Evaluation of open pollinated varieties of maize for resistance to the maize weevil in a controlled temperature and humidity laboratory in Zimbabwe

Maize weevil (Sitophilus zeamais Motschulsky) is one of the major maize storage pests among smallholder farmers in eastern and southern Africa (ESA), thereby, reducing total on-farm maize harvests. Experiments were conducted in a controlled temperature and humidity (CTH) laboratory at CIMMYT-Zimbabwe to compare the resistance of new maize open pollinated varieties (OPVs) from regional trials undertaken in ESA to maize weevils. Twenty maize OPVs were shelled and cleaned before being placed in a deep freezer at ?20 °C to kill any pests and eggs in the grain from the field. Fifty grams of grain from each OPV was measured after 3 weeks and placed in the CTH lab for conditioning. The samples were placed in 250-mL jars with brass-screened lids and then infested with 32 maize weevils aged between 10 and 14 days. Data were collected for kernel hardness prior to weevil infestation, as kernel hardness to confer resistance to weevils. The components of maize weevil resistance considered were: median development period, Dobie index of susceptibility, weevil emergence, weevil mortality, weevil fecundity, grain weight loss, kernel damage and germination. There were highly significant differences in maize kernel characteristics and median development period (P < 0.001) among the maize OPVs. There were significant differences in the number of damaged kernels, grain weight loss (P < 0.01), weevil mortality and germination (P < 0.05) among the maize OPVs. There were no significant differences found for weevil progeny emergence (F₁), Dobie index of susceptibility and weevil fecundity, the last of which was positively and significantly correlated with kernel damage (P < 0.001). The DIS was positively and significantly correlated with weight loss and F₁ (P < 0.001). The maize OPVs 07WEEVIL, Chitedze6, Strigoff126, Strigoff128 and ZM625 were found to be resistant; on the other hand, Strigoff140, Strigoff125, Strigoff133, VP05199 and VP074 varieties were highly susceptible.     

Fusarium ear rot and how to screen for resistance in open pollinated maize in the Andean regions

Ears infected with ear rot were collected from five provinces in Ecuador. Of the 44 samples analysed 26 carried Fusarium verticillioides, 11 F. subglutinans, two F. graminearum and five carried fungi different from Fusarium. The pathogenicity of ten isolates, seven of F. verticillioides and three of F. subglutinans, were tested. Per isolate 30 ears of the susceptible cultivar Mishca were inoculated by pricking a steel pin, dipped into a spore suspension, through the husks in the central part of the ear 14 days after mid-silk. Ears inoculated with sterile water and ears without any treatment, natural infection, served as controls. The disease severity (DS) of the ears ranged from 14 to 58% ear rot, the range being similar for both species. The DS of the water control, 19%, was much higher than that of the natural control of 2%. Five strains gave a DS of over 40%, significantly higher than the water control. The DS of the others were similar to the water control. In a series of experiments the effect of various methods of applying Fusarium spores through the husks into young ears were compared. All tested methods resulted in DSs significantly higher than those of the two controls. Inoculation with tooth picks and steel pins dipped in a spore suspension gave similar ear rot percentages. Inoculations at 7 to 14 days after mid-silk produced the highest DS’s. There was no significant effect of spore concentration on the DS. Cultivars differed considerably, the range being from around 20% to over 50%. Surprisingly, only wounding the husks, the sterile water control, resulted in a fairly high DS, much higher than that of the natural control. As the ranking order of the cultivars after wounding only and after inoculation did not seem to be different from the ranking order of the natural control it is suggested to use in areas with high inoculum pressures like the Andes only wounding by means of a steel pin for screening for resistance to maize ear rot.     

