57 Table 4.5: Mean squares for grain yield and other traits associated with nematode resistance in nematode-infested maize. 63 Table 5.1: Mean squares for grain yield and other traits as assessed by 32 maize hybrids at three locations in Uganda.
Introduction
Nematodes of maize
Genus Pratylenchus Filipjev, 1936
When soil moisture is low, some species survive well for more than a year without host plants. In the USA, overwintering occurs in dead roots of crabgrass (Digitaria spp.), corn, cotton and, to a lesser extent, tobacco (Fortuner, 1976).
Genus Meloidogyne Goeldi, 1887
Staining maize root systems is advisable to assess nematode penetration when root knot nematodes are suspected or juveniles are detected in the soil (McDonald and Nicol, 2005). Root knot nematodes are widely distributed and are of economic importance to most crops in the world, including weeds (Sasser, 1977; Meyer and Van Wyk, 1989).
Other nematodes associated with maize
Nematode management options in maize
- Chemical control
- Cultural control
- Biological control
- Host resistance
In particular, some insecticides have been reported to have nematicidal properties and thus indirectly additionally control parasitic nematodes in maize fields. Weeding of maize plots has been reported to suppress populations of Ditylenchus spp., Heterodera spp.
Mechanisms of resistance to nematodes
For example, terthienyl and bithienyl, which are effective against Pratylenchus penetrans and Meloidogyne spp., activate oxygen radicals, which in turn activate enzymes and damage nematode cell membranes (Dropkin, 1989). In fact, high levels of phenolic compounds were found in tomato and tobacco cultivars resistant to Meloidogyne spp., compared to susceptible cultivars.
Resistance to nematodes in maize
Resistance to Meloidogyne spp
A diallel cross between maize inbred lines has shown the importance of general combining ability (GCA) and specific combining ability (SCA) in influencing resistance to M. In the US, open-pollinated cultivars (OPVs) have been screened as potential sources of resistance to M.
Resistance to Pratylenchus spp
Windham and Williams (1994b) observed retarded growth or failure of juveniles to mature in maize hybrids exhibiting resistance. Using separated populations obtained from the lines Col 2(22) (resistant) and Ip48-5-3 (susceptible), Sawazaki et al.
Resistance to other maize nematodes
Rearing Meloidogyne and Pratylenchus spp
The method is also laborious and results in low nematode populations, unless the nematode populations generated are further reared in sandy loam soil prior to use as inoculum (Martin et al., 1983). Sterile root discs offer a cost-effective and relatively less laborious alternative to rearing nematodes, which can lead to greater nematode reproduction compared to other methods (Speijer and De Waele, 1997).
Recurrent selection
The most common intrapopulation methods used in recurrent selection are paternal or maternal half-siblings; families with full brothers and sisters; Inbred lines S1 and S2 (Ramírez-Díaz et al., 2000). The recurrent S1 selection improves a trait by taking advantage of the additive genetic effects, and is therefore a suitable approach for improving the maize population.
Participatory rural appraisal
Five cycles of phenotypic recurrent selection for early vigor in red clover (Trifolium pratense) reduced root gall counts by and 0.26 units per cycle and egg mass counts by and 0.30 units per cycle (1-5 rating scale) when the cycles were infected with M .Two additional cycles of greenhouse half-sib family selection decreased gall counts by 0.45 and 0.31 units per cycle in the M.
Conclusions from review of literature
Effect of fluorescent rhizosphere Pseudomonas strains on plant-parasitic nematodes Radopholus similis and Meloidogyne spp. 2Awareness of plant-parasitic nematodes and preferred maize cultivars among smallholder farmers in eastern and southern Uganda: implications for assessment.
Introduction
Therefore, a participatory rural assessment was conducted to assess farmers' awareness of nematodes and identify preferred traits in a new maize germplasm. Samples of corn roots and soil were also collected in the farmer's fields, and the occurrence of nematodes was determined.
Materials and methods
Selection of sites and farmers
To promote the acceptance of new varieties, farmers should be involved early in the variety development process (Witcombe et al., 1996). The objectives of this study were to: (i) evaluate farmers' perceptions about nematodes;. ii) to determine the nematode infestation levels on maize in farmers' fields; and (iii) other important traits that farmers value in a maize cultivar.
