DSpace Community:

Investigation of grain postharvest technologies and systems for managing climate-related risks in smallholder farms of shire valley, southern Malawi.

2023-12-15T01:19:50Z

Title: Investigation of grain postharvest technologies and systems for managing climate-related risks in smallholder farms of shire valley, southern Malawi. Authors: Singano, Charles Abstract: The world’s climate is changing. Increasing temperatures and incidence of dry spells and droughts are projected to continue into the next century. These factors will negatively affect household (HH) food security, crop production and pest problems, including storage insect pests and the performance of storage technologies. A study to evaluate maize postharvest management options was conducted to help farmers strengthen the climate-resilience of their HH food security strategies. The work began with a survey using structured and semi-structured questionnaires and checklists to learn about the postharvest systems and climate-related experiences of farming HHs in Shire Valley, southern Malawi. The results showed that food insecurity in Shire-Valley was perceived to have increased in the last 10-20 years due to crop failure, and most HHs (~65 %) thought the mean ambient temperature had increased during that period. Many respondents (~42.9 %) reported an increased usage of synthetic pesticides compared to 10-20 years ago due to a perceived increase in insect pest pressure. These findings emphasised the need for urgent implementation of increased awareness-raising and training in improved postharvest management in the face of global-warming. Following the survey, farmer-managed participatory trials were conducted comparing existing and newly-introduced storage technologies over a 32 week period in two consecutive seasons. The seven treatments were Neem leaf powder (NM), Actellic Super dust (ASD), ZeroFly® storage bag (ZFB), Purdue Improved Crop Storage bag (PICS), Super Grain Bag (SGB), metal silo (MS) and untreated grain in a polypropylene bag (PP). The trials showed that the storage technology choice and duration significantly affected the level of insect grain damage and the number of insect pests, and that the level of pest attack can differ significantly between seasons. Hermetic bags (PICS, SGB) kept storage insect infestation low for up to 32 weeks, and were more effective than the ASD, NM, or PP. The study recommended the use of PICS and SGB for long-term grain storage. To examine the effect of higher ambient temperatures on the efficacy of maize grain storage protectants and facilities, two laboratory trials were conducted. Experiment I compared five grain protectants [Actellic Gold dust (AGD), Shumba Super dusts (SSD), Wivokil Super dust (WSD), NM and wood ash (WA)] admixed with maize, while experiment II assessed four facilities (PICS, SGB, MS and PP) using untreated maize. Both experiments ran for 12 weeks using climate chambers set at 32 °C and 38 °C, and mean ambient temperature (26 °C). Significantly higher grain damage and weight loss occurred in the non-synthetic (NM, WA) than synthetic protectants (AGD, SSD, WSD) at all experimental conditions. The hermetic containers (PICS, SGB, MS) kept mean insect grain damage below 6.4% compared to 24.5% in the untreated control at all the experimental conditions. These findings imply that the efficacy of synthetic grain storage protectants and hermetic storage containers may not be negatively affected by warmer temperatures (32 °C or 38 °C). Warehouse receipt systems (WRS) and community grain banks (CGB) are being promoted in SSA to reduce grain storage losses and improve market access and food security. However, no information on their potential as adaptation strategies in climate change (CC) prone areas existed. Interviews with WRS and CGB managers and beneficiaries, and rapid loss assessment methods were used to learn about the systems and analyse grain weight loss during a 24-week period. Grain deposits ranged from 0.1 and 15 mt per depositor, and quantities of maize produced and deposited were correlated. Weight loss of maize and pigeon peas in WRSs were less than 4.6 % and 9 % respectively. In conclusion, food insecurity has increased in Shire Valley, mainly contributed by climate change. The PICS and SGB are recommended for use by farmers for grain storage in Shire Valley including SSA. Results suggest farmers can continue to use SGB, PICS and MS, or AGD, SSD and WSD for stored maize protection as temperatures increase in CC-prone areas. The WRSs and CGBs could act as grain reserves for use during climate-related events and play a role in the distribution of emergency relief food to the affected HHs.

Genetic characterisation of Striga gesnerioides and its control strategies in tobacco (Nicotiana tabacum L).

