryComparisons of the growth and mature head characteristics of field grown lettuce cv Cobham Green were made between plants shaded from 50% emergence until the start of hearting, plants shaded from the latter period until maturity, and unshaded plants. Early shading lengthened the outer non-hearting leaves and the outer heart wrapper leaves by 12% but reduced the length of those leaves which, at the start of hearting, were destined to form the inner heart wrapper leaves and the first few heart ‘filler’ leaves. As a result, early shading decreased mature head weight but head density and volume were not significantly affected. For a sowing in May, late shading of plants increased head volume and decreased head density but head weight was unaffected. For a sowing in July late shading had no significant effect on head volume but head weight and density were significantly reduced. This reduction in weight and density was associated with an increase in the length/breadth ratio of the inner heart wrapper le...

Correlations between variability in carrot (Daucus carota L.) plant weight and variability in embryo length

SummaryThe variation in embryo length of Chantenay type carrot seeds, seedling and root weight were examined for 16 lots of commercial origin in 1983, and for six lots in 1984 at three sites for crops grown at low plant densities. The coefficients of variation (CV) of embryo length of the seed lots varied from c. 19 to 50%. The CVs of seedling weight ranged from c. 45 to 75% and of root weight from c. 50 to 70%. The ranking of lots by the CV of seedling weight in both years was similar at each site and both the CV of seedling weight and, in 1984, the CV of root weight increased with an increase in the CV of embryo length. The Spearman rank correlation coefficients (rs) for the relation between the CV of seedling weight and the CV of embryo length in both years ranged from 0.49 to 0.94 and rs for the CV of root weight and the CV of embryo length in 1984 from 0.83 to 0.94.

A relationship between sowing date and harvest date for radish (Raphanus sativus)

SummaryThe relationship between sowing date and harvest date was examined for a number of successional sowings of radish over the period 1971–1977. Harvest date was curvilinearly related to sowing date, a fitted curve accounting for 99.3% of the variation in harvest date. No improvement in the fit was obtained by replacing chronological time by a temperature-time scale.