Data collection
Semi-structured interviews were conducted, based on the results of focus group discussions, with 15 farmers per parish. Cross-country walks were done with key informants and farmers through the fields and residential areas of the villages mainly for: (i) observation of general land use; (ii) identify cultivated crops; (iii) collect soil and corn root samples; and (iv) collect seeds of local breeds for inclusion in the breeding programme.
Data analysis
The elements are placed along the horizontal axis of the matrix, and the criteria for evaluating each item are placed along the vertical axis of the matrix. Transect walks were conducted with key informants starting from nearby fields and ending with fields furthest from the sub-country headquarters.
Results
- Farmers’ perceptions of nematodes
- Nematode related symptoms observed by farmers
- Nematode populations and related symptoms
- Farmers’ preferred traits
- Estimated yield of the cultivars and associated production constraints
37 Table 2.6: Farmers' estimated yields (%) for the cultivars they grow in Iganga and Masaka in Uganda. Farmers also cited inadequate marketing channels and natural floods as major constraints to maize production in Iganga and Masaka, respectively.
Discussion
Conclusion
Sterile root discs are more cost-effective and relatively less laborious for rearing most root-lesion nematodes, but information on their effectiveness for P. The aim of this study was to determine the effectiveness of sterile root discs for mass cultivation of P.
Introduction
Twenty live nematodes were transferred to the edges of each of 40 sterile root discs contained in 3.5 cm diameter sterile glass Petri dishes. Therefore, the aim of this study was to evaluate the efficiency of sterile root discs for mass cultivation of P.
Materials and methods
Results
Discussion
The SCA was important for increasing plant height and grain yield, contributing 43% and 58% of the phenotypic variance under nematode infestation, respectively. Parent CML444 contributed most of the dominant genes to improved grain yield in all its crosses.
Introduction
This can form the basis to start studies to determine the genetics of nematode resistance and later be able to incorporate this resistance into elite lines. Adequate genetic variation, including both additive and dominance, is involved in conditioning nematode resistance in maize.
Materials and methods
- Germplasm sources and selection criteria
- Diallel crosses and evaluation of the parents and F 1 progeny
- Data collection
- Nematode damage and population density assessment
- Assessment of other agronomic traits and yield
- Statistical analysis
In the laboratory, the roots were washed with tap water and their fresh weight was recorded. Yiijkl = value of the F1 crossing of the i-th female and the j-th male in the k-th block and l plot/observation µ = population mean;.
Results
Combining ability effects
General combining ability (GCA) and specific combining ability (SCA) were highly significant (P < 0.001) for all traits measured. Under nematode infestation, reciprocal effects were significant (P < 0.05) for plant height and grain yield (Table 4.2).
Genetic effects for resistance to nematodes
Parents CML395 and 5057 had the highest Wr+Vr values, but the lowest Wr-Vr values. CML312 and CML206 had the highest Wr+Vr values, but the lowest Wr-Vr values.
Discussion
Combining ability effects
- General combining ability effects of parents
- Specific combining ability effects
Hybrids 5057/CML206 and MP709/CML206 had positive and significant SCA effects on grain yield, even though they were derived from parents with negative and significant GCA effects for the same trait under nematode attack. Hybrids MP709/CML444 and MP709/CML395 had negative and significant reciprocal effects on grain yield under nematode attack.
Genetic effects
The presence of maternal effects for wheat yield confirms the results obtained earlier in the present study using Griffing's analysis. Parents CML206 and CML312 had most recessive genes for reduced grain yield under nematode pressure.
Conclusions
Proceedings of the 3rd Research Planning Conference on Root-Knot Nematodes, Meloidogyne spp., Ibadan, Nigeria. Growth performance and other characteristics of the inbred line accessions under nematode infested field conditions at IITA-Namulonge.
Introduction
80 maize hybrids; ii) estimate heterosis for nematode resistance and grain yield in maize; and iii) estimate grain yield losses associated with nematode infestation in maize. It was hypothesized that: i) variations in nematode resistance exist among maize hybrids; ii) hybrid vigor for nematode resistance and grain yield can be achieved among nematode-resistant maize hybrids; and iii) plant-parasitic nematodes, if left unchecked, can cause significant grain yield loss in susceptible maize hybrids.