Participatory varietal selection in rice in Nepal in favourable agricultural environments – A comparison of two methods assessed by varietal adoption

Two participatory approaches to varietal selection were compared in February-sown (Chaite) rice and main-season rice in high potential production systems in Nepal. One method, called farmer managed participatory research (FAMPAR), was researcher intensive, while the other, called informal research and development (IRD), demanded fewer resources. The trials were conducted in 18 villages in high potential production systems in Chitwan and Nawalparasi districts of Nepal. Six new varieties of Chaite rice and 16 of main-season rice were tested in over 300 trials of Chaite rice and nearly 1100 trials of main-season rice over two years in 1997 and 1998. Surveys were done in 1997, 1998 and 1999 to record the extent of adoption and spread of the new rice varieties in the study villages. In many cases, farmers tested varieties for two years before deciding whether to adopt or drop them. Varieties were quite widely accepted, adopted for niches in a few villages, or rejected. The two participatory approaches identified the same varieties, but FAMPAR, which used formal survey methods, was more useful for diagnosing reasons for adoption or rejection. However, IRD used much cheaper anecdotal methods of evaluation, so it was more cost-effective. Moreover,farmer-to-farmer seed dissemination was higher in IRD villages, probably because farmers in FAMPAR villages felt that the project would re-supply seed if needed. The benefits from both approaches are considerable, but to adopt them substantial policy changes in varietal testing, release and extension systems will be required. This revised version was published online in August 2006 with corrections to the Cover Date.     

Participatory plant breeding with maize in Mexico and Honduras

Maize is a staple food crop in many developing countries. However, if seven major maize producing countries are excluded from this group, data indicate that only 34% of the maize area is planted with improved seed despite considerable effort invested in maize breeding. This has led researchers to investigate other options, such as farmer-participatory plant breeding, for delivering the benefits of plant breeding knowledge and technology to farmers in developing countries. This paper describes short-term results from participatory maize breeding studies in Mexico and Honduras. Results from three selection cycles in Mexico suggest that stratified mass selection without pollination control, with selections carried out by researchers in farmers' fields, may be effective at improving yield in farmers' local varieties. In Honduras, mass selection with pollination control, where selections were done by collaborating farmers in their own fields on their own varieties, showed trends (non-significant) towards yield improvement. Farmer selection seemed to offer the greatest yield benefit over experiment station selection on the farm with the lowest yield potential, suggesting that farmer-participatory approaches may be most advantageous in marginal environments where experiment station conditions differ most dramatically from farmers' conditions. These studies highlighted the importance of seed systems knowledge in designing participatory plant breeding programs. For cross-pollinated crops, they also highlighted the need to balance progress from selection and demands on farmers' time and labor in choosing breeding methods. Further work is needed to investigate farmer-participatory breeding approaches that can address post-harvest traits. This revised version was published online in August 2006 with corrections to the Cover Date.     

Participatory plant breeding in maize: A case study from Gujarat, India

This paper describes how plant breeders and farmers worked together to produce improved varieties of maize for the low-resource farmers of the Panchmahals district of Gujarat, India. Initially, farmers tested a range of maize varieties in a participatory varietal selection (PVS) programme. However, none of these proved to be very popular with farmers, although farmers who had more fertile fields adopted the variety Shweta from Uttar Pradesh. Hence, in 1994 a participatory plant breeding (PPB)programme was begun to generate new, more appropriate varieties. Yellow- and white-endospermed maize varieties were crossed that had been either adopted to some extent following PVS or had attributes, such as very early maturity,that farmers had said were desirable. In subsequent generations, the population was improved by mass selection for traits identified by farmers. In some generations,farmers did this in populations which were grown by breeders on land rented from a farmer. Soil fertility management was lower than that normally used on the research-station. The breeding programme produced several varieties that have performed well in research-station and on-farm trials. One of them, GDRM-187, has been officially released as GM-6 for cultivation in hill areas of Gujarat state,India. It yielded 18% more than the local control in research-station trials, while being seven days earlier to silk. In farmers' fields, where average yields were lower, the yield advantage was 28% and farmers perceived GDRM-187 to have better grain quality than local landraces. PPB produced a variety that was earlier to mature than any of those produced by conventional maize breeding, and took fewer years to do so. The returns from PPB,compared to conventional breeding, are higher because it is cheaper and benefits to farmers are realised earlier. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heterotic groups based on yield-specific combining ability data and phylogenetic relationship determined by RAPD markers for 28 tropical maize open pollinated varieties