2023-05-27T01:08:16Z

Title: Genetic characterisation of Striga gesnerioides and its control strategies in tobacco (Nicotiana tabacum L). Authors: Koga, Chapman Abstract: Tobacco (Nicotiana tabacum) is an important contributor to the GDP and export revenue of Zimbabwe. One of the emerging threats to tobacco production is Striga gesnerioides, a root parasitic weed which belongs to the Orobanchaceae family. Striga gesnerioides infection in tobacco can cause up to 100 percent leaf yield loss. The objectives of this study were as follows: first, to determine genetic characterization of S. gesnerioides; second, to determine the impact of trap crops on the S. gesnerioides seed banks and S. gesnerioides emergence; third, to determine tobacco leaf yields in S. gesnerioides environments; and fourth, to evaluate tobacco varieties for the production of strigolactones using S. gesnerioides seed germination percentages and maximum germination distances from tobacco main roots in agar gel assays. For the first objective, specimens of S. gesnerioides plants were collected from parasitized tobacco and other host plants during the 2016/17 and 2017/18 growing seasons in Mvuma, Chegutu, Selous, Norton and Dotito areas in Zimbabwe. The specimens were identified to species level using morphological characters and further characterized using molecular techniques (modified CTAB method). For the second objective, trap cropping treatments were implemented at Mvuma and Chegutu in Zimbabwe in the 2016/17 and 2017/18 cropping seasons. At these sites, cowpea, bambara nut, groundnut, common bean, sunn hemp and tobacco, were grown for two years, and some plots were left to lie fallow for two years, followed by tobacco as a bio-test crop. These treatments were replicated three times in a randomized complete block design in the 2016/17 and 2017/18 cropping seasons. During these periods, the S. gesnerioides seed bank size was estimated after extracting seeds from 200g soil samples at the beginning and end of the field experiment, using the sucrose method. For the third objective, 15 tobacco varieties were grown in experimental plots at Mvuma and Chegutu in the 2016/17 and 2017/18 cropping seasons, with 3 replications for each tobacco variety arranged in a randomized complete block design. For the fourth objective, the agar gel bioassay was used to evaluate 15 tobacco genotypes for the production of strigolactones under laboratory conditions. The 15 tobacco varieties were replicated three times in a randomized complete block design in the laboratory. For the first objective, the DNA from specimens collected from Striga plants infesting tobacco in the three reported areas (Chegutu, Mvuma and Selous) were 100% similar. Parasitic plants collected on Richardia scabra in Dotito and Dalbergia melanoxylon in Mvuma, on the assumption that they were S. gesnerioides races were genetically different from the tobacco Striga and were identified as Sopubia lanata. For the second objective, it was established that growing trap crops for two seasons did not have significant (p>0.05) effects on S. gesnerioides seed banks at both Mvuma and Chegutu sites. However, bambara nut appeared to reduce S. gesnerioides seeds in the soil at both sites. Trap crops had significant effects (p<0.05) on S. gesnerioides counts at Mvuma. It was found that growing bambara nut, common bean, sunn hemp, groundnut and cowpea and letting land lie fallow for two years decreased the emergence of S. gesnerioides at Mvuma. In contrast, growing soyabean and tobacco for two seasons followed by tobacco had the highest number of S. gesnerioides counts at Mvuma. Trap crop effects were not significant (p<0.05) at Chegutu. However, growing soyabean and letting land lie fallow for two seasons had low S. gesnerioides counts, whereas groundnut had the highest S. gesnerioides at Chegutu. For the third objective, the tobacco varieties had no significant (p>0.05) effect on tobacco leaf yield for two seasons at Mvuma. However, tobacco varieties were significantly (p<0.05) different with regard v to leaf yield in the 2017/18 season at Chegutu. KRK66 was the best performing variety in terms of leaf yield at Chegutu in the 2016/17 season. For objective four, the tobacco variety effects were significant (p<0.05) on the S. gesnerioides germination and maximum germination distances. KRK66 and T74 had low S. gesnerioides seed germination percentages and maximum germination distances, whereas KM10, KRK22, KRK26, KRK28, KRK29, KRK60, KRK64, T70, T71, T72, T73, T75 and T76 had high S. gesnerioides seed germination percentages and maximum germination distances. It was concluded that the genetic diversity in S. gesnerioides was low. Trap cropping did not reduce S. gesnerioides seed banks. It was also concluded that bambara nut, common bean, sunn hemp, groundnut, cowpea and letting land lie fallow for two seasons reduced S. generioides infestation in tobacco grown in the third year at Mvuma. However, trap crops had no impact on S. gesnerioides emergence at Chegutu. The tobacco varieties produced similar leaf yields, which were below their potential at Mvuma. KRK66 was the best tobacco variety at Chegutu. It was estimated that S. gesnerioides could have contributed to the tobacco leaf yield loss of about 59.9 and 70 % in the 2016/17 and 2017/18 seasons, respectively at Mvuma. The tobacco leaf yield loss was 53.1 % at Chegutu. Based on the agar gel assay, it was concluded that KRK66 and T74 could have pre-attachment resistance to S. gesnerioides, whereas KM10, KRK22, KRK26, KRK28, KRK29, KRK60, KRK64, T70, T71, T72, T73, T75 and T76 were susceptible to S. gesnerioides infection. Description: Supervisors Prof. U Mazarura (UZ); Dr S. Mabasa (UZ); Dr. D Garwe (TRB)

Combining ability and heterosis of heat and drought stress tolerance in maize (Zea mays L.).

