Screen house and field resistance of taro cultivars to taro leaf blight disease (Phytophtora colocasiae)

Article PurchasedIntroduction: Taro leaf blight disease cause by Phytophtora colocasiae has become an economic disease in Cocoyam growing regions of Cameroon. Aims: To screen for resistance 10 improved and 4 local cultivars of taro against taro leaf blight disease. Study Design: A randomized complete block design study. Place of Study: Studies were conducted at the International Institute of Tropical Agriculture (IITA) Yaounde Nkolbisson from July 2013 to January 2014. Methodology: Taro cultivars from tissue culture were planted in the screen house conditions and tested for virulence and pathogenicity with 4 isolates of Phythophthora colocasiae at spore density of 3×104 spores /ml of distilled water. Plants were planted in the field to assess disease incidence and severity. Results: The results obtained on the different taro cultivars, revealed that all the 4 isolates showed variable pathogenicity. They caused lesions on inoculated leaves. There was variability in pathogenicity based on the small lesion lengths produced on cultivars, these included BL/SM132 and Red petiole. Isolate 3 showed a stronger sensitivity to leaf collapse and defoliation irrespective of the cultivar tested. There was a significant difference (p = 0.05) in tissue collapse and leaf defoliation on exposure to the different fungal isolates. The result of field infection rates of P. colocasiae at 126 DAP-154 DAP on 10 improved and 4 local cultivars indicated that there was significant variability (p = 0.05) in incidence and disease severity, with high incidence and severity occurring at 154 DAP in all cultivars. Improved cultivar BL/SM132 showed no classic symptoms of P. colocasiae and therefore it was resistant to Phytophthora colocasiae. Conclusion: The results obtained on virulence and pathogenicity of Phythophthora colocasiae on the different taro cultivars revealed that all the 4 isolates showed variable pathogenicity. They caused lesions, on inoculated leaves. Isolate 3 showed a stronger sensitivity to leaf collapse and defoliation irrespective of the cultivar tested. The result of field infection rates of P. colocasiae at 126 DAP-154 DAP on 10 improved and 4 local cultivars indicated that there was a significant variability (p = 0.05) in disease incidence and severity, with high incidence and severity occurring at 154 DAP in all cultivars. Improved cultivar BL/SM132 showed no classic symptoms of P. colocasiae and therefore it was resistant to Phytophthora colocasiae as compared to all the other cultivars which showed high severity rates of infection of the disease and thus were susceptible to the disease

Impact of fungicide application on taro leaf blight disease in three regions of Cameroon

Open Access JournalThe study was conducted in the research field sites of the Institute of Agricultural Research (IRAD), Bambui, North West Region, (IRAD), Ekona South West Region and the International Institute of Tropical Agriculture (IITA) Nkolbisson, Yaoundé, Center Region of Cameroon. Four cultivars of taro (Dark green petiole with small leaves (L1), Red petiole with small leaves (L2), Light green petiole with large leaves (L3) and Light green petiole with small leaves(L4)) were planted in four seasons, for two years, in the months of March and July 2015, March and July 2016 in all the research farms. Ninety corms of the each cultivar were treated before planting with fungiforce at 0.33% concentration while others were not treated. Fungiforce is a contact and systemic fungicide containing high levels of copper oxide (600 grams) and mild levels of metalaxyl (120 grams), various concentrations of 0.4%, 0.33%, 0.27%, at the onset of the first symptom of leaf blight on the leaves using knapsack sprayer of 15 litres at two weeks interval, while the control experiment consisted of unsprayed taro leaves. Data for the disease incidence of taro leaf blight was recorded from the onset of disease in fields and continued at two weeks interval for 6 weeks. The results of planting taro in four seasons in three experimental field sites revealed that there was a decrease in disease incidence in fields sprayed with fungiforce than in the control field. Plots sprayed with fungicide at different concentrations showed no variation on the 4 cultivars in the different field sites. The disease incidence ranged from 10% to 100% in the 4 seasons, at the three experimental field sites. The variation in disease incidence in the three planting sites is an indication of possible genotypes by environment (GXE) interaction that may have significant influence on the taro leaf blight resistance potential

Clinical studies on seroprevalence of rubella virus in pregnant women of Cameroon regions.

