Developing cultivars of the common bean (Phaseolus vulgaris L.) for southern Africa: bean common mosaic virus resistance, consumer preferences and agronomic requirements

The requirements that must be met by bean common mosaic virus (BCMV)-resistant cultivars of the common bean in Zimbabwe, and the feasibility of developing such cultivars, were investigated by a survey among farmers, evaluation of resistant and locally adapted inbred genotypes, and backcrossing to transfer the bc-3 resistance gene to the genetic background of the locally adapted genotypes. Genotypes were evaluated by field trials in a range of environments, by consumer assessment and by measurement of seed size, water absorption capacity (WAC) and cooking time. Backcross generations were evaluated in the field and by measurement of the same seed characters.

Most farmers produced beans in monoculture, using bush or semi-climbing cultivars and a single seed type, the most common colour type being cream with red mottles. This is in strong contrast to the production system in many parts of eastern and central Africa, where intercropping, climbing types and seed-type mixtures are common. The BCMV-resistant genotypes had a similar range of flowering dates, maturity dates and canopy heights to locally adapted genotypes, and a similar range of environmental responses with respect to these variables, but were generally small-seeded. Consumers preferred large seeds, and seed colours that were not generally found in the resistant genotypes. However, the bc-3 gene was readily combined with large seed by backcrossing. The resistant genotypes generally had shorter cooking times than the locally adapted genotypes.

It is concluded that it will not be difficult to combine BCMV resistance with the other characteristics required of bean cultivars in Zimbabwe, with the possible exception of seed colour, and that the same is probably true for other production regions in southern Africa.     

Effect of imazamox plus bentazon on dry bean (Phaseolus vulgaris L.)

Imazamox plus bentazon has the potential to provide broad spectrum weed control in dry bean (Phaseolus vulgaris L.). Field trials were conducted in Ontario over a two year period (2003 and 2006) to evaluate the effect of imazamox plus bentazon applied post-emergence at 25 + 600 and 50 + 1200 g ai ha⁻¹ on black, brown, cranberry, kidney, otebo, pinto, white and yellow eye beans. Treatments included a non-treated check. All treatments were maintained weed free during the growing season. The eight market classes responded similarly to imazamox plus bentazon. Imazamox plus bentazon applied post-emergence caused less than 4% visible injury at 7, 14 and 28 days after treatment. Imazamox plus bentazon applied post-emergence did not have any effect on plant height, shoot dry weight, seed moisture content and yield of dry bean. Based on these results, imazamox plus bentazon at the proposed maximum use dose can be safely used for weed management in black, brown, cranberry, kidney, otebo, pinto, white and yellow eye bean production in Ontario. Additional research is needed to determine if cultivars within a market class of dry bean differ in their response to imazamox plus bentazon.     

银合欢豆象生物学特性及其防治

银合欢豆象[Acanthoscelides macrophthalmus(Schaeffer,1907)]是银合欢属Leucae植物种子上的重要害虫,除银合欢外,也可蛀食南洋楹(Falcataria moluccana)种子。在75%RH及20~35℃的条件下,卵期为4～12 d。幼虫期为18～37 d,蛹期为5～11 d。成虫寿命17~31 d,雌雄性别比约为1∶1。在75%RH及26℃条件下,银合欢豆象完成1个世代需要44～48 d。在野外,银合欢豆象在幼龄阶段常被一种姬小蜂科(Eulophidae)的柄腹姬小蜂属(Pediobius Walker)寄生。在75%~80%RH及25～30℃条件下,使用56%磷化铝片剂对银合欢豆象进行熏蒸,用药量7~9 g/m3,熏蒸时间48~72 h,成虫、幼虫及蛹死亡率100%。     

Larvicidal property of essential oils against Culex quinquefasciatus Say (Diptera: Culicidae)

Essential oils from 22 aromatic plant species were tested for mortality of the mosquito larvae Culex quinquefasciatus. Lethal concentrations were determined for individual essential oils. Essential oils obtained from Thymus vulgaris, Satureja hortensis and Thymus satureioides plants showed the highest effect, with LC₅₀ found lower than 50 μg/ml (33, 36 and 44 μg/ml, respectively). Analyses showed that majority substances for T. vulgaris were thymol and p-cymene (60.3 and 10.1%, respectively); carvacrol and γ-terpinene for S. hortensis (48.1 and 36.7%, respectively), and borneol and thymol for T. satureioides (30.3 and 32.5%, respectively).The selected essential oils also showed very good effectiveness with respect to mortality and percentage of adult emergence upon short-term exposure in water contaminated with lethal doses of individual oils. While there was 77% adult emergence from the larvae in the control, in T. vulgaris, T. satureoides and S. hortensis there was only 12.3, 15.3 and 16.0% adult emergence, respectively. High antioviposition effectiveness was found in all selected oils. Almost 100% deterrence of female oviposition was determined for all oils in concentrations of 0.02%. Significant differences were seen with tested concentrations of 0.01 and 0.005%, where the oil of T. vulgaris proved most effective (repellency about 99.8 and 62.3%, respectively).     