2023-05-27T01:08:22Z

Title: Combining ability and heterosis of heat and drought stress tolerance in maize (Zea mays L.). Authors: Gonhi, Tinovonga Abstract: Drought and heat stress are major abiotic stresses limiting maize production in Zimbabwe and Africa at large causing low yields. In order to bridge on this gap of low yields, within its Stress Tolerant Maize for Africa (STMA) program, CIMMYT-Zimbabwe breeders have resorted to look for other sources of heat and drought tolerance genes from exotic populations. Recently, CIMMYT-Zimbabwe breeders sourced 14 heat and drought inbred line donors from India and these were crossed with seven sub-tropically adapted CIMMYT elite lines, using the North Carolina Design II, during the 2017 winter season and 61 single cross hybrids were developed. These single cross hybrids were evaluated under optimum, high density, random stress, natural heat stress and managed drought conditions using a 0.1 alpha lattice design replicated twice in the 2017-18 summer and winter season. The objectives of this study were (i) to estimate combining ability effects among the drought and heat stress tolerant donors and tropically adapted CIMMYT elite inbred lines and identify the best combinations, (ii) to evaluate genotype x environment interaction (GEI) of the single crosses developed and identify high yielding and stable hybrids across all sites. All the data from each site was analyzed using the REML model in CIMMYT Fieldbook. Across site Analysis was done using Minitab Software and GEI was observed to be significant. Analysis of Genetic Designs in R (AGD-R) was used to analyze the combining ability of the inbred lines used in the single cross formation. For grain yield and other secondary traits evaluated across environments, significant general combining ability (GCA) and specific combining ability (SCA) effects indicated the importance of both additive and non-additive gene effects in the expression of these traits although additive gene effects was more prominent. Additive gene action contributed more to genotypic variation amongst testcrosses or the traits measured as evidenced by the higher mean squares for lines and testers than their interaction. For grain yield, additive gene action due to females had much contribution to the genotypic variation therefore highlighting the importance of maternal effects in the expression of grain yield. The best combination was reviewed as the cross between CML566 and CAL14140 that has the highest specific combining ability (SCA) estimates across all sites. CML566 and CML571 were the best females with highest GCA estimates hence recommended to be used as female testers in producing hybrids that are adapted for both stress and non-stress conditions. CAL1440 and CAL14138 were the best male exotic inbred lines with high GCA estimates. There was significant GEI across all the sites used and it was exploited using iii | P a g e Additive main effect and multiplicative interactions (AMMI) in the Genstat. It reviewed that entry 6 (CML566/CAL14138) was the most high yielding and stable across all sites. It was interesting to find out that best commercial checks were out competed by the best experimental hybrids under stress conditions; this shows the potential ability of the newly developed single hybrids to replace the current checks on the market.

Genomic selection in rubber tree (Hevea brasiliensis) using single nucleotide polymorphisms (SNPS) marker data obtained from genotyping by sequencing (GBS).

2023-05-29T01:08:04Z

Title: Genomic selection in rubber tree (Hevea brasiliensis) using single nucleotide polymorphisms (SNPS) marker data obtained from genotyping by sequencing (GBS). Authors: Munyengwa, Norman Abstract: Genomic selection (GS) in rubber tree (Hevea brasiliensis) has huge potential to meet future demands of rubber in an economically and environmentally sustainable way. In Hevea breeding programmes, genomic selection can be used early in the breeding pipeline to obtain genomic estimated genetic values (GEGVs) for making clonal selections for further large-scale evaluation as potential commercial clonal cultivars. Thus, genomic selection could enhance the efficiency of Hevea breeding significantly through decreasing the generation interval and increasing selection intensity, therefore increasing genetic gains per cycle. Within-family genomic selection for rubber latex yield was performed using two sets of 179 and 125 F1 clones from a cross between RRIM600 and PB260 evaluated in two separate phenotypic trials in Côte d‘Ivoire. The clones were genotyped using the genotyping-by-sequencing (GBS) approach, which resulted in 3,420 SNPs. A genetic linkage map of the rubber clones was constructed using the JoinMap 5.0 software and two marker imputation methods (Beagle 3.3 and random forest algorithm) were used to impute the missing marker data. The ridge regression best linear unbiased prediction (rrBLUP) was used to predict the GEGVs of clones across-sites. In addition, the effect of marker density on genomic selection accuracy was investigated. Furthermore, the GS accuracies obtained were compared to the GS accuracies obtained using SSR markers and the same phenotypic data. The genetic map contained 1,769 SNPs spanning 2600.9 Centimorgans (cM) and with an average of one SNP in every 1.47 cM. The genetic map also encompassed 308 SSR markers which spanned across 18 linkage groups and with a density of one marker in every 8.4 cM. Beagle imputation performed better than random forest imputation (RFI) as it gave a GS accuracy of 0.52, against 0.48 with RFI. Results also showed that GS accuracy increased with an increase in marker density, and a plateau was reached at 1,000 SNPs with Beagle imputed marker data and at 2,000 SNPs with RFI marker data. The mean between site GS accuracy obtained in this research is similar to the one obtained using SSR markers and the same phenotypic data, opening the way to a cost-effective application of GS in rubber. Results of this study demonstrate that GBS is a rapid, efficient and cost-effective approach for implementing genomics-assisted breeding. This research also showed that GS has high potential to increase yield genetic gain in rubber breeding. Key words: genomic selection, genomic estimated genetic values, genotyping-by-sequencing, genetic gain, rubber tree.