Efficacy of chemotherapy and thermotherapy in elimination of east African cassava mosaic virus from Tanzanian cassava landrace

Cassava mosaic disease is caused by cassava mosaic begomoviruses (CMBs) and can result in crop losses up to 100% in cassava (Manihot esculenta) in Tanzania. We investigated the efficacy of chemotherapy and thermotherapy for elimination of East African cassava mosaic virus (EACMV) of Tanzanian cassava. In vitro plantlets from EACMV‐infected plants obtained from coastal Tanzania were established in the greenhouse. Leaves were sampled from the plants and tested to confirm the presence of EACMV. Plantlets of plants positive for EACMV were initiated in Murashige and Skoog (MS) medium. On the second subculture, they were subjected into chemical treatment in the medium containing salicylic acid (0, 10, 20, 30 and 40 mg/L) and ribavirin (0, 5, 10, 15 and 20 mg/L). In the second experiment, EACMV‐infected plantlets were subjected to temperatures between 35 and 40°C with 28°C as the control. After 42 days of growth, DNA was extracted from plant leaves and PCR amplification was performed using EACMV specific primers. It was found that plant survival decreased with increasing levels of both salicylic acid and ribavirin concentrations. In general, plants treated with salicylic acid exhibited a lower plant survival % than those treated with ribavirin. However, the percentage of virus‐free plants increased with an increase in the concentration of both ribavirin and salicylic acid. The most effective concentrations were 20 mg/L of ribavirin and 30 mg/L of salicylic acid; these resulted in 85.0% and 88.9% virus‐free plantlets, respectively. With regard to thermotherapy, 35°C resulted in 79.5% virus‐free plantlets compared to 69.5% at 40°C. Based on virus elimination, ribavirin at 20 mg/L, salicylic acid 30 mg/L and thermotherapy at 35°C are recommended for production of EACMV free cassava plantlets from infected cassava landraces

Morphological Characterization And Identification Of Phytophthora Species Causing Citrus Gummosis In Kenya

Frequent outbreaks of citrus gummosis in Kenyan citrus orchards have been reported, yet the identity and distribution of the Phytophthora species causing the disease are unknown. Work was carried out to (i) characterize and identify Phytophthora species associated with citrus gummosis based on cultural and morphological traits and (ii) determine the distribution of these species associated with gummosis in different agroecological zones (AEZ). Some 59 plant and soil samples obtained from symptomatic trees and the rhizosphere were evaluated by direct isolation and baiting, respectively, using Phytophthora semi-selective media. Phytophthora species were identified on the basis of colony morphology, mycelial characteristics, cardinal growth temperatures, morphology and dimensions of sporangia, oogonia and antheridia. For colony morphology and growth temperature studies, a 5 mm diameter mycelial plug of each isolate was transferred to amended cornmeal agar (ACMA) and incubated at 5, 24 and 35°C for 7 days in the dark. Growth rates were evaluated based on daily records of mycelial growth for 7 days. The occurrence and distribution of these species were determined by recording the number of isolates recovered from samples from each AEZ. P. citrophthora was the most prevalent (76.3 %) of all the Phytophthora species identified in all the AEZs, followed by P. nicotianae (22 %). P. syringae was the least (1.7 %) prevalent. P. citrophthora was the only species present in all AEZs sampled whereas P. nicotianae was confined to the coastal lowlands although also present in other zones in a lower scale. P. syringae was present only in low midland zones and was the only species not found in coastal lowland zones. The forty five isolates of P. citrophthora, thirteen isolates of P. nicotianae and one isolate of P. syringae were tested for virulence on fruits of lemon var. rough lemon. The three most virulent isolates of P. citrophthora, two most virulent isolates of P. nicotianae and the only isolate of P. syringae were selected for pathogenicity testing on lemon seedlings. Based on these studies, it may be concluded that P. citrophthora, P. nicotianae (syn. P. parasitica) and P. syringae are the Phytophthora species associated with citrus gummosis in Kenya. Molecular characterization of the pathogens is recommended to confirm true genetic identity of the species

Storage root yield of sweetpotato as influenced by sweetpotato leaf curl virus and its interaction with sweetpotato feathery mottle virus and sweetpotato chlorotic stunt virus in Kenya.

In this study, the effect of a Kenyan strain of Sweetpotato leaf curl virus (SPLCV) and its interactions with Sweetpotato feathery mottle virus (SPFMV) and Sweetpotato chlorotic stunt virus (SPCSV) on root yield was determined. Trials were performed during two seasons using varieties Kakamega and Ejumula and contrasting in their resistance to sweetpotato virus disease in a randomized complete block design with 16 treatments replicated three times. The treatments included plants graft inoculated with SPLCV, SPFMV, and SPCSV alone and in possible dual or triple combinations. Yield and yield-related parameters were evaluated at harvest. The results showed marked differences in the effect of SPLCV infection on the two varieties. Ejumula, which is highly susceptible to SPFMV and SPCSV, suffered no significant yield loss from SPLCV infection, whereas Kakamega, which is moderately resistant to SPFMV and SPCSV, suffered an average of 47% yield loss from SPLCV, despite only mild symptoms occurring in both varieties. These results highlight the variability in yield response to SPLCV between sweetpotato cultivars as well as a lack of correlation of SPLCV-related symptoms with yield reduction. In addition, they underline the lack of correlation between resistance to the RNA viruses SPCSV and SPFMV and the DNA virus SPLCV

Development of a multiplex PCR technique for simultaneous detection of sweet potato feathery mottle virus and sweet potato chlorotic stunt virus

