A survey of farmers’ perceptions and management strategies of the sweet potato weevil in Homa bay county, Kenya

Sweet potato (Ipomoea batatas L.) is one of the most widely grown root cropsworldwide. In Africa, it is grown in small plots by poorer farmers. Production of thecrop is extremely low in Kenya as compared to other African countries due to theexistence of common insect pests. Sweet potato weevil (Cylas spp.) is known as thebiggest pit fall for production and productivity of the crop in the country. This studysought to determine the opinion of sweet potato farmers concerning sweet potatoresistance to Cylas spp. and determine control strategies employed by sweet potatofarmers in managing the pest. The study also sought to determine the sweet potatoproduction constraints faced by the farmers in Homa Bay County, Kenya. The studywas conducted using a Participatory Rural Appraisal approach in which 269 farmers inthe County were interviewed on the sweet potato varieties with field resistance to Cylasspp., the crops’ production constraints (with emphasis on damage by Cylas spp.) andfarmers’ control strategies in regard to the weevil. Data were also collected from thefarmers whose sample size was determined using the table on sample size selection andstandardization equation. Data were analysed using descriptive statistical techniquesthat were frequencies, percentages and standard errors. The study established thatmajority of the farmers from Rachuonyo (89.7%) and Ndhiwa (91.9%) were not awareof any variety that had field resistance to Cylas spp. However, 10.5% of the farmers inRachuonyo and 8.1% of the farmers in Ndhiwa identified nine varieties which haveshown relative field resistance to root damage by Cylas spp. The varieties that wereidentified to be resistant to Cylas spp. by farmers in Rachuonyo were Kalamb Nyerere,Tombra, Sinia, Odinga, Kemb 10, Wera and Zapallo. However, the varieties that wereidentified to be resistant to Cylas spp. by farmers in Ndhiwa were Amina, Mugandeand Ndege Oyiejo. Further, the findings revealed that Cylas spp. was the mostproblematic pest by 90.3% and 96.8% of households in Rachuonyo and Ndhiwa,respectively. Majority (64.5%) of the farmers in Ndhiwa did not use any methods tomanage Cylas spp. However, farmers in Rachuonyo (26.2%) and Ndhiwa (15.3%)preferred re-ridging during weeding as a management strategy in regard to Cylas spp.These findings reiterate the importance of the sweet potato weevil in rural sweet potatofarming systems and thus innovative management strategies are necessary.Key words: Sweet potato, control strategies, Cylas spp., resistance, pest, variety,constraint

Levels of control of Chilo partellus stem borer in segregating tropical Bt maize populations in Kenya

In Kenya, stem borers destroy an estimated 400,000 metric tons, or 13.5%, of farmers' annual maize harvest costing about US$80 millions. Bacillus thuringiensis (Bt) maize controls stem borers without harming humans, livestock and the environment and was sown to 140m ha-1 globally in 2009. Two public Bt maize lines of cry1Ab::ubi gene (Event 216 and Event 223) were crossed with two non-Bt maize inbred lines, CML144 and CML159. The efficacy in the control of Chilo partellus stem borers in the parents, F1 and F2:3 successive generations were studied in a biosafety level 2 greenhouse. The Btgene effectively reduced stem borer damage with lower values for number of exit holes, tunneling length, proportion of stalk tunneled, number of larvae and number of pupae than the non Bt-maize and the check cultivars. The F1 generations values for all damage parameters studied were comparable to those for the Bt-maize inbred lines as expected. The F2:3 generations showed a spread of damage parameters from resistant to susceptible. These results suggest that the Cry1A(b) genes in the study was inherited following the Mendelian segregation.Key words: Bt maize, Chilo partellus, Bt -endotoxins, biosafety, greenhouse

Analysis of the genetic diversity of selected East African sweet potato (Ipomea batatas [L.] Lam.) accessions using microsatellite markers

Sweet potato (Ipomea batatas [L.] Lam.) is an economically important crop in East Africa chiefly grown by small holder farmers. Sharing of vines for planting is a very common occurrence among these farmers and eventually varieties are given local names, making it hard to trace the original pedigree. It is therefore important to characterise the sweet potato germplasm for purposes of breeding and germplasm conservation. In this study, 68 sweet potato accessions were evaluated for diversity using 12 microsatellite markers. The genetic relationship of the germplasm was evaluated using the Jaccard’s coefficient for dissimilarity analysis, unweighted pair group method with arithmetic means (UPGMA) tree and principal component analysis (PCoA) on DARwin software, while summary statistics was done using PowerMarker and Popgene softwares. The polymorphic information content of the markers ranged from 0.1046 for markers J67b and J67 to 0.3671 for marker J1809a, with a mean value of 0.2723. The total number of alleles amplified was 21. The major allele frequency ranged from 0.5882 for marker JB1809a to 0.9412 for markers J67b and J67c. Cluster analysis divided the accessions into four major clusters. Principle component analysis divided the accession into four groups which were different from those by cluster analysis. This study was able to identify several distinct accessions as well as a few possible duplicate accessions that overlapped on the cluster analysis.Key words: Sweet potato, cluster analysis, genetic diversity, principal component analysis, Simple SequenceRepeats

Effects of biofertilizer containing N-fixer, P and K solubilizers and AM fungi on maize growth: A greenhouse trial.

