Julia Sibiya

Farmers' knowledge of cassava brown streak disease and its management in Malawi

ABSTRACT There is little information on farmers’ knowledge about cassava (Manihot esculenta Crantz) brown streak disease (CBSD), despite extensive studies on incidences and severities. The objective of this study was to assess farmers’ knowledge of CBSD diagnosis and management. The study was conducted in three districts of Malawi by administering semi-structured interviews in combination with disease incidence and severity surveys. Farmers’ knowledge of disease diagnosis and management was associated with CBSD incidence and severity. High levels of knowledge about CBSD were observed in areas with high disease incidence. Only 10.1% of the farmers were capable of identifying the foliar symptoms of the disease. On average, 75.0% and 71.7% of the farms had leaf and storage root incidences, respectively. At harvest, 88.3% of the farmers’ fields exhibited storage root necrosis. CBSD leaf and storage root severities differed significantly (P < 0.001) from one district to the other and between varieties. Most farmers were found to lack a source of clean planting material. High needs for extension services on cassava cultivation methods and pest management were identified, but few farmers received such services. The lack of new improved varieties was reported as the most important constraint of cassava production, beyond CBSD. Education of farmers on the efficient management of this viral disease through selection of clean planting material should be provided. Additionally, the development of early root bulking cultivars as a long-term solution in avoiding CBSD impact should be supported.

Screening of Tanzanian sweet potato germplasm for yield and related traits and resistance to sweet potato virus disease

Sweet potato (Ipomoea batatas [L.] Lam) is a versatile crop globally serving as food, feed and raw material for industries. Designed selection for higher yields and related traits is crucial to identify complementary sweet potato clones for breeding. The objective of this study was to determine phenotypic variation among diverse sweet potato collections with regard to yield, dry matter content (DMC) and sweet potato virus disease (SPVD) resistance and to identify suitable clones for breeding. A total of 144 sweet potato genotypes were evaluated at 2 sites in Tanzania using a 12 × 12 simple lattice design. Data collected included 10 quantitative and 17 qualitative agro-morphological traits and virus reaction. Results indicated differences among genotypes for most traits studied. The mean DMC was 36% with clones Zapallo and Ukerewe exhibiting the lowest and highest values of 29% and 45%, respectively. The mean storage root yield of clones was 5.1 t/ha with genotype Jewel expressing the highest yield of 11.3 t/ha. Genotypes Resisto and Mataya were early flowering at 40 and 50 days, respectively, while Ex-Mwanza and Kandoro did not flower at all. Fifty-eight per cent of the genotypes showed resistant reaction to SPVD, while 31% and 11% were moderately susceptible and susceptible to the disease, respectively. A positive correlation was observed for the number of roots and fresh root yield. Seven clones including Simama, Ukerewe, Mataya, Resisto, 03–03, Ex-Msimbi-1 and Gairo were selected for high storage root yield and related traits or SPVD resistance. The selected genotypes are recommended as potential parents for sweet potato breeding.

Smallholder farmers' perceptions of maize diseases, pests, and other production constraints, their implications for maize breeding and evaluation of local maize cultivars in KwaZulu-Natal, South Africa

Diseases and pests are among the major constraints limiting maize productivity in the smallholder (SH) farming sector of sub-Saharan Africa. The objectives of this study were therefore, to determine how SH farmers perceive and cope with diseases and pests, identify with farmersother constraints to maize production. Data were collected from three villages of KwaZulu-Natal (KZN) province in South Africa using surveys and participatory rural appraisal (PRA) methodology. Local maize varieties were further evaluated for disease resistance and grain yield potential at two locations in KZN. Cob rots, grey leaf spot (GLS), maize streak virus (MSV), northern leaf blight (NLB), phaeosphaeria leaf spot (PLS) and common rust were the main diseases identified by farmers, but their incidence was low and occurrence infrequent. More than 75% of the farmers did not control both insect pests and diseases, while the rest used chemicals or everyday household remedies for control. Stalk borers and cutworms were the most prevalent insect pests, where as drought, excessive rains, hail storms, and soil fertility were the most important abiotic constraints identified. Field trial results of local varieties indicated high yield potential and genetic variability for disease resistance to PLS, GLS, and NLB. These findings suggest that; if the main production constraints are addressed, farmers could realize high yields from their local varieties. Breeding opportunities, therefore, exist for incorporating resistance or tolerance to these stresses into the local varieties.

