摘要:

‘Forelle’ pear trees (Pyrus communisL.) were established at the Bien Donné experimental farm in the Western Cape Province of South Africa on BP1, BP3 and Quince A rootstocks at three planting densities, i.e., 889, 1667 and 2857 trees. ha−1, to determine the rootstock and planting density effect on precocity and fruit quality. Production per tree and per hectare, tree size and yield efficiency were measured for the first three crops. Fruit quality was determined by mass, colour, firmness and TSS values. Quince A was more productive than the BP-rootstocks and also resulted in smaller trees, thus higher yield efficiency. Higher planting densities resulted in higher production per hectare and higher yield efficiencies for all three rootstocks. Quince A at a planting density of 2857 trees. ha−1resulted in a cumulative production of 69.7 t.ha−1from the fourth to the sixth leaf. BP3 was more productive than BP1, while the tree size was similar. This resulted in BP3 having higher yield efficiency than BP1. Quince A significantly increased fruit mass, blush development and total soluble solids compared to the BP-rootstocks.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634867

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A stem rust survey is conducted annually in the major bread wheat and triticale producing areas of South Africa to monitor pathogenic variability inPuccinia graminisf. sp.tritici.During 1991 to 1996 the incidence of stem rust on susceptible wheat and triticale cultivars and lines planted in trap nurseries was low. No stem rust was found during 1997. The low incidence of stem rust was also evident by the absence of the disease in commercial wheat and triticale fields. During the survey period stem rust pathotypes 2SA4, 2SA36 and 2SA100 were detected on bread wheat and 2SA102 and 2SA103 on triticale.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634868

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

MCPA [2-methyl-4-chloro phenoxy acetic acid] is applied with various water sources containing antagonistic salts. It is applied without an adjuvant but is often mixed with bromoxynil for a broader spectrum of weeds. MCPA (K-salt) was applied in carriers containing calcium chloride and sodium bicarbonate. Ammonium salts and other adjuvants were tested to overcome possible antagonism. Control ofFallopia convolvuluswith MCPA was decreased with the calcium chloride as carrier but not when sodium bicarbonate was the carrier. Ammonium sulphate and ammonium nitrate overcame the calcium chloride antagonism and ammonium bicarbonate partially overcame the antagonism. Ammonium hydroxide and potassium chloride could not overcome calcium chloride antagonism, even in the presence of other adjuvants. An alkylated phenol-ethylene oxide surfactant could not overcome antagonism when applied in the absence of ammonium nitrate. Calcium chloride antagonism of MCPA in a mixture with a bromoxynil formulation blank was similar to the antagonism of MCPA applied alone. Both a petroleum oil/nonionic surfactant blend and the alkylated phenol-ethylene oxide surfactant reduced the ability of ammonium bicarbonate to overcome calcium chloride antagonism. MCPA (K-salt) should be registered with ammonium sulphate or ammonium nitrate in areas with hard water.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634869

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

When sorghum hybrids replaced varieties in South Africa, the average malt quality quantified as sorghum diastatic units (SDU) declined. Additionally, malt quality of sorghum needs to be increased if sorghum is to be used as extenders or substitutes for barley malt in the lager beer industry. Trials were carried out in order to study the effect of Xenia and heterosis in F1and F2seeds produced in various hybrid combinations. Large Xenia effects were observed in the F1but this was entirely lost in the F2generation. Effectively, most hybrids showed negative heterosis. One R-line seemed to pass on stability in SDU to its offspring. Ways of improving malt quality are discussed.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634870

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Field experiments were conducted during two growing seasons to investigate the effect of different Common thorn-apple (Datura stramoniumL.) densities on seed production of this specie. Maize (Zea maysL.) was planted in 2.1 m rows with a plant population of 16000 plants. ha−1.D. stramoniumwas planted at five densities in association with maize. The time of weed seed production, total seed production of eachD. stramoniumplant and of each plant population were determined. Seed production ofD. stramoniumdecreased with increasing density stress, with a substantially greater effect during an unfavourable season. The study provided information on timing of weed control and the implications of weed seed contamination in the absence of weed control. This may contribute to more effective, economic and environmentally friendly weed control.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634871

