Showing papers on "Sowing published in 1981"

The effects of delayed sowing and weather on growth, development and yield of winter oil-seed rape (Brassica napus)

Abstract: Sowing winter oil-seed rape cv Victor late in autumn (late September or October) in seven seasons from 1970 to 1977 gave enormously variable seed yields, from 120 to 450 g/m2 All crops made little growth before winter, and yield was related to the size of the crop at flowering, a function of the length of time for radiation interception and growth between the ‘beginning of spring’, when mean temperatures rose consistently above 5 °C, and full flower in late May A late spring in 1970 gave the poorest growth and lowest yield, whereas in 1977 an early spring coincided with late flowering to give exceptional growth, and yields higher than from any early sowingCrops sown in early autumn (before mid-September) produced more consistent seed yields, 280–360 g/m2, except in the dry year of 1976 All grew well in autumn, overwintered with a large leaf area, and once temperatures rose in spring, rapidly reached peak area and full flower in early May They were all large at flowering, and yield was apparently limited more by post-flowering eventsWith all sowings numbers of pods and seeds were largely determined during a 3-week phase in late May and early June, extending from full flower until most pod hulls had finished growing Late sowings produced 3000–6000 pods/m2, and the number of seeds retained per pod varied widely, from 7 on a poorly grown crop to 22 on a well grown crop, thus expressing the yield potential determined by crop size at flowering Early sowings, however, produced apparently excessive numbers of pods (6000–12000/m2) and few seeds per pod (6–10), so that yield varied little, regardless of crop size Early in the phase, when the number of seeds was determined, the mass of yellow flowers at the top of the crop reflected or absorbed up to 60 % of incoming radiation, and then the large number of pods increasingly shaded each other and competed for assimilate, resulting in heavy seed losses A high-yielding crop type may therefore need to incorporate the restricted pod production and good seed retention of some well-grown latesown crops with the reliability and desirable agronomic features of early-sown cropsFinal seed weight varied more between seasons (3·7–5·3 nag) than between sowings Seed growth mainly took place after the number of seeds had been determined, the duration depending on temperature, but rate of growth apparently more on assimilate supply, a function of environmental factors and the number of competing seeds

Seed production and longevity, seasonal emergence and phenology of wild radish (Raphanus raphanistrum L.).

Abstract: Experiments conducted from 1977 to 1979, at Rutherglen, north-eastern Victoria, investigated seed production, seed longevity, seasonal emergence and phenological development in wild radish (Raphanus raphanistrum L.), a weed of field crops. Seed production of wild radish reached 17 275 seeds/m2; seeds retained viability and germinated over a period of three years. The loss of viability was faster at the soil surface or at 1 cm depth than at 5 or 10 cm. Of 1000 wild radish seeds buried at 1 cm depth, 737 emerged after three years, compared with 367, 167 and 5 at 0.5 and 10 cm, respectively. Phenological development of wild radish was affected by time of planting, and the duration of the period from plant emergence to plant senescence ranged from 5 to 10 months. Temperature appeared to influence development up to flowering, but photoperiod affected the length of flowering. Plants emerging at any time during the year were able to flower and seed successfully. The implications of these findings for control programs are discussed.

Conservation tillage row crop planter system

Abstract: The planter includes a number of forward tillage units each followed by an aligned planting unit. Both units are independently mounted by four-bar linkages to the planter frame. Each tillage unit includes a leading banded coulter followed by a pair of rolling row cleaning discs which are, in turn, followed by a fluted coulter. The system may be used in any of the following planting modes: (1) no-till planting, in which the fluted coulter only is used to prepare a narrow band of soil for planting with no trash removal; (2) ridge planting or till-planting, in which the row cleaning discs clear a deeper wide band before the fluted coulter while leaving bands between the row crops untilled; (3) minimum tillage planting, in which the row cleaning discs may be used to clear a shallow band of surface trash before the fluted coulter; and (4) conventional planting, in which the tillage units are raised and not used. Simple field adjustment can quickly convert the system to any of these plow modes as field conditions require. In each of the first three modes, an adjustable weight may be used to set the weight on the tillage units.

