Differential effect of hot water treatment on whole tubers versus cut setts of yam (Dioscorea spp.)

BACKGROUND: The use of thermotherapy or hot water treatment (HWT) is recommended for the management of plant‐parasitic nematodes and other pathogens for a range of planting material, especially vegetatively propagated crops including yams, Dioscorea spp. The sprouting (germination) and consequent viability of yam following HWT, however, appear to be influenced by the post‐treatment method of planting (whole or cut setts) and cultivar. The present study was established to evaluate the sensitivity of the most popular yam cultivars in Benin and Nigeria, West Africa, to HWT at 50–53 °C for 20 min. RESULTS: Sprouting of both setts and whole tubers of most cultivars was affected by HWT. Across experiments, 47% of HWT material, compared with 61% of non‐HWT material, sprouted over 8 weeks. When cut into setts, 41% of HWT or untreated tubers sprouted, compared with 72% of whole tubers. Whole, untreated tubers had highest sprouting rates (84%), and setts following HWT had the lowest (38%). Yam planting material was also not completely free of parasitic nematodes following HWT. The reaction to HWT or cutting was highly cultivar specific. CONCLUSION: Yam cultivars vary in their sensitivity to hot water therapy. Care is therefore advised in selecting yam cultivars for HWT, especially when using cut setts. Copyright © 2009 Society of Chemical Industry     

Farmers' knowledge and perceptions of termites as pests of yam (Dioscorea spp.) in Central Benin

Destruction of yam (Dioscorea spp.) tubers by termites is a major constraint to yam production in Central Benin. To obtain the basic information for the development of appropriate strategies of termites management in yam, a structured questionnaire was used to interview 142 farmers about their knowledge of termite species of yam, susceptibility of yam landraces, and management practices in 14 villages through the study area. A total of 45 vernaculars names of termites were recorded corresponding to 10 species. All the names given to termite species had a signification, mainly related to morphological aspects, type of damage, and termite caste. Eleven features were used by farmers to identify yam termites. The infestation of yam fields mostly occurred from October to April with Amitermes evuncifer and Trinevitermes oeconomus being the most damaging termite species. Overall, eight factors were identified by farmers as favouring the proliferation of termites in yam fields with drought being the most frequently reported factor. Farmers identified 11 yam landraces that were highly susceptible to termites attack, while 12 yam landraces were listed as resistant. Application of chemicals was the most commonly reported control method, followed by destruction of termite nest, and application of botanical extracts. According to farmers, the high multiplication rate of termites is the most important constraint in managing the issue of termites in yam.     

Phenotypic and genetic characterization of Erwinia carotovora from mulberry (Morus spp.)

Phenotypic and genetic characteristics of nine bacterial strains isolated from mulberry ( Morus spp.), which were originally described as Erwinia carotovora ssp. carotovora (Ecc), were investigated. Based on the results of biochemical tests, these bacterial strains were divided into two different types, type 1 and type 2. Two strains of type 1 were similar to Ecc, whereas seven strains of type 2 were distinct from Ecc. A polyphasic study that included serological assay, specific PCR assay for E. carotovora ssp. atroseptica (Eca), PCR-RFLP of a pectate lyase ( pel ) gene and RAPD-PCR was performed on the type 2 strains, and the data were compared with those of related E. carotovora subspecies. The results of serological and specific PCR assays for Eca showed that the type 2 strains were distinct from Eca. In RFLP analysis of the pel gene using Sau 3AI, the type 2 strains showed a unique RFLP pattern. On the basis of RAPD analysis, similarity of RAPD patterns within the type 2 strains was very high. A unique RAPD fragment was isolated from the type 2 strains and used as a probe for Southern hybridization. This probe hybridized only with PCR products from the type 2 strains. Based on phenotypic, serological and genetic characteristics, the type 2 strains isolated from mulberry may belong to a distinct E. carotovora subspecies other than Eca or Ecc.     

山西省窖藏薯类块茎中2种短体线虫的种类鉴定

本文采用传统形态学与分子生物学相结合的方法,对采自山西省窖藏马铃薯和薯蓣块茎中的短体线虫进行了种类鉴定.结果 表明,从马铃薯块茎中分离出的短体线虫形态学特征与斯克里布纳短体线虫Pratylenchus scrib-neri一致,其SSU序列与P.scribneri美国群体相似性达99.8％.从薯蓣块茎中分离出的短体线虫...     

Distribution and genetic diversity of root‐knot nematodes (Meloidogyne spp.) in potatoes from South Africa

A molecular‐based assay was employed to analyse and accurately identify various root‐knot nematodes (Meloidogyne spp.) parasitizing potatoes (Solanum tuberosum) in South Africa. Using the intergenic region (IGS) and the 28S D2–D3 expansion segments within the ribosomal DNA (rDNA), together with the region between the cytochrome oxidase subunit II (COII) and the 16S rRNA gene of the mtDNA, 78 composite potato tubers collected from seven major potato growing provinces were analysed and all Meloidogyne species present were identified. During this study, M. incognita, M. arenaria, M. javanica, M. hapla, M. chitwoodi and M. enterolobii were identified. The three tropical species M. javanica, M. incognita and M. arenaria were identified as the most prevalent species, occurring in almost every region sampled. Meloidogyne hapla and M. enterolobii occurred in Mpumalanga and KwaZulu‐Natal, respectively, while M. chitwoodi was isolated from two growers located within the Free State. Results presented here form part of the first comprehensive surveillance study of root‐knot nematodes to be carried out on potatoes in South Africa using a molecular‐based approach. The three genes were able to distinguish various Meloidogyne populations from one another, providing a reliable and robust method for future use in diagnostics within the potato industry for these phytoparasites.     