Phenotypic characterisation of potato (Solanum tuberosum) genotypes in Uganda

Identification of genetic variation and interrelationships among germplasm collections is essential for parental selection and trait identification among parents for use in breeding programmes. The aim of this study was to characterise 48 potato genotypes to identify suitable parents for crop improvement purposes. Genotypes were evaluated in the field using an alpha lattice design with three replications at the Kachwekano and Karengyere research stations in Uganda. Site had significant effects on genotype performance for all measured parameters. Genotypic effects were significant (p < 0.01) for total tuber yield, main stem number and plant height. The mean tuber yield for the two sites was 29.8 t ha−1 and tuber yield was higher in Kachwekano than Karengyere. The highest-yielding genotype in Kachwekano was 396038.105 (54.5 t ha−1) and in Karengyere was NAKPOT5 (50.9 t ha−1). Significant positive correlations (p ≤ 0.001) were observed between tuber yield and plant height; duration of flowering, and days to flowering and plant height. The most stable genotypes with regard to tuber yield were Rutuku, 395112.32, 395017.14 and 393220.54. Cluster analysis revealed three principal clusters with nine subclusters. Variation for the different traits exhibited by genotypes in this study should be exploited in crop improvement programmes.

Genetic variability of faba bean genotypes for chocolate spot (Botrytis fabae) resistance and yield

Faba bean (Vicia faba L.) has high utility as a food and soil fertility improving crop. One of the major fungal pathogens of faba bean is Botrytis fabae, the causative agent of chocolate spot. The disease affects significantly the leaf, stem, pod and seed of faba bean compromise its productivity in the smallholder farming sector. Nonetheless, there are limited resistant/tolerant faba bean varieties available and disease control technology options. Therefore, it was prudent to evaluate faba bean landraces for chocolate spot resistance. Fifty landraces together with ten improved varieties were evaluated both in the field and in the greenhouse under natural and artificial inoculation with previously selected aggressive Botrytis fabae isolate (Iso-016) from West Gojjam, in Ethiopia. There were highly significant differences (p < 0.001) among the landraces for reaction to the disease and agronomic traits. Significant positive correlation was recorded between reaction of genotypes in the field and greenhouse disease data. The overall mean disease epidemics varied from 92.5 to 697.5 for the area under disease progress curve (AUDPC). The highest level of resistance was found in the ICARDA lines, ILB-4726, ILB-938 and BPL-710. Of all 18 landrace collections displayed significantly lower disease reaction than the susceptible check. However the resistance was moderate. The selected eighteen landraces will be recommended for use in breeding for chocolate resistance. Overall, resistance was highly heritable, suggesting that phenotypic selection can be exploited to improve chocolate spot resistance in faba bean varieties.

Assessment of sweetpotato farming systems, production constraints and breeding priorities in eastern Tanzania

Sweetpotato is an important food security crop in Tanzania. The crop is grown under diverse farming systems with very low yields. The objective of this study was to assess the present sweetpotato farming systems, farmers’ preferences, production constraints and breeding priorities in eastern Tanzania. Participatory rural appraisal was conducted in the Gairo, Kilosa and Kilombero districts of the Morogoro region and Mkuranga district of the Coast region of Tanzania. Primary and secondary data were collected using semi-structured interviews, focus group discussions and field observations. The study showed that more than 94% of the respondents depended on farming for their livelihoods. Main sweetpotato production constraints were Sweetpotato virus disease (SPVD) and pests, drought, unavailability of markets and lack of transport, low prices, inadequate extension services and postharvest losses. Preferred sweetpotato attributes included high yield, high dry matter content, tolerance to diseases and early maturity. Farmers expressed their persuasive needs towards improved extension service delivery, SPVD-tolerant cultivars, and reliable and coordinated market systems for sweetpotatoes.

Assessment of genetic diversity of rice based on SNP markers for selection of parents for sheath rot (Sarocladium oryzae) resistance breeding

Sheath rot of rice, caused by Sarocladium oryzae, is an important emerging rice disease not only in Rwanda, but also in other rice-growing countries. Given that cultivar resistance is a sustainable management strategy for small-scale farmers, the aim of this study was to identify genetically distant parental materials for sheath rot resistance breeding. Ten resistant and fifteen susceptible accessions were analysed using 94 single nucleotide polymorphism (SNP) markers. The number of alleles amplified per locus ranged from 1 to 4 with a mean of 2.01 and a total of 189 alleles detected from the 25 genotypes. The number of observations per marker locus ranged from 11 to 25 with an average of 23. The mean major allele frequency was 76.2%, whereas the mean polymorphic information content was 0.263, and gene diversity was estimated at 0.325. Consequently, the markers were highly informative and revealed good estimates of genetic diversity among the studied accessions. Genetic distances ranged from 0 to 0.63 and a UPGMA dendrogram distinguished resistant and susceptible genotypes. This study revealed the possibility of improving resistance to sheath rot with minimum risk of genetic depression or reduced variability among progenies through hybridisation of locally adapted germplasm.