Osmoconditioning of Carrot Seeds to Improve Seedling Establishment and Yield in Cold Soil1

Abstract: Cold soil interferes with early establishment of uniform, vigorous seedlings in vegetables and other crops. The aim of this work was to determine if the changes induced in carrot (Daucus carota L.) seeds during partial hydration by low osmotic potential polyethylene glycol 6000 (PEG) solution would allow early planting in cold soil and thereby improve germination, growth, and yield. Seeds of two carrot cultivars, ‘Nantes’ and ‘Perfekcja’, were treated in —8.6 bars PEG solution for 6 days at 15 C. The effects of the seed treatment were evaluated by germinating the seeds on filter paper at 10 C, in Cornell Soil Mix (peat-lite Mix A) in a growth chamber at an alternating temperature regime of 5 and 10 C and in the field (Glossoboric Hapludalf, fine loamy, mixed mesic soil) where the average soil temperature during the first 2 weeks after field planting was 10.5 C and during the first 5 weeks 12.6 C. Seed osmoconditioning unproved the emergence time, stand size, and uniformity of stand in the field and increased the total yield. The increase in fresh weight of roots in Nantes and Perfekcja from PEG treated seeds were 32 and 93% and in number of roots 37 and 100%, respectively, compared to the untreated seeds

The effects of seed size, autumn nitrogen and plant population density on the response to delayed sowing in winter oil-seed rape (Brassica napus)

Abstract: The aim of the experiments reported here was to investigate the possibility of minimizing yield losses due to late sowing by increasing leaf area and radiation interception during the pre-flowering period. The use of large seed did increase leaf area, radiation interception and crop weight at flowering. Normally this would be expected to lead to increased yield of late sowings, but hot, dry conditions severely affected all crops during seed growth. Applying fertilizer nitrogen in the seed bed boosted pre-flowering growth of early but not late sowings, probably because low temperatures prevented a response in the latter. Increasing plant population density did improve leaf cover and radiation interception until just before flowering, but leaf canopies in late-sown, low density crops were then able to expand more and function for longer owing to less shading by flowers and pods. Seed retention was improved and, even with as few as 8 plants/m3 in 1973–4, a worthwhile yield was still obtained.

Evidence for a ‘uniculm effect’ in spring wheat (Triticum aestivum L.) in a mediterranean environment

Abstract: The concept of the uniculm habit as an important feature of a wheat ideotype for a mediterranean environment was evaluated under field conditions. A uniculm plant produces a single shoot and when sown in a stand exemplifies a non-tillering crop with a fixed density of shoots throughout the growing season. Yield and harvest index of normal tillering spring wheat was compared with that of the same crop surgically detillered throughout the growing season to a constant density of 2 shoots per plant. The use of a biculm, whilst retaining the uniculm principle of a fixed density of shoots throughout the growing season, permitted comparison on a single crop sowing at normal field density.

Effects of Soil Temperature and Planting Date of Wheat on Meloidogyne incognita Reproduction, Soil Populations, and Grain Yield.

Abstract: Wheat cultivars Anza and Produra grown in winter in California were planted in Meloidogyne incognita infested and noninfested sandy loam plots in October (soil temperature 21 C) and November (soil temperature 16 C) of 1979. Meloidogyne incognita penetrated roots of mid-October planted Ataza (427 juveniles/g root), developed into adult females by January, and produced 75 eggs/g root by harvest in April. Penetration and development did not occur in late plantings. Anza seedlings grown in infested soil in pots buried in field soil in early spring were not invaded until soil temperature exceeded 18 C. Meloidogyne incognita juveniles can migrate through soil and penetrate roots at temperatures above 18 C (activity threshold), however development can occur at lower temperatures. Grain yields were not significantly different between nematode infested (3,390 kg/ha) and noninfested (2,988 kg/ha) plots. Winter decline of eggs and juveniles in two late plantings anti in fallow soil were 69, 72, and 77%, respectively, but egg and juvenile decline was only 40% in the early Anza plots that supported nematode reproduction in the spring. Delay of planting date until soil temperature is below 18 C is suggested to maximize the use of wheat in rotation as a nematode pest management cultural tactic for suppressing root-knot nematodes.

Response of Determinate and Indeterminate Soybeans to varying Cultural Practices in the Northern USA1