Twenty eight maize open pollinated varieties (OPVs) were crossed in a diallel scheme and the 378 F₁'s were evaluated in 10 environments in Brazil. Based on yield-specific combining ability data (SCA), these varieties were classified in four heterotic groups. The consistence of the proposed heterotic groups was confirmed comparing intra- and inter-group F₁ values and midparent heterosis. Superior OPVs combinations for use as a source of inbreds in hybrid breeding programs were determined. RAPD markers were used to genotype these varieties. A UPGMA dendogram, based on marker data from 50 primers and 178 polymorphic bands, was obtained. Phylogeny obtained with RAPD markers agreed with known pedigree data. Dent germplasm tended to group separately from flint germplasm. Multidimensional Scaling Analysis on marker data and morphological data showed a higher degree of genetic divergence among the dent germplasm than among the flint germplasm used in this study. Correlation between RAPD marker estimated genetic distance and SCA for yield was low and positive (r = 0.16^**). This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of maize streak virus disease on the growth and yield of maize as influenced by varietal resistance levels and plant stage at time of challenge

Field experiments were conducted from 1989 to 1991 at Ibadan, Nigeria, to assess effects of maize streak virus (MSV) disease on growth and yield of maize varieties having different levels of disease resistance. MSV disease reduced yield and growth in all years, but varieties differed significantly in amount of loss, disease severity and incidence. MSV disease was negatively correlated with plant height and dry weight, grain weight per plot, 1000-grain weight, ear length and diameter. In 1989 MSV disease decreased yield of resistant variety TZB-SR by 1.5%, of resistant hybrid 8321-21 by 10%, and of moderately resistant hybrid 8329-15 by 17%. Yield of susceptible variety TZB Gusao was reduced significantly more, by 71%. Plant age at time of virus challenge had significant effects on yield and growth characters, with earlier infection resulting in greater disease severity and yield reduction. A significant interaction between variety × age at challenge was also detected, indicating that varieties were differentially affected by MSV in relation to the growth stage when challenged. Disease incidence after challenge was lower for the most resistant varieties. This property of lower disease incidence under equal challenge opportunities (tolremicity) is an important aspect of resistance. The resistant varieties discussed here were bred for tolerance - good yield performance when diseased -, but TZB-SR and 8321-21 also exhibited tolremicity. Tolremicity combined with tolerance constitutes the overall disease resistance of a variety to a systemic pathogen such as MSV. This revised version was published online in July 2006 with corrections to the Cover Date.     

Farmers' highland maize (Zea mays L.) selection criteria: Implication for maize breeding for the Hararghe highlands of eastern Ethiopia

Despite the presence of large numbers of improved maize cultivars, farmers in the Hararghe highlands of eastern Ethiopia persistently grow local cultivars and are not benefiting from the varietal improvement program. By growing local cultivars farmers obtain an average yield of 1.2 t ^-1 whereas research has released cultivars yielding 5–11 t ^-1under on-station conditions. Recognizing this and the important role maize is playing in the livelihood system of farmers in eastern Ethiopia; Participatory Varietal Selection (PVS) was conducted for three consecutive seasons (1996–1998) in three locations. The objectives of the study were to identify farmers' cultivar selection criteria for future breeding, to enable farmers to assess the performance of improved cultivars under their management, to increase farmers' access to the cultivars of their preference by injecting source seed into the local seed system, and to investigate whether breeding for wide adaptation like for the Hararghe highlands has any drawbacks or not. The study indicated farmers' maize varietal selection criteria together with the differences in selection criteria across locations classified under the same adaptation zone. Though farmers selected some of the many improved cultivars tested, no improved cultivar had all the characteristics, which farmers want in a single cultivar. To be able to combine cultivar selection traits farmers considered cultivar combinations in all locations, but not the single `best' cultivar. Despite the yield advantage of hybrids, farmers selected Open Pollinated Varieties (OPVs) because they had more preferred traits. Farmers also preferred to retain their local cultivars despite their lower yield compared to most of the improved cultivars. Both situations confirmed how resource poor farmers' cultivar requirements are much more diverse than yield per se. Gender and social group-driven difference in cultivar preference was also observed. The study revealed the need for proper zoning of the Hararghe highlands as a prerequisite to developing better adapted maize cultivars to the varied agro ecological and socioeconomic niches. As shown in this study, proper zoning, due consideration to farmers' relevant selection traits and wider use of participatory approaches should be adapted to develop cultivars which can gain farmers acceptance. This revised version was published online in August 2006 with corrections to the Cover Date.     

