Factors Affecting Yield of Crops

A good understanding of dynamics involved in food production is critical for the improvement of food security. It has been demonstrated that an increase in crop yields significantly reduces poverty. Yield, the mass of harvest crop product in a specific area, is influenced by several factors. These factors are grouped in three basic categories known as technological (agricultural practices, managerial decision, etc.), biological (diseases, insects, pests, weeds) and environmental (climatic condition, soil fertility, topography, water quality, etc.). These factors account for yield differences from one region to another worldwide. The current chapter will discuss each of these three basic factors as well as providing some recommendations for overcoming them. In addition, it will provide the importance of climate-smart agriculture in the increase of crop yields while facilitating the achievement of crop production in safe environment. This goes in line with the second goal of 2030 Agenda for Sustainable Development of United Nations in transforming our world formulated as end hunger, achieve food security, improve nutrition and promote sustainable agriculture

The Search for Molecular Markers, Parental Characterisation and inheritance Studies of Witchweed [Striga Asiatica (L.) Kuntze] Resistance in Sorghum [Sorghum Bicolor (L.) Moench].

Sorghum [Sorghum bicolor (L.) Moench] is ranked the third most important cereal crop in Zimbabwe, after maize and wheat. The major biotic constraint to sorghum production by resource poor farmers (RPFs) is attack by the parasitic weed Striga asiatica (L) Kuntze, or witchweed. Striga asiatica resistant sorghum cultivars could be a major component of integrated witchweed management, if resistance was available in adapted and productive germplasm. The objectives of this work were to; characterize available sorghum cultivars for resistance to witchweeds, study the inheritance of low S. asiatica seed germination stimulant production and identify molecular markers that are linked to the genes for S. asiatica resistance. Crosses were made between witchweed resistant (SAR 16, SAR 19 and SAR 29) and susceptible (SV-1) cultivars in a half-diallel arrangement. The F1s were selfed to generate F2 generation progeny. Parental lines and F2 progeny were screened for S. asiatica resistance using the pot culture and agar gel techniques. Combining ability analysis for witchweed counts and path coefficient analysis of sorghum grain yield and its components were conducted for parent materials that were grown under S. asiatica infestation in pots. The inheritance of low S. asiatica germination stimulant production was evaluated using seedlings of F2 progeny that were screened in water agar and using petri dishes. Parental and F2 genotypes were transferred from petri dishes into pots filled with clay. Deoxyribonucleic acid (DNA) was then extracted from the potted sorghum seedlings after two weeks for molecular marker analysis using random amplified polymorphic DNA (RAPD) and microsatellite or simple sequence repeat (SSR) markers. A total of 440 RAPD, 24 sorghum SSRs and six maize SSRs were used to screen SV-1 and SAR 29 for polymorphisms. Linkage analysis was conducted using the software Mapmaker/exp 3.0b. Cultivars SV-1 and SAR 16 were susceptible, while SARs 19 and 29 were resistant to witchweeds. Combining ability analysis revealed that GCA components of genotypic variance were significant. Additive genetic factors were therefore important in determining the response of a cultivar to witchweed infestation. Cultivars SAR 19 and SAR 29 were good general combiners for low S. asiatica counts. These resistant cultivars reduced the number of parasite counts in their F2 progeny, though this was more conspicuous for SAR 19 whose negative GCA effects were significantly different from zero. Cultivars SV-1 and SAR 16 had positive and highly significant GCA effects. These cultivars therefore increased parasite counts among progeny from crosses that involved them. Grain yield components that were important for the cultivars tested were head weight, 100 seed weight, plant height and days to 50 % flowering. However, the direct and indirect contribution of each of these parameters to yield was influenced by the type of cultivar (resistant or susceptible) and whether there was witchweed infestation or not. In general, head weight was the most important sorghum grain yield determinant, having moderate to high direct contributions. Direct effects of S. asiatica counts on sorghum grain yield were low. Striga asiatica indirectly caused yield reduction by affecting sorghum grain yield components, mostly head weight. A single recessive gene controlled low S. asiatica seed germination stimulant production in sorghum genotypes SAR 19 and SAR 29. A total of 199 markers (187 RAPDs; 10 sorghum SSRs and 2 maize SSRs) were polymorphic between cultivars SAR 29 and SV-1. Molecular markers that are linked to the gene(s) for low S. asiatica seed germination stimulant production could not be identified. Instead, a molecular marker linkage map was constructed and it consisted of 45 markers that were distributed over 13 linkage groups (LGs). The LGs consisted of 2 to 8 markers that were identified at a LOD grouping threshold of 4.0. The map spanned a total distance of 494.5 cM. Cultivars SAR 19 and SAR 29 are good sources of genes for resistance to witchweeds since they had negative GCA effects, which enabled them to reduce witchweed counts in progeny derived from them. Specifically, these resistant cultivars are a good source of the low S. asiatica seed germination stimulant trait. However, sustainable use of S.asiatica resistance can be achieved through pyramiding different mechanisms of resistance. This should be combined with the use an integrated Striga management package involving host-plant resistance and other appropriate technologies, to provide a long-term and effective way of combating witchweeds. Field screening for witchweed resistance requires independent and concurrent selection for low Striga counts and high yield under S. asiatica infested conditions. Improvement in sorghum grain yield can be primarily based upon selection for improved head weight, though 100 seed weight, plant height and days to 50 % flowering should also form part of the selection criteria. The molecular linkage map that was constructed in this investigation can be useful for practical plant breeding purposes, since the polymorphisms that were identified are within the cultivated gene pool of sorghum