Abstract: Determinate soybean [Glycine max (L) Merr] cultivars adapted to the northern US soybean growing region have been developed and released in recent years The purpose of this research was to compare the response of determinate and indeterminate soybean cultivars to varying cultural practices The determinate cultivars, ‘Gnome’ and ‘Elf’, and the indeterminate cultivars, ‘Beeson’ and ‘Williams’, were grown at two Illiiois locations in planting dates ranging from early May to early July The soil was Flanagan silt loam (Acquic Argiudoll) at Urbana and Cisne silt loam (Mollis Albaqualf) at Brownstown Within each planting date, cultivars were planted in 80, 50, and 20 cm row widths A separate seeding rate study was conducted with the determinate cultivar Elf, using seeding rates of 350,000, 500,000, and 650,000 seeds/ha in both 76 and 20 cm row widths Planting date contributed most to variation in seed yield Seed yield in central Illinois decreased an average of 33y0 as planting date was delayed from early May to early July Seed yield of the indeterminate cultivars d e clined steadily after the early May planting date, whereas, seed yield of the determinate cultivars did not decrease until planting date was delayed past early June The indeterminate cultivars showed a linear decline in plant height and main stem node number as planting date was delayed, whereas, plant height and main stem node number of the deternunate cultivars were greatest in early June plantings Lowest pod height of the determinate cultivars planted after mid-June or in drought-prone soils was sufficiently close to the soil surface (less than 10 an) to cause concern about excessive harvest losses Seed yields of both the determinate and indeterminate cultivars increased significantly (9 and 5% at Urbana and Brownstown, respectively) as row widths were narrowed from 80 to 50 cm, whereas, seed yields in 50 and 20 cm row widths did not differ The determinate cultivar Elf exhibited the ability to perform well over plant densities at harvest ranging from 279,000 to 494,000 plants/ha A seeding rate of 400,000 to 500,000 seeds/ha for determinate cultivars appears sufficient to maximize seed yield, reduce potential harvest losses due to low basal pod height, and insure adequate and uniform stands in unfavorable seedbeds

Growth analysis of soybeans (Glycine max) in competition with jimsonweed (Datura stramonium).

Abstract: Field experiments were conducted to study the effects of jimsonweed ( Datura stramonium L.) densities and planting dates on the growth and yield of soybeans [ Glycine max (L.) Merr. ‘Amsoy 71’]. Jimsonweed densities of 1.5 and 2 plants/m 2 did not reduce the dry weight of soybean leaf, stem, root, or pod and seed tissues, leaf area index, plant height, pod number, or seed yield when soybeans and jimsonweed were planted at the same time. Weed densities ranging from 3 to 16 plants/m 2 did reduce one or more of these soybean growth parameters. A significant density-by-year interaction was observed in which soybean growth reductions caused by high jimsonweed densities were less when competition for water was minimized by above-average precipitation in 1 of the 2 yr. No density of jimsonweed that emerged when soybeans were at the fourth trifoliolate-leaf stage reduced crop growth or yield.

Fungicide Enhancement of Nitrogen Fixation and Colonization of Phaseolus vulgaris by Rhizobium phaseoli.

Abstract: The number and weight of pods and the weight and nitrogen content of the tops of beans (Phaseolus vulgaris) derived from seeds inoculated with a thiram-resistant strain of Rhizobium phaseoli were increased if the seeds were treated with thiram before sowing in soil. A greater percentage of the nodules on 21-day-old plants were derived from the resistant strain, more nodules were formed, and these nodules were more effective in the presence of the fungicide than in its absence. These differences in nodule numbers were no longer present in 56-day-old plants, and only a small percentage of the nodules contained the resistant strain. The abundance of the fungicide-tolerant R. phaseoli increased rapidly soon after planting the seed and subsequently fell markedly, but the rate of decline was less if the seeds had been treated with the chemical. Protozoa also proliferated if thiram had not been applied to the seed, but their numbers were deleteriously influenced by thiram. Bdellovibrio, bacteriophages, and lytic micro-organisms acting on R. phaseoli were rare under these conditions. Ciliates and flagellated protozoa were initially suppressed by planting thiram-coated bean seeds in nonsterile soil, but the former were inhibited longer than the latter and the ciliate numbers never fully recovered if the seeds were treated with the fungicide. The resistant strain grew well in sterile soil also inoculated with a protozoa-free mixture of soil microorganisms whether thiram was added or not, but after an initial rise in numbers, its abundance fell if the mixture contained protozoa; the rate of this fall was delayed by the fungicide. The numbers of R. phaseoli were consistently less in sterile soil inoculated with the rhizobium plus a mixture of soil microorganisms containing ciliates and other protozoa than if the inoculum contained other protozoa but no ciliates. These results suggest that a suppression of protozoa, and possibly especially the ciliates, accounts for the enhanced growth of beans and the greater initial frequency of nodules formed by the thiram-resistant R. phaseoli in the presence of this fungicide. Thiram applied to uninoculated seed enhanced bean growth if thiram-resistant R. phaseoli were present in soil.

