Biological and Physical Constraints on Maize Production in the Humid Forest and Western Highlands of Cameroon

The aim was to identify biological and physical factors responsible for reducing maize yield in Cameroon. Two surveys were conducted in 137 fields in two agroecological zones in 1995–1997. In the Humid Forest (HF), Bipolaris maydis, Stenocarpella macrospora, Puccinia polysora, Rhizoctonia solani and soil fertility were factors that reduced maize production in 1995 and 1996. In the Western Highlands (WHL), Cercospora zeae-maydis, and the interaction between soil fertility and maize variety were the most important constraints to maize production in 1996. In 1997, C. zeae-maydis, S. macrospora, physiological spot and stem borer damage (Busseola fusca) were negatively related to ear weight. The combination of these biological factors (diseases and insects), and the physical parameter of soil fertility were responsible for reducing maize yield in these selected benchmarks of Cameroon. Maximum potential yield reductions were estimated at 68% due to B. maydis and 46% due to S. macrospora, respectively, in the HF in 1995. In 1996, maximum potential yield reductions in the HF were estimated at 34%, 41% and 30% due to S. macrospora, P. polysora and R. solani, respectively. In the WHL, C. zeae-maydis had the potential to cause a yield reduction of 79% in 1996. In the WHL in 1997, the interaction between C. zeae-maydis and B. fusca, stem diseases and the physiological spot caused potential reductions of 52%, 34% and 39%, respectively.     

Identification of Resistance to Common Bacterial Blight Disease on Bean Genotypes Grown in Turkey

Common bacterial blight (CBB) in edible beans (Phaseolus vulgaris), incited Xanthomonas campestris pv. phaseoli, reduces bean yields and seed quality. The main objective of this study was to determine resistance to common bacterial blight in bean genotypes. Twenty-two bean genotypes grown in Turkey including common and snap bean cultivars/lines were collected from different parts of Turkey and tested for resistance against to Xanthomonas campestris pv. phaseoli strain MFD-11. All the common and snap bean lines/cultivars tested were moderately susceptible, susceptible or highly susceptible, except AG-7117 which was found resistant to Xanthomonas campestris pv. phaseoli. This is the first report of a resistance source in a common bean line (AG-7117) against Xanthomonas campestris pv. phaseoli.     

Modelling spatio-temporal dynamics of herbicide resistance

A mathematical model has been developed for the risk assessment of the spread of genes conferring herbicide resistance in plant populations. The model combines an age-and-stage-structured population dynamic model, a population genetic model and a model of spatial spread. This is achieved by embedding a local matrix population model into a cellular automaton model with raster cells as spatial units. The dynamics of each cell is determined by both its local dynamics and the interaction with neighbouring cells. The model is applied to the evaluation of management strategies to delay or even to prevent long-term evolution of resistance in an annual grass weed. The results show that the appearance and spread of resistant genes is a highly non-linear process exhibiting threshold phenomena, which occur for a wide range of parameters. The properties of the seed survival curve constitute the `genetic memory' of the system and thus determine its long-term dynamics. It is possible to delay the evolution of resistance by suspension of treatment, reduction in herbicide application rate and introducing fallow periods. Spatial spread from an infested plot is inhibited by leaving untreated strips between adjacent fields.     

Genetic analyses of resistance of the wheat differential cultivars Carstens V and Spaldings Prolific to two races of Puccinia striiformis

Genetic analysis of resistance of wheat seedlings to two races of Puccinia striiformis was conducted on F₁, F₂ and F₃ generations from crosses Carstens V (CV) × Lee, Spaldings Prolific (SPA) × Lee and CV × SPA. F₂ generations from crosses of CV and SPA with Strubes Dickkopf (SD) were also studied. The plants were classified into six resistance classes and analysed by factorial correspondence analysis and nonhierarchical classification. The two P. striiformis isolates tested were a French isolate of race 43E138 and a Lebanese isolate of race 2E16, selected for the differences in their virulence spectra for the common differential cultivars Strubes Dickkopf and Nord Desprez. Resistance of CV and SPA was recessive and dominant to races 43E138 and 2E16, respectively. CV possessed three or four resistance genes, one of them being expressed with both races. Two genes of CV had a cumulative effect for resistance to 43E138 and two or three gave dominant resistance to 2E16. SPA had three resistance genes, all of which gave resistance to 2E16 and two of which also gave resistance to 43E138. SPA had one gene in common with CV for resistance to both races. Furthermore, the gene for resistance to race 2E16 in CV and SPA was allelic with a gene in SD, and was probably Yr25 .     