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The response of farmers' varieties and maize hybrids commonly grown in Lesotho was evaluated in field trials under natural infestations ofBusseola fusca(Fuller). Plant response of varieties and hybrids was evaluated in relation to a susceptible and resistant maize hybrid. The incidence of infested plants, number of damaged inter- nodes and number ofB. fuscaindividuals that successfully colonised plants of different varieties as well as yield loss was determined. All the local varieties and commercial hybrids were susceptible to damage byB. fuscaand sustained yield losses higher than that of the experimental resistant check hybrid. Maize varieties generally suffered lower yield losses than hybrids. Differences in yield losses between hybrids and farmers' varieties were ascribed to differences in length of growing season requirements (days to 50% flowering) and the incidence of damage to maize ears. Results indicate that Lesotho farmers can benefit from a stem borer resistance breeding programme and that adaptation of planting date can lead to escape of damage and reduced yield losses.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634872

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634873

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The low tolerance of maize (Zea maysL.) to imazethapyr ((±)-2-[4,5-dihydro-4 methyl-4-(1 -methylethyl)-5-oxo 1H-imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid) resulted in extensive crop damage in 1992/93 due to residue carry-over from resistant soybean (Glycine maxL.). Pot experiments were conducted to assess the role of cultivar differences in maize tolerance, as well as the potential for synergistic interaction between imazethapyr and a fungicide. A selection of white and yellow maize cultivars were tested. The fungicide captab (3a, 4, 7, 7a- tetrahydro-2-[(trichloromethyl)thio]-1H-isoindole-1, 2(2H)-dione) was investigated in terms of its potential to exacerbate damage caused by imazethapyr to various maize cultivars. White cultivars were significantly more sensitive to imazethapyr than the yellow cultivars, with damage in shoot dry mass ranging from 13 to 63% at the lowest herbicide rate of 5 g ai ha−1. The ED50-values derived from linear regression equations for the relationship between imazethapyr rate and maize damage confirmed the differential tolerance of white and yellow cultivars, and indicated that the sensitivity of all six cultivars of the former type increased in the presence of captab. Except for one of six yellow cultivars, the same tendency was found in this group. The mechanisms involved in these differential plant responses are not known. Their elucidation could introduce flexibility into the safety (waiting) period specified for maize, through rational cultivar selection and promote the breeding of cultivars that are tolerant to the broad spectrum of acetolactate synthase (ALS)-inhibiting herbicides.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634874

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Streak resistant maize inbred lines released by the Grain Crops Institute in 1995 were evaluated in the absence of streak disease as hybrid combinations in field trials. The evaluation of single crosses between three lines in each of a B73 and Mo17 background identified one line which transfers resistance to northern leaf blight (Exserohilum turcicum) in all combinations. Modified single crosses of the same lines using I137TN as tester yielded significantly less than a commercial standard hybrid. In three-way hybrid combinations of B73 related lines crossed to MSV-resistant germplasm in seven other genetic backgrounds, and using I137TN as tester, several hybrids yielded equivalent to a commercial standard. Significant differences in the incidence of ear rot (Stenocarpella maydis) were observed. The results comfirm that MSV-resistant breeding material derived from the improved Vaalharts composite are competitive with commercially proven susceptible varieties.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634875

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

DNA from six dry bean cultivars was analysed with a total of thirty two primers in RAPD analysis to develop a method to distinguish between the different cultivars. The varieties are cultivated in three African countries and belong to two different gene pools. The cultivars analysed were Lyamunga 85 and Lyamunga 90 from Tanzania, CAL 96 and K 20 from Uganda, and Awash I and Mexican 142 from Ethiopia. The two types of beans, the Mesoamerican white seeded and large seeded Andean calima types, were separated in the two genetic pools. RAPD analysis revealed a close relationship between Lyamunga 85 and CAL 96. All the cultivars tested could be distinguished with a minimum of six primers.

ISSN:0257-1862    

DOI:10.1080/02571862.2000.10634876

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor