Discrimination of citrus tristeza virus (CTV) strains using Mexican lime/citrange Troyer combinations (Citrus poncirus/Citrus trifoliata x Poncirus sinensis)

Two strains of citrus tristeza virus (CTV) were studied for six years in Yaounde in the forest zone of Cameroon. These strains, SNCL2 and SNCL4, were characterized on Lisbon lemon in Nyombe in thelittoral zone of Cameroon. They were inoculated onto combinations of Mexican lime/citrange Troyer. The virulent strain SNCL2 induced a lower lateral growth of the trunk of stocks and scions of six yearsold combinations. These observations were made three years after inoculation. Tristeza symptoms could not allow for differentiation between the two strains of CTV

Phytiatrie et fonction du phytiatre en phytoprotection

La phytiatrie est une branche de la phytoprotection dont la définition est peu claire, variable et très confuse dans la littérature. Dans cet article dont les données sont issues de sources secondaires, nous essayons de : (1) clarifier la définition des mots phytiatrie et phytiatre ; (2) préciser le contenu d’une formation de base en phytiatrie ; (3) proposer une organisation de la fonction de phytiatre. Le phytiatre (médecin de la plante), s’occupe de la gestion des maladies, des agresseurs et des traumatismes des plantes. La phytiatrie se distingue clairement de la phytopathologie, science qui étudie les maladies des plantes causées par les microorganismes et les facteurs environnementaux. Le phytiatre a des connaissances en phytopharmacie, mais n’est pas un phytopharmacien. Le diplômé en phytiatrie doit être capable d’analyser et de comprendre les exigences de la phytoprotection afin de développer et de proposer des solutions adéquates, dans un contexte de protection de l’environnement. Le grade de phytiatre devrait être réservé aux ingénieurs en phytiatrie, aux titulaires d’un Master ou d'un Doctorat / Ph.D en phytiatrie. Une meilleure structuration des formations en phytiatrie et de la fonction de phytiatre, peut contribuer à une meilleure prise en charge des affections des plantes dans les systèmes de production en Afrique. English title: Phytiatrics and function of the phytiatrist in plant protection Abstract Phytiatrics is a branch of Phytoprotection whose definition is unclear, variable and very confused in the literature. In this article, whose data come from secondary sources, we try to: (1) clarify the definition of phytiatrics and phytiatrist; (2) specify the content of basic training in phytiatrics; (3) propose an organization of the function of phytiatrist. The phytiatrist (plant medical doctor) deals with the management of plant diseases, pests and trauma. Phytiatrics is clearly distinguished from phytopathology which is the science that studies plant diseases caused by microorganisms and environmental factors. The phytiatrist has knowledge in phytopharmacy, but is not a phytopharmacist. The graduate in phytiatrics must be able to analyze and understand the requirements of phytoprotection in order to develop and propose adequate solutions, in a context of environmental protection. The rank of phytiatrist should be reserved for engineers in phytiatrics, holders of a Master’s degree or a doctorate in phytiatrics. A better structuring of training in phytiatrics and the function of phytiatrist can contribute to better management of plant ailments in plant production systems in Africa. Keywords: plant, disease, aggressors, training, phytiatrist

Farmers’ perceptions of practices and constraints in cassava (Manihot esculenta Crantz) chips production in rural Cameroon

A survey aimed at collecting information on practices and constraints in the production of cassava (Manihot esculenta Crantz) chips, a transformed cassava product obtained through fermentation anddrying of its fresh roots was carried out in 45 villages located in three geographical regions (Yaoundé, Mbalmayo, and Ebolowa) of the humid forest zone of Cameroon. A structured questionnaire to interviewfarmers was employed. Out of 225 farmers sampled, 212 (94%) relying on chips as food and source of income were women. Overall, 51% of all farmers marketed chips locally. Three distinct forms of chipssuch as broken pulp (62%), balls (25%), and pellets (13%) were cited as being locally produced by farmers. These were obtained either through air fermentation (cassava pellets), or submergedfermentation (broken pulps and balls), using starters or fermenting agents (31% of responses) or without using them (69%). Chips were mainly home-stored in jute and or/plastic bags (43% ofresponses), open or closed containers (36%), or on devices hanging over the fireplace (21% of responses) for as long as 180 days. Dark spots or discolouration occurring as a result of chips damagewere reported by the majority of respondents (82%) as frequent on cassava chips. These were related to insufficient drying (42%), the use of infected cassava roots by plant pathogenic microbes from thefields (12%), or too long drying of chips under sun light (11% of responses). To avoid dark spots and/or discolouration, 112 farmers out of a total of 185 who were aware about chips damage, practiced sundrying, and 21% of this total dried their chips over the fireplace to control chips damage. Pests and diseases problems (47% of responses), mainly related to the incidence of Stictococcus vayssiereiRichard (Homoptera: Stictococcidae) and lack of market (26%) were cited by farmers as the most important constraints in cassava chips production. From the results obtained, this study outlined thatthe potential utilization of cassava and its derived products for industrial purposes is not yet exploited in the locations investigated. Additionally, the study also raised concerns about the safety and hygiene associated with traditionally processed and stored cassava chips in the investigated areas

Postharvest Adaptation Strategies to the Effects of Temperature Variations and Farmer-Miller Practices on the Physical Quality of Rice in Cameroon

In order to develop simple and adaptable measures to reduce the impact of changing climatic con ditions and poor postharvest practices on grain quality, data on temperature and postharvest practices were collected and correlated with physical grain quality parameters for 3 rice devel opment hubs (Ndop, Lagdo and Mbam) in Cameroon. Inter-annual variations in temperature and thermal amplitudes were the highest in Ndop followed by Mbam and the least in Lagdo. When the same rice variety was grown in the hubs and milled with a laboratory hand dehusker, the mean chalky score was highest in Ndop (18%) and least in Mbam (11%). In addition, Ndop recorded higher grain fissures and broken fractions compared to Mbam or Lagdo. Positive correlations were observed between thermal amplitudes, grain fissures and the proportion of broken fractions. However, rice milled using commercial mills located in the hubs recorded the highest broken frac tions in Mbam (54% - 63%), followed by Lagdo (43% - 52%) and the least in Ndop (35% - 38%). The type of mills in the hubs was responsible for these differences as Mbam had only Engelberg types mills that recorded higher broken fractions than in Ndop where only rubber roll mills were present (P < 0.05). Lagdo had a mixture of Engelberg and rubber roll mills and recorded interme diate broken fractions. Proper parboiling, recovery and processing of poorly filled and immature grains during parboiling and processing of low-grade and fine broken rice into product generally accepted by the local population were demonstrated as simple adaptation strategies to mitigatethe adverse effects of changing climatic conditions and poor postharvest practices on the physical quality of rice especially in sub-Saharan African countries

Aqueous extracts effects of seeds of Thevetia peruviana and Azadirachta indica on the development of Phytophthora megakarya in locality of Biakoa (Cameroon)

Objective: The objective of this work was to evaluate, the impact of aqueous extracts of seeds of “yellow oleander” Thevetia peruviana (AETP), Azadirachta indica (AEAI) “neem” and Ridomil Gold Plus 66WP in black pod disease in Cameroon during two consecutive years.Methodology and results: A completely randomize bloc device containing four treatments (control, AETP, AEAI and RidomilR and three replications was used in the farm. Extracts were applied twice in a month at the dose of 16.67 g/l while RidomilR was applied one time a month at the dose of 3.33 g/l to the heights H1 and H2. Disease distribution across various pod distribution development stages showed that mature pods were the most susceptible to P. megakarya. A significantly difference is observed between the different treatments on all parameters evaluated. The disease rates were 7.92 %, 5.38 %, 8.94 % and 36.24 % in the plots treated with fungicide, AETP, AEAI and untreated respectively, in 2013, and 10.95 %, 7.85 %, 16.21 % and 37.83 % in the same plots in 2014. The major results obtained compared to the rate of rot showed that AETP was more efficient than RidomilR and AEAI during these campaigns.Conclusion and application of results: This study showed that aqueous extracts are promising and could be an effective and cheap formulation for the biological control of black pod disease. They have to be applied twice in a month at the dose of 16.67 g/l.Keywords: Black pod disease, biological control, plants extracts, RidomilR, neem, yellow oleander

Résistance à la mosaïque virale de Manihot glaziovii par greffage sur M. Esculenta

Resistance to Mosaic Disease of M. glaviozii by Grafting on M. Esculenta. African cassava mosaic virus (ACMV) is an epidemic disease that causes great yield losses (&gt; 50%). The grafting in the field of M. glaziovii on 3 cultivars of M. esculenta (Alot- Bikon, IITA 8034 and IITA 8061), permitted to evaluate the number of leaves per plant and the evolution of ACMV four times at one month intervals starting from 30 days after planting and the tuber yield, which was determined after 11 months. Crown grafting was realised 100 days after cuttings were planted. Controls consisted of ungrafted plants of each cultivar. After four months development, average number of leaves on the scion and controls varied from 41.3-50.0 and 24.2-45.3 leaves per plant respectively, showing a significant difference (P&lt; 0.05) between grafted plants and controls. ACMV severity (expressed as %: cf. Material and methods) on controls was 54.3 ± 1.4, 51.6 ± 1.4 and 24.1 ± 0.9%, respectively for Alot-Bikon, IITA 8034 and IITA 8061. Meanwhile on grafted treatments, the severity was 9.4 ± 0.6; 7.8 ± 0.6 and 3.1 ± 0.6%, respectively. The use of M. glaziovii as scion led to about 85% reduction of viral infection. Grafted plants yielded fresh tubers varying from 23.9 ± 1.1 to 51.0 ± 0.9 t/ha contrary to controls for which 16.6 ± 1.1 to 38.1 ± 1.1 t/ha were recorded. The yield of grafted plants significantly increased (Fcal&gt; Flu) by 11.0 t/ha (about 40%), compared to controls

Cyanogenic acid content of cassava (Manihot esculenta Crantz.) leaves and tolerance to anthracnose disease caused by Colletotrichum gloeosporioides

Anthracnose (caused by Colletotrichum gloeosporioides) is a fungal disease which attacks plant stem and leaves and it is expressed by excessive defoliation leading to low yield and even plant death. This study was carried out to determine the relation between cyanogenic (HCN) content of leaves from four cassava (Manihot esculenta) cultivars (one local cultivar: CV1 = LMR; three improved cultivars: CV2 = 92/0326, CV3 = 81/00110, CV4 = W94/009) and their tolerance to anthracnose disease. Disease severity and incidence, HCN content of leaves, percentage of defoliation and inhibitory effect of HCN extract (in vitro) were evaluated. HCN content was determined by titration using a solution of 0.02 N AgNO3. Disease severity was high in cultivars CV1 and CV3 (21.38 and 17.79 % respectively) with low levels of HCN (0.44 and 0.59 mg.g-1 respectively), and low in cultivars CV2 (5.50 %) and CV4 (5.31 %) with high levels of HCN (1.23 and 1.77 mg.g-1 respectively). HCN extracts had inhibited 51.16 % of Colletotrichum gloeosporioides. A direct relation existed between HCN content in cassava leaves and their tolerance to anthracnose disease. The capacity of cassava to synthesize HCN can be used in selection programs to obtain cassava cultivars resistant to anthracnose disease. Keywords: Anthracnose, cassava cultivars, Colletotrichum gloeosporioides, cyanogenic acid, host resistance Cameroon Journal of Experimental Microbiology Vol. 4 (2) 2008: pp. 89-9

Effect of extracts of Thevetia peruviana (Pers.) K.Schum on development of Phytophthora megakarya causal agent of black pod disease of cocoa

Objective: The in vitro and in vivo effects of seed extracts of Thevetia peruviana (Apocynaceae) on the growth and the germination of spores of Phytophthora megakarya causal agent of black pod of cocoa was evaluated. Methodology and results: Five extracts obtained by soxhlet apparatus (extracts of hexane, ethyl acetate, acetone, methanol and aqueous extract) were used. One fungicide (Ridomil ® gold plus) served as control reference. Five strains of P. megakarya (Mbal 121, Ngoke 111, Nom121, Mbal 212, njo111) were tested. Three concentrations of extracts (6.25, 12.5 and 25 =l/ml) and one concentration of fungicide were used in V8 medium. Detached fruit bioassay was performed. Spores of five strains of P. megakarya were inhibited by methanolic and acetonic extracts of T. peruviana with an inhibition percentage ranging from 99-100 %. Thus, the smallest concentration of extract is capable of acting on the germination of spores of the fungi. Only hexane extract did not inhibit the growth of strains. Methanol extract reduced the growth from 60 to 100% at 25 =l/ml. The detached fruits bioassays demonstrated the effectiveness of extracts on plant tissue when inoculated with P. megakarya zoospores. Conclusion and application of findings: Statistical analysis shows that methanol and acetone extracts are as effective as the tested fungicide on the growth and germination of zoospores, aqueous extract are effective as Ridomil ® on growth on the black pod disease of cocoa. These extracts could be used in the integrated pest management strategy of the plant pathogens tested.Keywords. Phytophthora megakarya; Thevetia peruviana; extract; biocontrol; black pod disease

Combined effect of host plant resistance and insecticide application on the development of cowpea viral diseases

Abstract Cowpea [Vigna unguiculata (L) Wap] is an important food crop which is widely grown in the Soudano-sahelian region of Cameroon. An integrated disease control approach involving insecticide treatment and plant host resistance was used to control virus-induced diseases, which are the most cowpea yield-limiting factor in this part of the country. A field experiment was conducted at Guirin-Maroua location in which three cowpea varieties (CRSP, LORI and VYA) that differ in their resistance to cowpea viral diseases were treated with Cyperdim 220 EC insecticide at different doses (1.75, 1.25 and 0.95 l/ha). In this experiment, severity of cowpea viral diseases including SMVD, YMVD, ABMVD and GMVD, were assessed. Population size of thrips (Megalurothrips sjostedti) and larvae of Maruca testuladis, two main vectors of cowpea viral diseases were evaluated. An evaluation of cowpea grain yield was also made. Visual diagnosis which was confirmed by ELISA test showed that only SMVD, YMVD, ABMVD were present during these investigations. Both viral diseases and the population of vectors reduced with combined treatment consisting of the less susceptible cowpea variety VYA and the highest insecticide dose (1.75 l/ha). This treatment combination also produced the highest cowpea grain yield (29.5 t/ha), a yield that was almost 3 times higher than the control (10.2 t/ha). Our results suggest that cowpea viral diseases that prevail in the Soudano-sahelian region of Cameroon are likely to be under control if less susceptible cowpea varieties such as VYA are treated with some insecticides including Cyperdim 220 EC

Effect of Thevetia peruviana seeds extract on in vitro growth of four strains of Phytophthora megakarya

Abstract Recently, a number of researchers have shown interest in finding out the potential of natural substances of plant origin in crop protection. A study was carried out in Yaounde (Cameroon) to test the antifungal activity of extracts of Thevetia peruviana seeds. Crude extracts were obtained after successive maceration with hexane, ethyl acetate and methanol. Seed extracts were tested for inhibition of P. megakarya, a causal agent of black pod disease of Theobroma cacao. Four strains of P. megakarya (BOK 11; BOYO; TA121 and TA123) were used. Antifungal tests were performed by using three concentrations (12.5, 25 and 50 µl ml -1 ) of crude extracts. Seven days after incubation on pea agar medium, the results showed that the use of 50, 25 and 12.5 µl.ml -1 of crude extracts with ethyl acetate resulted in 100, 70 and 50% inhibition rates respectively on P. megakarya. Methanol extract on the BOYO, TA121 and TA123 strains led to total inhibition, while 37.5, 43.2 and 63.9 % inhibition rates were recorded for BOK11 strain at 12.5, 25 and 50 µl.ml -1 concentrations of the extract respectively. These results suggest that crude extracts from T. peruviana seeds are efficient biocide substances with antifungal activity