Dimethylnaphthalene as a sprout suppressant for seed and ware potatoes

Abstract: Dimethylnaphthalene (DMN) was shown to be an effective sprout suppressant. In the laboratory and in a commercial seed potato store, a DMN isomer mixture applied at 100 mg kg−1 controlled sprout growth as effectively as tecnazene applied at 135 mg kg−1. When seed tubers, treated at 100 mg kg−1, were aired for 4 to 7 weeks before planting, subsequent emergence and total yield were not adversely affected but treatment at 300 mg kg−1 delayed emergence and reduced yield. Treatment with DMN at 100 mg kg−1 increased the yield of medium sized tubers more than did that by tecnazene at 135 mg kg−1.

The growth and phosphorus economy of the early potato (Solanum tuberosum)

Abstract: The growth and P economy of an early potato crop were studied. Fertilizer P uptake was measured by isotopic labelling of the fertilizer. Up to 46 days after planting there was a net loss of both P and of dry matter from the plant. The patterns of dry matter and P accumulation after this date were markedly different from each other. Fertilizer P increased the yield of tubers but only 4% of the applied P fertilizer was recovered by the crop. The contribution of P from the seed tuber to the plant was as great as that of the fertilizer. Attempts were made to supply P to the crop by treatment of the seed tuber prior to planting and also by foliar application. These attempts were largely unsuccessful.

Studies on some sources of variation in carrot root weight

Abstract: Five investigations were carried out to determine the magnitude of root-size variation within crops of cv. Chantenay Supreme grown under competitive and non-competitive conditions, and to study possible sources of inter-plant variation.In the first experiment root-size variation from crops grown at a high population density (245 plants/m2) and at a low density (25 plants/m2) were compared over a 21-week period from sowing. The c.v.s of root weight were always higher from the high density than from the low density over the harvesting period from 11 to 21 weeks after sowing, and ranged from 74 to 94% and from 50 to 63%, respectively. A second study showed that even with a very low population density (3 plants/m2) the c.v. of root weight at harvest was 58%. The third study showed that 40% of the root weight variation was accounted for by the time of seedling emergence. The results of a pot experiment indicated that when the size of seed, sowing depth, rooting medium and time of seedling emergence were made as uniform as possible, a very uniform population of roots was produced with a c.v. of root weight of 32%. In the final field experiment when time of seedling emergence, seed size and spatial distribution of the plants were the experimental variables, the results confirmed the importance of variability in time of seedling emergence and seedling size in creating variation at an early stage of growth.The results of these studies indicate that competition per se was not a prime source of variation in root size but magnified any initial variation within the crop at the time of seedling establishment. The importance of this early establishment phase in determining the spread of root-size distribution within a crop is discussed together with the factors which influence the time of seedling emergence and seedling size.

Studies on Meteorological Fluctuation in the Growth of Rice Plants. : V. Regional Differences of Thermo-Sensitivity, Photo-Sensitivity, Basic Vegetative Growth and Factors Determining the Growth Duration of Japanease Varieties.

Abstract: Thermo-sensitivity(X1), photo-sensitivity(X2) and basic vegetative growth(X3) of 70 rice varieties in Japan were obtained by growing plants in growth cabinets under possible 4 combinations of different daylength and temperature : short(SD:10h) or long(LD:14h) daylength and low(LT:20'C) or high(HT:30'C) tempcrature. The X1, X2 and X3 are expressed by nSDLT-nSDHT, nLDLT-nSDLT and nSDHT, respectively, where nSDLT Stands for the number of days from sowing to headlng under 10h and 20 C and so on. Duration (Y) from sowing to heading of the same varieties was examined in a paddy field with three different sowing dates. Multiple correlations between duration(Y) and a set of X1, X2 and X3 of early, medium and late maturing varieties in all sowing dates were highly significant, showing thatvarietal differences in duration(Y) could be largely explained by the combination of the three factors.

The potential of legumes as a nitrogen source for the reclamation of derelicht land

Abstract: White clover (Trifolium repens) growing in association with grasses on colliery spoil amended with lime and complete fertilizer proved to be an effective nitrogen source for the developing ecosystem. Nitrogen transfer from the clover to an associated grass became aparent within 22 months of sowing.