Response of Yellow Quality Protein Maize Inbred Lines to Drought stress at Seedling Stage

This study seeks to evaluate the response of 17 yellow Quality Protein Maize (QPM) inbred line seedlings to drought stress (DS), using different morphophysiological traits (plant height (PH), chlorophyll content (CC), stem diameter (SD), proline content (Pro), photochemical efficiency of photosystem II (PS II), canopy temperature (CT) and substomatal carbon dioxide concentration (Ci). The experiment was laid out in a randomized complete block design (RCBD) and replicated three times in a growth chamber. The seedlings were exposed to DS treatment by growing them at 20% field capacity. The control/well-watered (WW) treatments were kept at 80% field capacity throughout the experiment. Highly significant differences (p < 0.001) were observed for PH, SD, and Pro across environments. On the other hand, significant differences (p < 0.05) were observed for CC and PS II, while DS had no significant effects on Ci and CT. Proline content increased under DS compared to WW conditions. Inbred lines L34, L7, L5, L2, L16, and L6 had approximately equal or more Pro than the drought tolerant check (ZM1523). As such, these lines were regarded as drought tolerant. Taking all measured parameters into consideration, L7 performed notably better than the other inbred lines under DS

Combining Ability of Quality Protein Maize Inbred Lines for Yield and Morpho-Agronomic Traits under Optimum as Well as Combined Drought and Heat-Stressed Conditions

Drought and heat stress have perceptibly become major maize (Zea mays L.) yield reducing factors in Sub-Saharan Africa. As such, the objectives of this study were to: (i) determine the type of gene action conditioning tolerance to combined drought and heat stress (CDHS), and (ii) identify inbred lines with good combining ability for yield and other morpho-agronomic traits under CDHS. Twenty-four single cross hybrids (SCHs) obtained from crossing 10 inbred lines in a 4 × 6 North Carolina Design II, and a drought-tolerant check, were evaluated under CDHS and optimum conditions in the field. The experiment was laid out in a 5 × 5 alpha lattice incomplete block design, replicated three times. Additive gene effects influenced all the traits under CDHS except grain yield, which was influenced by non-additive gene effects. A preponderance of additive genetic effects was observed for all traits recorded under optimum conditions. Inbred lines L30, L6, L5, L17 and L2 showed good combining ability for yield under CDHS, indicating that they could be good parental lines in hybridization programs. Based on the results, SCHs L2*30, L6*13 and L5*18 exhibited high specific combining ability (SCA) effects for yield under CDHS. These hybrids are recommended for further multi-locational evaluation to determine the stability of their performance

Estimation of Maize (Zea mays L.) Yield Per Harvest Area: Appropriate Methods

Standardization of crop yield estimation methods at various levels of farming helps to obtain accurate agricultural statistics as well as assessing the suitability of agricultural practices under various production conditions. The current paper reviews various maize yield estimation methods, taking into account available yield parameters, and it also analyses the yield gap between maize potential and attainable yield. The easiest and more reliable methods of yield estimation are based on yield parameters collected from the field. However, farmer estimation methods are cheaper and faster compared to any other method of yield estimation from farmers’ fields. This paper also elaborates on the importance of the use of more complex methods for yield estimation, such as remote sensing and crop modelling. These complex methods are more accurate and can predict yield before field harvest with less deviation from the exact harvest yield. However, they are very expensive and not efficient for small plots of land (less than 1 ha). Factors that contribute to the gap between potential and actual yield include poor implementation of agricultural policies, strict regulation of fertilizer inputs, vulnerability of smallholder cropping systems to adverse climatic conditions, occurrence of biotic and abiotic constraints, as well as unavailability of seeds and labor

Climate-Smart Agriculture and Food Security in Southern Africa: A Review of the Vulnerability of Smallholder Agriculture and Food Security to Climate Change

Southern Africa is facing chronic food insecurity mainly because of the multistressor context in which agriculture is practiced in this region. Climate-change-related constraints are fueling food shortages for marginalized rural communities. Climate-smart agriculture (CSA) has been recognized as a key strategy for mitigating the effects of climate change. However, there has been a minimal level of adoption of CSA among smallholder farmers in southern Africa. Factors contributing to the limited adoption of CSA include poor access to resources by smallholder farmers, poverty, poor infrastructure, and an inadequate level of farmer advisory and resource service provision. These are the same factors that have resulted in the increased vulnerability of smallholder farmers to climate shocks in southern Africa. Currently, there are a limited number of reviews that simultaneously address the impacts of climate change and CSA on southern Africa’s smallholder agricultural sector. The current review synthesizes information on the contribution of smallholder agriculture to food security in southern Africa, highlighting the vulnerability of smallholder agriculture to climate shocks and the effect of CSA activities practiced in the region. To come up with this writeup, we reviewed information from reliable, published journal articles, institutional reports, and our knowledge of agricultural systems in southern Africa. The adoption of CSA agriculture can be enhanced by the advancement of favorable policies by national governments. This includes adequate participation from smallholders, particularly women, in governance via bottom-up policymaking

Mulching offers protection from Striga asiatica L. Kutnze parasitism in Sorghum genotypes

The production of sorghum is hampered by the parasitic weed Striga asiatica L. Mulching is promoted as a component of the conservation agriculture systems in sub Saharan Africa. The objective of the study was to assess the effects of mulching and Striga infestation on sorghum chlorophyll content, Striga attachments, sorghum height, and yield. The 2 × 2 × 10 factorial experiment was replicated three times for two seasons. The pot experiment was laid out as a completely randomised design. The first factor was mulching at 0 and 3 tons/ha. The second factor was infestation at two levels: infested and uninfested while the third factor was sorghum varieties at 10 levels. Data collected was plant height, chlorophyll content, Striga counts and sorghum yield. Results indicated that mulching increased chlorophyll content in the second season and not first. Infestation reduced chlorophyll content in both seasons. For the second season, mulching increased chlorophyll content in all genotypes except Ruzangwaya, Mukadziusaende and SC Sila. The genotypes Mukadziusaende, Chiredhi and Hlubi were able to maintain height despite infestation by Striga. Generally yield was higher in uninfested pots across all varieties except Mukadziusaende for the first season. Sorghum arundinaceum was highly susceptible to Striga and hence cannot be a source of resistant traits for Sorghum bicolour breeding. Mulching in Striga infested plants increased plant height and chlorophyll content. Mulching tended to diminish the pathological effects of the Striga parasite in some varieties. Therefore, mulching negated the effect of Striga parasitism and resulted in yield maintenance in some genotypes and hence can be taken up by farmers in Striga infested areas as a beneficial cultural practice

Dry Matter Yield Stability Analysis of Maize Genotypes Grown in Al Toxic and Optimum Controlled Environments

Breeding for Al tolerance is the most sustainable strategy to reduce yield losses caused by Al toxicity in plants. The use of rapid, cheap and reliable testing methods and environments enables breeders to make quick selection decisions. The objectives of this study were to (i) identify high dry matter yielding and stable quality protein maize (QPM) lines grown under Al toxic and optimum conditions and (ii) compare the discriminating power of laboratory- and greenhouse-based testing environments. A total of 75 tropical QPM inbred lines were tested at seedling stage for dry matter yield and stability under optimum and Al toxic growing conditions across six laboratory- and greenhouse-based environments. The nutrient solution method was used for the laboratory trials, while the soil bioassay method was used for the greenhouse trials. A yield loss of 55% due to Al toxicity was observed, confirming the adverse effects of Al toxicity on maize productivity. The ANOVA revealed the presence of genetic variation among the set of genotypes used in this study, which can be exploited through plant breeding. Seventeen stable and high-yielding lines were identified and recommended. Greenhouse-based environments were more discriminating than laboratory environments. Therefore, we concluded that greenhouse environments are more informative than laboratory environments when testing genotypes for Al tolerance