A study was conducted to investigate the seroprevalence of the rubella virus amongst pregnant women and the relationship it has with the duration of pregnancy, premature delivery, and past history of abortion in pregnant women visiting the Yaoundé Gynecological, Obstetric and Pediatric Hospital (HGOPY). 211 pregnant women attending the prenatal consultation of mean age 27±5.99 years were randomly selected and screened for rubella IgG antibodies. 39.3% of them were in their third trimester of pregnancy while 25.6% and 35.1% were in their first and second trimester of pregnancy respectively. 11.73% of the women had a history of premature delivery and 40.3% had a history of at least one abortion. Spearman's correlation was calculated between antibody titre and age. 88.6% of pregnant women were seropositive while 9% (susceptible) were seronagative and 2.4% had equivocal results. The most susceptible women to rubella infection were in the age group 26-30 years while women in the age group 21-25 years band were the most seropositive. There was a strong correlation between the antibody titre and age (r=0.549

Evaluation of the cytotoxic and genotoxic potential of Khat (Catha edulis Forsk) extracts on human T lymphoblastoid cell line

This paper reports on an investigation of the cytotoxic and genotoxic potential of khat extract using a human T lymphoblastoid cell line (CEM). Exponentially growing CEM cells were cultured for 12 h in the presence of khat extract (0-2000 μg ml-1). Statistically significant, dose-dependent increases in; CEM cell death at dose (> 400 μg ml-1), in DNA damage at dose (>200 μg ml-1) and in micronuclei frequency, at dose (>200 μg ml-1) were observed. The genetic damage effects of khat extract on human cell line observed in this study could serve as a major contribution towards the understanding and creating of awareness of an increased risk of cancer amongst long-term khat consumers

Rapid screening method of cassava cultivars for resistance to Collectotrichum gloeosporioides f.sp. manihotis

Published online: 08 March 2002An in vitro method for assessing cassava anthracnose disease (CAD) resistance was developed as a preliminary screen to a CAD‐resistant breeding programme. Potato dextrose agar (PDA) media was amended by extracts from the stem cortex of 10 cassava cultivars (30001; 30572, 30211, 88/02549, 88/00695, 88/01336, 91/00344, 91/00313, 91/00684 and 91/00475), and assayed for efficacy of inhibition of the growth of Colletotrichum gloeosporioides f. sp. manihotis isolates (05FCN, 10FCN, 12FCN, and 18FCN). Morphological and physiological data indicated that there was a significant difference (P ≤ 0.05), in mycelial growth, spore germination and sporulation among the four isolates on PDA amended with cassava stem extracts. Extracts from cassava cultivars 30211, 91/00684 and 91/00313 showed higher inhibition of germ tube development, mycelial growth and sporulation of the fungal isolates, whereas cultivars 88/02549 and 88/01336 showed the least inhibition. The 10 cultivars were further tested in both greenhouse and field conditions, under disease pressure for two planting seasons, to corroborate resistance to the fungus as observed in vitro. Greenhouse and field trials with the 10 cassava cultivars showed a significant difference (P ≤ 0.05) in CAD resistance. Cultivars 88/02549 and 88/01336 were highly CAD‐susceptible, as shown in the in vitro assays and confirmed in the greenhouse and field tests. The other eight cultivars were either resistant (30211, 91/00684), or moderately resistant (30572, 88/00695, 91/00475, 91/00344, 30001 and 91/00313) to CAD. The study shows that an in vitro screening assay of cassava for resistance to CAD could serve as a convenient preliminary screening technique to discriminate CAD‐resistant from CAD‐susceptible cassava cultivars. The in vitro screening method considerably reduces time and labour in comparison with the current screening techniques of cassava, which involve field planting, inoculation and evaluation

Postharvest evaluation of Colletotrichum gloeosporiodes f. sp. manihotis on cassava genotypes

The aim of this study was to evaluate the post-harvest survival of Colletotrichum gloeosporioides f. sp. manihotis on infected cassava materials. Infected stem cuttings from 5 cassava cultivars 88/01084, 88/01983, 91/00395, 91/00317 and 91/00052, incubated at 25±2°C for 8 months, showed a significant decrease in fungal survival amongst the cassava cultivars. At 8 months incubation fungal recovery was lowest below 10% among the infected cultivars. Cassava stakes, stored at humid conditions under tree shades for 16 months, showed a gradual decrease in fungal survival up to the 10th month, after which survival peaked again from the 12th up to the 16th month of storage. Survival of the fungus on soil significantly reduced with incubation time and at the 6th month of sampling, there was no recovery recorded for all the soils from the field plot sites. Burial of infected materials for 150 days below 20-30 cm depth significantly reduced the survival of C. gloeosporioides f. sp. manihotis on infected materials. Burial at 30 cm depth for 150 days completely eradicated the fungus on the infected cuttings. These studies have shown that C. gloeosporioides f. sp. manihotis could survive on infected cuttings for more than 8 months, but less likely to survive in soil for up to 4 months. The potential of high cassava anthracnose disease transmission in cassava planting materials during storage is also reported

In vitro, greenhouse, and field assessment of cassava lines for resistance to anthracnose disease caused by colletotrichum gloeosporiodes f. sp. Manihotis