The extent and significance of seed size variation in New Zealand wheats

Abstract: The mean 1000 seed weight of machine-dressed seed lines of seven New Zealand wheat cultivars varied from 27 to 57 g over three seasons, depending on both cultivar and season. Seed size distribution tended to follow a normal distribution. When equal numbers of seeds per unit area were sown, large seed outyielded small seed by 3–17% through the production and maintenance of more ears per unit area. No other yield components were significantly affected. The ability of large seed to produce and retain more ears arose from greater emergence and greater vigour of the seedlings produced. When seed was sown on a constant weight basis, the yield from large seeds was equal to or less than that from small seeds because there were fewer ears per unit area. When sowing on a constant weight basis, no advantage is gained from the use of large seed. Sowing on a seed number basis, which is beginning to be used to achieve optimum plant populations, will exploit the advantages of large seed.

Apparatus for spray-treating seeds during planting

Abstract: An in-the-field seed treating method and apparatus in which a treating fluid, such as an emulsion containing an insecticide, fungicide, or bactericide or the like, is sprayed onto seeds as they move from a seed hopper to a planting tube and into a planting furrow. The system is particularly directed to a plateless planter using an air pick-up system, either positive or negative pressure relative to atmosphere, for selecting seeds from a rotating drum or an intermediate pick-up chamber. In one form, the system permits air, heated by compression, to flow over the coated seeds to dry the coating as they rotate in a planting drum or disk; thus, the coating is dried on the seeds before introduction into the planting tube so that coating is not lost and the planting tubes remain clean. A hydraulic control circuit is disclosed for regulating flow of treating fluid from a "bypass" nozzle to an exceptionally low range, from about 0.2 to 5 gallons per hour. Such low rates also assure that seed coating is dried before the seeds are planted.

Establishment of buffel grass, green panic and Siratro from seed broadcast into a speargrass pasture in Southern Queensland

Abstract: The establishment and survival of seedlings from pasture seed oversown into a native speargrass (Hetevopogon contortus) pasture were studied in southern Queensland. Lime pelleted and unpelleted seed of buffel grass (Cenchrus ciliaris), green panic (Panicum maximum var, trichoglume) and Siratro (Macroptilium atvopuvpureum) were either sown into a cultivated seedbed or broadcast into native pasture pretreated as follows: untreated control; mown to 3 cm; or killed with herbicide. Buffel grass was sown both as fascicles and as caryopses. Establishment was similar in all oversown seedbeds with seedling numbers accounting for 37 % of the germinable seed sown, compared to 49% in the cultivated seedbed. Pelleting increased establishment where competition was present, the effect being greatest for Siratro and least for buffel grass fascicles. Establishment of buffel grass caryopses was markedly inferior to that of fascicles. Seedling survival rather than seed germination was the main factor influencing the success of the pasture sowing. Less than 1 % of the grass seedlings survived in the mown and control plots, but 38 % survived where competition was controlled by herbicides. Siratro survived equally as well as the grasses in the herbicide-treated plots, but survived markedly better when in competition with native grasses. Surface broadcasting into native pasture is therefore considered a satisfactory, though risky method of establishment for legumes such as Siratro, but not for grasses, unless competition is controlled.

Nitrogen requirements of irrigated wheat on the Darling Downs

Abstract: Eighteen fertilizer trials, each with five levels of nitrogen (N) and three levels of phosphorus (PI, were conducted on black earth soils of the Darling Downs to establish optimal economic rates of N fertilizer in commercial, irrigated wheat crops. The optimal economic rate of N with a fertilizer: wheat price ratio (kg N: kg grain) of 5:l, the yield response of 100 kg/ha of applied N, the yield without fertilizer, and the yield with fertilizer not limiting were calculated from derived yield response relations at each site. A multi-variate regression procedure was used to determine which soil or crop management factors significantly influenced the rate of N needed to optimize wheat yield. Delay in planting after June 1 and the level of residual mineral N in the soil at planting had strong negative effects on the response to fertilizer and the optimal rate of fertilizer required. The results indicate that yields of irrigated wheat may be below the economic optimum because of sub-optimal applications of N. Other soil and management factors such as available soil P and number of irrigations also affected grain yield. At 1 3 sites low protein wheat (< 1 1.4¦1~) was produced with all but the highest two rates of N fertilizer and at two sites even the highest rate produced low protein wheat. The effect of N fertilizer applied at planting on grain protein concentration was changed by the yield response to the fertilizer application. Grain protein concentration was curvilinearly related (R2 = 0.81) to relative grain yield (yield as a proportion of the maximum yield); grain protein was at its minimum at a relative yield of 0.5. Although heavy rates of N fertilizer at planting increased grain protein concentration on a few sites, usually these applications led to an inefficient use of N fertilizer; apparent incorporation of fertilizer N into grain decreased with increasing rate of fertilizer.