Agronomic and economic assessment of intensive pest management of dry bean (Phaseolus vulgaris)

Two common production constraints of dry bean (Phaseolus vulgaris) in Ontario are annual weeds and anthracnose (caused by Colletotrichum lindemuthianum). Dry bean is not considered a competitive crop and weed interference can result in substantial yield losses, while anthracnose is considered one of the most devastating diseases in dry bean production. A study conducted in Ontario Canada, examined the effect of two herbicide programs on weed management, thiamethoxam insecticide treatment on plant enhancement and three fungicide programs on anthracnose development in a navy bean cv. ‘OAC Rex’. The premium herbicide program (s-metolachlor + imazethapyr) reduced percent weed ground cover relative to the economic herbicide program (trifluralin) in five of six locations. Thiamethoxam increased emergence and vigour at only one location, which contradicts reported benefits of thiamethoxam on plant health. The herbicide or thiamethoxam treatments did not affect anthracnose disease severity, visible seed quality, net yield or economic return. The fungicide seed treatment was often superior to the untreated control, for a number of the parameters measured. The application date of the foliar fungicide, relative to the onset of disease, varied between site-years. This dramatically influenced the fungicide’s effectiveness. Foliar fungicides increased seed quality and net economic return compared to the control when applied prior to disease development. The combination of fungicide seed treatment followed by a foliar fungicide provided the largest reduction in anthracnose severity.     

普通大蓟马产卵选择性初探

采用叶盘法对普通大蓟马的产卵选择性进行研究。二元选择性实验结果表明,该虫产卵时对豇豆嫩叶正面和反面的选择性没有差异,但喜欢在菜豆和花生嫩叶的正面产卵。以豇豆嫩叶反面、菜豆嫩叶正面和花生嫩叶正面供普通大蓟马产卵时,产卵选择性顺序为豇豆>菜豆=花生,近85%的卵产在豇豆嫩叶上。寄主植物叶表茸毛密度对普通大蓟马的产卵选择性有一定的影响。     

Effect of Untreated, Roasted and Germinated Black Gram (Phaseolus mungo) Flours on the Physico-chemical and Biscuit (Cookie) Making Characteristics of Soft Wheat Flour

Determination of the physico-chemical characteristics of composite soft wheat flours in which 5–25% (w/w) of the wheat flour was replaced with untreated, roasted and germinated black gram (Phaseolus mungo) flours (BGF) showed that when roasted BGF comprised 20% (w/w) of the blend, the increases in the ash and protein contents were 123% and 35%, respectively. The values for the gluten contents and the Zeleny and sodium dodecyl sulphate sedimentation test volumes for the composite flours indicated a weakening effect of BGF on the quality of soft wheat flour proteins, which could be beneficial for the preparation of biscuits (cookies). The alkaline water retention capacity values increased with the increasing addition of differently processed BGFs. Biscuit baking studies indicated that the diameter and spread ratio of biscuits were reduced, while the thickness increased, with increasing addition of all three BGFs, but the maximum reduction in diameter was observed with the addition of germinated BGF. The hardness value for biscuits increased with the addition of BGFs, but the effect was minimal with roasted BGF and maximal with germinated BGF. The surface grain score was reduced with increasing addition of BGF, but, in general, the roasted BGF showed the minimum adverse effect. From the overall biscuit making quality, addition of untreated BGF at the 15% level and of roasted and germinated BGFs at the 20% level were considered optimal for supplementing wheat flour.     

Insecticidal and repellent activity of selected essential oils against of the pollen beetle, Meligethes aeneus (Fabricius) adults

The essential oils from 9 aromatic plants were tested on repellency and mortality of Meligethes aeneus adults. All the tested essential oils caused high mortality of M. aeneus adults in the tarsal tests. The lethal doses after 6 h exposure were ranged between 197 and 1508 μg cm⁻². Essential oils obtained from Carum carvi and Thymus vulgaris were most efficient where LD₅₀ was estimated as 197 and 250 μg cm⁻², respectively.Repellency declined in all the essential oils as a function of time. The longest persistence time was determined for essences obtained from C. carvi and T. vulgaris where significantly the highest repellent index of 65.6% and 63.8%, respectively, was determined. Repellent index lower than 15% was determined for the remaining essential oils.     

Impacts of transgenic Bt cotton on a non-target pest, Apolygus lucorum (Meyer-Dür) (Hemiptera: Miridae), in northern China

Transgenic Bt (Bacillus thuringiensis) cotton has been effectively used to control the cotton bollworm, Helicoverpa armigera (Hübner) in China. However, in recent years, following the wide commercialization of Bt cotton in northern China there have been frequent outbreaks of the non-target pest Apolygus lucorum (Meyer-Dür). To clarify how transgenic cotton contributes to these outbreaks, a four-year field investigation of population dynamics and laboratory life table studies were carried out from 2007 to 2010 to evaluate the impact of two transgenic cotton cultivars (SGK321 expressing Cry1Ac + CpTI and GK12 expressing Cry1Ac) and their corresponding parental non-transgenic lines (Shiyuan321 and Simian3) on A. lucorum. There were no significant differences in the population densities of A. lucorum found in Bt cotton and non-Bt cotton plots, whether one compared those that had received insecticide treatments or those that had not. However, population densities of A. lucorum were significantly lower in pesticide treated plots than in controls. Furthermore, there were no significant differences in the net reproductive rates, generation times or intrinsic rates of increase of A. lucorum when reared on either Bt or non-Bt cotton cultivars. These results suggest that Bt cotton has no direct positive or negative effects on the biology of A. lucorum, so the most logical explanation for the observed outbreaks is the decrease in pesticide applications following the commercial release of Bt cotton.