Fifty-three cassava lines were selected from breeding populations at the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria and screened in vitro for resistance to cassava anthracnose disease (CAD). The in vitro inoculation of stem cuttings with the fungus Colletotrichum gloeosporioides f.sp. manihotis showed significant differences (p ± 0.05) in acervuli production and in the sensitivity of the cassava lines to the fungal infection after 7 days of incubation at 25 ◦C. Cassava lines 88/01084, 91/00595, 91/00475, 91/00344, 91/00684, 91/00313, 91/00422, and 91/00344 were highly resistant, with necrotic lesion sizes less than 7 mm. In contrast pedigree lines 88/02549, 89/0008, 91/00390 and 91/00402 were highly susceptible with the largest necrotic lesion size being greater than 20 mm. Ten cassava lines from the in vitro screening that showed varying levels of resistance to CAD were selected, based on their flowering abilities for diallel hydridization trials, and were further screened in greenhouse and field trials for CAD resistance. The greenhouse and field screening showed significant varietal differences (p ± 0.05) in sensitivity to the fungus. In all cases, the progeny lines showed correlated levels of resistance irrespective of the type of screening or assessments. Correlation analysis of the in vitro, greenhouse and field assessments showed that there was a good correspondence among all three methods of evaluating for CA

Anthracnose: an economic disease of cassava in Africa

Cassava anthracnose disease (CAD) caused by the fungus Colletotrichum gloeosporioides f.sp. manihotis has become one of the major economic diseases of cassava in Africa. The expansion of cassava production farmlands particularly in the humid rainfall zones of West and Central Africa has led to an increase in pathological problems of the crop. The increased epidemic levels of CAD had caused significant crop failure leading to severe food shortages for the poor subsistent farming population depending on the crop for their livelihood. This paper reviews the importance of the crop in terms of food security, CAD disease symptoms, epidemiology, yield losses and the possible control options within the frame work of integrated pest management systems (IPMS)

Role of insect vector Pseudotheraptus devastans in cassava anthracnose disease development

The aim of this study was to investigate the role of Pseudotheraptus devastans in cassava anthracnose disease transmission and development. P. devastans, Dist (Het. Coriedae) insects were collected from cassava (Manihot esculenta Crantz) field plots at the International Institute of Tropical Agriculture, Ibadan, Nigeria and reared in large cages. The insects were separated at different developmental growth stages of eggs, first to fifth instar nymph, and adults. The different stages of P. devastans showed the presence of Colletotrichum gloeosporioides both externally and internally. Isolates of C. gloeosporioides derived from the insects produced cassava anthracnose disease symptoms (necrotic lesions, wilt and defoliation) 8 weeks after inoculation on two cassava clones. Re-infectivity of cassava plants by the insect-derived fungus established that P. devastans was a potential vector in anthracnose transmission. Except for the first and second instar nymphs, all nymph stages and adult insects produced significant anthracnose symptoms on cassava plants. Defoliation and lesion diameters were greatest using fifth instar nymphs and adult insects. The association between P. devastans feeding and C. gloeosporioides f.sp. manihotis, showed that feeding by P. devastans followed by fungal inoculation and vice versa resulted in more severe anthracnose symptoms than insect feeding or fungal inoculation alone. It was also observed that the influence of P. devastans damage/infection on the development of anthracnose depended on cassava cultivar resistance to both the fungus and the insect feeding

Field reaction of cassava genotypes to anthranose, bacterial blight, cassava mosaic disease and their effects on yield

Thirteen cassava genotypes were evaluated at the International Institute of Tropical Agriculture, Ibadan, Nigeria for anthracnose (CAD), bacterial blight (CBB) and cassava mosaic disease (CMD) incidence and severity, and their effects on yield, for three consecutive planting seasons. There were significant differences (P<0.05) in CAD, CBB and CMD incidence and severity amongst the cassava genotypes across the planting seasons. Yield assessment showed significant differences (P<0.05) in storage root number, plant stand, root fresh weight and dry matter content among the cassava genotypes. There was no significant variation in tuber rot among the genotypes, and 80% of the genotypes did not show any tuber root rot when harvested 12 months after planting. CBB and CAD incidences were significantly and positively correlated (r=0.43), whereas CBB and CMD incidences were not significantly correlated (r=0.03). CAD and CMD incidence and severity were highly correlated (r=0.82 and r=0.76, respectively). CBB incidence was negatively correlated with storage root weight and fresh root tuber number (r=-0.45 and r=-0.48, respectively). CMD severity showed a significant negative correlation with storage root weight (r=0.44). Cassava genotypes TMS 30001, 30211 and 88/01087 showed a stable resistance over 3 planting seasons to CAD, CBB and CMD