Characterization and pathogenicity of Colletotrichum species associated with anthracnose on chilli (Capsicum spp.) in Thailand

Fungal isolates from chilli ( Capsicum spp.) fruits in Thailand that showed typical anthracnose symptoms were identified as Colletotrichum acutatum , C . capsici and C . gloeosporioides . Phylogenetic analyses from DNA sequence data of ITS rDNA and β-tubulin ( tub 2) gene regions revealed three major clusters representing these three species. Among the morphological characters examined, colony growth rate and conidium shape in culture were directly correlated with the phylogenetic groupings. Comparison with isolates of C . gloeosporioides from mango and C . acutatum from strawberry showed that host was not important for phylogenetic grouping. Pathogenicity tests validated that all three species isolated from chilli were causal agents for chilli anthracnose when inoculated onto fruits of the susceptible Thai elite cultivar Capsicum annuum cv. Bangchang. Cross-infection potential was shown by C . acutatum isolates originating from strawberry, which produced anthracnose on Bangchang. Interestingly, only C . acutatum isolates from chilli were able to infect and produce anthracnose on PBC 932, a resistant genotype of Capsicum chinense . This result has important implications for Thai chilli breeding programmes in which PBC 932 is being hybridized with Bangchang to incorporate anthracnose resistance into chilli cultivars.     

Variability in reproductive fitness and virulence of four Radopholus similis nematode populations associated with plantains and banana (Musa spp.) in Uganda

Burrowing nematodes (Radopholus similis) are among the most serious nematode pests affecting banana and plantain (Musa spp.). In Uganda, bananas, which are known locally as “matooke”, are the main staple. Radopholus similis populations collected in four banana-growing locations (Namulonge, Mbarara, Ikulwe and Mukono) were cultured monoxenically on carrot discs, and we compared the variability in reproductive fitness and virulence (as a function of time and inoculum level) of different populations of R. similis from Uganda. Their level of pathogenicity was determined by assessing the nematode reproductive ratio; that is, final population divided by the initial population. These in vitro experiments showed that the R. similis population from Mbarara had the highest reproduction ratio, while the population from Mukono had the lowest reproduction ratio. This assessment along with pathogenicity experiments on host Musa plants provides a means for defining pathogenicity groups among R. similis populations.     

Sensitivity of Colletotrichum gloeosporioides species complex (CGSC) isolated from strawberry in Taiwan to benzimidazole and strobilurin

Colletotrichum gloeosporioides species complex (CGSC) is the major pathogen causing strawberry anthracnose in Taiwan. Benzimidazoles and strobilurins are common fungicides used to control strawberry anthracnose. A total of 108 CGSC isolates were collected from five major strawberry-producing areas in Taiwan. The half-maximal effective concentration (EC₅₀) values of most CGSC isolates for benomyl (59 isolates), carbendazim (70 isolates), and thiabendazole (63 isolates) were higher than 500 µg a.i./mL. Strobilurin tests showed that the EC₅₀ values of most CGSC isolates for azoxystrobin (66 isolates), kresoxim-methyl (42 isolates), and trifloxystrobin (56 isolates) were higher than 500 µg a.i./mL. However, most CGSC isolates were sensitive to pyraclostrobin at 100 µg a.i./mL. Fungicide tests indicated that CGSC isolates show multi-resistance to benzimidazoles and strobilurins. Benzimidazole-resistant isolates were associated with a point mutation in codon 198 of the β-tubulin gene, and strobilurin-resistant isolates did not correspond with mutation in the cyt b gene or alternative oxidase activity.     

Characterization of the cytochrome b (cyt b) gene from Monilinia species causing brown rot of stone and pome fruit and its significance in the development of QoI resistance

BACKGROUND: Quinone outside inhibitor (QoI) resistance as a consequence of point mutations in the cytochrome b (cyt b) gene has been reported in numerous plant pathogenic fungi. To examine the potential for QoI resistance development in those Monilinia species causing brown rot of stone and pome fruits [Monilinia fructicola (G Winter) Honey, M. laxa (Aderhold & Ruhland) Honey and M. fructigena (Aderhold & Ruhland) Honey], an examination was made of the sequence and exon/intron structure of their cyt b genes for the presence of any point mutations and/or introns commonly associated with resistance to QoIs in fungal plant pathogens. RESULTS: None of the point mutations typically linked to QoI resistance was present in any of the Monilinia isolates examined. Furthermore, the cyt b genes from M. fructicola and M. laxa, but not M. fructigena, possessed a group‐I‐like intron directly after codon 143. Based on the results obtained, a simple PCR assay using a single primer pair was developed, allowing discrimination between the three Monilinia species without the need for culturing. CONCLUSIONS: Results suggest that resistance to QoI fungicides based on the G143A mutation is not likely to occur in M. fructicola or M. laxa. Conversely, M. fructigena may be at higher risk for developing QoI resistance owing to the absence of a G143‐associated intron. Copyright © 2010 Society of Chemical Industry