Agronomic Performance and Economics of Yield Loss Associated With Angular Leaf Spot Disease of Common Bean in the Southern Highlands of Tanzania

Angular leaf spot (ALS) caused by Pseudocercospora griseola is among the devastating diseases of common bean (Phaseolus vulgaris L.) in the Southern Highlands of Tanzania (SHT). This study was conducted to assess the agronomic performance and economics of yield loss associated with the disease on five bean cultivars that are widely grown by farmers. The cultivars were evaluated in a split plot design with a randomized complete block arrangement during 2012/2013 and 2013/2014. The main plots were two rates of fungicide and a control whereas the subplots consisted of cultivars. Data were collected on disease severity, yield, and yield components. Analysis of variance was done and marginal rate of returns determined using partial budget. Results indicated significant decrease in yields, number of pods, seeds, and seed weight at P < 0.05 for untreated plots. Decreases in yield were associated with ALS disease severity that in turn was influenced by cultivar and rate of fungicide used. Higher grain yield losses of as much as 61% and the lowest marginal rate of returns were recorded for unsprayed plots during heavy rains. Fungicide usage at the recommended rates should be considered during heavy rains and breeding for resistance should be taken as an economical and sustainable strategy for managing the disease.

Diversity analysis and genome-wide association studies of grain shape and eating quality traits in rice (Oryza sativa L.) using DArT markers

Microarray-based markers such as Diversity Arrays Technology (DArT) have become the genetic markers of choice for construction of high-density maps, quantitative trait loci (QTL) mapping and genetic diversity analysis based on their efficiency and low cost. More recently, the DArT technology was further developed in combination with high-throughput next-generation sequencing (NGS) technologies to generate the DArTseq platform representing a new sequencing tool of complexity-reduced representations. In this study, we used DArTseq markers to investigate genetic diversity and genome-wide association studies (GWAS) of grain quality traits in rice (Oryza sativa L.). The study was performed using 59 rice genotypes with 525 SNPs derived from DArTseq platform. Population structure analysis revealed only two distinct genetic clusters where genotypes were grouped based on environmental adaptation and pedigree information. Analysis of molecular variance indicated a low degree of differentiation among populations suggesting the need for broadening the genetic base of the current germplasm collection. GWAS revealed 22 significant associations between DArTseq-derived SNP markers and rice grain quality traits in the test genotypes. In general, 2 of the 22 significant associations were in chromosomal regions where the QTLs associated with the given traits had previously been reported, the other 20 significant SNP marker loci were indicative of the likelihood discovery of novel alleles associated with rice grain quality traits. DArTseq-derived SNP markers that include SNP12_100006178, SNP13_3052560 and SNP14_3057360 individually co-localised with two functional gene groups that were associated with QTLs for grain width and grain length to width ratio on chromosome 3, indicating trait dependency or pleiotropic-effect loci. This study demonstrated that DArTseq markers were useful genomic resources for genome-wide association studies of rice grain quality traits to accelerate varietal development and release.

Development of sequence-based markers for seed protein content in pigeonpea

Pigeonpea is an important source of dietary protein to over a billion people globally, but genetic enhancement of seed protein content (SPC) in the crop has received limited attention for a long time. Use of genomics-assisted breeding would facilitate accelerating genetic gain for SPC. However, neither genetic markers nor genes associated with this important trait have been identified in this crop. Therefore, the present study exploited whole genome re-sequencing (WGRS) data of four pigeonpea genotypes (~ 12X coverage) to identify sequence-based markers and associated candidate genes for SPC. By combining a common variant filtering strategy on available WGRS data with knowledge of gene functions in relation to SPC, 108 sequence variants from 57 genes were identified. These genes were assigned to 19 GO molecular function categories with 56% belonging to only two categories. Furthermore, Sanger sequencing confirmed presence of 75.4% of the variants in 37 genes. Out of 30 sequence variants converted into CAPS/dCAPS markers, 17 showed high level of polymorphism between low and high SPC genotypes. Assay of 16 of the polymorphic CAPS/dCAPS markers on an F2 population of the cross ICP 5529 (high SPC) × ICP 11605 (low SPC), resulted in four of the CAPS/dCAPS markers significantly (P < 0.05) co-segregated with SPC. In summary, four markers derived from mutations in four genes will be useful for enhancing/regulating SPC in pigeonpea crop improvement programs.