Thesis (MScAgric (Agronomy)--University of Stellenbosch, 1999. / The Western Cape is one of the most important onion producing regions in South Africa. It is well suited for the production of intermediate daylength onion cultivars. Annually about 2500 ha are planted with a yield of about 120 000 tons. Only 9 000 tons was exported in 1998 and of these 9 000 tons 4.9% was rejected due to poor quality. In South Africa there are no guidelines for the production of intermediate daylength onions. It is very important to have fertiliser guidelines, because optimal yields of good quality can be achieved with a good fertiliser program. Produce with exceptional quality can boost exports and at the same time stabilize local markets. However fertilisers are very expensive and could be damaging to the environment ifused incorrectly. To produce fertiliser guidelines N, P and K field trials were planted at three differen~ localities (Koue Bokkeveld, Stellenbosch and Caledon). The localities were chosen according to the difference in climate and soil texture, and these are important onion growing areas. The minimum and maximum temperature for the Koue Bokkeveld, Stellenbosch and Caledon was 11123, 12/25 and 13/27 °C respectively. At all the localities 3 nitrogen-, 4 phosphorus- and 4 potassium levels were used. Treatments were factorially arranged in a randomised block design, with two replicates. At Stellenbosch a N fertiliser trial was planted with four N levels and four N application methods. The treatments were factorially arranged in a completely randomised block design, with three replicates. N, P and K was applied as limestone ammonium nitrate, single superphosphate and potassium sulphate. Marketable and unmarketable bulbs were quantified at harvest. Weight loss during storage was determined over a six month period and storage disorders were evaluated. It was clear that high N levels, especially on soil with a high potential for releasing N, had a negative effect on yield and keeping quality. At Caledon a significant reduction in yield took place with the highest N level. High N levels also had a significant effect on weight loss at Stellenbosch and Caledon. The same trend with high N levels occurred in the N fertiliser trial. Weight loss was increased with the late application ofN in the growing season. In spite of the fact that the P levels were high (58 - 66 mg.kg-I) in the different soils, the onions reacted very well to phosphorus fertiliser. As a result of the higher P levels there was more foliage in the leaf canopy and the bulbs were larger. This P reaction only occurred in the Koue Bokkeveld and at Caledon. At Stellenbosch yield was not improved with P fertilisation and bulbs were of poor quality. The highest P level resulted in the greatest weight loss in storage. K had an effect where the K status and clay content of the soil was low. High potassium levels improved yield and keeping quality remarkably in the Koue Bokkeveld. Some interactions also occurred. The percentage unmarketable bulbs were influenced by a P and K interaction. An increase in double bulbs was responsible for the increase in the percentage unmarketable bulbs. At the lowest P level, higher K levels decreased the percentage unmarketable bulbs. Alarming proportions were reached when high K levels were combined with the highest P level. The P and K interaction also had an effect on the percentage sprouting. K did not have any effect' on sprouting at low P levels. A combination of the highest P level and the lowest K level produced the highest percentage sprouting. The interaction between N and P, like the P and K interaction had an effect on the percentage sprouting. The highest N level in combination with the highest P level increased the percentage sprouting significantly. The N, P and K field trials showed that the optimum N level is less than 130 kg N.ha-l on a soil with 16 % clay. On a sandy soil it can be as high as 160 kg N.ha•l The optimum P level varied from 30 to 130 kg P.ha-l Where a poor P reaction was observed the Ca and S status in the soil was low. It is possible that the drastic P reaction with superphosphate (10.5 % P, 20.3 % Ca, 12.1 % S) in the Koue Bokkeveld can be a result of the application of Ca and S. On the shale soil at Caledon, with a K status of 288 mg.kg-\ the optimum K level is less than 75 kg K.ha-l On the sandy soil of the Koue Bokkeveld, with a K status of 43 mg.kg•l , the optimum K level was 200 kg K.ha•l . The N fertilisation trial was done on a soil with an optimum N level of 115 kg N.ha-l (10 % clay). It was demonstrated that the standard N application method (40 % N with planting and the rest divided in three equal applications of 20 % N on 2, 4 and 7 weeks after planting) is still an acceptable practice. Follow-up trials are being done to determine the exact optimum level of fertilisation.

No description available.

Revised; Originally Published: 2009 / 2 pp. / This publication discusses water in in dry bulb onion production in Arizona.