Differential effects of -mannose and 2-deoxy- -glucose on attempted powdery mildew fungal infection of inappropriate and appropriate ramineae

Barley, oat and wheat were used as both inappropriate hosts (IH) and appropriate hosts (AH) for three formae speciales of the fungus Blumeria graminis, the causal agent of powdery mildew disease. Treatment with either the glucose analog 2-deoxy- -glucose (DDG) or with -mannose dramatically suppressed penetration resistance in IH and to a much lesser extent in AH combinations. Other effects of DDG and -mannose were strikingly dissimilar. DDG greatly reduced localized autofluorescence at fungal attack sites on epidermal cells, and prevented hypersensitive epidermal cell death (HR). -mannose had little effect on autofluorescence or HR. DDG arrested the development of fungal haustoria and apparently prohibited biotrophy leading to secondary hyphae. -mannose allowed haustorial development and functional biotrophy leading to the production of elongating secondary hyphae. This suggests that B. graminis is in some way capable of utilizing -mannose as a carbon substrate. Results with IH combinations paralleled those of known mlo -barley responses to DDG and -mannose. Results are discussed in relation to specific physiological processes known to be influenced by either DDG or by -mannose, or by both compounds.     

单对汰选方法在加速抗高效氯氟氰菊酯棉铃虫品系汰选中的应用

通过设计杂合种群单对杂交方式,研究了加速获得抗性品系的方法。以高效氯氟氰菊酯群体汰选后抗性倍数为4.9倍的棉铃虫种群及其同源对照种群为材料,同时设置常规群体汰选方法与单对汰选方法,研究单对汰选方法在加速抗高效氯氟氰菊酯棉铃虫品系汰选中的作用。结果表明,群体汰选两代后抗性倍数由4.9倍提高到7.4倍, 而单对汰选两代后抗性倍数由4.9倍提高到27.3倍。表明在常规群体汰选中穿插几代单对汰选方法可明显加快棉铃虫种群对高效氯氟氰菊酯的抗性汰选进程。     

山西菜田捕食性食蚜蝇优势种及其对菜蚜的控制效果

对山西菜田捕食性食蚜蝇优势种及对菜蚜的控制效果进行了研究，菜田常见捕食性食蚜蝇有黑带食蚜蝇，大灰食蚜蝇，斜斑鼓额食蚜蝇，野食蚜蝇，四条小食蚜蝇，短翅细腹食蚜蝇6种，以黑带食蚜蝇种群数量最大，平均占全年发生总量的36.3%，通过对食蚜蝇产卵量，卵化率，幼虫期捕食量和羽化率测试，筛选出的黑带食蚜蝇，大灰食蚜蝇，斜斑鼓额食蚜蝇幼虫对菜蚜均有较强的捕食能力，其中黑带食蚜蝇为山西菜田菜蚜捕食性食蚜蝇优势种，用黑带食蚜蝇三龄幼虫对菜蚜进行防治试验，结果以1：180防效最佳，72h后控制效果达93.5%。     

水稻白叶枯病菌对噻枯唑的抗药性监测

采用活体寄主法和离体含药平板法 ,测定了 1999年安徽省滁州市田间水稻白叶枯病菌对噻枯唑的抗药性。结果表明 ,在水稻活体上存在噻枯唑抗药突变体 ,其比例为67.65%,比1997、1998年有较大程度升高 ,但是离体含药平板上未能监测到抗药突变体。     

甘薯根腐病抗性在不同环境条件下的表现及遗传趋势

结果表明,甘薯根腐病发病轻重与环境条件有很大关系,表现为干旱少雨的年份发病较重,降雨量较多的年份发病较轻;土壤瘠薄的发病较重,肥力条件较好的则发病较轻;通常情况下,年份间品种的抗性表现较为一致,但遇特殊气候则年份间品种的抗性有一定的差异。对1150份甘薯品种资源及育种材料的根腐病抗性鉴定结果表明,高抗型材料占14.6％,抗病型占15.7％,感病型占26.0％,高感型占43.7％。对754份材料及亲本的抗性分析表明,不同的抗性组合后代中均可分离出高抗至高感类型的材料,杂交后代的抗性强弱随双亲抗性水平的提高而提高。中国自1970年以来采用品种间杂交和种间杂交育种技术,先后育成了一批高产、优质的高抗型优良品种。     

一种监测棉铃虫对Bt杀虫晶体蛋白抗性的技术

研究了以诊断试剂盒监测棉铃虫对苏云金杆菌(Bt)杀虫晶体蛋白(ICP)抗性的技术。将1日龄幼虫在含诊断剂量的饲料中(每毫升饲料含Bt ICP0.01mg)取食7天,以生长至3龄以上的个体作为抗性个体的判断指标;筛选出人工饲料中防腐剂剂量的最佳值为每350毫升饲料中含丙酸2.5ml。经对多个棉铃虫不同抗性种群的验证试验,证明诊断试剂盒检测抗性个体频率较为精确且应用简便。