An in vitro study was undertaken to evaluate the compatibility of indigenous plant growth promoting rhizobacteria (PGPR) with commonly used inorganic and organic sources of fertilizers in tea plantations. The nitrogenous, phosphatic and potash fertilizers used for this study were urea, rock phosphate and muriate of potash, respectively. The organic sources of fertilizers neem cake, composted coir pith and vermicompost were also used. PGPRs such as nitrogen fixer; Azospirillum lipoferum, Phosphate Solubilizing Bacteria (PSB); Pseudomonas putida, Potassium Solubilizing Bacteria (KSB); Burkholderia cepacia and Pseudomonas putida were used for compatibility study. Results were indicated that PGPRs preferred the coir pith and they proved their higher colony establishment in the formulation except Azospirillum spp. that preferred vermicompost for their establishment. The optimum dose of neem cake powder

Inheritance of resistance to fusarium wilt in pigeonpea (Cajanus cajan (L.) Millsp.)

The inheritance of resistance in pigeonpea (Cajanus cajan (L.) Millsp.) to fusarium wilt (Fusarium udum Butler) was studied in crosses between a resistant line ICP 8863 and two susceptible (ICP 2376 and LRG 30) pigeonpea lines. The parents, F1, F2 and backcross populations were screened for resistance to F. udum in a wilt-sick nursery at the ICRISAT Center. Resistance to fusarium wilt is controlled by a single recessive gene, which has been designated as pwr1

Mode of inheritance of common bean (Phaseolus vulgaris L.) traits for tolerance to low soil phosphorus (P)

Low soil phosphorus (P) has been singled out as a major constraint leading to perpetually low bean (Phaseolus vulgaris L.) grain yield far below the expected yield potential. In developing countries beans are mainly produced by small-scale farmers who have little capacity to use inorganic fertilizers to replenish their soils. Yet bean production contributes significantly to their income and provides a cheap source of protein to rural and urban populations. The genetics of inheritance of the traits conferring low soil P tolerance is not well understood. The identification and understanding of the mode of inheritance of the traits for P-efficiency in bean will go along way in boosting bean yields through development of varieties adapted to low soil P. The objective of this study was to determine the inheritance of the traits conferring adaptation to low soil P, for the important large seeded red mottled bean market class. Three parents with known tolerance to low soil P were crossed with five adapted but non-tolerant genotypes in an 8 × 8 half diallel mating scheme. The resulting F1 seeds were evaluated under medium and low soil P conditions at two locations. Both general combining ability (GCA) and specific combining ability (SCA) variances were highly significant (P ? 0.01) for all five characters studied except SCA variance for root dry weight at one location. The magnitude of GCA variance was up to twelve times higher than the SCA variance. The GCA:SCA ratio varied from 0.62 to 0.96 for the characters studied. The additive genetic variance was more important than the dominance variance for tolerance to low soil P

Genetic mapping and legume synteny of aphid resistance in African cowpea (Vigna unguiculata L. Walp.) grown in California

The cowpea aphid Aphis craccivora Koch (CPA) is a destructive insect pest of cowpea, a staple legume crop in Sub-Saharan Africa and other semiarid warm tropics and subtropics. In California, CPA causes damage on all local cultivars from early vegetative to pod development growth stages. Sources of CPA resistance are available in African cowpea germplasm. However, their utilization in breeding is limited by the lack of information on inheritance, genomic location and marker linkage associations of the resistance determinants. In the research reported here, a recombinant inbred line (RIL) population derived from a cross between a susceptible California blackeye cultivar (CB27) and a resistant African breeding line (IT97K-556-6) was genotyped with 1,536 SNP markers. The RILs and parents were phenotyped for CPA resistance using field-based screenings during two main crop seasons in a ‘hotspot’ location for this pest within the primary growing region of the Central Valley of California. One minor and one major quantitative trait locus (QTL) were consistently mapped on linkage groups 1 and 7, respectively, both with favorable alleles contributed from IT97K-556-6. The major QTL appeared dominant based on a validation test in a related F2 population. SNP markers flanking each QTL were positioned in physical contigs carrying genes involved in plant defense based on synteny with related legumes. These markers could be used to introgress resistance alleles from IT97K-556-6 into susceptible local blackeye varieties by backcrossing. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11032-015-0254-0) contains supplementary material, which is available to authorized users