Onions are highly responsive to endomycorrhizae and improved plant growth is among the benefits associated with this symbiosis, particularly in low phosphorus soils. Although this crop is grown extensively in organic soils, few studies have been conducted on these. Onion plants (Allium cepa L. cv. Norstar) were inoculated with Glomus aggregatum Schenck & Smith, Glomus clarum Nicolson & Schenck, Glomus fasciculatum Gerdemann & Trappe, Glomus intraradix Schenck & Smith and Glomus versiforme (Karst.) Berch and grown in the field and under controlled conditions to evaluate their efficiency in newly reclaimed organic soil of low P fertility. Three species were selected to evaluate the effects of introduced endomycorrhizal fungi effects and P fertilization (equivalent to 0, 24 and 48 kg P ha$ sp{-1}$) on the growth and mineral nutrition of onion plants. / Introducing endomycorrhizal fungi in non-sterile soil did not affect the growth and mineral nutrition of onion. Crop maturity was advanced when plants were inoculated, however. Increasing levels of P fertilization did not depress root colonization and onion growth was increased significantly at the highest rate only. These results suggest that higher levels than recommended could be used in this soil. Inoculation in $ gamma$-irradiated (10 kGy, $ sp{60}$Co) soil alleviated excessive Mn absorption by onion plants. Adding P fertilizer depressed growth and root colonization when plants were inoculated with G. clarum and G. intraradix and was related to the low irradiance levels used in this study. G. versiforme appeared to be the most efficient of the introduced species.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1963. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 55-58).

Additive weed competition experiments were undertaken to study the effect of lamb's-quarters (Chenopodium album) interference on direct seeded broccoli. Lamb's-quarters (3, 8, 10, 12, and 15 plants m⁻²) began to affect broccoli growth 28 to 36 days after seeding. Decreases in crop growth increased with weed density as time after seeding increased. Yield data were fitted to a rectangular hyperbolic model which indicated that even one lamb's-quarters plant m⁻² could reduce total yield by 18 to 20 percent and marketable yield (head >10 cm across) by 22 to 37 percent. Lamb's-quarters reduced total yield by reducing average head weight and not by lowering the number of heads per plot. On the other hand, the weed reduced marketable yield by reducing both the average head weight and the number of heads per plot. The feasibility of using liquid ammonium nitrate as a post-emergent weed control spray in cole crops was studied. The relative susceptibility of different weed species grown by themselves (1989) and with two crops (broccoli and onion; 1987) to ammonium nitrate (800 L ha⁻¹; 0, 7.5, 10, 15, 20 percent N) burning was investigated. The fertilizer controlled shepherd's-purse (Capsella bursa-pastoris), chickweed (Stellaria media), cudweed {Gnaphalium uliginosum), and redroot pigweed (Amaranthus retroflexus), but not lamb's-quarters, purslane (Portulaca oleracea), and annual bluegrass (Poa annua). Corn spurry (Spergula arvensis) varied in its tolerance. Although weed populations were reduced by 70 percent in 1987, the remaining weeds competed so strongly with the onion and broccoli that the crop plants did not reach a harvestable size. The large initial weed population (799 plants m⁻²), the large number of tolerant weeds present, and the possible recovery of some of the susceptible weeds may all have been factors responsible for crop failure. The effect of different shepherd's-purse densities (52 to 988 plants m⁻²) on the degree of ammonium nitrate (800 L ha⁻¹; 20 percent N) control in broccoli was also studied. The initial weed control achieved was reduced over time either because some weeds counted as dead had recovered or new plants were being recruited to the population through seed germination. Although the maximum density of shepherd's-purse plants that survived was 219 plants m⁻², these plants did not significantly reduce crop yield possibly because shepherd's-purse is not a very competitive species and all the surviving weeds had been damaged to varying degrees, further reducing their competitive ability. The relative susceptibility of various crop cultivars to ammonium nitrate (800 L ha⁻¹; 0, 10, 15, 20 percent N) burning was also studied. In 1987, the growth rates of 'Lunet' (Brussels sprouts), ‘SGI' (broccoli), 'Elgon' (cauliflower), and 'Matra' (cauliflower) initially decreased but the plants recovered; they were largely unaffected in 1988. The growth rates of 'White Lisbon' (onion), 'Emperor' (broccoli), and 'Early Marvel' (cabbage) were largely unaffected in either year. Although some cultivars had shown initial signs of lower growth rates, there was no decrease in crop yield. Leaf surfaces of tolerant and susceptible crop and weed species were examined by scanning electron microscopy to determine the basis of ammonium nitrate selectivity. Leaf surfaces of tolerant species were completely covered with a crystalline wax layer, while susceptible species had little or no epicuticular wax. Cellulose acetate was used to remove the epicuticular wax from cabbage leaves. The stripped leaves showed far greater ammonium nitrate retention and salt injury than unstripped leaves, demonstrating the importance of the epicuticular wax in providing protection against ammonium nitrate injury. Trichomes, observed on the leaf surfaces of some susceptible species, may further increase ammonium nitrate retention and, therefore, salt injury. / Land and Food Systems, Faculty of / Graduate