Materials and methods
- Study area
- Germplasm
- Experimental designs for screening of the hybrids for nematode resistance
- Evaluation of the hybrids under field conditions
- Evaluation of the hybrids under screenhouse conditions
- Pratylenchus zeae and Meloidogyne spp. inoculum preparation
- Quantification of nematode densities and assessment of root damage
- Assessment of yield and other agronomic traits
- Statistical analysis
84 I = 100 represents nematode-tolerant hybrids, meaning that yield is not affected by the presence of nematodes; RI > 100 represents nematode-resistant hybrid, which increased grain yield because nematode presence was suppressed. Log where necessary to transform the data before transforming while comparing grain yield between means using Tukey's studentized.
Results
- Performance of maize hybrids under nematode infested and nematicide treated
- Performance of the hybrids across sites and treatments in the field
- Mean performance of the hybrids under nematode treatments per site, associated
- Yield losses and resistance index for each maize hybrid per site, and across sites . 89
- Linear regression analysis
- Response of the hybrids to P. zeae infection under screenhouse conditions
- Means for P. zeae densities, reproduction factor (RF) and other traits following P
- Relative yield and heterosis for nematode resistance and grain yield of the maize
- Heterosis for resistance to P. zeae, Meloidogyne spp. and grain yield under field
- Performance of maize hybrids under field conditions
- Response of the F 1 hybrids to P. zeae infection in the screenhouse
- Heterosis and relative yield
All hybrids showed positive heterosis for grain yield under nematode attack and nematode-treated plots in the field (Table 5.8c). Results of standard heterosis for grain yield (relative yield) and classification of hybrids under nematode and nematode-treated plots in the field are presented in Table 5.9.
Conclusions
Managing Antagonistic Potential in Agricultural Ecosystems for Biological Control of Plant Parasitic Nematodes. Occurrence of plant parasitic nematodes and factors enhancing population accumulation in cereal-based cropping systems in Uganda.
Introduction
1999) reported 38% increase in grain yield after three cycles of repeated selection of S1 in water stressed environments. The hypothesis tested was that nematode resistance could be improved through two cycles of repeated selection of S1 progeny and a significant increase in grain yield could be achieved.
Materials and methods
- Study area and germplasm description
- Formation of S 1 lines
- Pratylenchus zeae and Meloidogyne spp. inoculum preparation
- Field evaluation of S 1 families and generation of nematode resistant C 1 seed
- Field and screenhouse evaluation of C 1 seed and recombination of nematode resistant
- Nematode damage and population density assessment
- Assessment of agronomic traits and grain yield
- Statistical analyses
Similarly, seed from the ears within each of the 10 S1 nematode-susceptible lines was harvested, dehulled, dried, and bulked. Split plot tests: field and screen house evaluation of the 20 C1R lines (non-bulked lines used) and 4 controls.
Results
Correlations between traits
Number of root lesions was significant (P < 0.05) and positively correlated with days to silk, anthesis to silk interval, Meloidogyne spp. The main effects of site were significant (P < 0.05) for plant height, root mass, number of root lesions and grain yield, but were not significant for P.
Grain yield of the three maize populations in relation to nematode densities
130 Table 6.4: Mean squares for traits for all cycles under nematode-infested and nematicide-treated conditions at three sites in Uganda. Grain yield was relatively higher under nematicide-treated plots than nematode-infested plots in both Longe 4 and ZM521.
Performance of the original and advanced cycles of the three maize populations across
Net increase in root mass was higher relative to C1S than to C0 in Longe 1 and ZM521. The number of root lesions in C2R decreased much more relative to C1S than to C0 in Lung 1 and Lung 4.
Discussion
Susceptible genotypes were expected to have a high number of root lesions, and this was the case in C0 and C1S for all three maize populations. However, net reduction in number of root lesions was higher in ZM521 and lowest in Lunge 1.
Conclusion
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Introduction
Summary of the major findings
- Awareness of plant-parasitic nematodes and preferred maize cultivars among
- Monoxenic culture of P. zeae on carrot discs
- Combining ability and genetic effects for nematode resistance in maize
- Nematode resistance, grain yield, heterosis and yield losses among the maize hybrids
SCA contributed most of the phenotypic variance (43–58%) in plant height and grain yield under nematode infestation. SCA effects on grain yield were positive and significant for 11 hybrids under nematode infestation.
Implications and way forward
Two cycles of recurrent selection of S1 progeny were used to improve nematode resistance and grain yield of three OPVs (Longe 1, Longe 4 and ZM521). Broad sense heritability (H2) for grain yield in cycle 2 ranged from 74-97% for the three maize populations.