Experimental evaluation of several cycles of marker-assisted selection in maize

A program was initiated in 1994 to compare the efficiency of marker-assisted selection (MAS) and conventional phenotypic selection. A population of 300 F_3:4 families was generated from the cross between two maize inbred lines F2 and F252 and selected on an index combining grain yield and grain moisture at harvest. This population was characterised for 93 RFLP markers and evaluated as testcrosses in a large range of environments. Three methods of selection were applied (i) two cycles of conventional phenotypic selection; (ii) two cycles of MAS based on an index combining phenotypic values and QTL genetic values and (iii) one cycle of combined MAS followed by two cycles of selection based only on the QTL effects estimated in the first generation. The different populations were characterised for RFLP markers. The evolution of allele frequencies showed that selection on only-markers was very efficient for fixing QTL alleles found favourable in the initial population. This evolution was quite different from that observed for phenotypic selection or combined MAS. Genetic gain was evaluated and found significant for each method of selection. Nevertheless, the difference between phenotypic selection and combined MAS was not significant. The two additional cycles of MAS on only-markers did not improve significantly the genetic value of the population. Moreover, the genetic variance of this population remained high, despite most of the QTL initially detected were almost fixed. The results suggest that the QTL effects estimated in the initial population were not stable due to epistasis and/or QTL by environment interactions. This revised version was published online in July 2006 with corrections to the Cover Date.     

The concept of varietal ability in plant breeding

Summary At the population level, the general varietal ability of a genotype is defined as the expectation of all possible varieties of a given type with this genotype. Specific varietal abilities of order 1, 2, 3..., are defined as interactions from the combined effect of 2, 3, 4... parents in varietal combinations. Genetic effects for varietal value and for the criterion of test are introduced. They allow an expression of the covariance between the value of a genotype according to the testing system and the value of its progeny from random mating in varietal combination. So a general expression of the genetic advance in the varietal value of a population improved by recurrent selection can be given whatever the type of variety and the testing system. The genetic advance is also considered at the level of the varieties. Some examples of prediction formulae for varietal abilities are given for hybrids, synthetics and lines. The problem of prediction of the ability of a genotype to give lines with the best general varietal abilities is also considered.Communication given at the 3rd meeting of the Eucarpia section Biometrics in Plant Breeding, Cambridge, April 4–7, 1978, and in a revised version on the occasion of the Professor Schnell's 65th birthday, Stuttgart, University of Hohenheim, May 19, 1978.     

Improving participatory varietal selection processes: participatory varietal selection and the role of informal seed diffusion mechanisms for upland rice in Ghana

This paper considers the process of Participatory Varietal Selection (PVS) and presents approaches and ideas based on PVS activities conducted on upland rice throughout Ghana between 1997 and 2003. In particular the role of informal seed systems in PVS is investigated and implications for PVS design are identified. PVS programmes were conducted in two main agroecological zones, Forest and Savannah, with 1,578 and 1,143 mm of annual rainfall, respectively, and between 40 and 100 varieties tested at each site. In the Savannah zone IR12979-24-1 was officially released and in the Forest zone IDSA 85 was widely accepted by farmers. Two surveys were conducted in an area of the Forest zone to study mechanisms of spread. Here small amounts (1–2 kg) of seed of selected varieties had been given to 94 farmers. In 2002, 37% of 2,289 farmers in communities surveyed had already grown a PVS variety and had obtained seed via informal mechanisms from other farmers, i.e. through gift, exchange or purchase. A modified approach for PVS is presented which enables important issues identified in the paper to be accommodated. These issues include: utilising existing seed spread mechanisms; facilitating formal release of acceptable varieties; assessing post-harvest traits, and; the need for PVS to be an ongoing and sustainable process.     