Center rot of onion, caused by Pantoea ananatis, was first described in the USA, in 1997. P. ananatis is seed-borne in onions and it was suggested that it was introduced into the USA on infected seed lots from South Africa. Center rot has not been observed in South Africa and it was essential to determine if P. ananatis is present in local onion seed. Colonies resembling those of P. ananatis were isolated from four South African seed lots on PA 20, a new semi-selective medium. Pathogenicity tests demonstrated that the South African and America strains induced the same symptoms on onion. Phenotypic and genotypic analyses identified the strains from seed as P. ananatis. In 2004/2005, an unreported disease of maize, brown stalk rot, was observed on commercial fields in South Africa. The representative strains induced disease symptoms similar to those observed in the field. The phenotypic and genotyping tests showed that the strains belonged to the genus Pantoea and separated them into two groups. The first group was identified as P. ananatis. The F-AFLP genomic fingerprints generated by the second group of strains, were distinctly different from those generated by known Pantoea species. To resolve the taxonomic position of Pantoea isolated from onion and maize, sixty-seven strains were subjected to a polyphasic study. The methods used included phenotypic characterisation, genomic fingerprinting, 16S rRNA gene sequence analysis and DNA-DNA hybridisation. The results revealed that the strains belong to three different species within the genus Pantoea: P. ananatis, P. vagens and a novel species, Pantoea allii sp. nov. / Thesis (PhD (Microbiology))--University of Pretoria, 2009. / Microbiology and Plant Pathology / unrestricted

No description available.

No description available.

Magistratūros studijų baigiamajame darbe įvertintas ir pritaikytas Botrytis spp. infekcijos prognozavimo modelis ropiniuose svogūnuose apsaugai nuo ligų vegetacijos metu. Darbo objektai – ropiniai svogūnai (Allium cepa L.); ligos sukėlėjai - kekerinis lapų dėmėtumas (Botrytis squamosa) ir lapų taškuotoji dėmėtligė (Botrytis cinerea); internetinė „iMETOS®sm“ prognozavimo sistema (Botrytis spp. infekcijos prognozavimo modelis). Tyrimo metodai: tiriamas meteorologinės stotelės „iMETOS®sm“ Botrytis spp. infekcijos prognozavimo modelių pritaikymas ropiniuose svogūnuose. Tirti dviejų Botrytis rūšių sukeliamų ligų prognozavimo modeliai: 1) Botrytis squamosa infekcijos modelis; 2) Botrytis cinerea rizikos modelis. Mikologiniams tyrimams ėminiai surinkti nuo Botrytis grybais pažeistų svogūnų vegetatyvinių dalių vystymosi tarpsniu ir tirti taikant vizualinį – simptomatinį, drėgnų kamerų, sėjimo į Petri lėkšteles, mikroskopavimo metodus. Išskirti izoliatai identifikuoti iki rūšies, remiantis kolonijų kultūrinėmis ir morfologinėmis savybėmis bei lyginant su literatūros duomenimis, naudojant apibūdintojus (Domsch ir kt., 1980, p. 859). Tyrimams pasirinktos dvi apsaugos sistemos: pagal faktinį ligos simtomų aptikimo laiką ir pagal „iMETOS®sm“ Botrytis spp. infekcijos svogūnuose modelio parodymus. Darbo rezultatai. Botrytis squamosa infekcijos prognozavimo modelis parodė, kad svogūnų kekeriniam dėmėtumui plisti palankios sąlygos abiejuose tirtuose rajonuose susidarė birželio–rugpjūčio mėn... [toliau žr. visą tekstą] / The master's degree thesis is evaluated and applied to the Botrytis spp. infection in onion forecasting model for the protection against disease during the growing season. Object of the work - onion (Allium cepa L.) pathogens - Botrytis leaf blight discoloration (Botrytis squamosa) and Botrytis leaf spot in (Botrytis cinerea), an online „iMETOS®sm” Forecasting System (Botrytis spp. infection prediction model). Methods of the work: studied meteorological station „iMETOS®sm” Botrytis spp. infection forecasting models use onion. To explore the two types of diseases caused by Botrytis forecasting models: 1) Botrytis squamosa infection model, 2) risk model Botrytis cinerea. Mycological examination of samples collected fungi Botrytis damaged vegetative parts of the onion stage of development and exploration through visual - symptomatic, moist chambers, seeding in petri dishes, microscopy techniques. Distinguish isolates identified to species based on cultural and morphological colony characteristics and comparison with literature data using apibūdintojus (Domsch et al., 1980, p. 859). For this work, the two security systems based on the actual detection of the disease symptoms at the time and under „iMETOS®sm” Botrytis spp. evidence of infection onion model. The results of work. Botrytis squamosa infection prediction model showed that the onion gray mold to spread favorable conditions in both regions studied occurred between June and August. Kaunas district. B... [to full text]