Virus diseases, especially those caused by mixed infections, are among the economically most devastating diseases of sweet potato. Sweet potato virus disease (SPVD), which is caused by mixed infection of Sweet potato feathery mottle (SPFMV) and Sweet potato chlorotic stunt virus (SPCSV), is the most widespread in East Africa. Lack of rapid and sensitive techniques for detecting the two viruses makes their control almost impossible. In this study, a multiplex polymerase chain reaction (mPCR) protocol was developed and subsequently evaluated for its effectiveness in simultaneous detection of SPFMV and SPCSV using 13 samples. Total RNA extracts were subjected to reverse transcription followed by PCR with two sets of virus-specific primers. DNA bands of 703 and 235 bp were obtained for SPFMV and SPCSV, respectively. No amplification products were obtained from healthy controls. Results obtained from nitrocellulose membrane enzyme-linked immunosorbent assay (NCM-ELISA) confirmed the efficiency of the mPCR protocol. We recommend the developed mPCR technique for routine molecular diagnostic purposes

Survey of sweet potato viruses in Western Kenya and detection of cucumber mosaic virus

Sweet potato is an important food crop worldwide, but several pests and diseases limit its production. In eastern Africa, virus-induced diseases rank second to weevils in causing yield reduction. Symptomatic sweet potato cuttings (327) were collected from Nyanza and Western Provinces in western Kenya in 2009. The samples were tested for Sweet potato feathery mottle virus (SPFMV), Sweet potato chlorotic stunt virus (SPCSV), Sweet potato mild mottle virus (SPMMV), Sweet potato chlorotic fleck virus (SPCFV), Sweet potato latent virus (SPLV), Sweet potato caulimo-like virus (SPCa-LV), Cucumber mosaic virus (CMV), C-6, Sweet potato virus G (SPVG) and Sweet potato mild speckling virus (SPMSV) using nitrocellulose membrane enzyme-linked immunosorbent assay (NCM-ELISA). SPFMV, SPCSV, SPCFV, SPMMV and CMV were detected and 89% of the samples as a whole were found to be infected. SPFMV was detected in all infected samples followed by SPCSV (55%). Multiple infections were detected in the majority of the samples (80%) and the most common dual infection was with SPFMV and SPCSV (52%). The occurrence of CMV was low (5%) but was confirmed by RT-PCR with amplification of a 670 bp coat protein gene fragment from total RNA. This is the first record of CMV in sweet potato in Kenya

Triterpenes from Elaeodendron schweinfurthianum and their Antimicrobial Activities against Crop Pathogens

DOI: 10.5923/j.chemistry.20170703.03Phytochemical evaluation of Elaeodendron schweinfurthianum (Loes) extracts led to the isolation of nine compounds which were identified as 3-oxofriedelane (1), 3α-hydroxyfriedelane (2), 3-oxo-29-hydroxyfriedelane (3), 3-oxofriedelan-28-al (4), α-amyrin (5), α-amyrin acetate (6), β-sitosterol (7), stigmasterol (8) and lanosterol (9). The structures of the compounds were determined using spectroscopic and physical methods as well as by comparison with literature data. The in vitro antimicrobial activities of the extracts and isolates were investigated against fungi and bacteria which infect food crops. All the crude extract inhibited the growth of the tested pathogens with EtOAc and n-hexane extracts being the most active with 11.3 and 7.3 mm diameter zone of inhibition respectively. All the compound showed antimicrobial activity except compounds 3 which did not exhibit any visible activity at concentrations ≤ 200 µg/ml. Finding from this study confirm that plant extracts can provide alternative readily available and environmentally safe antimicrobials for managing crop infections

Evaluating Diversity Among Kenyan Papaya Germplasm Using Simple Sequence Repeat Markers

Papaya is an important fruit crop, produced in Kenya for local consumption and export. Despite a history of varietal introductions, no attempts concerned on developing varieties suited to Kenyan conditions have been documented. The objective of this study was to provide information on the diversity of germplasm available in Kenya, as a precursor to systematic plant breeding program. Forty two papaya accessions were collected from farmers’ fields located in Coast, Rift Valley, Western, Nyanza, Central and Eastern provinces. Genetic diversity was determined using seven simple sequence repeat (SSR) markers, computing allelic richness and frequency, expected heterozygosity and cluster analysis. Results indicated that the markers were highly polymorphic among the accessions, with polymorphic information content (PIC) varying from 0.75 to 0.852 with an average of 0.81. The genetic similarity among the 42 papaya accessions ranged from 0.764 to 0.932 with an average of 0.844 showing that most papaya accessions used in this study were closely related. About 96.9% of the pair-wise comparisons among papaya accessions exhibited genetic similarity greater than 0.802, while less than 4% (3.1%) showed genetic similarity lower than 0.802. The phylogenetic analysis grouped the 42 accessions into two main clusters A and B. Cluster A had four sub-clusters while cluster B had one cluster. Accessions from Coast, and some from Rift Valley Provinces, presented the highest variation, being scattered throughout the tree, with little or no differentiation from most accessions, whereas some accessions from Coast regrouped in clusters A (iv) and B. The genetic differences among the accessions revealed by the formation of distinct clusters suggest significant genetic variability emanation from varying sources of the papaya germplasm in Kenya. Although the level of genetic diversity revealed by SSR markers in this study is sufficient to distinguish between breeding lines for varietal protection, the rather narrow genetic diversity demonstrated indicates the need to introduce new germplasm or use other techniques such as mutation and genetic engineering to provide breeding materials for the future improvement of papaya in Kenya