An agronomic and seed-quality evaluation of noug (Guizotia abyssinica Cass.) germplasm in Ethiopia

Noug (Guizotia abyssinica Cass.), a member of the Compositae family, is grown as an oilseed crop in Ethiopia. The crop grows best on poorly drained, heavy clay soils. This study investigates the genetic variability of agronomic and seed quality characteristics of 241 noug germplasm collections from different parts of Ethiopia evaluated in a field test at Ghinchi, near Addis Ababa, Ethiopia, in 1992. The maturity of the noug accessions ranged from 132 to 168 days. Seed oil contents ranged from 39.8 to 46.9% with linoleic acid being the major fatty acid of the oil (76.6% of total fatty acids). The results of this field study indicated that genetic differences for maturity existed among the noug accessions. Oil content variation was continuous, without clear separation of accessions into oil content groups. It is concluded that the genetic variation observed among these accessions could be utilized in a breeding programme to develop high-yielding, well-adapted, high-oil-content noug cultivars for production in Ethiopia.     

Accurate evaluation and verification of varietal ranking for flooding tolerance at the seedling stage in barley (Hordeum vulgare L.)

Soil flooding or waterlogging is a major abiotic stress in upland crops. In barley, there have been several reported studies of selection for flooding-tolerant genotypes, but it is difficult to obtain varietal rankings that are consistent among researchers. Our objectives were to establish experimental conditions that could be applied by other research groups and to verify the varietal ranking conducted in an earlier study. We conducted greenhouse experiments on 14 barley varieties. At the 2.5-leaf stage, they were flooded with 0% or 0.1% soluble starch solution (mimicking reducing conditions). At 13 to 15 days after the start of treatment, the degree of leaf injury and the shoot dry weight ratio (treatment:control) were recorded. Reliable and highly repeatable results were obtained for the criterion of leaf injury under reducing conditions, whereas shoot dry weight ratio was unstable. The varieties OUJ820 and OUA301 were highly tolerant, whereas OUA002 and OUJ247 were sensitive; these results matched those of the earlier study. The experimental conditions that we developed here may be useful for selection testing and genetic analysis of flooding tolerance in other laboratories.     

辽西雨养玉米农田土壤水分变化特征及其模拟

土壤含水量是作物生长发育的关键影响因子之一,确定土壤含水量变化及预测土壤含水量变化趋势,对于雨养农业更加有效地保墒、提高作物水分利用效率和增强抗旱防灾能力有着重要的现实意义。利用2008-2011年锦州玉米生长季逢三逢八土壤湿度观测数据,日气温降水数据和2008年玉米生长发育期数据资料,结合CERES-MAIZE土壤水分模块,分析了雨养玉米农田土壤水分时空变化特征和模拟了土壤水分时空变化特征。结果表明：生长季降水并不能反映土壤水分条件的好坏,生长季中雨以下的降水量和降水频次与土壤水分条件的好坏较好的一致性;土壤水分随土层深度而增加,0-40cm土壤含水量平均值和最低值分别是田间持水量的69%-82%和49%-64%;玉米根系生物量与生长时间呈二次曲线关系,所建根系生物量模型解释率达89.7%;耦合根系生物量模型和叶面积指数模型的CERES-MAIZE中的土壤水分模块能够较好的模拟雨养玉米生态系统土壤水分的时空变化特征。     

鲜食糯玉米新品种引进和综合评价

对引进的27个鲜食糯玉米品种进行品比试验,调查生育期、植株性状、果穗性状、抗逆性、产量、品质性状6个方面内容.结果表明:金糯628和美玉5号2个品种品质优、产量高、综合性状好,适合在广东省汕头市及生态条件相近的地区推广种植.     

玉米种质资源主要品质性状鉴定与评价

对2003—2004年收集、整理的400份玉米种质资源的主要品质性状进行了鉴定评价。结果表明，不同类型的玉米种质资源中地方品种的粗脂肪、粗淀粉性状和自交系粗蛋白、赖氨酸性状具有更大的遗传多样性。通过鉴定，筛选出一批品质性状优异的玉米种质资源．并对现行玉米种质资源品质的评价标准进行了讨论。     

9个CIMMYT玉米群体的灰色关联度综合评价

对9个CIMMYT玉米群体的几个性状进行灰色关联度分析，结果表明pob21、pob43、pob49综合表现好，在育种中具有较高的价值；pob45、staygreen、poo119、pob28综合表现较好，个别性状存在缺陷，在育种中可选择应用；pob32和pob46产量水平较低．应用中可选择其个别优良性状加以利用。