Effects of sowing date and oospore seed contamination upon subsequent crop incidence of white rust (Albugo candida) in rapeseed

Abstract: The only other record in Australia for P. capsellae on rapeseed is from Guyra (Northern Tablelands), New South Wales, in February 1956 (Dar 4908, personal communication, J. Walker, who informs us that it is not commonly seen now). The identification of both P. capsellae (IMI 252791) and M. verrucaria (IMI 246189) have been confirmed and material deposited at DAR. Rydalmere, N.S.W. (DAR 37070 and 37071 respectively).

Intercropping Pigeonpea to Conserve Fertilizer Nitrogen in Maize and Produce Residual Effects On Sugarcane

Abstract: Field experiments were conducted for 3 years covering 4 crop seasons at Lucknow to study the utility of pigeonpea (Cajanus cajan) as an intercrop in economizing N for maize (Zea mays) and to assess the residual fertility of kharif crops on autumn-planted sugarcane (Saccharum officinarum). Pigeonpea increased the soil N content due to substantial nodulation, but as an intercrop it did not increase the yield of maize at any level of nitrogen. Sugarcane grown after pigeonpea yielded 43% more than when grown after maize. Intercropping pigeonpea in maize would be more beneficial than growing a pure crop of maize before planting sugarcane.

Soybean Emergence from Field Seedbed Environments

Abstract: SEEDLING emergence and yield were used as indi-cators of the effects of controlled variables on several commercially grown soybean varieties. A planting depth of 4 cm was optimum for Drummer silty clay loam soil, and average planting conditions at Urbana, IL. Fungicide seed treatment did not result in improved emergence percentages or yields under our test condi-tions. Soil penetration resistance was used to assess the effect of different planter and drill press-wheel tires on the soil's physical environment. Penetration resistance levels differed significantly for the drill and planter press-wheel tires throughout the planting-depth range.

Growth and yield responses of cowpea and maize to inoculation withGlomus mosseae in sterilized soil under field conditions

Abstract: The effects of inoculation of cowpea and maize withGlomus mosseae and sowing into field soil fumigated with formalin are reported. Root infection was significantly, though temporarily, decreased and grain yield increased, by sterilization. Inoculation increased root infection, shoot yields, P contents and grain yield.

Germination, emergence and surface establishment of wheat and ryegrass in response to natural and artificial hydration-dehydration cycles

Abstract: The emergence and establishment of wheat and annual ryegrass (Lolium rigidum) from seeds that had been hydrated and dehydrated in such a way as to double the speed of their germination was examined in controlled environments. In addition, the effects of rain on the germination characteristics of surface-sown ryegrass were monitored for 4 months during summer and autumn. Seed pretreatment was of no benefit to the establishment of wheat seedlings. Ryegrass seedlings from pretreated seeds emerged earlier and 3 weeks after sowing had higher dry weights than controls. When conditions in the seed-bed favoured establishment for only a short time, some pretreated seeds of ryegrass established where none of the controls did. It is concluded that seed pretreatment has potential application in autumn or winter establishment of pasture grasses, but not of wheat. Initially, the effect of rain insufficient for establishment was to increase the potential germinability of ryegrass by reducing dark dormancy, but seed viability decreased later. A proportion of the seeds previously exposed to rain always germinated before controls. The ability of naturally dispersed seeds to establish depends not only on the timing of establishment rains, but on the cumulative length of the wet periods that occurred before the break of season.

Effects of common scab (Streptomyces scabies) on potatoes

Abstract: SUMMARY Seed tubers with severe (71% cover) or slight (12% cover) common scab selected from a badly infected crop of cv. Maris Piper were boxed for sprouting in November and February and planted in field experiments at Woburn and Rothamsted in 1980. The severely scabbed seed lost more moisture than the slightly scabbed seed during sprouting and sprouted from a larger number of eyes but total stem numbers were greater on plants from the slightly scabbed seed. Plant growth during the first 6–9 wk after planting was less from the severely scabbed than from the slightly scabbed seed. This was shown by records of ground cover, leaf area index, fresh weights of stems and leaves, total tuber yield (18% lower at 9 wk) and tuber number. Subsequently these differences became non-significant. Seed with slight scab boxed in November produced smaller numbers of progeny tubers than that boxed in February but there were no other consistent effects of boxing date on growth and yield. Scab incidence on progeny tubers was very slight and unrelated to the severity of disease on the seed tubers. It seems unlikely that severe scab infection of seed tubers would significantly decrease tuber yields except perhaps in early potato production.